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J O U R N A L O F C H E M I S T R Y Materials Synthesis and thermotropic liquid crystalline properties of calamitic molecules with laterally attached hydrophilic groups: Y-shaped three-block molecules which can form smectic and columnar mesophases Rene Plehnert, Jo�rg Andreas Schro�ter and Carsten Tschierske* Institute of Organic Chemistry, University Halle, D-06015 Halle, Kurt-Mothes-Str. 2, Germany.E-mail: coqfx@mlucom6.urz.uni-halle.de Received 23rd April 1998, Accepted 23rd September 1998 The synthesis and the thermotropic liquid crystalline properties of calamitic mesogens ( p-terphenyl derivatives, a biphenyl and a p-quintaphenyl derivative) with a laterally attached hydrophilic group (1,2-diol groups, primary and secondary amides, polyether chains, crown ether units, carbohydrate units, a hydrazide, a quaternary ammonium salt, a carboxylic acid and a sodium carboxylate) are reported.The compounds were investigated by means of polarizing microscopy and calorimetry. The influence of the type of the polar group, of the length of the rigid core and the position of the connection of the hydrophilic group with the rod-like rigid core have been investigated. Many of these amphiphilic molecules can form monolayer SA phases.If a suYcient amount of hydrogen bonding is available their mesophase stability can be higher than that of related compounds with other lateral substituents. Rectangular columnar mesophases can be found for compounds with rather large and flexible polar lateral substituents (polyether chains) fixed to the center of the rigid terphenyl unit.These columnar phases should represent ribbon phases resulting from the collapse of the smectic layers (modulated smectic phases). The proposed model is also related to that suggested for supermolecular structures of triblock copolymers. Thus, these molecules can be regarded as low molecular weight block compounds consisting of three diVerent and incompatible molecular parts.hydrophilic functional groups such as diol groups, polyether 1. Introduction chains, carbohydrate units or ionic groups were laterally Liquid crystalline materials are of great interest for material attached to a rigid rod-like oligo-p-phenylene rigid core. These science as well as for life science. Their properties can be tuned molecules are of special interest, because two diVerent organizby appropriate molecular design.Thus, it is well known that ing forces of liquid crystalline phases are perpendicularly the mesomorphic properties of calamitic liquid crystals can directed to each other in these compounds (Fig. 1). Firstly, largely be influenced by lateral substituents, like halogens,1–3 the tendency of the rigid calamitic units is to adopt an alkyl or alkoxy groups.4,5 This can influence the melting orientational long range order which is characteristic for points, the mesophase types, the dielectric properties, etc.In thermotropic liquid crystals and provides nematic and smectic most cases, however, a significant mesophase destabilization mesophases. Secondly, there is the tendency of amphiphilic is connected with this structural variation.Especially large molecules to segregate their incompatible (e.g. hydrophilic and lateral groups suppress smectic phases and therefore nearly all hydrophobic) parts into segregated regions, giving rise to large calamitic mesogens with long lateral alkyl chains show exclus- aggregates which themselves are the basis of lamellar, columnar ively nematic phases.5 However, in rare cases lateral substitu- or cubic thermotropic and lyotropic mesophases.8 In the ents can have a mesophase stabilizing eVect.The earliest compounds described here, the parallel arrangement of the example was provided by the laterally substituted 5-alkoxy- rigid units should be disturbed by the segregation of hydrophilic and hydrophobic parts of the molecules and, conversely, the aggregation of the amphiphilic molecules should be disturbed because of the unfavorable size and shape of their lipophilic parts.Indeed, these unusual molecules represent a new class of amphiphiles with an unique organization in Langmuir films at the air–water interface,9 but their liquid crystalline behavior is also remarkable.They represent novel amphotropic compounds10 which can form thermotropic as well as lyotropic liquid crystalline phases.11,12 The lyotropic naphthoic acids.6 The smectic tendency of the chloro substiphase behavior will be reported in detail in a separate paper.13 tuted naphthoic acid is remarkably high, whereas the naphthoic acid without the lateral chloro substituent is only a nematic liquid crystal.It seems that a significant mesophase stabilizing eVect is provided by the polar chloro substituent which can override its steric disturbance. Likewise suitable molecular design, especially the introduction of electron withdrawing substituents like cyano or nitro in laterally attached aromatic rings, can produce strongly branched calamitic mesogens with unexpectedly high mesophase stabilities.5,7 Fig. 1 Structure of the amphiphilic molecules under investigation. We have synthesized a novel class of liquid crystals in which J. Mater. Chem., 1998, 8, 2611–2626 2611Herein we describe the synthesis and summarize the results (compounds 33) to the 2¾-position and in some cases to the 3-position of the p-terphenyl unit. obtained during investigation of their thermotropic liquid crystalline properties. 2. Syntheses Pd0-catalyzed cross-coupling reactions between aryl halides and arylboronic acids (Suzuki coupling)14 represent the key steps of all syntheses which are outlined in Schemes 1–5. There are three diVerent approaches to the compounds 1–3 and 29–31 all carrying a lateral group connected via an ether linkage to the 2¾-position of the p-terphenyl rigid core.Compounds 1 and 3, which all have the 4,5-dihydroxy-2- oxapentyl group but diVer in the type of the terminal substituents, have been synthesized starting with 4-(2,5-dibromobenzyloxymethyl )-2,2-dimethyl-1,3-dioxolane 36 (Scheme 1). After cross-coupling of 36 with the appropriate 4-substituted phenylboronic acids, the 1,2-O-isopropylidene protecting groups were cleaved by acidolysis.In an analogous manner the quinquaphenyl derivative 5 was obtained by cross coupling of 36 with 4-(4-decyloxyphenyl )phenylboronic acid (Scheme 1). The terphenyl derivatives 29–31, which diVer in the structure of the lateral group in the 2¾-position, and the optically active compound (S)-1e were synthesized using another strategy shown in Scheme 2 for the syntheses of compounds 29b and First the p-terphenyl derivatives 1 and 3 (1: R=alkoxy; 3: R=alkyl, n=m=1) both carrying a lateral 4,5-dihydroxy-2- 29c.Here, the p-terphenyl rigid core was built up first and the lateral groups were introduced in a second step. This allowed oxapentyl group were synthesized and the influence of changes of the terminal substituents R was investigated.Afterwards a broad variation of the lateral hydrophilic groups. 2,5-Bis(4- decyloxyphenyl )toluene was obtained by cross coupling of we changed the structure of the rigid core. Besides m-terphenyl derivative 4, a biphenyl derivative 6, a molecule without a two equivalents of 4-decyloxyphenylboronic acid with 2,5- dibromotoluene.15 The methyl group was brominated using rigid unit 7 and a quinquaphenyl derivative 5 were synthesized.In the next step the position of the lateral hydrophilic group NBS.15 The 2,5-bis(4-decyloxyphenyl )benzyl bromide 3715 obtained was afterwards etherified with diVerent functionalized was shifted along the p-terphenyl unit (compounds 11 and 13). Finally, a wide variation of the structure of the lateral alcohols, followed by deprotection, if necessary. The best yields in the etherification step were obtained using phase hydrophilic group was carried out in the series of 4,4>- didecyloxy-p-terphenyl derivatives by appending amido groups transfer conditions.The optically active compound (S)-1e was obtained by etherification of 37 with enantiomerically pure (compounds 15–24), ionic groups (compounds 27 and 28), polyether chains (compounds 29, 30 and 34) or crethers (R)-(-)-4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane. 2612 J.Mater. Chem., 1998, 8, 2611–2626Scheme 3 Reagents and conditions: i, HOCH2CH2OCH2CHLCH2, Scheme 1 Reagents and conditions: i, NBS, AIBN, hn, CCl4, reflux, 2 NaOH, Bu4NHSO4, H2O, 60 °C, 12 h; ii, cat. OsO4, NMMNO, h; ii, NaOH, H2O, Bu4NHSO4, 60° C, 15 h; iii, cat.Pd(PPh3)4, acetone–H2O, 25 °C, 24 h. Na2CO3, H2O, benzene–EtOH, reflux, 4 h; iv, HCl, H2O–EtOH, reflux 2 h. benzyl bromides 39 and 40, respectively.18 The benzyl bromides 39 and 40 were synthesized as outlined in Scheme 4.18 Also compound 7, the biphenyl derivative 6 and the m-terphenyl derivative 4 were prepared in an analogous procedure to that given in Scheme 2 starting with 2,5-didecyloxybenzyl bromide,18 5-decyloxy-2-(4-decyloxyphenyl )benzyl bromide19 and 3,5-bis(4-decyloxyphenyl )benzyl bromide,20 respectively.All 2,5-bis(4-decyloxyphenyl )benzoyl derivatives 15–24 were synthesized according to Scheme 5. Cross-coupling of methyl 2,5-dibromobenzoate is possible with NaHCO3 as base in a water–glyme solvent system without saponification during the reaction (which would lead to a failure of the reaction).15 The 2,5-bis(4-decyloxyphenyl )benzoic acid 25 which is obtained after saponification is treated with oxalyl chloride21 to yield the acid chloride 26.The use of oxalyl chloride at low temperatures is crucial, because other conditions (e.g. SOCl2) would lead to an intramolecular Friedel–Crafts acylation with formation of 7-decyloxy-2-(4-decyloxyphenyl )fluoren-9-one. The acid chloride 26 was aminolyzed to give the amides 15–24.The crown compounds 33 were obtained by esterification of 25 with 2-hydroxymethyl substituted crown ethers. The detailed procedure and the analytical data for the crown compounds 33 are reported in a separate paper concerning their monolayer behavior.22 Additionally, two ionic amphiphiles were synthesized.The ammonium salt 28 was obtained by quaternization of triethylamine with 37.23 The sodium carboxylate 27 was isolated after saponification of the methyl carboxylate 14. Scheme 2 Reagents and conditions: i, cat. Pd(PPh3)4, Na2 CO3, H2O, benzene–EtOH, reflux, 4 h; ii, NBS, AIBN, hn, CCl4, reflux, 2 h; iii, NaOH, Bu4NHSO4, H2O, reflux, 15 h; iv, HCl, H2O–EtOH, 3.Experimental reflux, 2 h. 3.1. General Confirmation of the structures of intermediates and products Only compound 29a carrying the 7,8-dihydroxy-2,5-dioxaoctyl group was prepared in a slightly diVerent way, as shown was obtained by 1H and 13C NMR spectroscopy (Varian Unity 500 and Varian Gemini 200 spectrometers) and by mass in Scheme 3.The benzyl bromide 37 was at first etherified with 2-allyloxyethanol.16 The resulting allyl ether 38 was dihy- spectrometry (Intectra GmbH, AMD 402, electron impact, 70 eV). All materials were purified by chromatography and/or droxylated using catalytic amounts of OsO4 in the presence of the oxidant N-methylmorpholine N-oxide.17 recrystallization until constant transition temperatures were obtained. The purity was checked by thin layer chromatogra- The amphiphiles 11, 13 (Scheme 4), 34 and 35 (see Fig. 15) carrying their lateral substituents in the 2-position (compound phy (TLC, aluminum sheets, silica gel 60 F254 from Merck) and elemental analysis. Some compounds take up moisture 11) or in the 3-position (compounds 13, 34 and 35) at the pterphenyl rigid core were obtained in an analogous manner to during sample preparation which causes a deviation of the microanalysis from the calculated values.In these cases the the corresponding 2¾-substituted materials, starting with the J. Mater. Chem., 1998, 8, 2611–2626 2613Scheme 4 Reagents and conditions: i, C10H21Br, K2CO3, CH3CN, reflux, 17 h; ii, BuLi, THF, -78 °C, then B(OMe)3, -70 °C, then HCl, H2O; iii, cat.Pd(PPh3)4, Na2CO3, H2O–EtOH, reflux, 4 h; iv, NBS, AIBN, hn, CCl4, reflux, 2 h; v, NaOH, Bu4NHSO4, H2O, reflux, 12 h; vi, HCl, H2O–EtOH, reflux, 2 h. purity (>99%) was additionally checked by HPLC (Merck-Hitachi, RP-18, CH2Cl2–methanol 151). Microanalyses were performed using an LECO CHNS-932 elemental analyzer. 2,5-Dibromotoluene (Acros), N-bromosuccinimide (Merck), oxalyl chloride (Lancaster), osmium tetroxide (Berlin Chemie), N-methylmorpholine N-oxide solution (Aldrich), 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane (Aldrich), (R)-(-)-4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane (Aldrich), 3-aminopropane-1,2-diol (Merck), 1-amino-1- deoxy-D-glucitol (Fluka), 1-deoxy-1-methylamino-D-glucitol (Acros) and 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (Aldrich) were used as obtained. 2-Allyloxyethanol, phenylboronic acids,24 4-(7-hydroxy-2,5-dioxaheptyl )-2,2-dimethyl-1,3- dioxolane,25 4-(10-hydroxy-2,5,8-trioxadecyl )-2,2-dimethyl- 1,3-dioxolane,25 4-(9-hydroxynonyl )-2,2-dimethyl-1,3-dioxolane, 26 bromomethyl-substituted 4,4>-didecyloxy-p-terphenyls 3715, 3918 and 4018 and methyl 2,5-bis(4-decyloxyphenyl )benzoate 1415 were obtained according to the procedures described in the corresponding references.Transition temperatures were measured using a Mettler FP 82 HT hot stage and control unit in conjunction with a Nikon Optiphot-2 polarizing microscope and were confirmed using diVerential scanning calorimetry (Perkin-Elmer DSC-7, the transition enthalpies are collected in Table 1).Because some of the compounds are very hygroscopic, the samples were dried prior to investigation either in vacuo over phosphorus pentoxide for 48 h or by heating for 1 min to a temperature of approximately 150 °C. Afterwards the samples were immediately sealed and investigated. 3.2. Synthesis of the terphenyl derivatives 1 and 3 3.2.1. 4-(2,5-Dibromobenzyloxymethyl)-2,2-dimethyl-1,3- dioxolane 36.A solution of 2,5-dibromotoluene (20 mmol, 5 g) and N-bromosuccinimide (24 mmol, 4.27 g) in dry tetrachloromethane (50 ml ) was placed in a quartz flask and heated to the boiling point. AIBN (50 mg) was added and the refluxing mixture was irradiated with UV light (366 nm). After 2 h the mixture was cooled to room temperature and the succinimide Scheme 5 Reagents and conditions: i, cat.Pd(PPh3)4, NaHCO3, formed was filtered oV. The solvent was removed in vacuo and Glyme, H2O, reflux, 5 h; ii, NaOH, H2O, reflux, 4 h; iii, HCl, H2O, reflux, 2 h; iv, (COCl )2, 25°C, 1 h; v, HNR1R2, DMF, 80 °C, 4 h. the residue was purified by crystallization from ethanol. Yield: 2614 J. Mater. Chem., 1998, 8, 2611–2626Table 1 Phase transition enthalpiesa separated and the aqueous phase was extracted twice with diethyl ether (50 ml ).The combined organic phases were Compound DH/kJ mol-1 washed with brine and dried with Na2SO4. The solvent was removed in vacuo and the products obtained were purified by 1b K–Iso 43.2 SA–Iso 1.2 column chromatography (silica gel, chloroform). 1c K–SA 37.2 SA–Iso 3.8 1d K–SA 50.5 SA–Iso 4.4 1e K–SA 55.5 SA–Iso 6.1 4-[2,5-Bis(4-decyloxyphenyl)benzyloxymethyl]-2,2- 1f K–SA 66.2 SA–Iso 6.8 dimethyl-1,3-dioxolane.dH(200 MHz, CDCl3, J/Hz) 0.87 (t, J 1g K–SA 60.7 SA–Iso 7.6 6.7, 6H, CH3), 1.18–1.27 (m, 28H, CH2), 1.34 (s, 3H, CH3), 1h K–SA 70.7 SA–Iso 8.0 1.38 (s, 3H, CH3), 1.73–1.86 (m, 4H, OCH2CH2), 3.42 (dd, J 2 K–Iso 60.1 N–Iso 3.4 9.8, 5.8, 1H, PhCH2OCHAHB), 3.53 (dd, J 9.7, 5.5, 1H, 3b K–SA 30.8 SA–Iso 3.7 5 K–SA 29.2 SA–Iso 9.0 PhCH2OCHAHB), 3.71 (dd, J 8.3, 6.3, 1H, OCHAHB), 6 K–Iso 24.7 SA–Iso 2.7 3.96–4.20 (m, 5H, OCHAHB, PhOCH2), 4.23–4.29 (m, 1H, 9 K–SA 49.1 SA–N 0.8 N–Iso 1.4 CHO), 4.50 (s, 2H, PhCH2O), 6.93 (d, J 8.7, 2H, H-Ar), 6.96 10 K–SA 51.5 SA–Iso 6.7 (d, J 8.7, 2H, H-Ar), 7.26–7.28 (m, 2H, H-Ar), 7.29 (d, J 8.7, 11 K–SA 42.9 SA–Iso 7.8 1H, H-Ar), 7.48–7.53 (m, 1H, H-Ar), 7.55 (d, J 8.7, 2H, 12 K–SC 12.1 SC–SA–Iso 9.2 H-Ar), 7.70 (d, J 1.8, 1H, H-Ar). 13 K–SA 35.7 SA–Iso 8.6 17 K–SA 71.4 SA–Iso 6.3 18 K–SA 74.6 SA–Iso 5.0 3.2.4. Deprotection of the 1,2-diol groups. The 2,2-dimethyl- 19 K–SA 47.3 SA–Iso 3.3 1,3-dioxolane derivatives obtained by the cross-coupling reac- 20 K–SA 25.5 SA–Iso 1.6 tions were used, without further purification, for deprotection. 22 K–Iso 28.3 SA–Iso 2.3 The appropriate 2,2-dimethyl-1,3-dioxolane derivative 29b K–Iso 45.2 Colr–SA 1.2 SA–Iso 0.5 (1 mmol) was dissolved in ethanol (50 ml ) and 10% hydro- 29c K–Iso 43.2 Colr–Iso 1.9 30b K–Iso 49.3 SA–Iso 0.7 chloric acid (10 ml ) was added. Then, the mixture was heated 32 K–Iso 51.8 under reflux for 2 h. After cooling the solvent was evaporated 33a K–Iso 61.6 SA–N 0.4 N–Iso 1.0 and 50 ml water and 50 ml diethyl ether were added to the 33b K–Iso 0.8 SA–N–Iso 0.9 residue.The aqueous phase was extracted three times with 33c K–Iso 42.1 SA–N 0.1 N–Iso 0.4 diethyl ether (30 ml ). Afterwards, the combined organic phases 34a K–SA 40.0 SA–Iso 5.7 were washed with saturated NaHCO3 solution and water, and 34b K–SA 23.6 SA–Iso 2.7 34c K–SA 36.7 SA–Iso 1.0 dried with Na2SO4.The solvent was removed in vacuo and the crude product was purified by column chromatography aAbbreviations: K=crystalline solid, N=nematic phase, SA=smectic A phase, SC=smectic C phase, Colr=rectangular columnar and recrystallization. mesophase, Iso=isotropic liquid. 5-[2,5-Bis(4-ethoxyphenyl)phenyl]-4-oxapentane-1,2-diol 1a.Synthesized from 36 and 4-ethoxyphenylboronic acid. Crystallized from light petroleum (60–80 °C). Yield: 46%; 60%; mp 89 °C; dH(200 MHz, acetone, J/Hz) 4.69 (s, 2H, PhCH2Br), 7.45 (dd, J 8.5, 2.4, 1H, H-Ar), 7.60 (d, J 8.5, 1H, transitions/°C: K 124 (N 58) Iso; elemental analysis (%): found (calc. for C26H30O5): C, 73.82 (73.91); H, 7.29 (7.16); H-Ar), 7.82 (d, J 2.4, 1H, H-Ar). The 2,5-dibromobenzyl bromide obtained in this way was used without further purifi- dH(200 MHz, CDCl3, J/Hz) 1.43 (2t, J 6.9, 6H, CH3), 1.76 (s, broad, 2H, OH), 3.4–3.7 (m, 4H, OCH2), 3.75–3.9 [m, 1H, cation for the next step.In a two-necked flask equipped with a reflux condenser and CH(OH)], 4.06 (t, J 6.8, 2H, PhOCH2), 4.09 (t, J 7.0, 2H, PhOCH2), 4.49 (s, 2H, PhCH2O), 6.93 (d, J 8.5, 2H, H-Ar), a magnetic stirring bar, Bu4NHSO4 (30 mg) was added to a mixture consisting of 4-hydroxymethyl-2,2-dimethyl-1,3- 6.98 (d, J 8.6, 2H, H-Ar), 7.3–7.35 (m, 3H, H-Ar), 7.5–7.6 (m, 3H, H-Ar), 7.63 (d, J 1.8, 1H, H-Ar); m/z (%) 422 dioxolane (0.1 mol, 13.2 g), 2,5-dibromobenzyl bromide (0.01 mol, 3.3 g) and 50% aq.NaOH (15 ml ) under argon ([M]+, 100). atmosphere. The mixture was stirred rapidly at 60 °C for 15 h. After cooling 50 ml water and 50 ml diethyl ether were added. 5-[2,5-Bis(4-hexyloxyphenyl)phenyl]-4-oxapentane-1,2-diol 1b. Synthesized from 36 and 4-hexyloxyphenylboronic acid. The organic phase was separated and the aqueous phase was extracted three times with diethyl ether (100 ml ). The com- Crystallized from n-hexane. Yield: 44%; transitions/°C: K 80 (SA 71) Iso; elemental analysis (%): found (calc.for C34H46O5): bined organic phases were dried with Na2SO4 and afterwards, the solvent was removed in vacuo. The residue was purified by C, 75.73 (76.37); H, 8.83 (8.67); dH(200 MHz, CDCl3, J/Hz) 0.91 (t, J 6.3, 6H, CH3), 1.21–1.58 (m, 12H, CH2), 1.69–1.88 column chromatography (silica gel, chloroform). Yield: 42%; yellow oil; dH(500 MHz, CDCl3, J/Hz) 1.37 (s, 3H, CH3), (m, 4H, OCH2CH2), 1.95 (dd, 1H, CH2OH), 2.42 [d, 1H, CH(OH)], 3.45–3.68 (m, 4H, OCH2), 3.74–3.86 [m, 1H, 1.43 (s, 3H, CH3), 3.57 (dd, J 10.0, 5.1, 1H, PhCH2OCHAHB), 3.64 (dd, J 10.0, 5.6, 1H, PhCH2OCHAHB), 3.78 (dd, J 8.3, CH(OH)], 3.99 (t, J 6.2, 4H, PhOCH2), 4.49 (s, 2H, PhCH2O), 6.91 (d, J 8.5, 2H, H-Ar), 6.96 (d, J 8.6, 2H, H-Ar), 7.29 (d, 6.3, 1H, OCHAHB), 4.08 (dd, J 8.3, 6.4, 1H, OCHAHB), 4.31–4.35 (m, 1H, CHO), 4.57 (m, 2H, PhCH2O), 7.25 (dd,J J8.5, 2H, H-Ar), 7.31 (d, J 8.3, 1H, H-Ar), 7.49–7.59 (m, 3H, H-Ar), 7.62 (d, J 1.8, 1H, H-Ar); m/z (%) 534 ([M]+, 100). 8.3, 2.4, 1H, H-Ar), 7.36 (d, J 8.3, 1H, H-Ar), 7.62 (d, J 2.4, 1H, H-Ar). 5-[2,5-Bis(4-octyloxyphenyl)phenyl]-4-oxapentane-1,2-diol 1c. Synthesized from 36 (1 mmol, 380 mg) and 4-octyloxyphen- 3.2.3. General procedure for the Pd-catalyzed cross-coupling reactions.In a two-necked flask equipped with a reflux con- ylboronic acid (2.4 mmol, 600 mg). Crystallized from light petroleum (60–80 °C) and afterwards from methanol. Yield: denser and a magnetic stirring bar, Pd(PPh3)4 (0.03 mmol, 35 mg, 3 mol%) was added under an argon atmosphere to a 35%; transitions/°C: K 79 SA 102 Iso; elemental analysis (%): found (calc.for C38H54O5): C, 77.19 (77.25); H, 9.03 (9.21); mixture consisting of the appropriate dibromobenzene derivative (1 mmol), the boronic acid (2.4 mmol), benzene (30 ml ), dH(200 MHz, CDCl3, J/Hz) 0.88 (t, J 6.6, 6H, CH3), 1.29–1.37 (m, 16H, CH2), 1.43–1.48 (m, 4H, OCH2CH2CH2), 1.76–1.83 ethanol (30 ml ) and 2 M Na2CO3 solution (30 ml ).The mixture was stirred at reflux temperature for 4 h. After cooling the (m, 4H, OCH2CH2), 3.48–3.68 (m, 4H, OCH2), 3.80–3.89 [m, 1H, CH(OH)], 3.99 (t, J 6.5, 4H, PhOCH2), 4.50 (s, 2H, solvent was evaporated and the residue dissolved in diethyl ether (30 ml ) and water (30 ml ). The organic phase was PhCH2O), 6.93–6.98 (m, 4H, H-Ar), 7.28 (d, J 8.4, 2H, HJ.Mater. Chem., 1998, 8, 2611–2626 2615Ar), 7.31 (d, J 8.0, 1H, H-Ar), 7.51–7.53 (m, 1H, H-Ar), 7.54 J 8.2, 1H, H-Ar), 7.47–7.56 (m, 3H, H-Ar), 7.63 (d, J 1.8, 1H, H-Ar); m/z (%) 758 ([M]+, 100). (d, J 8.6, 2H, H-Ar), 7.64 (d, J 1.6, 1H, H-Ar). 5-[2,5-Bis(4-nonyloxyphenyl)phenyl]-4-oxapentane-1,2-diol 5-[2,5-Bis(4-propylphenyl)phenyl]-4-oxapentane-1,2-diol 1d.Synthesized from 36 (1 mmol, 380 mg) and 4-nonyloxy- 3a. Synthesized from 36 and 4-propylphenylboronic acid. phenylboronic acid (2.4 mmol, 632 mg). Crystallized from Crystallized from n-hexane. Yield: 37%; mp 60 °C; elemental light petroleum (60–80 °C). Yield: 32%; transitions/°C: K 82 analysis (%): found (calc. for C28H34O3): C, 79.72 (80.35); H, SA 106 Iso; elemental analysis (%): found (calc.for C40H58O5): 7.96 (8.19); dH(200 MHz, CDCl3, J/Hz) 0.97 (t, J 7.2, 3H, C, 77.56 (77.63); H, 9.53 (9.45); dH(200 MHz, CDCl3, J/Hz) CH3), 0.98 (t, J 7.2, 3H, CH3), 1.59–1.78 (m, 4H, CH2), 2.62 0.86 (t, J 6.4, 6H, CH3), 1.27–1.34 (m, 20H, CH2), 1.42–1.47 (t, J 7.5, 4H, PhCH2), 3.4–3.7 (m, 4H, CH2O), 3.7–3.9 [m, (m, 4H, OCH2CH2CH2), 1.75–1.82 (m, 4H, OCH2CH2), 1H, CH(OH)], 4.52 (s, 2H, PhCH2O), 7.20–7.31 (m, 7H, H- 3.44–3.67 (m, 4H, OCH2), 3.80–3.85 [m, 1H, CH(OH)], 3.98 Ar), 7.52–7.59 (m, 3H, H-Ar), 7.62 (d, J 2.0, 1H, H-Ar); m/z (t, J 6.6, 4H, PhOCH2), 4.50 (s, 2H, PhCH2O), 6.92–6.97 (m, (%) 418 ([M]+, 100). 4H, H-Ar), 7.26–7.31 (m, 3H, H-Ar), 7.49–7.54 (m, 3H, H-Ar), 7.63 (d, J 2.0, 1H, H-Ar). 5-[2,5-Bis(4-undecylphenyl)phenyl]-4-oxapentane-1,2-diol 3b.Synthesized from 36 and 4-undecylphenylboronic acid. 5-[2,5-Bis(4-decyloxyphenyl)phenyl]-4-oxapentane-1,2-diol Crystallized from n-hexane. Yield: 46%; transitions/°C: K 63 1e. Synthesized from 36 and 4-decyloxyphenylboronic acid. SA 78 Iso; elemental analysis (%): found (calc. for C44H66O3): Crystallized from n-hexane. Yield: 54%; transitions/°C: K 83 C, 81.98 (82.19); H, 10.52 (10.35); dH(250 MHz, CDCl3, SA 114 Iso; elemental analysis (%): found (calc.for C42H62O5): J/Hz) 0.71 (t, J 6.5, 6H, CH3), 1.0–1.3 (m, 32H, CH2), 1.5–1.6 C, 77.74 (77.98); H, 9.85 (9.66); dH(200 MHz, CDCl3, J/Hz) (m, 4H, CH2), 1.73 (dd, J 4.0, 1H, CH2OH), 2.34 [d, J 5.0, 0.87 (t, J 6.5, 6H, CH3), 1.18–1.58 (m, 28H, CH2), 1.71–1.89 1H, CH(OH)], 2.47 (t, J 6.4, 4H, PhCH2), 3.3–3.6 (m, 4H, (m, 4H, OCH2CH2), 3.43–3.72 (m, 4H, OCH2), 3.77–3.91 [m, OCH2), 3.6–3.7 [m, 1H, CH(OH)], 4.37 (s, 2H, PhCH2O), 1H, CH(OH)], 3.99 (t, J 6.5, 4H, PhOCH2), 4.50 (s, 2H, 7.1–7.45 (m, 10H, H-Ar), 7.51 (d, J 1.4, 1H, H-Ar).PhCH2O), 6.92 (d, J 8.6, 2H, H-Ar), 6.96 (d, J 8.7, 2H, HAr), 7.29 (d, J 8.5, 2H, H-Ar), 7.33 (d, J 8.2, 1H, H-Ar), 3.3. 5-{2,5-Bis[4-[4-decyloxyphenyl )phenyl]phenyl}-4- 7.4–4.5 (m, 1H, H-Ar), 7.55 (d, J 8.8, 2H, H-Ar), 7.64 (d, J oxapentane-1,2-diol 5 1.8, 1H, H-Ar); dC(125 MHz, CDCl3) 14.09 (CH3), 22.67, 26.08, 26.10, 29.32, 29.41, 29.56, 29.60, 31.91 (CH2), 64.08 Synthesized from 36 (1 mmol, 380 mg) and 4-(4-decyloxyphen- (CH2OH), 68.15 (PhOCH2), 68.17 (PhOCH2), 70.53 yl )phenylboronic acid (2.4 mmol, 850 mg) according to pro- [OCH2CH(OH)], 71.80 [OCH2CH(OH)], 72.03 (PhCH2O), cedures 3.2.3 and 3.2.4.Crystallized from n-hexane–ethyl 114.26, 114.90, 126.19, 127.60, 128.05, 130.16, 130.68, 132.67, acetate. Yield: 43%; transitions/°C: K 152 SA 258 Iso; elemental 132.92, 135.22, 139.81, 140.14, 158.57, 158.89 (C-Ar); m/z (%) analysis (%): found (calc. for C54H70O5): C, 80.92 (81.16); H, 646 ([M]+, 100). 8.98 (8.83); dH(200 MHz, CDCl3, J/Hz) 0.88 (t, J 6.4, 6H, CH3), 1.2–1.6 (m, 28H, CH2), 1.7–1.9 (m, 4H, OCH2CH2), 1.94 (dd, J 4.0, 1H, CH2OH), 2.43 [d, J 5.0, 1H, CH(OH)], 5-[2,5-Bis(4-undecyloxyphenyl)phenyl]-4-oxapentane-1,2- 3.5–3.77 (m, 4H, OCH2), 3.8–3.95 [m, 1H, CH(OH)], 4.00 (t, diol 1f. Synthesized from 36 (1 mmol, 380 mg) and 4-undecyl- J 6.5, 4H, PhOCH2), 4.57 (s, 2H, PhCH2O), 6.98 (d, J 8.8, oxyphenylboronic acid (2.4 mmol, 701 mg).Crystallized from 4H, H-Ar), 7.4–7.7 (m, 14H, H-Ar), 7.76 (d, J 1.7, 1H, H-Ar); light petroleum (60–80 °C). Yield: 39%; transitions/°C: K 89 m/z (%) 798 ([M]+, 100). SA 114 Iso; elemental analysis (%): found (calc. for C44H66O5): C, 78.46 (78.24); H, 9.63 (9.86); dH(200 MHz, CDCl3, J/Hz) 0.86 (t, J 6.5, 6H, CH3), 1.26–1.46 (m, 32H, CH2), 1.76–1.83 3.4.Synthesis of the diols (S)-1e, 4, 6, 7, 11, 13, 29b,c, 31, (m, 4H, OCH2CH2), 3.43–3.71 (m, 4H, OCH2), 3.79–3.86 [m, 34b,c, 35a,b 1H, CH(OH)], 3.99 (t, J 6.5, 4H, PhOCH2), 4.50 (s, 2H, 3.4.1. General procedure for the synthesis of benzyl ethers. PhCH2O), 6.94 (d, J 8.6, 2H, H-Ar), 6.96 (d, J 8.8, 2H, HIn a two-necked flask equipped with a reflux condenser and a Ar), 7.26–7.33 (m, 3H, H-Ar), 7.49–7.56 (m, 3H, H-Ar), 7.63 magnetic stirring bar, Bu4NHSO4 (5 mg) and 50% aq.NaOH (d, J 2.0, 1H, H-Ar). (3 ml ) were added to a solution of the alcohol (15 mmol) and the benzyl bromide (1.5 mmol) in 10 ml toluene under argon 5-[2,5-Bis(4-dodecyloxyphenyl)phenyl]-4-oxapentane-1,2- atmosphere. The mixture was stirred violently at 60 °C for diol 1g.Synthesized from 36 and 4-dodecyloxyphenylboronic 15 h. After cooling 30 ml water and 30 ml diethyl ether were acid. Crystallized first from light petroleum (60–80 °C) and added. The organic phase was separated and the aqueous afterwards from methanol. Yield: 47%; transitions/°C: K 86 phase was extracted with diethyl ether. The combined organic SA 116 Iso; dH(200 MHz, CDCl3, J/Hz) 0.87 (t, J 6.6, 6H, phases were dried with Na2SO4 and afterwards the solvent CH3), 1.27–1.55 (m, 36H, CH2), 1.77–1.84 (m, 4H, was removed in vacuo.The residue was purified by column OCH2CH2), 1.99 (br s, 2H, OH), 3.42–3.75 (m, 4H, OCH2), chromatography. 3.76–3.94 [m, 1H, CH(OH)], 3.99 (t, J 6.6, 4H, PhOCH2), 4.50 (s, 2H, PhCH2O), 6.9–7.0 (m, 4H, H-Ar), 7.27–7.39 (m, 3.4.2. Deprotection of the 1,2-diol group.The 2,2-dimethyl- 3H, H-Ar), 7.5–7.7 (m, 4H, H-Ar); m/z (%) 702 ([M]+, 100). 1,3-dioxolane derivatives obtained were used, without further purification, for deprotection as described in 3.2.4. 5-[2,5-Bis(4-tetradecyloxyphenyl)phenyl]-4-oxapentane- 1,2-diol 1h. Synthesized from 36 and 4-tetradecyloxyphenylboronic acid. Crystallized from ethanol.Yield: 48%; (S)-5-[2,5-Bis(4-decyloxyphenyl )phenyl]-4-oxapentane-1,2- diol (S)-1e. Synthesized from (R)-(-)-4-hydroxymethyl-2,2- transitions/°C: K 95 SA 118 Iso; elemental analysis (%): found (calc. for C50H78O5): C, 78.82 (79.09); H, 10.35 (10.36); dimethyl-1,3-dioxolane and 37. Eluent: chloroform–methanol (1051). Crystallized from n-hexane. Yield: 28%; transitions/°C: dH(200 MHz, CDCl3, J/Hz) 0.87 (t, J 6.4, 6H, CH3), 1.1–1.6 (m, 42H, CH2), 1.7–1.9 (m, 4H, OCH2CH2), 3.37–3.73 (m, K 83 SA 114 Iso; elemental analysis (%): found (calc.for C42H62O5): C, 77.86 (77.96); H, 9.70 (9.67); [a]58925+1.9, 4H, OCH2), 3.78–3.91 [m, 1H, CH(OH)], 3.99 (t, J 6.3, 4H, PhOCH2), 4.50 (s, 2H, PhCH2O), 6.93 (d, J 8.4, 2H, H-Ar), [a]43625+4.9 (c 1.0, CHCl3); all other analytical data correspond to those given for rac-1e. 6.96 (d, J 8.6, 2H, H-Ar), 7.29 (d, J 8.3, 2H, H-Ar), 7.31 (d, 2616 J. Mater. Chem., 1998, 8, 2611–26265-[3,5-Bis(4-decyloxyphenyl)phenyl]-4-oxapentane-1,2-diol 113.90, 114.84, 115.12, 126.37, 128.01, 129.60, 131.21, 132.94, 133.87, 136.13, 138.87, 139.43, 158.61, 158.83 (C-Ar); m/z (%) 4. Synthesized from 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane and 3,5-bis(4-decyloxyphenyl )benzyl bromide.20 Eluent: 646 ([M]+, 100).chloroform–methanol (1051). Crystallized from n-hexane– ethyl acetate. Yield: 43%; mp 67 °C; elemental analysis (%): 5-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}-4- oxapentane-1,2-diol 13. Synthesized from 4-hydroxymethyl- found (calc. for C42H62O5): C, 77.88 (77.98); H, 9.78 (9.66); dH(500 MHz, CDCl3, J/Hz) 0.87 (t, J 6.5, 6H, CH3), 1.2–1.5 2,2-dimethyl-1,3-dioxolane and 40.Eluent: chloroform–methanol (1051). Crystallized from n-hexane. Yield: 21%; (m, 28H, CH2), 1.7–1.8 (m, 4H, OCH2CH2), 2.06 (br s, 1H, CH2OH), 2.59 [br s, 1H, CH(OH)], 3.58–3.68 (m, 3H, transitions/°C: K 75 SA 144 Iso; elemental analysis (%): found (calc. for C42H62O5): C, 77.69 (77.98); H, 9.82 (9.66); CH2OH, OCHAHB), 3.72 (dd, J 11.3, 3.8, 1H, OCHAHB), 3.92 [m, 1H, CH(OH)], 3.99 (t, J 6.5, 4H, PhOCH2), 4.64 (s, dH(500 MHz, CDCl3, J/Hz) 0.88 (t, J 6.5, 6H, CH3), 1.2–1.4 (m, 24H, CH2), 1.4–1.5 (m, 4H, OCH2CH2CH2), 1.75–1.85 2H, PhCH2O), 6.96 (d, J 8.6, 4H, H-Ar), 7.41 (d, J 1.6, 2H, H-Ar), 7.53 (d, J 8.7, 4H, H-Ar), 7.64 (d, J 1.6, 1H, H-Ar); (m, 4H, OCH2CH2), 2.14 (br s, 1H, CH2OH), 2.72 [br s, 1H, CH(OH)], 3.6–3.8 (m, 4H, OCH2), 3.88–3.95 [m, 1H, m/z (%) 646 ([M]+, 100).CH(OH)], 3.99 (t, J 6.6, 2H, PhOCH2), 4.02 (t, J 6.6, 2H, PhOCH2), 4.62 (d, J 12.0, 1H, PhCHAHBO), 4.66 (d, J 12.0, 5-[5-Decyloxy-2-(4-decyloxyphenyl)phenyl]-4-oxapentane- 1,2-diol 6. Synthesized from 4-hydroxymethyl-2,2-dimethyl- 2H, PhCHAHBO), 6.93 (d, J 8.5, 1H, H-Ar) 6.96 (d, J 8.7, 2H, H-Ar), 7.2–7.6 (m, 3H, H-Ar), 7.59 (s, 5H, H-Ar); 1,3-dioxolane and 5-decyloxy-2-(4-decyloxyphenyl )benzylbromide. 18 Eluent: chloroform–methanol (1050.5).Crystallized dC(125 MHz, CDCl3) 14.07 (CH3), 22.66, 26.07, 26.11, 29.27, 29.31, 29.38, 29.41, 29.58, 29.60, 31.90, (CH2), 64.27 from methanol. Yield: 20%; transitions/°C: K 43 (SA 28) Iso; elemental analysis (%): found (calc.for C36H58O5): C, 75.58 (CH2OH), 68.18 (PhOCH2), 68.42 (PhOCH2), 68.95 [OCH2CH(OH)], 70.50 [OCH2CH(OH)], 72.26 (PhCH2O), (75.75); H, 10.37 (10.24); dH(500 MHz, CDCl3, J/Hz) 0.86 (t, J 6.5, 6H, CH3), 1.2–1.4 (m, 24H, CH2), 1.4–1.5 (m, 4H, 111.77, 114.89, 126.52, 126.99, 127.45, 127.93, 127.97, 133.04, 133.08, 138.95, 139.30, 156.49, 158.80 (C-Ar); m/z (%) 646 OCH2CH2CH2), 1.7–1.8 [m, 4H, OCH2CH2), 1.96 (dd, J 6.0, 6.0, 1H, CH2OH), 2.43 [d, J 5.1 1H, CH(OH)], 3.43 (dd, J ([M]+, 100). 9.6, 6.2, 1H, OCHAHB), 3.48 (dd, J 9.5, 3.9 1H, OCHAHB), 3.54–3.6 (m, 1H, CHAHBOH), 3.62–3.69 (m, 1H, CHAHBOH), 11-[2,5-Bis(4-decyloxyphenyl)phenyl]-4,7,10- trioxaundecane-1,2-diol 29b. Synthesized from 4-(7-hydroxy- 3.78–3.85 [m, 1H, CH(OH)], 3.96 (t, J 6.5, 2H, PhOCH2), 3.97 (t, J 6.5, 2H, PhOCH2), 4.41 (s, 2H, PhCH2O), 6.86 (dd, 2,5-dioxaheptyl )-2,2-dimethyl-1,3-dioxolane and 37.Eluent: chloroform–methanol (1050.3). Yield: 17%; transitions/°C: K J 8.6, 2.7, 1H, H-Ar), 6.91 (d, J 8.8, 2H, H-Ar), 6.99 (d, J 2.4, 1H, H-Ar), 7.16 (d, J 8.6, 1H, H-Ar), 7.19 (d, J 8.8, 2H, 54 (Colr 40 SA 48) Iso; elemental analysis (%): found (calc. for C46H70O7): C, 75.04 (75.16); H, 9.86 (9.60); dH(200 MHz, H-Ar); dC(125 MHz, CDCl3) 14.08 (CH3), 22.67, 26.10, 29.32, 29.35, 29.42, 29.56, 29.59, 31.90 (CH2), 64.10 (CH2OH), 68.14 CDCl3, J/Hz) 0.87 (t, J 6.7, 6H, CH3), 1.17–1.55 (m, 28H, CH2), 1.7–1.9 (m, 4H, OCH2CH2), 2.3 (br s, 2H, OH), (PhOCH2), 68.16 (PhOCH2), 70.51 [OCH2CH(OH)], 71.68 [OCH2CH(OH)], 71.99 (PhCH2O), 113.87, 114.18, 114.45, 3.45–3.66 (m, 12H, OCH2), 3.74–3.82 [m 1H, CH(OH)], 3.98 (t, J 6.5, 4H, PhOCH2), 4.48 (s, 2H, PhCH2O), 6.92 (d, J 8.7, 115.03, 130.24, 131.23, 132.77, 134.0, 136.18, 158.30, 158.39 (C-Ar); m/z (%) 570 ([M]+, 100). 2H, H-Ar), 6.96 (d, J 8.7, 2H, H-Ar), 7.29 (d, J 8.0, 2H, HAr), 7.31 (d, 1H, J 8.7, H-Ar), 7.50 (dd, J 8.0, 2.0, 1H, HAr), 7.57 (d, J 8.8, 2H, H-Ar), 7.72 (d, J 1.8, 1H, H-Ar); 5-(2,5-Didecyloxphenyl)-4-oxapentane-1,2-diol 7.Synthesized from 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane dC(125 MHz, CDCl3) 14.07 (CH3), 22.65, 26.07, 26.09, 29.30, 29.32, 29.34, 29.41, 29.55, 29.57, 30.84, 31.88, (CH2), 63.91 and 2,5-didecyloxybenzyl bromide.18 Eluent: chloroform– methanol (1050.5). Crystallized from n-pentane. Yield: 34%; (CH2OH), 68.11 (PhOCH2), 68.15 (PhOCH2), 69.62, 70.49, 70.53, 70.57, 70.81, [OCH2CH(OH), OCH2], 71.28 mp 42 °C; elemental analysis (%): found (calc.for C30H54O5): C, 72.65 (72.83); H, 11.34 (11.00); dH(200 MHz, CDCl3, [OC H2CH(OH)], 73.00 (PhCH2O), 114.16, 114.82, 125.85, 127.53, 128.05, 130.34, 130.46, 132.72, 133.12, 135.60, 139.63, J/Hz) 0.85 (t, J 6.4, 6H, CH3), 1.1–1.5 (m, 28H, CH2), 1.7–1.8 (m, 4H, OCH2CH2), 2.18 (br s, 1H, CH2OH), 2.76 [br s, 1H, 139.99, 158.46, 158.79 (C-Ar); m/z (%) 734 ([M]+, 100).CH(OH)], 3.5–3.7 [m, 5H, OCH2, CH(OH)], 3.87 (t, J 6.5, 2H, PhOCH2), 3.89 (t, J 6.6, 2H, PhOCH2), 4.50 (d, J 11.9, 14-[2,5-Bis(4-decyloxyphenyl)phenyl]-4,7,10,13- tetraoxatetradecane-1,2-diol 29c. Synthesized from 4-(10- 1H, PhCHAHBO), 4.57 (d, J 12.1, 1H, PhCHAHBO), 6.75 (s, 1H, H-Ar), 6.76 (s, 1H, H-Ar), 6.87 (s, 1H, H-Ar); m/z (%) hydroxy-2,5,8-trioxadecyl )-2,2-dimethyl-1,3-dioxolane and 37.Eluent: chloroform–methanol (1050.3). Yield: 16%; 494 ([M]+, 100). transitions/°C: K 45 (Colr 40) Iso; elemental analysis (%): found (calc. for C48H74O8): C, 73.56 (74.00); H, 9.53 (9.57); 5-{5-Decyloxy-2-[4-(4-decyloxyphenyl)phenyl]phenyl}-4- oxapentane-1,2-diol 11. Synthesized from 4-hydroxymethyl- dH(200 MHz, CDCl3, J/Hz) 0.87 (t, J 6.7, 6H, CH3), 1.27–1.45 (m, 28H, CH2), 1.76–1.83 (m, 4H, OCH2CH2), 3.50–3.62 (m, 2,2-dimethyl-1,3-dioxolane and 39.Eluent: chloroform–methanol (1050.5). Crystallized from n-hexane. Yield: 23%; 16H, OCH2), 3.71–3.87 [m, 1H, CH(OH)], 3.98 (t, J 6.5, 4H, PhOCH2), 4.49 (s, 2H, PhCH2O), 6.93 (d, J 8.5, 2H, H-Ar), transitions/°C: K 86 SA 114 Iso; elemental analysis (%): found (calc.for C42H62O5): C, 77.83 (77.98); H, 9.79 (9.66); dH 6.96 (d, J 8.6, 2H, H-Ar), 7.26–7.33 (m, 3H, H-Ar), 7.49 (dd, J 8.7, 1.7, 1H, H-Ar), 7.55 (d, J 8.7, 2H, H-Ar), 7.71 (d, J (200 MHz, CDCl3, J/Hz) 0.88 (t, J 6.5, 6H, CH3), 1.2–1.6 (m, 28H, CH2), 1.75–1.84 (m, 4H, OCH2CH2), 1.92 (dd, J 1.7, 1H, H-Ar); m/z (%) 778 ([M]+, 100). 6.0, 6.0, 1H, CH2OH), 2.41 [d, J 5.1, 1H, CH(OH)], 3.44–3.52 (m, 2H, OCH2), 3.55–3.60 (m, 1H, CHAHBOH), 3.62–3.68 13-[2,5-Bis(4-decyloxyphenyl)phenyl]-12-oxatridecane-1,2- diol 31. Synthesized from 4-(9-hydroxynonyl )-2,2-dimethyl- (m, 1H, CHAHBOH), 3.79–3.85 [m, 1H, CH(OH)], 3.98 (t, J 6.5, 2H, PhOCH2), 3.99 (t, J 6.5, 2H, PhOCH2), 4.47 (s, 2H, 1,3-dioxolane and 37. Eluent: chloroform–methanol (1051).Crystallized from n-hexane. Yield: 21%; transitions/°C: K 54 PhCH2O), 6.89 (dd, J 8.6, 2.6, 1H, H-Ar), 6.96 (d, J 8.8, 2H, H-Ar), 7.08 (d, J 2.4, 1H, H-Ar), 7.22 (d, J 8.8, 1H, H- (N 30) Iso; elemental analysis (%): found (calc. for C50H78O5): C, 78.86 (79.11); H, 10.74 (10.36); dH(200 MHz, CDCl3, Ar), 7.34 (d, J 8.1, 2H, H-Ar), 7.52–7.59 (2d, 4H, H-Ar); dC(50 MHz, CDCl3) 14.09 (CH3), 22.65, 26.05, 29.30, 29.39, J/Hz) 0.88 (t, J 6.5, 6H, CH3), 1.24–1.4 (m, 34H, CH2), 1.4–1.62 (m, 8H, CH2), 1.77–1.85 (m, 6H, OCH2CH2), 3.43 29.55, 31.87 (CH2), 64.02 (CH2OH), 68.10 (PhOCH2), 70.47 [OCH2CH(OH)], 71.64 [OCH2CH(OH)], 71.99 (PhCH2O), (t, J 6.5, 2H, PhCH2OCH2), 3.38–3.46 [m, 1H, CHAHBOH], J.Mater. Chem., 1998, 8, 2611–2626 26173.61–3.73, [m, 2H, CHAHBOH, CH(OH)], 4.02 (t, J 6.5, 2H, 7.31 (d, J 8.6, 1H, H-Ar), 7.52 (dd, J 8.1, 1.7, 1H, H-Ar), 7.55 PhOCH2), 4.04 (t, J 6.5, 2H, PhOCH2), 4.42 (s, 2H, PhCH2O), (d, J 8.7, 2H, H-Ar), 7.72 (d, J 1.7, 1H, H-Ar); m/z (%) 704 6.94 (d, J 8.5, 2H, H-Ar), 6.97 (d, J 8.6, 2H, H-Ar), 7.29–7.35 ([M]+, 67), 556 (59).(m, 3H, H-Ar), 7.50 (dd, J 8.7, 1.7, 1H, H-Ar), 7.56 (d, J 8.7, 2H, H-Ar), 7.71 (d, J 1.8, 1H, H-Ar); m/z (%) 758 ([M]+, 100). 14-[2,5-Bis(4-decyloxyphenyl )phenyl]-4,7,10,13- tetraoxatetradecanol 30b. Synthesized from tetraethylene glycol 11-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}- and 37. Eluent: chloroform–methanol (1050.5). Crystallized 4,7,10-trioxaundecane-1,2-diol 34b. Synthesized from 4-(7- from n-hexane. Yield: 25%; transitions/°C: K 44 (SA 31) Iso; hydroxy-2,5-dioxaheptyl )-2,2-dimethyl-1,3-dioxolane and 40.elemental analysis (%): found (calc. for C47H72O7): C, 75.08 Eluent: chloroform–methanol (1050.5). Yield: 32%; (75.36); H, 9.76 (9.69); dH(200 MHz, CDCl3, J/Hz) 0.91 (t, J transitions/°C: K 36 SA 97 Iso; dH(400 MHz, CDCl3, J/Hz) 6.4, 6H, CH3), 1.2–1.6 (m, 28H, CH2), 1.75–1.92 (m, 4H, 0.87 (t, J 6.4, 6H, CH3), 1.27–1.36 (m, 24H, CH2), 1.42–1.49 OCH2CH2), 3.54–3.78 (m, 16H, OCH2), 4.01 (t, J 6.5, 4H, (m, 4H, OCH2CH2CH2), 1.75–1.83 (m, 4H, OCH2CH2), 2.28 PhOCH2), 4.52 (s, 2H, PhCH2O), 6.93 (d, J 8.5, 2H, H-Ar), (br s, 2H, OH), 3.50–3.71 (m, 12H, OCH2), 3.78–3.83 [m, 6.96 (d, J 8.6, 2H, H-Ar), 7.28 (d, J 8.5, 2H, H-Ar), 7.31 (d, 1H, CH(OH)], 3.99 (t, J 6.6, 2H, PhOCH2), 4.00 (t, J 6.4, J 8.6, 1H, H-Ar), 7.5–7.6 (m, 3H, H-Ar), 7.74 (d, J 1.7, 1H, 2H, PhOCH2), 4.66 (s, 2H, PhCH2O), 6.90 (d, J 8.4, 1H, HH- Ar); m/z (%) 748 ([M]+, 68), 704 (27).Ar), 6.96 (d, J 8.8, 2H, H-Ar), 7.48 (dd, J 8.4, 2.3, 1H, HAr), 7.54 (d, J 8.6, 2H, H-Ar), 7.57–7.62 (m, 4H, H-Ar), 7.68 (d, J 2.3, 1H, H-Ar); m/z (%) 734 ([M]+, 74), 660 (79). 3.6. Synthesis of the p-terphenyl derivatives 29a and 34a 14-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}- At first the appropriate bromomethyl substituted 4,4>-didecyl- 4,7,10,13-tetraoxatetradecane-1,2-diol 34c.Synthesized from oxy-p-terphenyl derivatives 37 and 40 were etherified according 4-(10-hydroxy-2,5,8-trioxadecyl )-2,2-dimethyl-1,3-dioxolane to procedure 3.4.1 with 2-allyloxyethanol to give the allyl and 40.Eluent: chloroform–methanol (1050.3). Yield: 27%; ether. The allyl ethers were used without further purification transitions/°C: K 45 SA 72 Iso; dH(200 MHz, CDCl3, J/Hz) for the dihydroxylation reaction. 0.87 (t, J 6.4, 6H, CH3), 1.27–1.55 (m, 28H, CH2), 1.70–1.85 (m, 4H, OCH2CH2), 3.5–3.7 [m, 17H, OCH2, CH(OH)], 3.99 3.6.1. Procedure for the dihydroxylation. The appropriate (t, J 6.4, 4H, PhOCH2), 4.66 (s, 2H, PhCH2O), 6.90 (d, J 8.6, allyl ether (1 mmol, 657 mg) was added to a solution of N- 1H, H-Ar), 6.96 (d, J 8.6, 2H, H-Ar), 7.4–7.7 (m, 8H, H-Ar); methylmorpholine N-oxide (1.4 mmol, 0.15 ml of 60% aq.m/z (%) 778 ([M]+, 100). solution) in acetone (20 ml ). Osmium tetroxide (0.05 ml of 0.01 M solution in tert-butyl alcohol ) was added and the 8-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}-7- resulting mixture was stirred for 24 h at room temperature.oxaoctane-1,2-diol 35a. Synthesized from 4-(4-hydroxybutyl )- After this time starting materials could no longer be detected 2,2-dimethyl-1,3-dioxolane and 40. Eluent: chloroform–methand the mixture was worked up as follows: sodium hydrogen anol (1050.2). Yield: 37%; transitions/°C: K 75 SA 114 Iso; sulfite (4 ml saturated solution) was added and the resulting dH(200 MHz, CDCl3, J/Hz) 0.88 (t, J 6.6, 6H, CH3), 1.2–1.9 slurry was vigorously stirred at room temperature for 30 min.(m, 38H, CH2), 3.39 (dd, J 10.8, 7.6, 1H, CHAHBOH), 3.5–3.7 Afterwards, the solid were filtered oV, the residue was extracted [m, 4H, CHAHBOH, CH(OH), CH2O], 3.99 (t, J 6.6, 2H, three times with ethyl acetate (30 ml ) and the combined PhOCH2), 4.00 (t, J 6.5, 2H, PhOCH2), 4.59 (s, 2H, PhCH2O), organic phases were washed with 10% H2SO4, water and 6.90 (d, J 8.6, 1H, H-Ar), 6.96 (d, J 8.8, 2H, H-Ar), 7.47 (dd, brine.After drying with Na2SO4 the solvent was evaporated J 8.4, 2.4, 1H, H-Ar), 7.5–7.65 (m, 6H, H-Ar), 7.64 (d, 2.3, and the crude products were purified by column 1H, H-Ar); m/z (%) 688 ([M]+, 100).chromatography. 13-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}- 12-oxatridecane-1,2-diol 35b. Synthesized from 4-(9-hydroxy- 8-[2,5-Bis(4-decyloxyphenyl)phenyl]-4,7-dioxaoctane-1,2- nonyl )-2,2-dimethyl-1,3-dioxolane and 40. Crystallized from diol 29a. Synthesized from 2-allyloxyethanol and 37, followed light petroleum (60–80 °C).Yield: 17%; mp 110–112 °C; by dihydroxylation. Eluent: chloroform–methanol (1050.3). elemental analysis (%): found (calc. for C50H78O5): C, 78.87 Yield: 10%; transitions/°C: K 66 SA 73 Iso; dH(200 MHz, (79.11); H, 10.53 (10.36); dH(200 MHz, CDCl3, J/Hz) 0.89 CDCl3, J/Hz) 0.87 (t, J 6.7, 6H, CH3), 1.24–1.74 (m, 28H, (t, J 6.8, 6H, CH3), 1.29–1.40 (m, 44H, CH2), 1.74–1.85 (m, CH2), 1.76–1.83 (m, 4H, OCH2CH2), 3.5–3.7 (m, 8H, OCH2), 4H, OCH2CH2), 3.36–3.67 [m, 5H, CH(OH), OCH2], 4.01 3.7–3.9 [m, 1H, CH(OH)], 3.98 (t, J 6.5, 4H, PhOCH2), 4.49 (t, J 6.6, 2H, PhOCH2), 4.02 (t, J 6.5, 2H, PhOCH2), 4.61 (s, (s, 2H, PhCH2O), 6.93 (d, J 8.6, 2H, H-Ar), 6.96 (d, J 8.7, 2H, PhCH2O), 6.92 (d, J 8.6, 1H, H-Ar), 6.98 (d, J 8.8, 2H, 2H, H-Ar), 7.27–7.51 (m, 3H, H-Ar), 7.51 (d, J 8.8, 1H, H- H-Ar), 7.47–7.65 (m, 4H, H-Ar), 7.68 (d, 2.3, 1H, H-Ar); m/z Ar), 7.55 (d, J 8.7, 2H, H-Ar), 7.70 (d, J 1.7, 1H, H-Ar); m/z (%) 758 ([M]+, 18), 556 (100).(%) 690 ([M]+, 100). 3.5. Synthesis of the oligoethylene glycol ethers 30 8-{2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]phenyl}-4,7- These compounds were obtained by etherification of dioxaoctane-1,2-diol 34a.Synthesized from 2-allyloxyethanol appropriate benzyl bromides with triethylene glycol and tetraand 40, followed by dihydroxylation. Eluent: chloroform– ethylene glycol respectively, according to procedure 3.4.1. methanol (1050.5). Yield: 30%; transitions/°C: K 58 SA 121 Iso; elemental analysis (%): found (calc. for C44H66O6): C, 11-[2,5-Bis(4-decyloxyphenyl)phenyl]-4,7,10- 76.20 (76.48); H, 9.89 (9.63); dH(200 MHz, CDCl3, J/Hz) trioxaundecanol 30a.Synthesized from triethylene glycol and 0.87 (t, J 6.6, 6H, CH3), 1.2–1.6 (m, 28H, CH2), 1.7–1.9 (m, 37. Eluent: chloroform–methanol (1050.1). Yield: 18%; 4H, OCH2CH2), 3.5–3.75 (m, 8H, OCH2), 3.8–3.9 [m, 1H, transitions/°C: K 61 (SA 52) Iso; dH(200 MHz, CDCl3, J/Hz) CH(OH)], 3.98 (t, J 6.6, 2H, PhOCH2), 4.00 (t, J 6.4, 2H, 0.87 (t, J 6.5, 6H, CH3), 1.26–1.55 (m, 28H, CH2), 1.72–1.86 PhOCH2), 4.66 (s, 2H, PhCH2O), 6.90 (d, J 8.4, 1H, H-Ar), (m, 4H, OCH2CH2), 3.53–3.69 (m, 12H, OCH2), 3.98 (t, J 6.96 (d, J 8.8, 2H, H-Ar), 7.4–7.6 (m, 7H, H-Ar), 7.65 (d, J 6.5, 4H, PhOCH2), 4.48 (s, 2H, PhCH2O), 6.93 (d, J 8.5, 2H, H-Ar), 6.95 (d, J 8.6, 2H, H-Ar), 7.30 (d, J 8.0, 2H, H-Ar), 2.2, 1H, H-Ar); m/z (%) 690 ([M]+, 100). 2618 J. Mater. Chem., 1998, 8, 2611–26263.7. 2,5-Bis(4-decyloxyphenyl )benzyl(triethyl )ammonium the yellowish oil obtained was crystallized from n-hexane. Yield: 92%; transitions/°C: K 58 (N 40) Iso; elemental analysis bromide 28 (%): found (calc. for C39H53O3Cl ): C, 77.45 (77.39); H, 8.57 In a three-necked flask equipped with a magnetic stirring bar (8.83); Cl, 5.64 (5.86); dH(200 MHz, CDCl3, J/Hz) 0.88 (t, J and a dropping funnel 37 (1.25 mmol, 800 mg) was dissolved 6.5, 6H, CH3), 1.26–1.41 (m, 28H, CH2), 1.67–1.78 (m, 4H, in dry acetonitrile (70 ml ) at 50 °C under argon atmosphere.OCH2CH2), 3.81 (t, J 6.4, 2H, PhOCH2), 4.00 (t, J 6.5, 2H, Dry triethylamine (30 ml ) was added dropwise while stirring. PhOCH2), 6.87 (d, J 8.5, 2H, H-Ar), 6.92 (d, J 8.5, 2H, HThe reaction mixture was stirred under reflux for 15 h.After Ar), 7.29 (d, J 8.5, 2H, H-Ar), 7.30–7.32 (m, 1H, H-Ar), 7.49 cooling to room temperature the solvent was evaporated and (dd, J 8.7, 1.7, 1H, H-Ar), 7.53 (d, J 8.6, 2H, H-Ar), 7.75 (d, the residue dissolved in chloroform (100 ml ). The organic J 1.2, 1H, H-Ar). phase was washed several times with water and dried with CaCl2.The solvent was removed in vacuo and the crude 3.11. Synthesis of the 2,5-bis(4-decyloxyphenyl )benzamides product obtained was purified by column chromatography 15–24 (Silica gel, chloroform–methanol 1052) followed by recrystallization from ethyl acetate. Yield: 35%; mp 140 °C; elemental In a three-necked flask equipped with a magnetic stirring bar analysis (%): found (calc.for C45H70O2NBr): C, 72.96 (73.34); the appropriate amine (1,5 mmol) was dissolved in dry DMF H, 9.26 (9.57); Br, 10.53 (10.84); N, 1.96 (1.90); dH(200 MHz, (30 ml ) under argon atmosphere. A solution of 26 (0.5 mmol, CDCl3, J/Hz) 0.86 (t, J 6.6, 6H, CH3), 1.14 (t, J 6.4, 9H, 300 mg) in toluene (20 ml ) was slowly added dropwise to this NCH2CH3), 1.18–1.57 (m, 28H, CH2), 1.7–1.9 (m, 4H, stirred mixture at room temperature.The mixture was stirred OCH2CH2CH2), 3.15–3.35 (m, 6H, NCH2CH3), 3.97 (t, J 6.5, several hours at 80 °C, until the reaction was complete 4H, PhOCH2), 4.94 (s, 2H, PhCH2N), 6.94 (d, J 8.5, 2H, H- (TLC). After the solvent was removed in vacuo the residue Ar), 6.99 (d, J 8.6, 2H, H-Ar), 7.21 (d, J 8.4, 2H, H-Ar), 7.35 was dissolved in diethyl ether (100 ml ) and the organic phase (d, J 8.0, 1H, H-Ar), 7.56 (d, J 8.5, 2H, H-Ar), 7.65 (d, J 8.7, was washed first with 10% hydrochloric acid (40 ml ) and 1H, H-Ar), 7.87 (s, 1H, H-Ar).afterwards with water (50 ml ). The organic phase was dried with sodium sulfate. Then the solvent was evaporated and the 3.8. Sodium 2,5-bis(4-decyloxyphenyl )benzoate 27 crude product obtained was purified by flash column chromatography followed by recrystallization. Methyl 2,5-bis(4-decyloxyphenyl )benzoate 14 (1 mmol, 601 mg) was added to a stirred solution prepared from ethanol 2,5-Bis(4-decyloxyphenyl)benzamide 15.Synthesized by (50 ml ) and NaOH (0.25 mol, 10 g) and heated 4 h under introduction of ammonia into a solution of 26 in DMF at reflux.After termination of the reaction the solvent was room temperature. Eluent: chloroform–methanol (1051). removed in vacuo and 50 ml water were added. The aqueous Crystallized from ethyl acetate. Yield: 65%; mp 184 °C; elemen- phase was extracted three times with chloroform (50 ml ). The tal analysis (%): found (calc. for C39H55O3N): C, 79.99 (79.95); combined organic phases were washed several times with water H, 9.21 (9.46); N, 2.04 (2.39); dH(500 MHz, CDCl3, J/Hz) and brine and afterwards dried with calcium chloride.After 0.87 (t, J 6.7, 6H, CH3), 1.2–1.5 (m, 28H, CH2), 1.75–1.84 evaporation of the solvent the residue was recrystallized from (m, 4H, OCH2CH2), 3.97 (t, J 6.8, 2H, PhOCH2), 3.99 (t, J ethyl acetate. Yield: 86%; mp 216–218 °C; elemental analysis 6.7, 2H, PhOCH2), 5.28 (br s, 1H, NH), 5.44 (br s, 1H, NH), (%): found (calc.for C39H53O4Na): C, 77.25 (76.94); H, 8.85 6.94 (d, J 8.6, 2H, H-Ar), 6.97 (d, J 8.5, 2H, H-Ar), 7.35 (d, (8.77); dH(200 MHz, CDCl3, J/Hz) 0.85 (t, J 6.4, 6H, CH3), J 7.8, 1H, H-Ar), 7.38 (d, J 8.8, 2H, H-Ar), 7.56 (d, J 8.8, 1.1–1.8 (m, 28H, CH2), 1.9–2.2 (m, 4H, OCH2CH2), 3.56 (t, 2H, H-Ar), 7.65 (dd, J 8.1, 2.1, 1H, H-Ar), 7.96 (d, J 2.0, 1H, J 6.3, 4H, PhOCH2), 6.55 (d, J 8.3, 2H, H-Ar), 6.75 (d, J 8.5, H-Ar); m/z (%) 585 ([M]+, 100). 2H, H-Ar), 7.1–7.2 (m, 3H, H-Ar), 7.4–7.5 (m, 3H, H-Ar), 7.91 (s, 1H, H-Ar). 2,5-Bis(4-decyloxyphenyl)benzoylaminoethane 16. Synthesized from ethylamine and 26. Eluent: chloroform– 3.9. 2,5-Bis(4-decyloxyphenyl )benzoic acid 25 methanol (1050.5).Crystallized from methanol. Yield: 84%; Compound 27 (10 mmol, 6.1 g) was dissolved in ethanol mp 111 °C; elemental analysis (%): found (calc. for (250 ml ). Concentrated hydrochloric acid (100 ml ) was added C41H59O3N): C, 79.98 (80.21); H, 9.37 (9.69); N, 2.04 (2.28); while stirring and the mixture was heated under reflux for 2 h. dH(500 MHz, CDCl3, J/Hz) 0.87 (t, J 7.1, 9H, CH3), 1.2–1.5 After cooling, water (250 ml ) was added dropwise and the (m, 28H, CH2), 1.75–1.83 (m, 4H, OCH2CH2), 3.21 (dq, 2H, mixture was extracted three times with diethyl ether (150 ml ).NHCH2), 3.96 (t, J 6.8, 2H, PhOCH2), 3.98 (t, J 6.7, 2H, The combined organic phases were washed several times with PhOCH2), 5.19 (t, J 5.6, 1H, NH), 6.93 (d, J 8.7, 2H, H-Ar), aq.NaHCO3 solution and then with water. After drying with 6.95 (d, J 8.7, 2H, H-Ar), 7.34 (d, J 8.8, 2H, H-Ar), 7.36 (d, Na2SO4 the solvent was removed in vacuo. The crude product J 8.7, 1H, H-Ar), 7.55 (d, J 8.7, 2H, H-Ar), 7.61 (dd, J 8.0, was purified by recrystallization from a mixture of n-hexane 2.0, 1H, H-Ar), 7.87 (d, J 1.9, 1H, H-Ar); m/z (%) 613 and ethyl acetate. Yield: 80%; transitions/°C: K 151 (SA 125) ([M]+, 100).Iso; elemental analysis (%): found (calc. for C39H54O4): C, 79.67 (79.82); H, 9.46 (9.27); dH(200 MHz, CDCl3, J/Hz) 2,5-Bis(4-decyloxyphenyl)benzohydrazide 17. Synthesized by 0.87 (t, J 6.5, 6H, CH3), 1.1–1.6 (m, 28H, CH2), 1.7–1.9 (m, adding hydrazine hydrate (100%) to a solution of 14 in n- 4H, OCH2CH2), 3.96 (t, J 6.5, 2H, PhOCH2), 3.99 (t, J 6.4, butanol and stirring at reflux temperature for 10 h.Crystallized 2H, PhOCH2), 6.90 (d, J 8.4, 2H, H-Ar), 6.96 (d, J 8.5, 2H, from ethanol. Yield: 83%; transitions/°C: K 98 SA 131 Iso; H-Ar), 7.29 (d, J 8.5, 2H, H-Ar), 7.38 (d, J 8.4, 1H, H-Ar), elemental analysis (%): found (calc. for C39H56O3N2): C, 77.78 7.55 (d, J 8.7, 2H, H-Ar), 7.69 (dd, J 8.6, 1.4, 1H, H-Ar), 8.09 (77.96); H, 9.76 (9.39); N, 4.91 (4.66); dH(500 MHz, CDCl3, (d, J 1.2, 1H, H-Ar); m/z (%) 586 ([M]+, 100).J/Hz) 0.87 (t, J 6.7, 6H, CH3), 1.22–1.51 (m, 28H, CH2), 1.75–1.83 (m, 4H, OCH2CH2), 3.8–4.0 (br s, 2H, NH2), 3.97 3.10. 2,5-Bis(4-decyloxyphenyl )benzoyl chloride 26 (t, J 6.8, 2H, PhOCH2), 3.99 (t, J 6.7, 2H, PhOCH2), 6.53 (br s, 1H, CONH), 6.93 (d, J 8.7, 2H, H-Ar), 6.96 (d, J 8.7, Oxalyl chloride (2.5 mmol, 460 mg) was added slowly with a syringe to a solution of 25 (0.25 mmol, 150 mg) in dry 2H, H-Ar), 7.31 (d, J 8.6, 2H, H-Ar), 7.38 (d, J 8.1, 1H, HAr), 7.54 (d, J 8.5, 2H, H-Ar), 7.64 (dd, J 8.1, 1.9, 1H, H- dichloromethane (10 ml ) under argon atmosphere at room temperature.The reaction mixture was stirred for one hour.Ar), 7.83 (d, J 2.0, 1H, H-Ar); m/z (%) 600 ([M]+, 8), 567 (26), 466 (100). The solvent and excess oxalyl chloride were evaporated and J. Mater. Chem., 1998, 8, 2611–2626 26192-[2,5-Bis(4-decyloxyphenyl)benzoylamino]ethanol 18. elemental analysis (%): found (calc. for C43H63O5N): C, 76.43 (76.63); H, 9.32 (9.42); N, 2.04 (2.08); dH(500 MHz, CDCl3, Synthesized from 2-aminoethanol and 26.Eluent: chloroform– methanol (1051). Crystallized from n-hexane–ethyl acetate. J/Hz) 0.87 (t, J 6.5, 6H, CH3), 1.21–1.50 (m, 28H, CH2), 1.74–1.83 (m, 4H, OCH2CH2), 2.8–3.9 (m, 8H, CH2N, CH2O), Yield: 87%; transitions/°C: K 118 SA 131 Iso; elemental analysis (%): found (calc. for C41H59O4N): C, 77.99 (78.18); 3.96 (t, J 6.7, 2H, PhOCH2), 3.98 (t, J 6.7, 2H, PhOCH2), 6.92 (d, J 8.8, 2H, H-Ar), 6.95 (d, J 8.7, 2H, H-Ar), 7.39 (d, H, 9.37 (9.44); N, 2.04 (2.22); dH(500 MHz, CDCl3, J/Hz) 0.87 (t, J 6.5, 6H, CH3), 1.23–1.50 (m, 28H, CH2), 1.77–1.82 J 8.7, 1H, H-Ar), 7.43 (d, J 8.7, 2H, H-Ar), 7.53 (d, J 8.8, 2H, H-Ar), 7.55 (d, J 1.8, 1H, H-Ar), 7.61 (dd, J 8.1, 1.8, 1H, (m, 4H, OCH2CH2), 3.26 (dt, J 10.2, 5.5, 2H, NHCH2), 3.50 (t, J 5.1, 2H, CH2OH), 3.97 (t, J 6.7, 2H, PhOCH2), 3.99 (t, H-Ar); m/z (%) 674 ([M+1]+, 100).J 6.7, 2H, PhOCH2), 5.68 (t, J 6.0, 1H, NH), 6.94 (dd, J 8.8, 2.1, 2H, H-Ar), 6.96 (2d, 4H, H-Ar), 7.37 (d, J 8.7, 3H, H- 4-[2,5-Bis(4-decyloxyphenyl)benzoyl]morpholine 23. Synthesized from morpholine and 26. Eluent: ethyl acetate. Ar), 7.55 (d, J 8.0, 2H, H-Ar), 7.63 (dd, J 8.0, 2.0, 1H, H-Ar), 7.86 (d, J 2.0, 1H, H-Ar); m/z (%) 629 ([M]+, 100).Crystallized from n-hexane–ethyl acetate. Yield: 81%; mp 96 °C; elemental analysis (%): found (calc. for C43H61O4N): C, 78.69 (78.74); H, 9.51 (9.37); N, 2.08 (2.14); dH(500 MHz, 3-[2,5-Bis(4-decyloxyphenyl)benzoylamino]propane-1,2-diol 19. Synthesized from 3-aminopropane-1,2-diol and 26. Eluent: CDCl3, J/Hz) 0.87 (t, J 6.5, 6H, CH3), 1.24–1.51 (m, 28H, CH2), 1.71–1.87 (m, 4H, OCH2CH2), 2.49–3.75 (m, 8H, ethyl acetate.Crystallized from n-hexane–ethyl acetate. Yield: 90%; transitions/°C: K 115 SA 142 Iso; elemental analysis (%): CH2N, CH2O), 3.99 (t, J 6.7, 4H, PhOCH2), 6.97 (2d, 4H, H-Ar), 7.40 (d, J 8.9, 2H, H-Ar), 7.5–7.7 (m, 5H, H-Ar); m/z found (calc. for C42H61O5N): C, 76.19 (76.43); H, 9.21 (9.32); N, 2.04 (2.12); dH(500 MHz, CDCl3, J/Hz) 0.87 (t, J 6.5, 6H, (%) 655 ([M]+, 80), 429 (27).CH3), 1.22–1.50 (m, 28H, CH2), 1.74–1.85 (m, 4H, OCH2CH2), 3.21–3.27 (m, 1H, NHCHAHB), 3.32–3.37 (m, 16-[2,5-Bis(4-decyloxyphenyl )benzoyl]-1,4,7,10,13- pentaoxa-16-azacyclooctadecane 24. Synthesized from 1H, NHCHAHB), 3.40 (dd, J 11,2, 4.8, 1H, CHAHBOH), 4.35 (dd, J 11,4, 4.5, 1H, CHAHBOH), 3.55–3.59 [m, 1H, CH(OH)], 1,4,7,10,13-pentaoxa-16-azacyclooctadecane and 26.Eluent: ethyl acetate. Crystallized from n-hexane. Yield: 72%; mp 3.97 (t, J 6.7, 2H, PhOCH2), 3.99 (t, J 6.7, 2H, PhOCH2), 5.72 (dd, J 6.0, 6.0, 1H, NH), 6.93 (d, J 8.5, 2H, H-Ar), 6.95 73 °C; elemental analysis (%): found (calc. for C51H77O8N): C, 73.29 (73.61); H, 9.57 (9.33); N, 1.61 (1.68); dH(200 MHz, (d, J 8.7, 2H, H-Ar), 7.33 (d, J 8.7, 2H, H-Ar), 7.35 (d, J 8.0, 1H, H-Ar), 7.54 (d, J 8.7, 2H, H-Ar), 7.63 (dd, J 8.0, 2.0, 1H, CDCl3, J/Hz) 0.86 (t, J 6.4, 6H, CH3), 1.24–1.56 (m, 28H, CH2), 1.69–1.85 (m, 4H, OCH2CH2), 3.1–3.8 (m, 24H, NCH2, H-Ar), 7.86 (d, J 2.0, 1H, H-Ar); dC(125 MHz, CDCl3) 14.11 (CH3), 22.68, 26.04, 29.24, 29.28, 29.32, 29.41, 29.56, 29.58, OCH2), 3.94 (t, J 6.7, 2H, PhOCH2), 3.98 (t, J 6.7, 2H, PhOCH2), 6.87 (d, J 8.7, 2H, H-Ar), 6.94 (d, J 8.8, 2H, H-Ar), 31.89 (CH2), 42.70 (NHCH2), 63.63 (CH2OH), 68.13 (PhOCH2), 68.23 (PhOCH2), 70.89 [CH(OH)CH2OH], 7.3–7.6 (m, 7H, H-Ar); m/z (%) 831 ([M]+, 100). 114.74, 114.91, 126.97, 128.01, 128.45, 129.92, 130.78, 131.84, 134.95, 137.31, 139.94, 159.12 (C-Ar), 171.58 (CO); m/z (%) 4. Results and discussion 659 ([M]+, 100). 4.1.Facial amphiphiles with lateral propane-2,3-diol groups N-[2,5-Bis(4-decyloxyphenyl )benzoyl]-1-deoxy-1- The glycerol ether 1e was the first compound investigated.27 methylamino-D-glucitol 20. Synthesized from 1-deoxy-1- It exhibits an enantiotropic smectic A phase. A comparison methylamino-D-glucitol and 26. Eluent: chloroform–methanol of the diol 1 with compound 227 carrying a lateral alkyl (1052).Crystallized from n-pentane. Yield: 90%; mp 87 °C; substituent of comparable size (Fig. 2) indicates a significant elemental analysis (%): found (calc. for C46H69O8N): C, 71.98 mesophase stabilizing influence of the two hydroxy groups. (72.31); H, 9.37 (9.10); N, 1.74 (1.83); [a]D30 0.9 (c 1.05, Furthermore, it is obvious that the laterally attached hydrogen CHCl3); dH(500 MHz, CDCl3, J/Hz) 0.86 (t, J 6.1, 6H, CH3), bonding group increases the structural order, which means 1.21–1.48 (m, 28H, CH2), 1.71–1.82 (m, 4H, OCH2CH2), 2.47 that the layered smectic A phase is stabilized with respect to (s, 3H, NCH3), 3.2–4.95 [m, 8H, CH(OH), CH2O, CH2N], the nematic phase of the nonamphiphilic compound 2. 3.94 (t, J 6.7, 2H, PhOCH2), 3.96 (t, J 6.7, 2H, PhOCH2), Contrary to smectic phases of conventional amphiphiles and 6.93 (2d, 4H, H-Ar), 7.33 (d, J 8.6, 2H, H-Ar), 7.38 (d, J 8.1, 1H, H-Ar), 7.51 (d, J 8.6, 3H, H-Ar), 7.59 (dd, J 8.2, 1.8, 1H, H-Ar); m/z (%) 763 ([M]+, 18), 599 (28), 586 (23), 569 (100). 1-[2,5-Bis(4-decyloxyphenyl)benzoylamino]-1-deoxy-Dglucitol 21. Synthesized from 1-amino-1-deoxy-D-glucitol and 26.Eluent: chloroform–methanol (1052). Crystallized from nhexane –ethyl acetate. Yield: 76%; transitions/°C: K 112 SA 147 Iso; elemental analysis (%): found (calc. for C45H67O8N): C, 71.71 (72.06); H, 9.22 (9.00); N, 1.59 (1.87); [a]D25 -0.1 (c 1.09, CHCl3); dH(200 MHz, DMSO, J/Hz) 0.87 (t, J 6.5, 6H, CH3), 1.21–1.52 (m, 28H, CH2), 1.74–1.83 (m, 4H, OCH2CH2), 3.2–3.7 [m, 8H, CH(OH), CH2O, CH2N], 3.98 (t, J 6.7, 2H, PhOCH2), 3.99 (t, J 6.7, 2H, PhOCH2), 4.1–4.4 (m, 3H, OH), 4.48 (d, J 4.7, 1H, OH), 4.77 (d, J 4.5, 1H, OH), 6.93 (d, J 8.7, 2H, H-Ar), 6.99 (d, J 8.8, 2H, H-Ar), 7.34 (d, J 8.6, 2H, H-Ar), 7.38 (d, J 8.1, 1H, H-Ar), 7.62 (m, Fig. 2 Comparison of the mesomorphic properties of the laterally substituted compounds 1e and 2.27 The existence regions of the phases 4H, H-Ar), 8.19 (dd, J 5.4, 5.4, 1H, NH); m/z (%) 749 ([M]+, are displayed as bars.Black areas indicate the solid crystalline state 68), 627 (21), 586 (83), 569 (100). and hatched or blank areas correspond to liquid crystalline phases. If the liquid crystalline phase appears below the melting point, these are 3-[2,5-Bis(4-decyloxyphenyl)benzoyl]-3-azapentane-1,5-diol monotropic (metastable) mesophases which are given in brackets.The 22. Synthesized from diethanolamine and 26. Eluent: numbers above the bars indicate the phase transition temperatures. chloroform–methanol (1051). Crystallized from n-hexane– Abbreviations: K=crystalline solid, N=nematic Phase, SA=smectic A phase. ethyl acetate. Yield: 70%; transitions/°C: K 110 (SA 97) Iso; 2620 J.Mater. Chem., 1998, 8, 2611–2626amphiphiles containing terminally connected rigid units, which usually form bilayer structures, the smectic phase of 1e presents a monolayer structure. The fixation of the molecules in the single-layers should be provided by attractive hydrogen bonding28 between their hydroxy groups and probably also by hydrogen bonding between the hydroxy groups and the aromatic p-systems.Furthermore, the hydroxy groups signifi- cantly increase the polarity in the region of the rigid cores and thus favor micro-segregation of these regions from the lipophilic alkyl chains.29 Thus, the smectic layer structure is stabilized by the attractive forces provided by hydrogen bonding and by micro-segregation. The propane-2,3-diol group incorporates a stereogenic center.Remarkably, however, no measurable influence of chirality on the mesomorphic properties has been found. Both the racemic compound 1e and the optically active compound (S)-1e (K 83 SA 114 Iso) have identical melting and clearing temperatures. Therefore all other compounds described in this paper have been prepared only as racemic mixtures. The dependence of the mesomorphic properties on the length of the terminal chains is shown in Fig. 3. With the exception of the nematic ethoxy substituted compound 1a all other synthesized p-terphenyl derivatives 1 display smectic A phases. Remarkably, the mesophase stability significantly increases on elongation of the terminal lipophilic chains. Also the quinquaphenyl derivative 5 and the biphenyl derivative 6 exhibit SA phases.The corresponding methyl substituted biphenyl derivative 8, carrying the much smaller methyl group, exhibits a monotropic nematic phase with a significantly lower clearing temperature than the SA phase of 6. This again shows the stabilizing influence of the lateral diol group. However, compound 7, incorporating only a single benzene ring, is a non-mesomorphic compound.This shows that the amphiphilic structure alone does not cause the liquid crystallinity in this class of compounds. Mesomorphic properties are also lost if the linear p-terphenyl rigid core is replaced by an angular m-terphenyl central unit (compound 4). This is in accordance with the behavior of conventional calamitic liquid crystals. The mesophase destabilization on replacing the alkoxy substituents by alkyl groups (compounds 3) is also analogous to nonamphiphilic calamitic mesogens. 4.2. Influence of the position of the diol group In Fig. 4 the dependence of the mesomorphic properties on the position of the 4,5-dihydroxy-2-oxapentyl group is compared with the influence of a methyl group in the same positions. For the diol derivatives 1e, 11 and 13 the order of mesophase stability (1e~11<13) is principally the same as for the methyl substituted molecules (915~1018<1218).However, the SC phases of the methyl substituted derivatives are completely replaced by smectic A phases. Furthermore it seems that the mesophase stabilizing eVect of the lateral diol group is largest for the centrally substituted compound 1e and it decreases on migration of the lateral group to the terminal end of the rigid core.Thus, a mesophase stabilization in comparison with the corresponding methyl substituted compounds is observed only for the 2¾-substituted compound, whereas the clearing temperature of the diol 13 with its polar group in the 3-position is significantly lower than that of the corresponding 3-methyl derivative 12.Probably two diVerent reasons are responsible for this eVect. At first the mesophase Fig. 3 Mesomorphic properties of the compounds 1 as a function of the length of the terminal chains. destabilizing influence of lateral substituents depends on their J. Mater. Chem., 1998, 8, 2611–2626 2621Fig. 4 Influence of the position of the lateral groups on the liquid crystalline behavior.position at the rigid core. Those in central positions have a more pronounced destabilizing influence than those in more peripheral positions.1–3,5,18 The reason may be that the lateral Fig. 5 Properties of 4,4>-didecyloxyterphenyl derivatives with lateral substituents in a central position are forced to be located amide groups. between the rigid p-terphenyl cores, whereas those in a peripheral position can be expelled more easily into the region of the flexible terminal alkyl chains.This would be more favorable bonding is larger than the mesophase destabilizing eVect due for lipophilic substituents, like the methyl group, than for to unfavorable steric interactions from increasing the size of polar hydrophilic substituents which are incompatible with the the substituents by additional CH2OH groups.It is especially alkyl groups. This second eVect could be responsible for the remarkable that the acylated aminosugar 2027 exhibits the destabilization of the smectic layers of the 3-substituted diol most stable smectic phase of all compounds compared in derivative 13 with respect to the methyl substituted Fig. 5. This compound represents an entirely new type of compound 12. mesogenic carbohydrate derivative, which combines a rigid Remarkably, for all diol substituted compounds, no SC rod-like core laterally connected with a polyhydroxy unit. It phase was found even on supercooling the samples. It should seems, however, that this class of compounds is very sensitive be mentioned here that this phenomenon is often observed in to slight changes of the molecular structure.The N-methyl systems of calamitic molecules with strong attractive forces amide 21, for example, in which the NH group of 20 is between their rigid cores, especially in donor–acceptor replaced by a NCH3 group, is a non-mesogenic solid. It seems systems.30 For example, SA phases can be exclusively induced that the NH group plays an important role as a proton donor in mixed systems of calamitic molecules with donor and group in the mesophase stabilization of this class of comacceptor properties30 and in mixed systems consisting of pounds.Likewise, comparison of the ether 1e with the related calamitic mesogens and TNF.31 Steric eVects should also amide 19 reveals a mesophase stabilization of 28 K following contribute to the loss of SC phases. The large lateral substitu- replacement of the CH2O group by a CONH group. However, ents disfavor tilting, because this would further enlarge the the mesophase destabilization on introduction of the N-methyl lateral cross-section and additionally disturb the packing of the alkyl chains. 4.3. Variation of the lateral groups A wide variety of diVerent polar groups has been checked.In Fig. 5 the molecules with lateral amide groups are compared with the methyl carboxylate 1415,27 which has exclusively a nematic phase. The amide 15 and the N-ethyl amide 16 are high melting crystalline solids which rapidly crystallize on cooling. Therefore no liquid crystalline phases can be observed. However if one additional proton donating functional group (OH or NH2) is introduced into the lateral group, then liquid crystalline properties can be found.Both the hydrazide 17 and the 2-hydroxyethylamide 18 form SA phases with significantly higher mesophase stability than the ester compound 14.27 Furthermore, with an increasing number of hydroxy groups in the lateral chain the mesophase stability of the SA phase rises (compounds 18, 19 and 20 in Fig. 5). Remarkably, the mesophase stability increases despite the fact that the lateral groups are enlarged simultaneously. This means that the Fig. 6 Comparison of the mesomorphic properties of the amides 22, 23 and 24. mesophase stabilization provided by the additional hydrogen 2622 J. Mater. Chem., 1998, 8, 2611–2626Fig. 8 Influence of the length of the lateral polyether chain on the mesomorphic properties of 2¾-substituted 4,4>-didecyloxyterphenyl derivatives12 (Colr=rectangular columnar mesophase).Fig. 7 Comparison of the phase transition temperatures of the carboxylic acid 25,27 the corresponding acid chloride 2627 and the sodium carboxylate 27. group is much larger. Therefore, the complete loss of mesogenic properties for compound 21 could not be explained by the diminished degree of hydrogen bonding alone.Changes in the molecular conformation can probably also contribute to this eVect. Compounds with polar lateral groups without the possibility of forming hydrogen bonds are in most cases non-mesomorphic. This is obvious from a comparison of the diol 22 with the morpholide 23, which is the cyclic analogue of the diol 22 without hydroxy groups (Fig. 6). The azacrown compound 24 is also a crystalline solid. Intermolecular hydrogen bonding is also important in carboxylic acids which are known to form dimers.32 In Fig. 7 the carboxylic acid 2527 is compared with its acid chloride 26.27 Again the carboxylic acid 25, i.e. the compound which is able Fig. 9 Optical photomicrograph of the texture of compound 29b to form hydrogen bonding, displays the higher mesophase between crossed polarizers at 40 °C.The Colr phase (spherulitic texture at the left hand side) is growing out of the homeotropically aligned domains of the SA phase while cooling. Small regions of the homeotropically aligned SA phase with some oily streaks can still be seen at the right-hand side.stability. The ionic amphiphiles, the carboxylate 27 (Fig. 7) as well as the quaternary ammonium salt 28 are high melting solids without detectable thermotropic liquid crystalline properties. 4.4. Polyether amphiphiles In order to further clarify the relation between molecular structure and liquid crystalline behavior we have decoupled the lateral rac-propane-2,3-diol unit from the rigid p-terphenyl core via hydrophilic polyether chains.12 The phase transition temperatures of these compounds are collected in Fig. 8. The clearing temperatures as well as the melting temperatures decrease significantly with increasing length of the oligo- (oxyethylene) spacer which connects the propane-2,3-diol group to the rigid core. The clearing temperatures are more depressed per spacer length increment than the melting temperatures.This results in monotropic mesophases for compounds 29b and 29c with longer oligo(oxyethylene) spacers. However they can easily be supercooled. The diol 1e and the ethylene glycol derivative 29a form a smectic A phase as the Fig. 10 Schematic illustration of the SA phase and a possible ribbon only mesophase.On cooling of compound 29b a transition arrangement for the rectangular columnar phases (Colr) of compounds from the SA phase to a columnar mesophase occurs at 40 °C. 29b and 29c.12 The black areas represent the phase separated regions As shown in Fig. 9 the transition to the columnar phase can of the polar groups. The polar groups of the molecules in the middle be seen in the polarizing microscope by the formation of a of the ribbons cross over the neighboring calamitic terphenyl units. spherulitic texture in the homeotropically aligned SA phase.J. Mater. Chem., 1998, 8, 2611–2626 2623of these layers. The ribbons should consist of parallel rigid pterphenyl cores laterally separated by the hydrophilic domains of the lateral groups. The alkyl chains are molten and fill up the space between the ribbons in the other dimension.From the obtained lattice parameter it was calculated that between four and five molecules should be arranged in the cross-section of the ribbons.12 Therefore, the polar lateral groups of the molecules in the middle of these ribbons must cross over the neighboring calamitic terphenyl units in order to become incorporated into the polar regions.In Fig. 11 the CPK models of four molecules of the tris(oxyethylene) derivative 29c are placed side by side as they would be arranged in the crosssection of the ribbons. It shows that indeed the lateral groups of the molecules in the middle are suYciently long to reach the polar regions. Therefore, we propose that, in addition to a certain polarity and size, a suYcient length of the polar groups is also an important prerequisite for columnar mesophase formation in this class of compounds.Fig. 11 CPK model showing a possible arrangement of the molecules The proposed ribbon model seems reasonable, because it 29c in the cross-section of a ribbon. enables the segregation of polar and lipophilic units into separate regions whereby the parallel organization of the rodlike molecules is maintained.In respect of the local order within the ribbons, the columnar phase can be regarded as a modulated smectic phase, but in comparison to most other modulated phases the lateral diameter of the ribbons is rather small. Alternatively, this ribbon structure can be described as an alternating structure of two types of lamellae.One type consists of alkyl chains and the second type is composed of ribbons of rigid p-terphenyl units laterally separated by cylinders containing the hydrophilic groups [see Fig. 12(a)]. This model is related to that suggested for supermolecular structures which have recently been found in triblock copolymers consisting of three linearly combined flexible blocks [see Fig. 12 Schematic representation of the lamellae-cylinder structures Fig. 12(b)].33 Here, beside other superstructures, lamellae with of (a) the Colr phases of compounds 29b and 29c and (b) of a cylinders at the lamella interfaces have been found.34 Indeed, microphase segregated linear ABC triblock copolymers.33,34 the molecules described here can be regarded as low molecular weight three-block compounds composed of three diVerent and incompatible blocks: the rigid cores, the flexible and From the X-ray diVraction pattern and taking into account lipophilic alkyl chains and the flexible but polar polyether the molecular dimensions a rectangular columnar structure chains.In contrast to linear triblock copolymers, the Y-shaped was suggested for this mesophase.12 Compound 29c with a block molecules described here have the cylinders located longer polyether chain exhibits exclusively the (monotropic) within one of the distinct layers instead of being located at rectangular columnar mesophase (Colr).For these columnar their interface. There are at least two reasons for their position phases a ribbon structure as shown in Fig. 10 was proposed.12 within the layer of the rigid cores. At first, this organization According to this model, the flexible and polar polyether is provided by the fixation of the polar groups in a central chains should segregate from the rigid cores into separate lateral position. Additionally, the rigidity of central rod-like domains and thus give rise to a collapse of the smectic layers into ribbons which can be regarded as small band like segments block reduces the number of possible conformations and thus Fig. 13 Influence of the structure of the lateral group on the mesomorphic properties of the 2¾-substituted p-terphenyl derivatives (M=unknown mesophase with schlieren texture). 2624 J. Mater. Chem., 1998, 8, 2611–2626the rigid cores, and also a certain polarity of the lateral substituents (polyether chains instead of alkyl chains), are both necessary for the occurrence of columnar mesophases. 4.5. Crown ether derivatives The crown compounds 33a–c36 (Fig. 14) represent closed analogues of compounds 29 and 30. Because of the absence of proton donor groups they lack the possibility of hydrogen bonding. As mentioned in the introduction, such large lateral groups usually suppress smectic phases and give rise to nematic phases.Also the laterally alkyl-substituted terphenyl derivatives 2 (see Fig. 2) and 32 (Fig. 13) have exclusively nematic phases. No smectic phase can be observed on cooling compound 32 until crystallization sets in at 15 °C. The crown compounds 33, however, have an SA–N dimorphism in contrast to the alkyl substituted compounds 2 and 32.This means that layer structures are preferred by these polyethers. Probably the polar crown ether groups can force micro-segregation between the central regions consisting of the rigid cores and the crown ether units from the terminal lipophilic alkyl chains. Fig. 14 Influence of the size of laterally attached crown units on the Thus, in the crown compounds the steric disturbance of the mesomorphic properties of the facial amphiphiles.lateral groups is in competition with the layer stabilizing eVect provided by micro-segregation.37 inhibits the organization of the molecules in a conventional inverted hexagonal columnar mesophase as known for flexible 4.6. Influence of the position of the polyether chain double chain amphiphiles and taper shaped molecules.35 In order to further evaluate the structural requirements As mentioned above the 3-substituted diol 13 has a significantly higher smectic mesophase stability than the corresponding 2¾- which are responsible for the occurrence of columnar mesophases, compound 32 with a lateral alkyl chain, compound 31 substituted molecule 1e (see Fig. 4). Also the 3-substituted polyether compounds 34 (Fig. 15) have enhanced clearing with a 1,2-diol unit coupled via a hydrophobic alkyl spacer, and two oligo(oxyethylene) ethers without diol units (com- temperatures in comparison to the 2¾-substituted analogues 29 (Fig. 8). Remarkably however, only SA phases and no colum- pounds 30) were investigated. As shown in Fig. 13 the columnar phase is replaced by a smectic A phase if one of the nar mesophases could be detected for the diols 34b and 34c with long polyether chains in the peripheral 3-position at the hydroxy groups in the polar group is removed (compounds 30).A nematic phase is found if the polyether chain is replaced rigid core. It seems that the formation of columnar mesophases is bound to a very special molecular structure and it is favored by a lipophilic alkyl chain (compound 32).If a diol group is attached to the end of the lateral alkyl group (compound 31) by a central attachment of the polar group. Also in the series of 3-substituted compounds the polyether a monotropic mesophase with a schlieren texture is observed. Because compound 31 rapidly crystallizes we were not able to chains were replaced by alkyl chains (see Fig. 15). Compound 35a in which one ether oxygen in the lateral chain of 34a is diVerentiate between an SC phase and a nematic phase. Nevertheless, these structural variations show that a suYcient replaced by a CH2 group has a slightly decreased mesophase stability. No mesomorphic properties can be found for com- number of hydrogen bonding sites (diols vs. simple alcohols) providing suYciently strong attractive interactions between pound 35b in which the diol group is decoupled by a long Fig. 15 Influence of the structure of the lateral group on the mesomorphic properties of 3-substituted 2,2>-didecyloxyterphenyl derivatives. J. Mater. Chem., 1998, 8, 2611–2626 262514 (a) N. Miyaura, K. Yamada and A. Suzuki, Tetrahedron Lett., alkyl spacer.This could be due to the poor supercoolability 1979, 3437; (b)M. Hird, G. W. Gray and K. J. Toyne, Mol. Cryst. of this compound (85 °C). Liq. Cryst. Lett., 1991, 206, 187; (c) M. Hird, G. W. Gray and K. J. Toyne, Liq. Cryst., 1994, 16, 625. 15 J. Andersch and C. Tschierske, Liq. Cryst., 1996, 31, 51. 5. Conclusions 16 C. D. Hurd and M. A. Pollack, J. Am. Chem. Soc., 1938, 60, 1908.The investigations have shown that—depending on the 17 V. van Rheenen, R. C. Kelley and D. F. Cha, Tetrahedron Lett., 1976, 1973. molecular structure—facial amphiphiles can form monolayer 18 J. Andersch, C. Tschierske, S. Diele and D. Lose, J. Mater. Chem., SA phases and columnar mesophases. Micro-segregation and 1996, 6, 1297. cohesive forces provided by hydrogen bonding stabilize a 19 Obtained by NBS bromination of 5-decyloxy-2-(4-decyloxy- parallel layer-like arrangement of the calamitic molecules.If phenyl )toluene, which was prepared by Suzuki coupling of 2- the polar groups are hydrogen bonding functional groups, bromo-5-decyloxytoluene with 1 equiv. of 4-decyloxyphenyltheir mesophase stability can be higher than that of related boronic acid analogous to the synthesis of 39 (Scheme 4) (ref. 18). 20 Obtained by NBS bromination of 3,5-bis(4-decyloxyphenyl )tolu- compounds with smaller lateral substituents. However, the ene, which was prepared by Suzuki coupling of 3,5-dibromotolu- stabilization of layered mesophases is in competition with the ene with 2 equiv. of 4-decyloxyphenylboronic acid, analogous to disturbance provided by the space filling of these substituents.the synthesis of 2,5-bis(4-decyloxyphenyl )benzyl bromide Furthermore, in many cases (e.g. ionic amphiphiles) the high (ref. 15). melting temperatures and the poor supercoolability of the 21 R. Adams and L. H. Ulich, J. Am. Chem. Soc., 1920, 42, 599. materials prevents potential (monotropic) mesophases from 22 R. Plehnert, J. A. Schro� ter and C.Tschierske, Langmuir, 1998, 14, 5245. being observed. 23 J. Goerdeler, Houben-Weyl, Methoden der Organischen Chemie, In cases of compounds with rather large, flexible and polar Georg Thieme Verlag, Stuttgart, 1958, vol. 11/2, p. 591. lateral substituents fixed to the center of the rigid terphenyl 24 M. Hird, A. J. Seed, K. J. Toyne, J. W. Goodby, G. W. Gray and unit (compounds 29b and 29c, see Fig. 8) columnar mesophases D. G. McDonnell, J. Mater. Chem., 1993, 3, 851. can be found. These columnar phases should represent ribbon 25 F. Hentrich, C. Tschierske, S. Diele and C. Sauer, J. Mater. phases resulting from the collapse of the smectic layers. The Chem., 1994, 4, 1547. 26 D. Landini, F. Montanari and F. Rolla, Synthesis, 1979, 134. lateral polyether chains are incompatible with the rigid and 27 F.Hildebrandt, J. A. Schro� ter, C. Tschierske, R. Festag, lipophilic p-terphenyl units and segregate from them into R. Kleppinger and J. H.WendorV, Angew. Chem., 1995, 107, 1780; separate cylindrical domains which interrupt the smectic layers. Angew. Chem., Int. Ed. Engl., 1995, 34, 1631. These molecules can be regarded as block molecules composed 28 Although the mesophase stabilization by hydrogen bonding is well of three diVerent and incompatible molecular parts.It could documented for calamitic molecules with terminal hydrogen bondbe expected that the design of novel types of low molecular ing (ref. 10, 32) and for taper-shaped polyhydroxy compounds [ref. 35(c),(d)], the mesophase stabilization by a laterally attached weight block compounds consisting of three or even more diol group is rather surprising. The formation of an SA phase for a diVerent and incompatible molecular parts connected via compound with laterally attached hydroxy groups was only diVerent topologies might provide interesting new liquid reported for some inositol ethers (K.Praefcke and D. Blunk, Liq. crystalline materials.37,38 Cryst., 1993, 14, 1181; K.Praefcke, D. Blunk and J. Hempel, Mol. Finally, it should be mentioned that all compounds with Cryst. Liq. Cryst., 1994, 243, 323.) hydrophilic lateral groups can form lyotropic mesoph as 29 C. Tschierske, J. Mater. Chem., 1998, 8, 1485. 30 (a) K. Praefcke and D. Singer, in Handbook of Liquid Crystals, ed. will be reported in a separate paper.13 D. Demus, J. Goodby, G. W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH, Weinheim, 1998, vol. 2b, p. 945; (b) R. Dabrowski Acknowledgments and K. Czuprynski, in Modern Topics in Liquid Crystals, ed. A. Buka, World Scientific, 1993, p. 124. This work was supported by the Deutsche 31 (a) B. Neumann, D. Joachimi and C. Tschierske, Liq. Cryst., 1997, Forschungsgemeinschaft and the Fonds der Chemischen 22, 509; (b) R. Lunkwitz, B. Neumann and C. Tschierske, Liq. Cryst., 1998, 25, 403. Industrie. 32 C. M. Paleos and D. Tsiourvas, Angew. Chem., 1995, 107, 1839. 33 W. Zheng and Z.-G.Wang, Macromolecules, 1995, 28, 7215. 6. References 34 C. Auschra and R. Stadler, Macromolecules, 1993, 26, 2171. 35 (a) A. Eckert, B. Kohne and K. Praefcke, Z. Naturforsch., 1988, 1 K. J. Toyne, Crit. Rep. Appl. Chem., 1987, 22, 28. 43b, 878; (b) K. Praefcke, B. Kohne, A. Eckert and J. Hempel, 2 G. W. Gray, M. Hird and K. J. Toyne, Mol. Cryst. Liq. Cryst., Z. Naturforsch., 1990, 45b, 1084; (c) K. Praefcke, P. Marquardt, 1991, 195, 221. B. Kohne and W. Stephan, J. Carbohydr. Chem., 1991, 10, 539; 3 M. Hird, K. J. Toyne, P. Hindmarsh, J. C. Jones and V. Minter, (d) G. Lattermann and G. Staufer, Liq. Cryst., 1989, 4, 347; Mol. Cryst. Liq. Cryst., 1995, 260, 227. (e) K. Borisch, S. Diele, P. Go� ring, H. Mu� ller and C. Tschierske, 4 W. Weissflog and D. Demus, Cryst. Res. Technol., 1983, 18, K21. Liq. Cryst., 1997, 22, 427; ( f ) V. Percec, J. Heck, G. Johansson, 5 W. Weissflog, in Handbook of Liquid Crystals, ed. D. Demus, D. Tomazos, M. Kawasumi and G. Ungar, J. Macromol. Sci., J. Goodby, G. W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH, Pure Appl. Chem., 1994, A31, 1031; (g) V. Percec, G. Johannson, Weinheim, vol. 2b, p. 863. J. Heck, G. Ungar and S. V. Batty, J. Chem. Soc., Perkin Trans. 1, 6 G. W. Gray, J. Chem. Soc., 1955, 236. 1993, 1411. 7 A. Jacobi and W.Weissflog, Liq. Cryst., 1997, 22, 107. 36 J. A. Schro� ter, C. Tschierske, M. Wittenberg and J. H. WendorV, 8 (a) G. J. T. Tiddy, Phys. Rep., 1988, 57, 1; (b) J. M. Seddon and Angew. Chem., 1997, 109, 1160; Angew. Chem., Int. Ed. Engl., R. H. Templer, in Handbook of Biological Physics, ed. 1997, 36, 1119. R. Lipowsky and E. Sackmann, Elsevier, Amsterdam, 1995, 37 C. Tschierske, J. Mater. Chem., 1998, 8, 1485. vol. 1, p. 97. 38 Block molecules can also incorporate perfluorinated segments [e.g. 9 J. A. Schro� ter, R. Plehnert, C. Tschierske, S. Katholy, D. Janietz, polyphilic molecules: F. Tournilhac, L. Bosio, J.-F. Nicoud and F. Penacorada and L. Brehmer, Langmuir, 1997, 13, 796. J. Simon, J. Chem. Phys. Lett., 1988, 145, 452; L. M. Blinov, 10 C. Tschierske, Progr. Polym. Sci., 1996, 21, 775. T. A. Lobko, B. I. Ostrovskii, S. N. Sulianov and 11 C. Tschierske, J. A. Schro� ter, N. Lindner, C. Sauer, S. Diele, F. G. Tournilhac, J. Phys. II, 1993, 3, 1121) or oligosiloxane units R. Festag, M. Wittenberg and J.-H. WendorV, Dabrowski and (M. Ibn-Elhaj, A. Skoulios, D. Guillon, J. Newton, P. Hodge and J. Zielinski, Proc. SPIE-Int. Soc. Opt. Eng., 1998, 3319, 8. H. J. Coles, Liq. Cryst., 1995, 19, 373; J. Newton, H. Coles, 12 F. Hildebrandt, J. A. Schro� ter, C. Tschierske, R. Festag, P. Hodge and J. Hannington, J. Mater. Chem., 1994, 4, 869). M. Wittenberg and J. H. WendorV, Adv. Mater., 1997, 9, 564. 13 J. A. Schro� ter, C. Tschierske, M. Wittenberg and J.-H. WendorV, J. Am. Chem. Soc., in the press. Paper 8/03043J 2626 J. Mater. Chem., 1998, 8, 2

ISSN:0959-9428    

DOI:10.1039/a803043j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Ionic liquid crystals: hexafluorophosphate salts Charles M. Gordon,*a John D. Holbrey,b Alan R. Kennedya and Kenneth R. Seddonb aDepartment of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, UK G1 1XL. E-mail: c.m.gordon@strath.ac.uk bThe QUESTOR Centre, The Queen’s University of Belfast, Stranmillis Road, Belfast, Northern Ireland, UK BT9 5AG Received 5th August 1998, Accepted 19th October 1998 A series of novel hexafluorophosphate salts, based on N,N¾-dialkylimidazolium and substituted N-alkylpyridinium cations, display liquid crystalline behaviour at temperatures above their melting point.The temperature range over which liquid crystalline behaviour is observed increases markedly with increasing alkyl chain length.Alkyl substitution at the 3- and 4-positions on the pyridinium ring results in a decrease in the melting point compared with the equivalent unsubstituted salt, but also leads to a large decrease in the tendency towards liquid crystalline behaviour (or mesogenicity). The salts prepared are fully characterised using a wide variety of techniques, including NMR and IR spectroscopy, DSC, and single crystal X-ray diVraction in the case of 1-dodecyl-3-methylimidazolium hexafluorophosphate. The eVect of preparing mixtures containing diVerent proportions of two cations is also reported.Introduction A large variety of molecular thermotropic liquid crystalline materials have been prepared. In comparison, only a limited range of ionic liquid crystalline species is known.Alkali metal soaps were the first salts identified as displaying this type of behaviour,1 followed more recently by amphiphilic alkylammonium2 and N-alkylpyridinium salts.3 Amphiphilic 1-methyl- 4-alkylpyridinium iodides have also been shown to display thermotropic liquid crystalline behaviour.4 Liquid crystalline and thermochromic behaviour has been observed in 1-methyl- N R H3C N R H3C N R H3C R R = n-C12H25, n-C14H29, n-C16H33, n-C18H37 + 1 + 2 + + 3 4 N N 4-n-alkoxycarbonylpyridinium4 and 1-hexadecyl-4-cyanopyri- Fig. 1 Structures of the organic cations employed. dinium iodide salts.5 Further developments have involved the replacement of the 1-alkyl group with mesogens,6,7 while recent publications have demonstrated thermotropic liquid crystalline phosphate are neutral and extremely hydrophobic.17 By way behaviour in 1-alkyl-4-cholesterylpyridinium,8 1-ethyl-4-(5- of comparison, the eVect of chemical modification of the alkyl-1,3-dioxan-2-yl )pyridinium,9 and 1-alkylstilbazolium cation has been little studied.An increasing chain length in halide salts.10 All of these studies have concentrated on halide the cation will be expected to result in an alteration in the salts; only a few papers report ionic liquid crystalline materials melting point, and an increase in the viscosity and hydrocontaining other anions, notably metallomesogens,11 [MCl4]2- phobicity of the liquids.A further eVect, once chain lengths (M=Co, Ni),12 [ZnBr4]2-,13 [C12H25OSO3]-,14 and hydro- of a suYcient length are present, will be the formation of gentartrate.15 Practical applications of these materials are liquid crystalline phases on melting, as shown by the examples limited, particularly in the case of the simple alkylammonium described in the previous paragraph.salts, by the high melting points of the systems studied. A One ionic liquid which is finding increasing use is 1-butylrecent investigation of transition metal salts based on long 3-methylimidazolium hexafluorophosphate, [bmim][PF6], an chain 1-alkyl-3-methylimidazolium and N-alkylpyridinium cat- easily prepared, almost completely water insoluble liquid, ions showed that these possess relatively low melting points, which has been used as a solvent for two-phase catalysis combined with large mesophase ranges,12 thus showing greater reactions.18 In this study, we report the liquid crystalline potential for further development.properties of some hexafluorophosphate salts of alkyl-substi- Our interest in ionic liquid crystals arose from the study of tuted imidazolium ([R-mim]+ 1), pyridinium ([R-py]+ 2), 3- low melting ionic liquids. Ionic liquids is now a commonly and 4-methylpyridinium ([R-3-Mepy]+ 3 and [R-4-Mepy]+ 4) accepted term for low melting molten salts, and these materials cations,† as indicated in Fig. 1. are finding increasing application as solvents, particularly in Such salts are potentially of great interest as ordered ionic the area of clean technology as controls on conventional solvents, combining the advantages of ionic liquids with those solvents such as chlorinated hydrocarbons become more strin- of liquid crystal solvents.The aim of this study was to identify gent.16 Ionic liquids are prepared by combining bulky organic systems that combined a relatively low melting point with a cations such as 1-butyl-3-methylimidazolium or 1-butylpyridi- large mesophase range. Once the principles influencing the nium with a wide variety of anions.The properties of ionic thermal behaviour of these salts are understood, the intention liquids can be controlled to a large degree by variation in the is to develop more sophisticated systems that can be employed nature of both the cation and the anion. The eVect of altering as ordered solvents. The application of more ‘traditional’ the anion has been quite widely investigated: for example, salts based on aluminium(III ) chloride may be prepared which †Henceforth all cations will be referred to using the shortened form are Franklin acidic or basic, and extremely water sensitive, of the cation name, and the alkyl chain simply by its number of carbon atoms, i.e.[C12-mim]=1-n-dodecyl-3-methylimidazolium. while those based on anions such as triflate and hexafluoro- J.Mater. Chem., 1998, 8, 2627–2636 2627molecular liquid crystalline materials as ordered solvents for Thermal investigations polymerisation19 and stereochemically controlled organic reac- DSC measurements were carried out using a Perkin Elmer tions20 is an area of increasing interest. Only one other related DSC 2 or Perkin Elmer DSC 7.Heating and cooling rates of liquid crystalline salt containing the hexafluorophosphate 10 °Cmin-1 were typically employed. Each sample was pre- anion has been reported: the symmetrically substituted 1,3- heated to its clearing point, allowed to cool to its crystallisation dihexadecylimidazolium hexafluorophosphate, for which point, and then reheated for data collection. Polarised optical transition temperatures and energies were recently reported.21 microscopy (POM) studies on the salts were carried out using an Olympus Vanox microscope under cross-polarised light at Experimental 100× magnification. The samples were placed between two cover slips and heated using a Linkam PR600 hot stage, which Aqueous hexafluorophosphoric acid (60% w/w, ex-Aldrich), permitted control of the temperature to ±0.1 °C.Heating and pyridine, 3-methylpyridine and 4-methylpyridine (ex-Aldrich) cooling rates of 10 °Cmin-1 were once again generally were used as received. 1-Methylimidazole (ex-Aldrich) was employed, except when a very precise determination of trans- purified by distillation from KOH. 1-Chlorododecane, 1- ition temperatures was required, in which case slower rates chlorotetradecane, 1-chlorohexadecane and 1-chlorooctadewere used.As with the DSC measurements, data were only cane (ex-Lancaster or Aldrich) were used as received. Acetonerecorded after the sample had first been heated to its clearing d6 was purchased from Goss Scientific Instruments Ltd. point and then allowed to cool to its crystallisation point.Acetonitrile was dried by distillation from CaH2. Photographs of the mesophase were taken at the same magnification using a Polaroid Micro SLR camera. Synthesis of salts Chloride salts were prepared by mixing equimolar quantities Experimental crystallography of the appropriate amine and chloroalkane in a Carius tube (i ) Powder X-ray diVraction. Powder X-ray diVraction in a dinitrogen-filled drybox.The tube was removed from the studies were made at room temperature with Cu-Ka X-rays, drybox, degassed at -196 °C, sealed under vacuum, and (l=1.542 A° ) using a Siemens D5000 powder diVractometer. heated at 100 °C for 7 days, or until reaction was observed to Data were recorded in the range 2–20° in steps of 0.05°. be complete (the mixture formed a single viscous phase).The tube was then cooled, and opened in the drybox. The crude (ii ) Single crystal X-ray diVraction. Crystals of [C12- solid product was removed, recrystallised from dry CH3CN, mim][PF6] were grown by slow evaporation of a methanolic and then stored in the drybox until use. In general, the halide solution of the salt. Crystal data, data collection and refinement salts became less hygroscopic as the alkyl chain increased in parameters are given in Table 2.Measurements were made at length. The amines employed were 1-methylimidazole, pyri- 123 K with Mo-Ka X-rays, (l=0.71069 A° ), on a Rigaku dine, and 3- and 4-methylpyridine; salts were prepared with AFC7S diVractometer fitted with a graphite monochromator. alkyl chain lengths C12, C14, C16 and C18.Cell dimensions were based on 25 reflections with The hexafluorophosphate salts were prepared by reaction 18.2<2h<34.8°. Intensities, I, were derived from v–2h scans, of the appropriate chloride salt with HPF6 in aqueous solution. and corrections were applied for Lorentz polarisation and As the method was eVectively identical for all salts, the exact absorption eVects, the latter based on averaging several azi- method employed for [C14-py][PF6] will be discussed as a muthal scans.Equivalent intensities were then averaged and representative example: [C14-py]Cl (1.00 g, 3.20 mmol) was unobserved reflections with I<2s(I ) excluded from further dissolved in water (20 cm3), and then cooled to 0 °C in an ice consideration. bath. The mixture was stirred vigorously and 60% w/w HPF6 The structure was solved by direct methods22 and the solution (1.0 cm3, 6.80 mmol) was added using a glass syringe.examination of subsequent diVerence syntheses. All non-hydro- A rapid exothermic reaction then occurred, with the product gen atoms were refined anisotropically. H atoms were pos- forming as an insoluble white solid.This was collected by itioned as found with Biso=1.2Beq of the parent atom. An filtration, washed with a large excess of water to remove any isotropic extinction parameter [5.4(8)×10-7] was also refined. remaining traces of HPF6, then recrystallised from a minimum Final full-matrix, least-squares refinement was on F with w= quantity of methanol, and dried in vacuo. A final yield of 1/s2(F) and converged to give a maximum shift/esd ratio of 0.73 g (54.0%) was obtained. The solubility in methanol 0.003.All calculations were performed on a Silicon Graphics increased with decreasing chain length, generally resulting in Indy R4600 with the teXsan set of programs.23 somewhat lower yields for the shortest chain length products Full crystallographic details, excluding structure factors, and higher yields for the salts with longer alkyl chains.The have been deposited at the Cambridge Crystallographic Data pure recrystallised product formed as white plates, which were Centre (CCDC). See Information for Authors, J. Mater. dried in a vacuum desiccator for at least 24 h. The purity of Chem., 1998, Issue 1. Any request to the CCDC for this all the salts was checked by 1H NMR spectroscopy (in acetonematerial should quote the full literature citation and the d6), microanalysis (see Table 1) and DSC (see later).reference number 1145/1046. Mixtures of two salts were prepared by carefully weighing See http://www.rsc.org/suppdata/jm/1998/2627/for crystal- out the appropriate molar ratios of [C16-mim][PF6] and [C16- lographic details in cif format.py][PF6]. The mixtures were then ground thoroughly, heated to a temperature well above their clearing points, and then Results allowed to cool. This process was repeated three times for the resulting solids, by which stage it was assessed that broadly As stated above, N-alkyl substituted 1-methylimidazolium, homogeneous mixtures had been prepared. pyridinium, 3- and 4-methylpyridinium hexafluorophosphate salts were prepared with alkyl chain lengths of C12, C14, C16, Analytical methods and C18.Halide and tetrachlorometallate salts of some of these cations have been shown previously to display liquid 1H NMR spectra were recorded in acetone-d6 solution on 400 MHz Bruker AMX400 or 250 MHz Bruker WM250 FT crystalline phases at temperatures above their melting points.3,12 The products were prepared in aqueous solution by NMR spectrometers.IR spectra were run as KBr disks on a Nicolet Impact 400D FTIR spectrometer. FAB mass spec- metathesis of the appropriate organic cation halide with HPF6. The white crystalline solid products were insoluble in water, trometry was performed on a JEOL JMS-AX505HA instrument, using a glycerol matrix.and were thus simply collected by filtration. Purification was 2628 J. Mater. Chem., 1998, 8, 2627–2636Table 1 Microanalytical data for anhydrous [Q][PF6 ] salts Q+ C % found (calc.) H % found (calc.) N % found (calc.) C12-mim 48.6 (48.4) 8.2 (7.9) 7.0 (7.1) C14-mim 51.0 (50.9) 8.6 (8.3) 6.6 (6.6) C16-mim 53.1 (53.1) 8.9 (8.7) 6.1 (6.2) C18-mim 54.9 (55.0) 9.1 (9.0) 5.7 (5.8) C12-py 52.0 (51.9) 7.9 (7.7) 3.5 (3.6) C14-py 54.3 (54.1) 8.5 (8.1) 3.3 (3.3) C16-py 55.7 (56.1) 8.5 (8.5) 3.0 (3.1) C18-py 57.6 (57.8) 9.0 (8.9) 3.0 (2.9) C12-3-Mepy 53.0 (53.1) 8.2 (7.9) 3.4 (3.4) C14-3-Mepy 55.2 (55.2) 8.3 (8.3) 3.1 (3.2) C16-3-Mepy 57.0 (57.0) 8.7 (8.7) 3.0 (3.0) C18-3-Mepy 58.4 (58.6) 9.0 (9.0) 2.9 (2.9) C12-4-Mepy 51.8 (53.1) 7.9 (7.9) 3.5 (3.4) C14-4-Mepy 55.3 (55.2) 8.4 (8.3) 3.1 (3.2) C16-4-Mepy 57.0 (57.0) 8.8 (8.7) 3.0 (3.0) C18-4-Mepy 58.9 (58.6) 9.3 (9.0) 2.7 (2.9) Table 2 Crystal parameters for [C12H25-mim][PF6] Table 3 Summary of DSC data and polarising microscope measurements obtained for [Q][PF6] salts under studya Formula C16H31F6N2P Formula weight 396.40 [Q]+ T /°C Energy/kJ mol-1 Transition Crystal system Monoclinic Space group P21/a C12-mim 60 27.3 C�I C14-mim 74 30.9 C�SA a/A° 9.175(2) b/A° 9.849(3) 77 0.4 SA�I C16-mim 75 37.5 C�SA c/A° 22.197(4) b/° 94.132(18) 125 0.5 SA�I C18-mim 80 43.8 C�SA U/A° 3 2000.7(8) Z 4 165 1.1 SA�I C12-py 49 6.2 C�C1 Dc/g cm-3 1.32 Crystal size/mm 0.70×0.40×0.05 89 3.9 C1�C2 104 22.4b C2�C3 Crystal description Colourless plate m/mm-1 0.192 106 22.4b C3�I C14-py 53 5.8 C�C1 2h range/° 5 to 53 Rmerge 0.037 103 4.0 C1�C2 109 16.5 C2�C3 No.of reflections measured 4676 Unique data 4401 124 9.6 C3�I C16-py (86) (-4.9) Observed data 2497 No. of parameters 227 104 (98) 27.7 (-20.9) C�C1 126 8.4 C1�SA Absorption range 0.94–1.00 R, Rw 0.0394, 0.0436 138 0.8 SA�I C18-py (89) (-3.6) S 1.339 Max. Dr/e A° -3 0.219 107 (102) 32.3 (-22.2) C�C1 126 7.6 C1�SA Min.Dr/e A° -3 -0.235 176 1.2 SA�I C12-3-Mepy 55 28.2 C�I C14-3-Mepy 68 25.8 C�I achieved by recrystallisation from methanol. Using this C16-3-Mepy (58) (-35.9) (SA�C) method, the only by-product is hydrochloric acid, which 74 (61) 36.0 (-0.5) C�I (I�SA) remains in the aqueous solution. These salts are thus guaran- C18-3-Mepy 87 38.0 C�SA teed to be free of any traces of metal ions.Residual halide 94 0.5 SA�I C12-4-Mepy 56 20.3 C�I ions were removed by extended washing with water. C14-4-Mepy 71 28.1 C�I Contamination of low melting salts containing anions such as C16-4-Mepy (55) (-34.8) (SA�C) [BF4]- and [CH3CO2]- has been a problem due to the 75 (60) 36.7 (-1.1) C�I (I�SA) requirement to use metal salts, typically silver and lead respect- C18-4-Mepy (77) (-41.8) (SA�C) ively, in their preparation.24,25 88 (84) 33.6 (-0.4) C�I (I�SA) None of the salts containing alkyl chains shorter than C12 aThe entries in parentheses indicate transitions observed on cooling display liquid crystalline behaviour.26 The presence and tem- where these are significantly diVerent from those observed on heating.perature range of liquid crystallinity proved to vary greatly bPeaks were tions, and so each cation will be discussed would not be recorded.separately. The data referred to in the following sections are collected in Table 3. In general the behaviour on cooling was very similar to that observed on heating, except that solidifi- Mepy][PF6], [C16-4-Mepy][PF6] and [C18-4-Mepy][PF6], where the phase is only observed monotropically.cation points were always lower in temperature than melting points, thus giving larger mesophase ranges for the cooling Characteristic POM textures obtained on cooling of isotropic liquids are shown in Fig. 2 for [C16-mim][PF6] and [C16- cycles. The value of the solidification point was very dependent on the cooling rate employed.Therefore, only data recorded py][PF6]. These textures are typical of those observed, which in all cases showed spontaneous formation of homeotropic on heating cycles are reported except for the few examples where monotropic mesophases were observed, which are domains with the optical axis perpendicular to the slide.27 In the POM of [C16-mim][PF6] [Fig. 2(a)], small but characteristic recorded in parentheses in Table 3. The mesophases observed were identified using POM and DSC. For all of the meso- focal conic textures can also be seen in the dark homeotropic regions. The similarity of the textures observed for [R-mim]+ morphic examples, a single enantiotropic smectic mesophase was observed, except for the methylpyridinium salts [C16-3- and [R-py]+ salts indicates that the same type of mesophase J.Mater. Chem., 1998, 8, 2627–2636 2629Fig. 3 DSC traces observed on heating and cooling of (a) [C18- mim][PF6], and (b) [C18-py][PF6]. The peak labels indicate the type of phase transition occurring: C=solid < solid; S=solid < smectic; I=smectic < isotropic. Heating and cooling rates of 10 °Cmin-1 were employed.Fig. 2 Textures observed using POM (100× magnification) of (a) [C16-mim][PF6] at 98° C, and (b) [C16-py][PF6] at 121 °C. Both photographs were taken after cooling from the isotropic phase. is observed for both materials. The textures shown are typical for all salts that displayed liquid crystalline behaviour. In light of the evidence of the POM observations, the mesophases are assigned as smectic A (SA). Further support for the assignment of a smectic A mesophase comes from the fact that the [PF6]- salts displayed contact miscibility in the liquid crystalline state with the corresponding [CoCl4]2- analogues.For these studies small amounts of the two diVerent salts were placed slightly apart between two cover slips.The samples were heated on the microscope heating stage to above their melting points and then rapidly cooled to avoid excessive mixing. Further heating and cooling resulted in the observation of a uniform mesophase across the meeting point of the two samples. Such behaviour is only observed when the same mesophase structure is present. DSC heating and cooling curves for [C18-mim][PF6] and [C18-py][PF6] are illustrated in Fig. 3, from which it can be seen that the transition from the solid to the liquid crystalline phase was of much higher energy than the transition from the liquid crystal to the isotropic liquid. (i) 1-Alkyl-3-methylimidazolium salts The dodecyl-substituted salt showed no mesomorphic behaviour either on heating or cooling, while all the other salts displayed enantiotropic mesophases.The melting and clearing points are displayed graphically in Fig. 4(a). The close agreement between the clearing point on heating and the point at Fig. 4 Plots showing the melting and clearing temperatures observed which the mesophase reforms on cooling is further evidence on heating of (a) [Cn-mim][PF6], (b) [Cn-py][PF6], (c) [Cn-3- Mepy][PF6], and (d) [Cn-4-Mepy][PF6].for the purity of the salts. The melting points of the salts 2630 J. Mater. Chem., 1998, 8, 2627–2636increased only slightly with increasing alkyl chain length, while melting point recorded (55 °C) was slightly low due to the presence of trace amounts of impurities, although no impurity the clearing point increased markedly, ultimately giving a mesophase temperature range of 84 °C on heating and 93 °C peaks could be seen in the 1H NMR spectrum. 1H NMR spectroscopy provided a convenient method for confirming on cooling for the octadecyl substituted salt. Thus, the liquid crystalline range increased greatly with increasing alkyl chain the purity of the cation, and that no solvent residues remained in the salts. The IR spectra simply allowed confirmation of length.the presence of both the appropriate cation and the [PF6]- (ii) 1-Alkylpyridinium salts anion in the salts prepared. The anion displays a characteristic strong peak at 830 cm-1. No mesomorphic behaviour was observed for either the C12- Positive ion FAB mass spectrometry provided a convenient or [C14-py]+ salts. The melting points of all [R-py]+ salts were method for unequivocal characterisation of the salts.All of higher than those of the equivalent [R-mim]+ salts, concurring the data are collected in Table 4. Although the most intense with observations made previously for ionic liquids based on peak was the isolated cation, the next most intense peak such cations.29 The longer chain salts (C16, C18) did display generally corresponded to the species {[Q]2[PF6]}+ (Q= mesomorphic behaviour, and as was the case with the [Rorganic cation).The intensity of such peaks was typically ca. mim]+ salts the clearing temperature increased greatly on 5% that of the Q+ peak, with the intensity generally greater increasing the alkyl chain length by only two carbon atoms. for the shorter chain salts. This type of clustering phenomenon In contrast, the melting point only increased from 124 to has been observed before in similar organic cation salts.30 The 126 °C on increasing the alkyl chain length from 14 to 18.The data for [C18-mim][PF6] was slightly diVerent, with the second melting and clearing points of these species are displayed most intense mass peak occurring at m/z=574 (m/z for graphically in Fig. 4(b). Unlike the [R-mim]+ salts, however, {[C18-mim]2[PF6]}+ is expected at 816). This may correspond solid phase transitions were observed at temperatures below with the species {[C18-mim]3[PF6]}2+ (expected m/z=575), the melting point in all of the [R-py]+ salts studied. It can be although why such a species is only observed for this salt seen from Table 3 that the solid phase behaviour is quite is unclear. diVerent for the two non-liquid crystalline salts (C12 and C14) compared with those which do display liquid crystalline behav- The crystal structure of [C12-mim][PF6] iour (C16 and C18).In the latter case only one solid–solid phase transition was observed on heating and two on cooling, All of the salts investigated were crystalline, and in the case as shown in Fig. 3(b), while in the former there were three of [C12-mim][PF6] it proved possible to produce crystals of transitions both on heating and cooling. suYcient quality for single crystal X-ray diVraction. This is the first long chain 1-alkyl-3-methylimidazolium salt whose (iii) 1-Alkyl-3-methylpyridinium salts crystal structure has been reported, although the structure of 1,3-didodecylbenzimidazolium chloride was reported 3-Methylpyridinium is a more bulky headgroup than the simple pyridinium ring; this was expected to give the dual recently.21 The only other related salt for which a crystal structure has been determined is 1-ethyl-3-methylimidazolium eVects of lowering the melting points and reducing the tendency towards mesomorphic behaviour.This proved indeed to be hexafluorophosphate.31 The much shorter alkyl chain in this species means that the structure is quite diVerent from that the case, with the C16 salt only displaying a liquid crystalline phase on cooling (monotropic behaviour), and over a tempera- reported here. Furthermore, almost all other amphiphilic salts for which crystal structures have been determined are simple ture range of just 3 °C.The C18 salt, however, shows enantiotropic behaviour over a temperature range of ca. 10 °C. This halide salts, and this is one of the first containing a [PF6]- anion. information, and the behaviour observed for the shorter chain salts, is summarised in Table 3 and Fig. 4(c). The C12 and C14 The crystal structure of [C12H25-mim][PF6] consists of discrete cations (Fig. 5) and anions separated by at least van der salts display no mesomorphism, and simply melt directly to the isotropic liquid. Unlike the pyridinium salts, there are no Waals distances (see Fig. 6). The closest contact is 2.950(3) A° for F(2),C(2)*, (*x-1, y, z). Selected geometric parameters solid–solid phase transitions. are given in Table 5 and all are close to the expected values.(iv) 1-Alkyl-4-methylpyridinium salts The imidazolium ring is completely planar, within experimental error, and the bond lengths are very close to those observed As was the case for the [R-3-Mepy]+ salts discussed above, in other 1-alkyl-3-methylimidazolium salts.32 The straight the presence of a 4-methyl substituent on the pyridinium ring chain nature of the alkyl group is disrupted resulted in a lowering of the melting point and a reduction in close to the ring where it adopts a bent conformation, as the stability of the mesophase relative to the equivalent pyridinshown by the torsion angles N(2)–C(5)–C(6)–C(7), ium salt.In this case, both the C16 and C18-substituted salts C(5)–C(6)–C(7)–C(8) and C(6)–C(7)–C(8)–C(9) of displayed only monotropic smectic phases, while the C12 and -66.7(3), 176.4(2) and 60.2(3)° respectively.All other carbon C14 salts showed no mesophases. The other information is chain torsion angles approach 180°. The chain configuration collected in Table 3 and Fig. 4(d). These data show that the and the lack of any disorder in the structure appear to be a melting points for each alkyl chain length are almost identical consequence of the interdigitated molecular packing. The twist to the analogous [R-3-Mepy]+ salt.A further feature in in the alkyl chain occurs over a larger number of carbon common with the [R-3-Mepy]+ salts was the absence of phase atoms than is observed in the [(C12H25)2-benzimidazolium]Cl transitions in the solid phase. salt. The cation in the latter has a geometry described as being like a ‘two-legged stool’,21 whereas the [C12H25-mim]+ cation Characterisation could be described as having a spoon-shaped structure, as illustrated in Fig. 5. The X-ray powder diVraction pattern for Characterisation of the anhydrous salts was largely straightforward, being carried out initially using CHN analysis, 1H NMR the [C12H25-mim][PF6] showed the same unit cell and confirms that the single crystal is typical of the bulk synthetic sample.and IR spectroscopy. CHN analytical data for all salts prepared are summarised in Table 1, all being satisfactory except The crystal structure of the salt was similar to that of liquid crystalline alkylammonium and alkylpyridinium salts reported for [C12-4-Mepy][PF6], for which the carbon analysis was slightly low.This salt had proved very troublesome to purify previously.33,34 It consists of sheets of imidazolium rings and hexafluorophosphate ions, separated by interdigitated satisfactorily by recrystallisation as an oil formed on dissolving the crude solid in methanol. It is possible, therefore, that the alkyl chains; the unit cell is shown in Fig. 6, while Fig. 7 J. Mater. Chem., 1998, 8, 2627–2636 2631Table 4 Peaks observed in the positive ion mass spectra of [R-mim]+, [R-py]+, [R-3-Mepy]+ and [R-4-Mepy]+ salts of [PF6]- Salt m/z (relative intensity) Assignment [C12H25-mim][PF6] 251 (100) [C12H25-mim]+ 648 (14) {[C12H25-mim]2[PF6]}+ [C14H29-mim][PF6] 279 (100) [C14H29-mim]+ 704 (6) {[C14H29-mim]2[PF6]}+ [C16H33-mim][PF6] 307 (100) [C16H33-mim]+ 760 (3) {[C16H33-mim]2[PF6]}+ [C18H37-mim][PF6] 335 (100) [C18H37-mim]+ 574 (7) {[C18H37-mim]3[PF6]}2+ 816 (1.5) {[C18H37-mim]2[PF6]}+ [C12H25-py][PF6] 248 (100) [C12H25-py]+ 642 (10) {[C12H25-py]2[PF6]}+ [C14H29-py][PF6] 276 (100) [C14H29-py]+ 698 (6) {[C14H29-py]2[PF6]}+ [C16H33-py][PF6] 304 (100) [C16H33-py]+ 754 (4) {[C16H33-py]2[PF6]}+ [C18H37-py][PF6] 332 (100) [C18H37-py]+ 809 (4) {[C18H37-py]2[PF6]}+ [C12H25-3-Mepy][PF6] 262 (100) [C12H25-3-Mepy]+ 670 (7) {[C12H25-3-Mepy]2[PF6]}+ [C14H29-3-Mepy][PF6] 290 (100) [C14H29-3-Mepy]+ 726 (9) {[C14H29-3-Mepy]2[PF6]}+ [C16H33-3-Mepy][PF6] 318 (100) [C16H33-3-Mepy]+ 782 (3.5) {[C16H33-3-Mepy]2[PF6]}+ [C18H37-3-Mepy][PF6] 346 (100) [C18H37-3-Mepy]+ 837 (3.5) {[C18H37-3-Mepy]2[PF6]}+ [C12H25-4-Mepy][PF6] 262 (100) [C12H25-4-Mepy]+ 670 (6) {[C12H25-4-Mepy]2[PF6]}+ [C14H29-4-Mepy][PF6] 290 (100) [C14H29-4-Mepy]+ 726 (8) {[C14H29-4-Mepy]2[PF6]}+ [C16H33-4-Mepy][PF6] 318 (100) [C16H33-4-Mepy]+ 782 (3.5) {[C16H33-4-Mepy]2[PF6]}+ [C18H37-4-Mepy][PF6] 346 (100) [C18H37-4-Mepy]+ 837 (5) {[C18H37-4-Mepy]2[PF6]}+ interactions appear to be largely coulombic. This is consistent with earlier work which has shown that hydrogen-bonding is not observed in these and related systems when the charge density (r) on the halide atoms of the anion is <1, following the relation r=z2/x where z is the overall charge on the ion and x is the number of halide atoms in the complex.35 Powder X-ray diVraction studies Fig. 5 Structure of the unique 1-dodecyl-3-methyl cation in [C12- Powder X-ray diVraction studies were carried out on all of mim][PF6].the salts in order to gain further structural information. In all cases, the peak with the lowest value of 2h displayed the highest intensity. The d-spacing calculated from this peak increased relatively regularly with increasing alkyl chain length, as listed in Table 6. In addition, for each class of cation the patterns obtained were similar for all alkyl chain lengths, although with diVerent values of 2h.Thus all salts for each cation are isostructural. These data also indicate that the structures in all cases involve intercalated layers of cations as found for the structure of [C12H25-mim][PF6] discussed above, with a layer spacing corresponding to the lowest angle peak. The very small values of 2h for these peaks mean that there is some margin for error in the layer separation values obtained, owing to limits in the resolution of the diVractometer employed.Assuming that the values are correct to ±0.025°, the layer separations can be regarded as accurate to ±0.3 A° . Fig. 6 Unit cell of [C12-mim][PF6]. Thus the layer separation calculated from powder X-ray diVraction data for [C12H25-mim][PF6] (22.4 A° ) is equivalent demonstrates the interdigitated pattern.Of note is the stepped to that obtained from the single crystal data [22.197(4) A° ], to structure, with the alkyl chains tilted relative to the layers of within experimental error. cations and anions. The spacing between each layer was 22.197(4) A° . Mixtures of salts—binary systems The closest cation C(2),F–PF5 contact (2.950 A° ) is slightly shorter than the analogous closest contact taken from the In an attempt to reduce the melting point of the salts, preferably without decreasing their liquid crystalline tempera- crystal structure of the short chain 1-ethyl-3-methylimidazolium hexafluorophosphate salt (3.206 A° ).31 However, in both ture range, an investigation of the eVect of mixing the salts [C16-mim][PF6] and [C16-py][PF6] was carried out.Such cases, the contacts are close to the van der Waals distance and 2632 J. Mater. Chem., 1998, 8, 2627–2636Table 5 Selected interatomic distances (A° ) and torsion angles (°) for X N(1)–C(1) 1.468(3) N(1)–C(2) 1.322(3) N(1)–C(3) 1.373(3) N(2)–C(2) 1.326(3) N(2)–C(4) 1.374(3) N(2)–C(5) 1.477(3) C(3)–C(4) 1.334(4) P(1)–F(1) 1.591(2) P(1)–F(2) 1.610(2) P(1)–F(3) 1.593(2) P(1)–F(4) 1.602(2) P(1)–F(5) 1.584(2) P(1)–F(6) 1.599(2) N(2)C(5)C(6)C(7) -66.7(3) C(2)N(2)C(5)C(6) 112.4(2) C(4)N(2)C(5)C(6) -66.5(3) C(5)C(6)C(7)C(8) 176.4(2) C(6)C(7)C(8)C(9) 60.2(3) N(2)C(2)N(1)C(1) -176.8(2) procedure was repeated three times, by which stage it was assumed that a homogeneous mixture had been prepared.The melting and clearing points of the binary systems were then investigated by POM and DSC. In all cases a mesophase was observed which was of the same type as that of the individual components, and in no cases was biphasic behaviour observed. The data obtained are summarised in Fig. 8 and Table 7, where it can be seen that although the clearing point varied smoothly as the composition was changed, the melting point varied little between pure [C16-mim][PF6] and the 75% [C16-mim][PF6]–25% [C16-py][PF6] mixture.Thus, this mixture has a larger mesophase range (55 °C) than that of the pure [C16-mim][PF6] (49° C). It should also be noted that the melting transition for the mixed salts was not a sharp transition as observed for the pure salts, but was spread over a range of several degrees.This was reflected in broad peaks in the DSC traces obtained for the 50%–50% and 25% [C16- mim][PF6]–75% [C16-py][PF6] mixtures. It was disappointing that no depression in the melting point was observed, although this may be a reflection of the similarity in the structure of the cations. One additional benefit of carrying out the studies on the mixed salts, however, is that it allowed confirmation of the fact that the mesophase formed was the same for the [Rmim]+ and the [R-py]+ salts.This arises from the ‘miscibility Fig. 7 Overall structure of [C12-mim][PF6] showing the interdigitation and the tilted alkyl chains. methods are routinely used to lower the melting point of both molten salts and molecular liquid crystalline materials, by the formation of eutectic mixtures.The mixtures were prepared Fig. 8 Plot showing the variation in melting and clearing point on by grinding together various proportions of the two constitu- heating salts prepared from various proportions of [C16-mim][PF6] and [C16-py][PF6]. ents, followed by melting, re-cooling, and grinding again. This Table 6 Layer separations obtained from powder X-ray diVraction measurements Layer separation/A° Chain length (n) [R-mim]+ [R-py]+ [R-3-Mepy]+ [R-4-Mepy]+ 12 22.4 22.2 23.5 23.0 14 24.2 23.9 25.9 24.9 16 26.5 26.2 27.4 27.1a 18 27.7 27.4 29.1 27.4 aPoor quality data.J. Mater. Chem., 1998, 8, 2627–2636 2633Table 7 Transitions observed in on heating mixtures of [C16-mim][PF6] comes from the textures observed using POM, as illustrated and [C16-py][PF6], and transition energies obtained from DSC in Fig. 2. As has been stated in the previous section, these measurements were broadly similar for all salts, and were typical of smectic A phases. Smectic A mesophases have previously been ident- mol% [C16-py][PF6] T/°C DHa /kJ mol-1 Transition ified for other amphiphilic materials, for example [Cn-4- 100 104 27.7 C�C1 Mepy]Br (n=16, 18, 22) and [C22-4-Mepy]I.3,37 126 8.4 C1�S Previous investigations of the thermal behaviour of salts 138 0.8 S�I with interdigitated structures suggest that formation of the 75 72L C�C1 liquid crystalline phases results from melting of the alkyl 98K 32.5b C1�S chains, while the ionic layers between remain ordered until the 138 0.7 S�I clearing point.X-Ray studies have shown that in many cases 50 76L C�C1 89K 31.1b C1�S the layer separation actually decreases on moving from the 135 0.8 S�I crystalline solid to the smectic phase. For example, solid n- 25 77 32.2 C�S decylammonium chloride has a layer spacing of 28.1 A° in its 132 0.7 S�I solid phase, and 24.6 A° in its first smectic phase.2 The Raman 0 75 37.5 C�S spectrum of the same compound shows clear signs of loss of 125 0.5 S�I order in the alkyl chains as the temperature is increased.38 aCalculated using an averaged molecular mass for the relative pro- It is possible that the tilted orientation of the alkyl chains portion of the two constituents.bOverlapping of peaks prevented relative to the unit cell observed in the crystal structure of calculation of individual transition enthalpies. [C12-mim][PF6] gives a clue as to the structure of the mesophase in these systems.This solid state arrangement can be compared with the smectic C liquid crystal phase, as all of the alkyl rule’, which states that ‘all liquid crystalline modifications which exhibit an uninterrupted series of mixed crystals in chains are tilted at an angle of ca. 57° to the ab plane containing the anions and the cationic head groups. The binary systems without contradiction can be marked with the same symbol’.36 thermodynamic ordering of liquid crystalline phases allows only the smectic A and nematic phases at higher temperatures than smectic C phases. The relatively large enthalpy (and thus Discussion entropy) change on melting indicates a considerable change in the structure of the system.Thus, it may be postulated that In general, with increasing alkyl chain length the melting points increased only modestly. In the case of the liquid the mesophase structure involves conformational melting of the alkyl chains, accompanied by loss of the tilted orientation crystalline [R-mim]+ and [R-py]+ salts, however, the clearing temperature increased dramatically with increasing chain as indicated in Fig. 9, giving a smectic A phase. Further evidence can only be gained by use of variable temperature length. The widest mesophase range was observed for the salt [C18H37-mim][PF6], from 80 to 165 °C on heating, with an low angle X-ray studies of the salts, unavailable for this study. The enthalpy of the smectic–isotropic transition in the [R- even larger range on cooling (as was observed in all cases).The temperature at which texture was observed on cooling 3-Mepy]+ salts was much smaller than the value for the equivalent pyridinium salt, suggesting that the methyl group from the isotropic liquid (i.e. formation of a liquid crystalline phase) was almost identical to the clearing point in pure was lowering the stability of the mesophase.It is notable in this series that, unlike the [R-py]+ salts, the melting point samples. The solidification temperature varied according to the rate of cooling employed, owing to the supercooling often increases steadily through the series n=12–18. Similar behaviour was noted for the [R-4-Mepy]+ salts, although the observed for the mesophase–solid transition in liquid crystalline materials. The [R-3-Mepy]+ and [R-4-Mepy]+ salts dis- mesophases observed for these compounds were monotropic in nature.Overall, the widest liquid crystalline ranges were played liquid crystalline behaviour only over very small temperature ranges, and for the C16 and C18 salts only. In the observed for the [R-mim]+ salts, followed by those for the [Rpy]+ salts, while the [R-3-Mepy]+ and [R-4-Mepy]+ salts case of the [R-4-Mepy]+ salts the mesophases were exclusively monotropic, while for the [R-3-Mepy]+ salts the C16 salt showed the least tendency to form mesophases.A similar phenomenon was observed for liquid crystalline salts based displayed monotropic behaviour and the C18 salt enantiotropic behaviour. on pyridinium and ethylpyridinium halide salts containing Nsubstituted mesogenic groups.7 It is clear that the [R-mim]+ The data in Table 3 clearly indicate that the enthalpy of melting (DHfus) was always much larger than the enthalpy of salts, whose liquid crystalline behaviour has been little studied to date, present considerable advantages compared with the the clearing transition (DHclear).This is a common observation in thermotropic liquid crystals. The only other similar liquid pyridinium salts for future development in this area. One intriguing observation, which can be seen from the crystalline [PF6]- salt reported to date is [(C16H33)2bzm][PF6] (bzm=benzimidazolium). This forms a lamellar phase at data in Table 3, was that all of the pyridinium salts displayed solid phase polymorphism at temperatures below the melting 103.3 °C on cooling with an enthalpy of 2.0 kJ mol-1, followed by solidification at 61.3 °C with an enthalpy of 46.1 kJ mol-1.21 point.None of the other salts displayed this phenomenon. There was a noticeable diVerence between the non-liquid The equivalent values for [C16-mim][PF6] are the formation of a smectic phase at 122 °C with an enthalpy of 0.5 kJ mol-1, crystalline C12 and C14 sa transitions below their melting point both on heating and cooling, and and solidification at 62 °C with an enthalpy of 37.2 kJ mol-1.Thus, the two long alkyl chains in the benzimidazolium salt the liquid crystalline C16 and C18 salts which displayed just one transition before melting, and two transitions on cooling.result in a less stable mesophase than the single one in the [C16-mim]+ salt, although in the former case the transition These transitions have been shown to appear consistently on repeated heat–cool cycles, indicating that they are not simply enthalpy is somewhat higher. One noticeable observation from the DSC data was that the enthalpies of the melting (DHfus) artefacts. In the case of the C16 and C18 salts, the lowest temperature solid phase transition was ofmuch higher enthalpy and clearing (DHclear) transitions increased with increasing chain length.This suggests that chain interdigitation is of than the higher temperature one. This suggested that a large degree of disorder was occurring in the first transition, presum- increasing importance in stabilising the mesophase as the chain length increases.ably with the formation of a solid of structure more similar to that of the liquid crystalline phase. Clearly variable tempera- In the absence of variable temperature low-angle X-ray studies, the principle evidence for the mesophase structure ture powder X-ray diVraction or vibrational spectroscopic 2634 J.Mater. Chem., 1998, 8, 2627–2636analogous Cl-, [CoCl4]2- and [NiCl4]2- salts.12 The textures observed using POM were very similar, and were interpreted as indicating formation of a smectic A mesophase. The salts based on the pyridinium cation displayed higher melting points and smaller mesophase ranges than imidazolium salts of equivalent alkyl chain length.The pyridinium salts displayed interesting polymorphism, however, with phase transitions observed at temperatures below the melting points of the salts. Both this phenomenon and the structures of the smectic A mesophases would merit further investigation using variable temperature small angle X-ray techniques unavailable in the present study. Substitution of the pyridinium ring at the 3- and 4-positions with methyl groups reduced the melting points of the salts, but reduced the tendency to form liquid crystalline phases still further.Mixtures formed by combining salts with imidazolium and pyridinium cations did not result in depression of the melting point below that of the pure imidazolium salt. A slightly larger mesophase range was obtained for one of the mixtures, suggesting that further investigations, perhaps with cations of greater structural diVerence, might yield interesting results. The intention in future studies is to investigate how the mesophase range and stability are aVected by use of a mesogenic substituent in place of the simple alkyl chains.It is hoped that such a modification will increase the stability of the mesophase, important in any application, without signifi- cantly increasing the melting point of the salts.We also hope to extend the range of anions employed to investigate the eVect this has on mesophase formation. Acknowledgements We would like to thank Dr John Liggat, Margaret Adams and the Queen’s University of Belfast School of Chemistry analytical services for assistance with DSC measurements and CHN analysis; Dr Cecil Burdett and Mark Nieuwenhuyzen for assistance with powder X-ray diVraction studies; the mass spectrometry services of the University of Strathclyde and the Queen’s University of Belfast. We would also like to thank the University of Strathclyde (C.M.G.and A.R.K.), the ERDF N N N N N N N N N N N N N N N N N N N N N N N N (a) (b) Technology Development Programme and the QUESTOR Fig. 9 Schematic representation of (a) the cation structure in the solid Centre (J.D.H.) for financial support, and the EPSRC and state of the mim salts, and (b) a possible cation structure of the Royal Academy of Engineering for the award of a Clean smectic A phase, showing the eVect of conformational melting of the Technology Fellowship (to K.R.S.). alkyl chains.[PF6]- ions have been omitted for clarity. studies would help elucidate any changes of structure. Such References information might also provide valuable information on the 1 A. Skoulios and V. Luzzati, Acta Crystallogr., 1961, 14, 278. structure of the liquid crystalline phases. Behaviour of this 2 See, e.g.: V. Busico, P.Cernicchiaro, P. Corradini and type has been noted previously for liquid crystalline pyridinium M. Vacatello, J. Phys. Chem., 1983, 87, 1631. salts with dodecyl sulfate anions, although the authors also 3 See, e.g.: C. G. Bazuin, D. Guillon, A. Skoulios and J.-F. Nicoud, Liq. Cryst., 1986, 1, 181. did not attempt to explain the phenomenon.14 4 J. J. H. Nusselder, J. B. F. N. Engberts and H.A. van Doren, Liq. Cryst., 1993, 13, 213. Conclusions 5 Y. Kosaka, T. Kato and T. Uryu, Liq. Cryst., 1995, 18, 693. 6 S. Ujiie and K. Iimura, Chem. Lett., 1990, 995. In this paper we have described the properties of a series of 7 D. Navarro-Rodriguez, Y. Frere, P. Gramain, D. Guillon and novel hexafluorophosphate salts, many of which display liquid A. Skoulios, Liq. Cryst., 1991, 9, 321; E.Bravo-Grimaldo, D. Navarro-Rodriguez, A. Skoulios and D. Guillon, Liq. Cryst., crystalline properties on melting. The salts are closely related 1996, 20, 393. to ionic liquids which are finding increasing use as reaction 8 Y. Z. Yousif, A. A. Othman,W. A. Al-Masoudi and P. R. Alapati, solvents. They may be prepared very easily, and unlike many Liq. Cryst., 1992, 12, 363.ionic liquids are insoluble in water. It is clear that cations 9 Y. Haramoto, S. Ujiie and M. Nanasawa, Liq. Cryst., 1996, 21, based on the imidazolium ring give materials with much larger 923. mesophase ranges for a given alkyl chain length, compared 10 Y. Kosaka, T. Kato and T. Uryu, Liq. Cryst., 1995, 18, 693. 11 F. Neve, Adv. Mater., 1996, 8, 277. with the equivalent pyridinium salts.The existence or not of 12 K. R. Seddon, C. J. Bowlas and D. W. Bruce, Chem. Commun., a mesophase is extremely dependent both on the structure of 1996, 1625. the cationic head group and the length of the alkyl substituent. 13 V. Busico, D. Castaldo and M. Vacatello, Mol. Cryst. Liq. Cryst., In general, however, the longer the alkyl chain the more stable 1981, 78, 221.the mesophase formed. In the case of the nine salts which did 14 D. W. Bruce, S. Estdale, D. Guillon and B. Heinrich, Liq. Cryst., display liquid crystalline behaviour, only a single mesophase 1995, 19, 301. 15 S. Ujiie and K. Iimura, Chem. Lett., 1994, 17. was formed in each case, which is in common with the J. Mater. Chem., 1998, 8, 2627–2636 263516 K. R. Seddon in Proceedings of the 5th International Symposium 29 J.S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg. Chem., 1982, 21, 1263. on Molten Salt Chemistry and Technology, ed. H. Wendt, Trans 30 A. K. Abdul-Sala, A. M. Greenway, K. R. Seddon and T.Welton, Tech Publications Ltd., Uetikon–Zu� rich, 1998, p. 53. Org. Mass Spectrom., 1993, 28, 759; A. K. Abdul-Sala, A. E. 17 P. Bonho� te, A.-P. Dias, N. Papageorgiou, K. Kalyanasundaram Elaiwi, A. M. Greenway and K. R. Seddon, Eur. Mass Spectrom., and M. Gra�tzel, Inorg. Chem., 1996, 35, 1168. 1997, 3, 245. 18 Y. Chauvin, L. Mussmann and H. Olivier, Angew. Chem., Int. Ed. 31 J. Fuller, R. T. Carlin, H. C. De Long and D. Haworth, J. Chem. Engl., 1995, 34, 2698. Soc., Chem. Commun., 1994, 299. 19 R. Mukkamala, C. L. Burns, R. M. Catchings and R. G. Weiss, 32 See, e.g.: A. K. Abdul-Sala, A. M. Greenway, P. B. Hitchcock, J. Am. Chem. Soc., 1996, 118, 9498 and references therein. T. J. Mohammed, K. R. Seddon and J. A. Zora, J. Chem. Soc., 20 H. Kansui, S. Hiraoka and T. Kunieda, J. Am. Chem. Soc., 1996, Chem. Commun., 1986, 1753; P. B. Hitchcock, R. J. Lewis and 118, 5346 and references therein. T. Welton, Polyhedron, 1993, 12, 2039; P. B. Hitchcock, K. R. 21 K. M. Lee, C. K. Lee and J. B. Lin, Chem. Commun., 1997, 899. Seddon and T. Welton, J. Chem. Soc., Dalton Trans, 1995, 3467. 22 M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazz33 M. R. Ciajolo, P. Corradini and V. Pavone, Acta Crystallogr., Polidori, R. Spagna and D. Viterbo, J. Appl. Crystallogr., 1989, Sect. B, 1977, 33, 553. 22, 389. 34 H. H. Paradies and F. Habben, Acta Crystallogr., Sect. C, 1993, 23 TeXsan: Single Crystal Structure Analysis Software, Version 1.6. 49, 744. Molecular Structure Corporation, The Woodlands, TX 77381, 35 P. B. Hitchcock, K. R. Seddon and T. Welton, J. Chem. Soc., 1993. Dalton Trans., 1993, 2639. 24 J. S. Wilkes and M. J. Zaworotko, J. Chem. Soc., Chem. Commun., 36 H. Sackmann and D. Demus, Mol. Cryst. Liq. Cryst., 1973, 21, 1992, 965. 239. 25 B. Ellis, personal communication. 37 M. Tabrizian, A. Soldera, M. Couturier and C. G. Bazuin, Liq. 26 C. M. Gordon, J. D. Holbrey and K. R. Seddon, unpublished Cryst., 1995, 18, 475. work. 38 H. L. Casal, D. G. Cameron and H. H. Mantsch, J. Phys. Chem., 27 D. Demus and L. Richter, Textures of Liquid Crystals, Verlag 1985, 89, 5557. Chemie, Weinheim, 1978, p. 61. 28 G. W. Gray and J. W. Goodby, Smectic Liquid Crystals, Textures and Structures, Leonard Hill, Glasgow, 1984. Paper 8/06169F 2636 J. Mater. Chem., 1998, 8, 2627–2636

ISSN:0959-9428    

DOI:10.1039/a806169f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Discotic liquid crystals of transition metal complexes. Part 24† Synthesis and mesomorphism of porphyrin derivatives substituted with two or four bulky groups Kazuchika Ohta,* Noboru Yamaguchi and Iwao Yamamoto Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu University, 386–8567 Ueda, Japan. E-mail: ko52517@giptc.shinshu-u.ac.jp Received 21st July 1998, Accepted 2nd September 1998 We have synthesized nine novel porphyrin derivatives, 1–8 and 1-Cu, substituted with various steric hindrance groups and long flexible chains in order to investigate the relationship between the molecular type of porphyrin derivatives and the resulting mesophase.Type 4 disc-like (C12O)16-TTPH2 (1) and (C12O)16-TTPCu (1-Cu) derivatives exhibit Dh columnar mesophases, which are the first examples of meso-substituted porphyrin metal-free derivatives and copper complexes.Type 5 strip-like (CnO)8-BTPH2 [4 (n=12), 5 (n=16)] derivatives having eight long chains at the 5,15-positions exhibit Drd columnar mesophases. On the other hand, the type 5 (C12O)4-BTPH2 (6) derivative having four long chains exhibits discotic lamellar DL.rec1 and DL.rec2 mesophases which have a twodimensional rectangular structure within the layer.The (C12O)4-BPPH2 (7) type 6 derivative also shows a DL lamellar mesophase. Bruce et al. reported that type 3 rod-like porphyrin derivatives show calamitic mesophases of SB, SE and SE¾ phases. We revealed from these types of mesogenic porphyrin derivatives that such a successive change of the molecular structures causes their mesophases to change from discotic columnar to discotic lamellar, and further to calamitic. 1.Introduction Porphyrins and their analogues exist in various states in nature and act as centers of energy transfer and charge transfer processes. In order to reveal their mechanistic role in natural systems, a number of porphyrin derivatives have been synthesized and studied extensively as models of vital functions.2,3 Moreover, porphyrins are expected to find applications in functional materials because of their favorable electronic properties, chemical and thermal stabilities.For the eVective utilization of functionalities of a certain molecule, it is important to control the electronic and steric environments and the state of aggregation of the molecules.For this purpose, the following methods have been used: (a) enlargement of the p-conjugated system,4 (b) giving molecular recognizability by modification of the molecule with bulky substituent,3 and (c) formation of aggregates such as membranes, micelles, or microemulsions by introduction of aliphatic, hydrophilic, or amphiphilic substituents.5 It may be very useful to incorporate liquid crystallinity to organic metal complexes with various valuable characteristics, in order to provide new properties or to modify known properties of the original complexes.For example, it was reported that the third-order nonlinear optical susceptibility (x(3)) of tetrakis- (octylthio)phthalocyaninatocopper(II) in the mesomorphic state is larger than that in the solid state.6 The first study of mesogenic porphyrins was reported in 1980 for uroporphyrin I octa-n-dodecyl ester which shows a monotropic discotic mesophase.7 Since then, some mesogenic porphyrins have been synthesized and their mesomorphic properties investigated,8–17 although there are fewer mesogenic porphyrins than mesogenic phthalocyanines18 whose core shape is very analogous to porphyrin.Most of the mesogenic porphyrins have been synthesized mainly from the photophysical viewpoint. Liquid crystals containing the porphyrin core reported to date can be classified into three types by means of their molecular shapes (see Fig. 1). Type 1 consists of the b- N N N N R M R R R N N N N R M R R R R R R R N N N N M R R (Type 3) (Type 2) (Type 1) Fig. 1 Three types of mesogenic porphyrin derivatives reported to date. †Part 23: Ref. 1. J. Mater. Chem., 1998, 8, 2637–2650 2637substituted porphyrin derivatives. Greg et al. synthesized many octakis-substituted porphyrin derivatives which exhibit a discotic columnar mesophase.8,9 Octakis(alkoxyethyl )porphyrinatozinc( II) was investigated in terms of the photovoltaic eVect9 and radiation-induced conductivity.10 It was reported by Doppelt11 and Morelli et al.12 that octakis(octylthio)tetraazaporphyrin metal complexes show a discotic hexagonal columnar (Dh) mesophase.The compounds of this type tend to form a columnar mesophase in which the molecules stack one-dimensionally because of the flatness of the molecule.Type 2 is the meso-substituted porphyrin derivatives. Shimizu et al. synthesized a series of tetra-(long-alkyl chain)-substituted tetraphenylporphyrins and reported that they exhibit a discotic lamellar (DL) mesophase.13 They characterized several properties such as photoconductivity,14 third-order nonlinear optical susceptibility,15 and so on. Besides, some long chain esters of meso-tetrakis(p-carboxyphenyl )porphyrin were reported to exhibit an identified phase with a lamellar structure.16 From these examples mentioned above, compounds of type 2 show not a columnar mesophase but a lamellar mesophase because van der Waals interaction between the porphyrin macrocycles have been weakened by the existence of bulky groups (phenyl groups) near the porphyrin core, and because the small number of flexible chains around the core are not enough to occupy all the surrounding area to form a columnar structure.On the other hand, it was reported by Bruce et al. that 5,15- bis(p-alkoxyphenyl )porphyrinatozinc(II), belonging to type 3, shows smectic B, E, and E¾ phases (abbreviated as SB, SE and SE¾, respectively).17 It is interesting that this porphyrin, the molecular shape of which is basically discotic (disk-like), shows not discotic columnar mesophases but calamitic mesophases, although long-chain-substituted disk-like compounds generally tend to show columnar mesophases.We noticed that the porphyrin derivatives could more easily change their molecular shapes compared with other macrocyclic compounds such as phthalocyanines.From this synthetic viewpoint, a great variety of mesogenic porphyrin derivatives will be able to be obtained. In order to study how the mesomorphism may change with changing the kind of bulky group and/or the number of flexible long alkyl chains in the surroundings of a porpyrin core, we have synthesized nine novel porphyrin derivatives of four types, 1–8 and 1-Cu, as illustrated in Fig. 2, and investigated their mesomorphism. Compounds 1–3 have four o-terphenyl groups with long alkoxy chains at the 5, 10, 15 and 20-positions of the porphyrin, and they are abbreviated as (CnO)m-TTPM (n=8, 12; m=8, 16; M=H2, Cu). Compounds 4–6 have two of the o-terphenyl groups replaced by two o-terphenyl groups with long alkoxy chains at the 5 and 15-positions, and abbreviated as (CnO)m- BTPM (n=12, 16; m=4, 8).Compounds 7 and 8 are 5,15- bis(3,4-didodecyloxyphenyl )porphyrin [abbreviated as (C12O)4-BPPH2] and 5,15-bis(4-dodecyloxybiphenyl )porphyrin [abbreviated as (C12O)2-BBPH2], respectively. Although compounds 1–3 are similar to type 2, the number of the long chains attached to them are two or four times as many as those of type 2.These compounds are, therefore, classified as type 4. Compounds 4–6 have the structure in which the number of o-terphenyl moieties is halved compared with type 4, so that they are referred to as type 5. Compound 7 is classified as type 6, because the number of alkoxy long chains is twice those of conventional type 3. Compound 8 belongs to 1: R1=R2=C12H25O, M=H2; (C12O)16-TTPH2 1-Cu : R1=R2=C12H25O, M=Cu; (C12O)16-TTPCu 2: R1=R2=C8H17O, M=H2; (C8O)16-TTPH2 3: R1=C12H25O, R2=H, M=H2; (C12O)8-TTPH2 M N N N N R1 R1 R1 R2 R1 R2 R1 R2 R1 R2 R2 R1 R2 R1 R2 R2 (Type 5) 4: R1=R2=C12H25O; (C12O)8-BTPH2 5: R1=R2=C16H33O; (C16O)8-BTPH2 6: R1=C12H25O, R2=H; (C12O)4-BTPH2 NH N N HN R2 R1 R2 R1 R2 R1 R2 R1 (Type 6) 7: (C12O)4-BPPH2 NH N HN N C12H25O C12H25O OC12H25 OC12H25 (Type 3) 8: (C12O)2-BBPH2 NH N N HN C12H25O OC12H25 (Type 4) type 3.Fig. 2 Formulae of the porphyrin derivatives in this work. We wish to report here that such a successive change of the molecular structures causes their mesophases to change from In Scheme 1, the syntheses of alkoxybenzils (13) from the discotic columnar to discotic lamellar, and further to calamitic.starting materials (9) were carried out by the method of Wenz.19 In Scheme 2, 3,4-didodecyloxybenzaldehyde (19) was prepared by the method of Strzelecka et al.20 4-Bromo-4¾- 2. Results and discussion dodecyloxybiphenyl (21) was synthesized according to the 2-1. Synthesis procedure described by Gray et al.21 The syntheses of tetrakissubstituted porphyrin derivatives 1–3 (Scheme 3) followed the The porphyrin derivatives 1–8 in this work have been synthesized by using synthetic routes as shown in Scheme 1–4. conventional method described by Adler et al.,22 and these 2638 J.Mater. Chem., 1998, 8, 2637–2650MeO MeO O OH X CHO X X OMe O MeO X X O OMe Y HO O Y OH O R2 R1 R2 R1 O O R2 R1 R2 HO O R1 10 KCN 9a; X=OMe 9b; X=H 11 12 13 14 Pyridine CuSO4•5H2O AcOH HBr K2CO3 RBr ButOK p-TosOH 12a; Y=OH 12b; Y=H 13a; R1=R2=C12H25O 13b; R1=R2=C8H17O 13c; R1=R2=C16H33O 13d; R1=C12H25O, R2=H HC C CO2Me O R2 R1 R2 R1 CO2Me 15 R2 R1 R2 R1 CH2OH R2 R1 R2 R1 CHO 16 PDC 17 LiAlH4 Scheme 1 Synthetic route to aldehyde 17. 2-2. Liquid crystalline properties 2-2-1. (CnO)m-TTPM (1, 1-Cu, 2 and 3, type 4). Phase transition temperatures and enthalpy changes of (C12O)16- TTPH2 (1), (C12O)16-TTPCu (1-Cu), (C8O)16-TTPH2 (2) and (C12O)8-TTPH2 (3) are summarized in Table 3.(C12O)16- TTPH2 (1) and (C12O)16-TTPCu (1-Cu) exhibit mesomorphism in the low-temperature region. The DSC thermograms of (C12O)16-TTPH2 (1) were very complicated. When the pristine sample of this compound was at first cooled to ca. -100 °C and then heated at 10 °Cmin-1, we observed a very broad endothermic peak corresponding to the transition from the X1 phase to the M1 phase at ca.-80 °C and a comparatively large endothermic peak corresponding to the change from the M1 phase to the isotropic liquid (IL) at 39 °C. In addition, a small endothermic peak which overlapped with the peak at 39 °C was observed at 59 °C. This peak corresponds to the clearing point of the M2 phase.When this IL was once more cooled to ca. -100 °C HO HO CHO C12H25O C12H25O CHO C12H25O CHO C12H25O Br Br HO 1) BunLi 2) DMF C12H25Br KOH/EtOH 19 18 KOH, Aliquat 336 C12H25Br 20 21 22 and heated, a new broad endothermic peak appeared at ca. Scheme 2 Synthetic routes to aldehydes 19 and 22. -35 °C. This peak corresponds to the transition from the X2 phase to the M2 phase.Besides, a comparatively small peak corresponding to the X1–M1 transition at ca. -80 °C was also observed. This result indicates that when the IL of this resulting by-products, namely, chlorine derivatives were oxidcompound is cooled, it changes into not only the X2 phase ized as described in the literature.23 The copper complex (1- but also the X1 phase to some degree. On further heating, a Cu) of metal free derivative 1 was obtained by the conventional small endothermic peak near 39 °C appeared, followed by a synthetic procedure.24 Bis-substituted porphyrin derivatives broad exothermic peak due to relaxation from the IL to the 4–8 (Scheme 4) were synthesized by using the method of M2 phase, and a small endothermic peak due to clearing from Manka et al.25 Further details of these synthetic procedures the M2 phase to the IL was finally observed at 59 °C.The will be described in the Experimental section. thermogram areas of the M–IL transition varied with the non- Elemental analysis data of the porphyrin derivatives 1–8 virgin samples and their enthalpy changes were below one- are summarized in Table 1. Electronic absorption spectral data tenth of that of the pristine sample.This result indicates that for all of the porphyrin derivatives in this work are presented when a sample cleared to the IL is cooled, most of the sample in Table 2. Each of the electronic absorption spectra showed remains in a supercooled liquid state because of the low Soret- and Q-bands which are characteristic bands of porphyrin compounds.cohesivity of these molecules. Relaxation of this supercooled J. Mater. Chem., 1998, 8, 2637–2650 2639DMF CuCl2 C2H5CO2H DDQ (C12O)16-TTPH2 (C12O)16-TTPCu NH N HN N NH R1 R1 R1 R2 R1 R2 R1 R2 R1 R2 R2 R1 R2 R1 R2 R2 R2 R1 R2 R1 CHO 1: R1=R2=C12H25O; (C12O)16-TTPH2 2: R1=R2=C8H17O; (C8O)16-TTPH2 3: R1=C12H25O, R2=H; (C12O)8-TTPH2 17 1 Cu–1 Scheme 3 Syntheses of the porphyrin derivatives 1–3 and the copper(II) complex of 1 (1-Cu). 4: R1=R2=C12H25O; (C12O)8-BTPH2 5: R1=R2=C16H33O; (C16O)8-BTPH2 6: R1=C12H25O, R2=H; (C12O)4-BTPH2 1) , CF3CO2H 2) Chroranil , CF3CO2H 1) , CF3CO2H 2) Chroranil R1 R2 R1 R2 R1 R2 R1 R2 R2 R1 R2 R1 CHO NH N HN N HN NH C12H25O C12H25O CHO NH HN NH N HN N C12H25O C12H25O OC12H25 OC12H25 C12H25O CHO NH HN C12H25O NH N HN N OC12H25 17 1) 19 7: (C12O)4-BPPH2 2) Chroranil 22 8: (C12O)2-BBPH2 Scheme 4 Syntheses of the porphyrin derivatives 4–8. 2640 J. Mater. Chem., 1998, 8, 2637–2650Table 1 Elemental analysis data of the porphyrin derivatives in this work Found% (Calc.%) Molecular formula Compound (molecular weight) C H N C284H446N4O16 81.81(81.75) 10.89(10.77) 1.18(1.34) (C12O)16-TTPH2 (1) (4172.72) C284H444N4O16Cu 80.26(80.56) 10.40(10.57) 1.16(1.32) (C12O)16-TTPCu (1-Cu) (4234.21) C220H318N4O16 80.72(80.69) 9.80(9.79) 1.55(1.71) (C8O)16-TTPH2 (2) (3274.99) C188H254N4O8 83.78(83.69) 9.46(9.49) 1.99(2.08) (C12O)8-TTPH2 (3) (2698.13) C152H230N4O8 81.72(81.45) 10.36(10.34) 2.38(2.50) (C12O)8-BTPH2 (4) (2241.54) C184H294N4O8 81.94(82.15) 10.81(11.02) 1.94(2.08) (C16O)8-BTPH2 (5) (2690.38) C104H134N4O4 82.70(83.04) 8.82(8.98) 3.55(3.73) (C12O)4-BTPH2 (6) (1504.23) C80H118N4O4 80.17(80.08) 9.94(9.91) 4.26(4.67) (C12O)4-BPPH2 (7) (1199.85) C68H78N4O2 83.19(83.05) 7.99(8.00) 5.74(5.70) (C12O)2-BBPH2 (8) (983.39) liquid into the M1 phase is extremely slow; the non-pristine 9.55 A° , is twice the ordinary stacking distance, 3.5–4.7 A° , for columnar mesophases, so that it may be an interdimer distance. sample kept at room temperature (r.t.) for more than one year exhibited the same thermal behavior as the pristine sample.In this mesophase, dimerization may occur. We have calculated the number of molecules, Z, in the Considering from the results described above, the pristine state of this compound is the M1 phase at room temperature and two-dimensional hexagonal lattice with the possible interdimer distance h (a=41.5 A° , h=9.55 A° ) by the following equation: when it is cooled below ca.-80 °C it changes into the X1 phase. When it is heated, double clearing behavior of Z=rVL/M M1AIL—(relaxation)AM2AIL occurs. The X2 phase in the where r is the density; V, the unit cell volume; L, Avogadro’s non-pristine sample, which does not exist in the pristine number; and M, the molecular weight.Generally, it is con- sample, is obtained by cooling. However, the X1 and X2 phases sidered that the density of a compound in the liquid crystalline are mingled to some extent in the non-pristine sample which state is 0.9–1.0 g cm-3. Thereby, the density r of the present shows, as a result, more complicated phase transition behavior.compound 1 in the mesophase at 125 °C is assumed as Identification of each of the phases in the (C12O)16-TTPH2 1 g cm-3. (1) derivative was carried out by X-ray diVraction measurements and observation of the optical textures. However, the V=(Ó3/2)a2h X1 and X2 phases could not be identified because these two =(Ó3/2)×45.12×9.55 A° 3 phases exist in a very low temperature region beyond the range of our instrumental techniques. The M1 phase could be =1.42×10-20 cm-3 identified by using the pristine sample at r.t., and the M2 Z=1×1.42×10-20×6.02×1023/4172.72 phase could be also identified by using a sample prepared by annealing the supercooled liquid for 10 days between 39 °C =2.05 (clearing point of the M1 phase) and 59 °C (clearing point of theM2 phase).As summarized in Table 4, the X-ray diVraction Thus, we could confirm that two molecules exist in the unit cell. This means that the dimers stack with a periodicity of pattern of the M1 phase of (C12O)16-TTPH2 (1) at r.t. gave two narrow peaks in the low angle region, a fairly sharp peak 9.55 A° in the column. Hence, this phase could be assigned as a discotic hexagonal ordered columnar (Dho) mesophase.in the medium angle region, and a broad halo around 2h= 20° at wide angles. The spacing ratio of the first two, low- When this sample was heated to 55 °C and then annealed at this temperature overnight to make the M2 phase, the X-ray angle peaks was 15(1/Ó3), which is a characteristic of twodimensional hexagonal packing.The halo around 2h=20° diVraction pattern showed two reflections in the low angle region, a very broad and weak halo in middle angle region, corresponds to the melting of the alkoxy chains. The fairly sharp peak in the medium angle region may correspond to a and a broad and big halo around 2h=20° in the wide angle region. From the spacing ratio of the first peaks in the low stacking distance in the columnar structure.The spacing, Table 2 Electronic absorption spectral data of the porphyrin derivatives in chloroform lmax/nm( log e) Concentration/ Compound 10-6 mol l-1 Soret band Q band (C12O)16-TTPH2 (1) 5.92 426.9(5.71) 520.4(4.32), 557.2(4.18), 594.0(3.82), 649.8(3.85) (C12O)16-TTPCu (1-Cu) 6.10 422.4(5.71) 541.6(4.42), 579.0(3.75) (C8O)16-TTPH2 (2) 6.23 426.9(5.68) 520.4(4.28), 557.1(4.15), 594.2(3.77), 650.4(3.80) (C12O)8-TTPH2 (3) 6.45 426.6(5.69), 462.3(4.46) 519.7(4.27), 556.9(4.17), 594.2(3.83), 650.7(3.92), 678.4(3.92) (C12O)8-BTPH2 (4) 5.36 412.7(5.46) 505.6(4.17), 542.4(4.07), 578.0(3.83), 632.5(3.49) (C16O)8-BTPH2 (5) 6.18 411.8(5.51) 504.9(4.27), 540.2(4.04), 576.4(3.86), 631.7(3.62) (C12O)4-BTPH2 (6) 6.56 411.7(5.58) 504.6(4.25), 540.5(3.98), 576.7(3.78), 631.7(3.48) (C12O)4-BPPH2 (7) 5.58 412.5(5.58), 443.2(sh, 4.27) 504.9(4.30), 542.2(4.19), 580.4(4.06), 636.2(3.78) (C12O)2-BBPH2 (8) 6.48 411.4(5.59) 504.7(4.23), 540.0(3.97), 577.5(3.73), 631.9(3.36) J.Mater. Chem., 1998, 8, 2637–2650 2641Table 3 Phase transition temperatures and enthalpy changes of the porphyrin derivatives, 1–8 (Type 3) (Type 6) (Type 5) X 52.5 48 [ ca.15] K5 IL(decomp.) K 60.4[55.6] DL 200.7[49.8] IL K2 K1 K3 K4 X 40.1 98.2 190.8 430.9 450.5 ca.50 [7.24] [6.74] [24.2] [59.6] (C12O)4-BPPH2 7 (C12O)2-BBPH2 8 69.8[111.0] 39.2[42.2] DLa(DL.rec1) DLb(DL.rec2) IL 76.0[24.7] 228.6[43.3] 136.7[49.0] IL Drd(C2/m) X Drd(P21/a) Drd(C2/m) IL 132.9[48.2] X (C12O)8-BTPH2 4 (C16O)8-BTPH2 5 (C12O)4-BTPH2 6 204.5 202.2 Rapid cooling IL IL K2 K1 37 IL X X1 M1(Dho) IL X2 M2(Dhd) IL ca.-80 ca. -35 59 X Dhd IL -37[67.9] 57[23.1] : relaxation (C12O)8-TTPH2 3 (C8O)16-TTPH2 2 (C12O)16-TTPCu 1-Cu (C12O)16-TTPH2 1 Compound Phase* Phase Tt /°C[D H/(kJ mol–1)] 39[ ca. 90] (Type 4) b Phase nomenclature: K=crystal, Dhd=discotic hexagonal disordered columnar mesophase, Drd=discotic rectangular disordered columnar mesophase, DL=discotic lamellar mesophase, X=unidentified phase, and IL=isotropic liquid.angle region and the halo around 2h=20°, this higher-tempera- endothermic peak was observed at 37 °C in the DSC thermogram: 5.55 kJ mol-1 for the first heating run and 2.15 kJ mol-1 ture phase could be also assigned as a Dh mesophase, the same as the lower-temperature phase.In contrast to the lower- for the second heating run. Under a polarizing microscope, it showed an almost isotropic texture with very weak birefrin- temperature Dh mesophase, the higher one showed a very broad and weak halo in the middle angle region which gence. When the cover glass was pressed, it was too rigid to slip. For the X-ray diVraction study, only two broad reflections corresponds to the dimer-stacking distance.In this mesophase, the stacking distance fluctuates greatly, so that we assigned were observed in the low and wide angle regions. Therefore, this state is thought to be a glassy liquid phase26 or a this phase as a Dhd mesophase. However, we could still see the halo corresponding to the stacking distance. It is very supercooled liquid with a slightly crystallized portion.The crystalline part may melt at 37 °C. The enthalpy change diYcult to distinguish between Dho and Dhd mesophases for such a case. Therefore, we tentatively assigned these lower- depended on the degree of crystallization, as mentioned above. Since a glassy transition point was not detected by DSC and higher-temperature mesophases as Dho and Dhd, respectively (Table 4).When the IL was held at 58 °C, a focal-conic measurements, this state my be a supercooled isotropic liquid state with a partially crystallized portion. texture appeared for the Dh phase [Fig. 3(a)]. This texture is often observed in Dh mesophases. As summarized in Table 3, (C12O)8-TTPH2 (3) has very high melting points in comparison with 1 and 2 having sixteen As summarized in Table 3, (C12O)16-TTPCu (1-Cu) showed rather more simple phase transition behavior than the metal- long chains.Though the derivative 3 exhibits no mesomorphism, it shows double-melting behavior in a narrow free compound 1, and its clearing point is nearly the same as that of the Dhd phase of 1. From the results of X-ray diVraction temperature region. Type 2 meso-substituted porphyrin derivatives with bulky measurements at r.t.(Table 4), this phase could be identified as a Dhd mesophase. When the IL of (C12O)16-TTPCu (1-Cu) substituents (in Fig. 1) which have been reported to date show not columnar mesophases but lamellar mesophases.13,27,28 was held for some time, a focal-conic texture appeared in the same way as its metal-free compound 1.Although type 4 (C12O)16-TTPH2 (1) and (C12O)16-TTPCu (1-Cu) derivatives have larger steric hindrance groups than For the (C8O)16-TTPH2 (2) derivative, only a very small 2642 J. Mater. Chem., 1998, 8, 2637–2650Table 4 X-Ray diVraction data of the porphyrin derivatives 1–8 Spacing (A° ) Peak Miller indices Phase Compound No. dobserved dcalculated (hkl ) Lattice constant (C12O)16-TTPH2 (1) 1 36.0 36.0 (100) Dho at r.t.a 2 21.4 20.8 (110) 3 9.55 sharp (001) a=41.5 A° 4 ca. 4.3 — —b h=9.55 A° , Z=2 at 55 °C 1 34.4 34.4 (100) Dhd 2 19.9 19.9 (110) 3 ca. 9.1 broad (001) a=39.7 A° 4 ca. 4.4 — —b h=ca. 9.1 A° (C12O)16-TTPCu(1-Cu) 1 36.3 36.3 (100) Dhd at r.t. 2 21.2 20.9 (110) 3 ca. 9.3 broad (001) a=41.9 A° 4 ca. 4.4 — —b h=ca. 9.1 A° (C12O)8-BTPH2 (4) 1 33.2 33.2 (110) Drd (C2/m) at 125 °C 2 29.8 29.8 (200) 3 16.6 16.6 (220) a=59.7 A° 4 ca. 4.4 — —b b=40.0 A° (C16O)8-BTPH2 (5) 1 37.0 37.0 (200) Drf (P21/a) at 60 °C 2 34.8 34.8 (110) 3 18.8 19.1 (120) a=74.1 A° 4 13.4 13.5 (420) b=39.4 A° 5 10.7 10.7 (430) 6 4.41 — —c 7 4.14 — —c at 120 °C 1 41.7 41.7 (110) Drd(C2/m) 2 36.3 36.3 (200) 3 22.0 21.9 (310) a=72.6 A° 4 10.5 10.4 (440) b=51.0 A° 5 ca. 4.6 — —b (C12O)4-BTPH2 (6) 1 34.9 34.2 (001) DLa(DL.rec1) at r.t. 2 16.7 17.1 (002) 3 11.0 11.0 (010) a=16.1 A° 4 9.10 9.10 (110) b=11.0 A°5 5.40 5.37 (300) c=34.2 A° 6 4.79 4.83 (310) Z=2 7 4.53 4.55 (220) 8 ca. 4.1 — —b Alternative 1 34.9 34.2 (001) DLa(DL.rec1) assignment 2 16.7 17.1 (002) at r.t. 3 11.0 11.0 (100) a=11.0 A° 4 9.10 9.10 (010) b=9.1 A° 5 5.40 5.52 (200) c=34.2 A° 6 4.79 4.72 (210) 7 4.53 4.55 (020) Z=1 8 ca. 4.1 — —b at 220 °C 1 39.7 39.3 (001) DLb(DL.rec2) 2 19.7 19.7 (002) 3 12.9 13.1 (003) a=18.6 A° 4 10.9 10.9 (010) b=10.9 A° 5 9.40 9.40 (110) c=39.3 A° 6 6.38 6.19 (300) Z=2 7 ca. 5.0 — —b Alternative 1 39.7 39.3 (001) DLb(DL.rec2) assignment 2 19.7 19.7 (002) at 220 °C 3 12.9 12.9 (010) a=19.2 A° 4 10.9 10.7 (110) b=12.8 A° 5 9.40 9.60 (200) c=39.3 A° 6 6.38 6.40 (020) 7 ca. 5.0 — —b Z=4 aMeasured in virgin state. bHalo of melting of alkyl chain. cSee the main text. type 2 derivatives, they show Dh mesophases as described long chains at the b-positions of the pyrrole rings, the metalfree compounds tend to show no mesomorphism whereas the above. This may be attributed to the sixteen melting long alkyl chains which completely fill the space around the porphyrin metal complexes tend to exhibit columnar mesophases.8,12 On the other hand, in type 2 meso-substituted derivatives, both core to allow the molecules to form a columnar assembly.In conclusion of this section, the (C12O)16-TTPH2 (1) and the metal-free and metal compounds frequently have the same mesophase (in most cases DL mesophase).13,27,28 In this work, (C12O)16-TTPCu (1-Cu) derivatives are the first examples of tetraphenylporphyrin derivatives exhibiting Dh mesophases. both the metal-free compound 1 and its copper complex 1-Cu show the same Dhd mesophase.Thus, the eVect of the central Generally speaking, in type 1 porphyrin derivatives with J. Mater. Chem., 1998, 8, 2637–2650 2643Fig. 3 Photomicrographs of (a) the Dhd mesophase of (C12O)16-TTPH2 (1) at 58°C, (b) the Dhd mesophase of (C12O)16-TTPCu (1-Cu) at 56°C, (c) whiskers of the Drd (C2/m) mesophase of (C12O)8-BTPH2 (4) at 136 °C, (d) the DLb mesophase of (C12O)4-BTPH2 (6) at 226 °C, and (e) the DL mesophase of (C12O)4-BPPH2 (7) at 198 °C.metal on the mesomorphism in type 2 and 4 compounds may pattern for this compound at 125 °C (Table 4) gave three narrow peaks in the low angle region and a diVuse band be negligible Hence, we synthesized only metal-free compounds and studied their mesomorphism in our subsequent work.around 2h=20° which correspond to the melting of alkyl chains. This phase could be then assigned to a discotic rectangular disordered columnar (Drd) mesophase. 2-2-2. (CnO)m-BTPH2 (4, 5, and 6; type 5).Table 3 also summarizes the phase transition temperatures and the enthalpy Furthermore, it was established from the extinction rules in two-dimensional rectangular lattices that this Drd mesophase changes of (C12O)8-BTPH2 (4), (C16O)8-BTPH2 (5) and (C12O)4-BTPH2 (6). All the type 5 compounds 4–6 synthesized has C2/m symmetry (Table 4). (C16O)8-BTPH2 (5) in the pristine state at room temperature here exhibit mesomorphism.(C12O)8-BTPH2 (4) shows an unidentified phase (denoted is a mixture of an unidentified phase (X phase) and a Drd (P21/a) mesophase. The X and Drd (P21/a) phases both change as X phase) at r.t. On heating, this X phase transforms to a Drd (C2/m) mesophase at 39.2 °C, and it clears to the IL at into a Drd (C2/m) phase at 48 and 69.8 °C, respectively.The X phase does not appear without the first heating run. The 136.7 °C. The values of the enthalpy changes for these two phase transitions are roughly the same. The X-ray diVraction X-ray diVraction pattern for this compound at 120 °C showed 2644 J. Mater. Chem., 1998, 8, 2637–2650four narrow peaks in the low angle region and a broad fifth In conclusion of this section, type 5 (C12O)8-BTPH2 (4) and (C16O)8-BTPH2 (5) derivatives having eight long alkoxy chains peak 5 around 2h=20° (Table 4).This phase could be assigned to a Drd (C2/m) mesophase. It is the same phase as that in show Drd mesophases. On the other hand, the type 5 (C12O)4- BTPH2 (6) derivative having four long alkoxy chains exhibits (C12O)8-BTPH2 (4). When the sample was heated to clear, and then cooled to r.t., it gave a pure mesophase.The X-ray two DL.rec. mesophases. It is very interesting that the mesophases in type 5 change from the Drd phase with columnar diVraction pattern of the mesophase at 60 °C gave seven narrow peaks (Table 4). From five peaks in the low angle structure to the DL phase with lamellar structure when the number of attached long alkyl chains is reduced by half.region, this phase could be assigned to a Drd (P21/a) mesophase. The remaining two peaks at wide angles could not be Furthermore, it was found that the DL mesophases in the (C12O)4-BTPH2 (6) derivatives have two-dimensional assigned to reflections from the two-dimensional rectangular P21/a lattice. They probably indicate that the long aliphatic rectangular order within the layer.chains partially crystallize within the intercolumnar space, similarly to the Dh phase of bis(octaoctadecylphthalocyanina- 2-2-3. (C12O)4-BPPH2 (7; type 6). The phase transition behavior of (C12O)4-BPPH2 (7) is summarized in Table 3. The to)lutetium complex.29 When the IL of (C12O)8-BTPH2 (4) was held for a few pristine sample showed two endothermic peaks at 52.5 °C and 60.4 °C which were mutually overlapped in the DSC thermo- hours just below its clearing point, ‘whisker growth’ was observed [Fig. 3(c)]. Although the materials which were grams. The endothermic peak at 52.5 °C did not appear for the non-pristine sample. Thus, the pristine state of this com- reported to form whiskers are mainly inorganic compounds, polymers such as poly(4-hydroxybenzoate)30 and organic com- pound at r.t.is a mixture of an unidentified X phase and a crystalline K phase. The X phase could not be characterized pounds such as L-alanine31 were also reported to form whiskers. Generally, crystal whiskers are needle-like, whereas the because the pure phase could not be obtained. The nonpristine sample showed two reproducible endothermic peaks whisker in the case of (C12O)8-BTPH2 (4) is bent.Bending of whiskers has been described to be caused by characteristic at 60.4 °C and 200.7 °C. As can be seen in Table 3, the enthalpy change at the lower phase transition is somewhat larger than defects in structures composed of stacks of disc-like molecules, 32 so that it can evidence the columnar mesomorphism that of the higher phase transition.The X-ray diVraction pattern of this compound at 170 °C of (C12O)8-BTPH2 (4). Another example of such bent whiskers has been reported in 2,4,6-tris(didecylamino)-s-triazine.32 The gave large peaks in the low angle region which were characteristic of lamellar phases and the layer spacing could be calcu- same whiskers could be also seen for the homologous (C16O)8- BTPH2 (5) derivative under similar conditions to the (C12O)8- lated to be c=31.7 A° .Several comparatively small peaks on a diVuse halo at wide angles could not be assigned, because BTPH2 (4) derivative, although the whiskers were not so large in 5. these peaks became bigger and sharper during the several hours’ X-ray measurements and additional peaks appeared.Both (C12O)8-BTPH2 (4) and (C12O)4-BTPH2 (6) are classified as type 5, although 4 and 6 have eight and four long This phenomenon is due to relaxation from DL to another unidentified crystalline phase. chains (dodecyloxy groups), respectively. As summarized in Table 3, (C12O)4-BTPH2 (6) shows a transformation from the When the IL of (C12O)4-BPPH2 (7) was held at 198 °C for a few minutes, a texture with a terraced structure appeared as DLa to the DLb phase at 76.0 °C (subscripts a and b are used not to express phase features but only to distinguish the shown in Fig. 3(e). This indicates the existence of lamellar structure in the DL mesophase. diVerent phases), and DLb clears to the IL at 228.6 °C. The clearing point of this compound is ca. 90 °C higher than those As mentioned above, the X-ray diVraction pattern for (C12O)4-BPPH2 (7) showed a halo corresponding to the melt- of (C12O)8-BTPH2 (4) and (C16O)8-BTPH2 (5), and the stability of the mesophase rises.As summarized in Table 4, the X- ing of the alkyl chains around 2h=20°. Accordingly, the alkyl chains seem to fluctuate in this phase. The fluctuation of the ray diVraction pattern of (C12O)4-BTPH2 (6) at 220 °C gave seven peaks.Since peak 7 was broad, it corresponds to melting alkyl groups of 7 was then studied by means of temperaturedependent IR spectroscopy. The vibrational spectral changes of the alkyl chains. The ratio of the spacings of peaks 1–3 in the low angles is 151/251/3, which represents the existence of of the phase transitions of n-paraYn34,35 bilayer systems36 and discotic liquid crystals37 have been reported.The temperature lamellar structure. The remaining peaks 4–6 could be assigned to the reflections from a two-dimensional rectangular lattice. dependence of the methylene rocking band of phase II (‘rotator’ or ‘hexagonal’38 phase) of n-paraYns has been Hence this mesophase was proven to be a lamellar mesophase having two-dimensional rectangular order within the layer studied in detail, because this band which usually appears near 720 cm-1 is very sensitive to structural changes caused by (DLb=DL.rec.2).Besides, from the X-ray diVraction data at r.t., the DLa phase is also a lamellar mesophase with two- phase transitions. The crystalline state of 7 showed two bands near 745 and dimensional rectangular order within the layer (Table 4, DLa= DL.rec.1).Interestingly, alternative two-dimensional lattice con- 723 cm-1 at 30 °C. The band near 720 cm-1 is usually assigned to the methylene rocking mode in all-trans alkyl chains. It stants, 11.0 A° ×9.10 A° and 19.2 A° ×12.8 A° , also fit well for DLa at r.t. and for DLb at 220 °C, respectively, as listed in splits into two bands in the solid state because of factor group splitting.The interval (ca. 22 cm-1) between these two bands Table 4. Generally, a limited number of sharp peaks in mesophases make it diYcult to reach an unambiguous two-dimen- is fairly wide in comparison with general splitting width (ca. 10 cm-1) of the well-discussed factor group splitting.35,36,38 sional lattice assignment.Further investigation is required for the detailed structural diVerences between these DLa and DLb Therefore, it seems that the two bands of the present case are not usual. Snyder39 reported that the methylene rocking band phases. We recently found two novel discotic lamellar DL.rec mesophases,33 whose structures in the layers may be closely of molten polyethylene had been graphically resolved into two components at 719 cm-1 and 745 cm-1, and that the higher- related to those of the present DLa and DLb mesophases.As shown in Fig. 3(d), the terrace texture with piles of frequency component at 745 cm-1 was near the value calculated for alternating trans–gauche sequences. Hence, this com- plates could be observed under a polarizing microscope when the IL of (C12O)4-BTPH2 (6) was slowly cooled to 226 °C. pound at 30 °C may have a considerable proportion of gauche bonds in the aliphatic chains, as is the case in the references This indicates the existence of lamellar structure in the DLb mesophase.The plates in the texture were striated in the mentioned above. The ratios of the absorbances of the two bands for 7 are temperature region of the DLa mesophase below 76.0 °C, but no dramatic change was observed.This also suggests that both plotted against temperature in Fig. 4. When the sample was heated to 60.4 °C above the melting point of 7, the intensity DLa and DLb phases have lamellar structure. J. Mater. Chem., 1998, 8, 2637–2650 2645and long flexible chains in order to investigate their mesomorphism.Fig. 5 summarizes the relationship between the molecular type of porphyrin derivatives, 1–8 and 1-Cu, and the resulting mesophase. Type 4 disc-like (C12O)16-TTPH2 (1) and (C12O)16- TTPCu (1-Cu) derivatives exhibit Dh columnar mesophases, which are the first examples of meso-substituted porphyrin metal-free derivatives and copper complexes. Type 5 strip-like (CnO)8-BTPH2 [4 (n=12), 5 (n=16)] derivatives having eight long chains at the 5,15-positions show the Drd columnar mesophases.On the other hand, type 5 (C12O)4-BTPH2 (6) derivative having four long chains exhibits DL.rec1 and DL.rec2 lamellar mesophases which have two-dimensional rectangular structure within the layer. The (C12O)4-BPPH2 (7) derivative, of type 6, also shows a DL lamellar mesophase. Bruce et al.17 reported that the type 3 rod-like porphyrin derivatives show calamitic mesophases of SB, SE and SE¾ phases.As can be seen from the top derivative to the bottom one in Fig. 5, it is, therefore, apparent that such a successive change of the Fig. 4 Temperature dependence of the absorption ratio of two methylene rocking bands at ca. 720 and 740 cm-1 (A720/A740) for molecular structures causes their mesophases to change from (C12O)4-BPPH2 (7).discotic columnar to discotic lamellar, and further to calamitic. It is also apparent that the porphyrin core is very useful to obtain various kinds of mesomorphism from discotic to calam- of the lower-frequency band at ca. 723 cm-1 suddenly decreased, and the higher-frequency band at ca. 745 cm-1 itic with alteration of the substituted positions and/or substituents.slightly shifted to lower frequency. On further heating, the bands gradually broadened, and a broad band remained at 734 cm-1 in the isotropic liquid at 210 °C. The ratio discontinuously altered at the melting point. As can be seen in Fig. 4, 4. Experimental the absorption band at 723 cm-1 suddenly decreased at the 4-1.Measurements phase transition. This may suggest that some trans bonds of the methylene groups change into gauche bonds upon heating The products synthesized here were identified by 1H NMR to break all-trans sequences. The broadening of the bands may (JOEL JNM-PMX60SI) and IR (Jasco A-100). Further identibe due to disorder of the alkyl chains melted by heating. fication of the porphyrin derivatives was made by elemental However, since trans bonds in n-hydrocarbons are normally analysis (Perkin-Elmer elemental analyzer 240B) and electronic more stable than gauche bonds, the absorption of trans bonds absorption spectroscopy (Hitachi 330 spectrophotometer).should be more intense than gauche ones. In the molten state, The phase transition behaviors of these compounds were e.g., liquid n-paraYn and molten polyethylene, all-trans meth- observed by using a polarizing microscope (Olympus BH2), ylene rocking bands remain fairly even when they broaden. equipped with a heating plate controlled by a thermoregulator An explanation for the diVerence between the conventional (Mettler FP80 and FP82), and diVerential scanning calorresults and the present results has not been obtained. imetry (Shimadzu DSC-50 and Rigaku Thermoflex DSCNevertheless, it is at least supported that the long alkyl chains 8230).The X-ray diVraction measurements were performed of 7 are fairly disordered in the liquid crystalline state of the with Cu-Ka radiation (Rigaku Geigerflex) equipped with a DL phase. hand-made heating plate40 controlled by a thermoregulator.Temperature-dependent infrared spectra were measured by a 2-2-4. (C12O)2-BBPH2 (8; type 3). In an attempt to obtain Jasco FT/IR-7300 instrument equipped with a hand-made a calamitic mesophase in porphyrin derivatives, a rod-like heating plate41 controlled by a thermoregulator for a thin film (C12O)2-BBPH2 (8) derivative was synthesized. The phase of (C12O)4-BPPH2 (7).This thin film was prepared by casting transition behavior of (C12O)2-BBPH2 (8) is summarized in from a dichloromethane solution on a silicon wafer, then the Table 3. It was revealed by means of DSC measurements that solvent was removed by heating, and the film covered by this compound shows many phase transitions, and that it another wafer. finally showed an endothermic peak at 450.5 °C which may be assigned to the clearing point with decomposition.All the 4-2. Synthesis phases exhibited below 300 °C turned out to be crystalline phases according to polarizing microscopic observations and 3,4-Bis(3,4-didodecyloxyphenyl )-4-hydroxycyclopent-2-en-1- one(14a). This compound was synthesized by a similar method X-ray diVraction study. The phase between 430.9 °C and 450.5 °C, only detected by DSC measurements, could not be as described in previous papers.42,43 14a: Purified by column chromatography (silica gel, chloro- identified because of the high temperature which exceeds our instrumental limits.Consequently, this phase is termed an X form–ethyl acetate 551; Rf=0.68). Yellow liquid crystal (SA). Clearing point (c.p.) 55 °C ( lit.43 54 °C).Yield 74%. 1H NMR phase. The possibility of mesomorphism of this X phase still remains because the value of DH at the XAIL transition is (CDCl3, TMS) d 0.90 (m, 12H, CH3), 1.27 (m, 80H, CH2), 2.73 (s, 2H, CH2CO), 3.40–4.06 (m, 9H, OH and OCH2), 6.27 smaller than that at the K4AX transition. This compound has a highly rigid molecule in comparison with the aforemen- (s, 1H, NCHCO), 6.43–7.03 (m, 6H, Ph).IR(neat) nmax 3400 (OH), 2930, 2860 (CH2), 1680 (CO), 1590, 1510 (Ph), tioned compounds exhibiting mesomorphism. Thus, (C12O)2- BBPH2 (8) retains its crystal structure even at high 1260 cm-1 (ROPh). 14b: Purified by column chromatography (silica gel, temperature. chloroform–ethyl acetate 551; Rf=0.60). Yellow liquid crystal (SA). c.p. 42.5 °C.Yield 55%. 1H NMR (CCl4, TMS) d 0.85 3. Conclusion (m, 12H, CH3), 1.30 (m, 48H, CH2), 2.67 (s, 2H, CH2CO), 3.47 (s, 1H, OH), 3.57–3.97 (m, 8H, OCH2), 6.23 (s, 1H, We have synthesized nine novel porphyrin derivatives, 1–8 and 1-Cu, substituted with various steric hindrance groups NCHCO), 6.37–7.10 (m, 6H, Ph). IR (neat) nmax 3350 (OH), 2646 J. Mater. Chem., 1998, 8, 2637–2650Mesophase Type 3* Type 6 (7) Type 5 (6) Type 5 (4,5) Type 4 (1, 1-Cu) Type No.(Compound) DL.rec Dh Drd DL SB,SE,SE' NH N HN N C12H25O C12H25O OC12H25 OC12H25 C12H25O C12H25O OC12H25 OC12H25 NH N HN N N N N N Zn OCnH2 n+1 CnH2 n+1O N N N N C12H25O OC12H25 OC12H25 C12H25O OC12H25 OC12H25 OC12H25 C12H25O OC12H25 OC12H25 C12H25O C12H25O OC12H25 C12H25O C12H25O OC12H25 M NH N N HN OCnH2 n+1 OCnH2 n+1 CnH2 n+1O OCn H2 n+1 CnH2 n+1O CnH2 n+1O OCnH2 n+1 CnH2 n+1O Fig. 5 The relationship between the molecular type of porphyrin derivatives and the resulting mesophase. (*see ref. 17). 2930, 2860 (CH2), 1675 (CO), 1590, 1510 (Ph), 1260 cm-1 3380 (OH), 2930, 2860 (CH2), 1680 (CO), 1590, 1510 (Ph), 1250 cm-1 (OPh). (ROPh). 14c: Purified by column chromatography (silica gel, chloroform–ethyl acetate 551; Rf=0.74).Yellow solid. Methyl 3,4,3,4-tetradodecyloxy-o-terphenyl-4¾-carboxylate (15a). A mixture of cyclopentenone 14a (4.60 g, 4.66 mmol) m.p. 56–57 °C. Yield 62%. 1H NMR (CDCl3, TMS) d 0.83 (m, 12H, CH3), 1.20 (m, 112H, CH2), 2.80 (s, 2H, CH2CO), and methyl propiolate (1.17 g, 13.9 mmol) in 50 ml of odichlorobenzene was heated at 70 °C. A solution of p-tolu- 3.57 (s, 1H, OH), 3.80 (m, 8H, OCH2), 6.33 (s, 1H, NCHCO), 6.53–7.03 (m, 6H, Ph).IR (KBr) nmax 3350 (OH), 2930, 2860 enesulfonic acid monohydrate (47.8 mg, 0.25 mmol) in 2 ml of 1,4-dioxane was added dropwise. The mixture was stirred (CH2), 1675 (CO), 1590, 1510 (Ph), 1260 cm-1 (ROPh). 14d: Purified by column chromatography (silica gel, for 4 h at 70 °C, and then refluxed for 8 h 40 min.The reaction mixture was extracted with chloroform. The organic layer was chloroform–ethyl acetate 551; Rf=0.54). Pale yellow solid. m.p. 66–69 °C ( lit.42 65–68 °C). Yield 49%. 1H NMR (CCl4, washed with water, dried over sodium sulfate, and the solvent was removed. The purification was carried out by column TMS) d 0.87 (m, 6H, CH3), 1.30 (m, 40H, CH2), 2.70 (s, 2H, CH2CO), 3.50 (s, 1H, OH), 3.80 (t, J=6.0 Hz, 4H, OCH2), chromatography (silica gel, benzene–carbon tetrachloride 151; Rf=0.50), to obtain 2.24 g of 15a as a yellowish-brown solid. 6.27 (s, 1H, NCHCO), 6.47–7.57 (m, 6H, Ph). IR (neat) nmax J. Mater. Chem., 1998, 8, 2637–2650 2647m.p. 55 °C. Yield 47%. 1H NMR (CCl4, TMS) d 0.88 (m, NMR (CCl4, TMS) d 0.88 (m, 12H, CH3), 1.27 (m, 48H, CH2), 3.17–4.00 (m, 8H, OCH2), 6.27–7.80 (m, 9H, Ph), 9.83 12H, CH3), 1.27 (m, 80H, CH2), 3.42, 3.83 (t+t, 8H, OCH2), 3.83 (s, 3H, COOCH3), 6.40–7.97 (m, 9H, Ph).IR (neat) nmax (s, 1H, CHO). IR (neat) nmax 1695 cm-1 (CO). 17c: Purified by column chromatography (silica gel, benzene; 1720 cm-1 (CO). 15b: Purified by column chromatography (silica gel, benzene; Rf=0.55). Yellowish white solid.m.p. 58 °C. Yield 93%. 1H NMR (CCl4, TMS) d 0.88 (m, 12H, CH3), 1.25 (m, 112H, Rf=0.60). Yellowish brown syrup. Yield 44%. 1H NMR (CCl4, TMS) d 0.87 (m, 12H, CH3), 1.30 (m, 48H, CH2), CH2), 3.40–4.07 (m, 8H, OCH2), 6.37–7.80 (m, 9H, Ph), 9.87 (s, 1H, CHO). IR (KBr) nmax 1695 cm-1 (CO). 3.27–4.00 (t+t, 8H, OCH2), 3.83 (s, 3H, COOCH3), 6.33–8.00 (m, 9H, Ph). IR (neat) nmax 1725 cm-1 (CO). 17d: Purified by column chromatography (silica gel, benzene; Rf=0.60). Yellow syrup. Yield 95%. 1H NMR (CCl4, TMS) 15c: Purified by column chromatography (silica gel, benzene–carbon tetrachloride 251; Rf=0.56). Light brown d 0.90 (m, 6H, CH3), 1.30 (m, 40H, CH2), 3.83 (t, J=6.0 Hz, 4H, OCH2), 6.40–7.77 (m, 11H, Ph), 9.87 (s, 1H, CHO). IR solid. m.p. 50 °C. Yield 49%. 1H NMR (CCl4, TMS) d 0.87 (m, 12H, CH3), 1.30 (m, 112H, CH2), 3.40–4.00 (m, 8H, (neat) nmax 1700 cm-1 (CO). OCH2), 3.83 (s, 3H, COOCH3), 6.33–7.90 (m, 9H, Ph). IR (KBr) nmax 1720 cm-1 (CO). 5,10,15,20-Tetrakis(3,4,3,4-tetradodecyloxy-o-terphenyl )- porphyrin [1; (C12O)16-TTPH2]. A mixture of aldehyde 17a 15d: Purified by column chromatography (silica gel, benzene–carbon tetrachloride 151; Rf=0.45).Yellowish brown (1.48 g, 1.49 mmol) and pyrrole (0.23 g, 3.43 mmol) in propionic acid (10 ml, 0.13 mol ) was refluxed for 30 min. After the syrup. Raw yield 71% (this product contained some impurities.). 1H NMR (CCl4, TMS) d 0.90 (m, 6H, CH3), 1.27 (m, reaction mixture was cooled to room temperature, sodium hydroxide (5.20 g, 0.13 mol) was added. The mixture was 40H, CH2), 3.80 (m, 7H, OCH2, COOCH3), 6.47–7.87 (m, 11H, Ph). IR (neat) nmax 1725 cm-1 (CO).extracted with diethyl ether, and the organic layer was washed with water. After being dried and concentrated, the residue was purified by column chromatography (alumina, benzene; 3,4,3,4-Tetradodecyloxy-4¾-hydroxymethyl-o-terphenyl (16a). Under a nitrogen atmosphere, a solution of carboxylate Rf=1.00) to yield 0.38 g of the crude (chlorin-contained) porphyrin derivative.The crude product was dissolved in the 15a (2.11 g, 2.06 mmol) in 20 ml of dry diethyl ether was added dropwise to a suspension of lithium aluminium hydride minimum amount of chloroform and a small amount of benzene. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ; (LiAlH4; 0.31 g, 8.17 mmol) in 15 ml of dry diethyl ether.The mixture was gently refluxed for 1 h. After the reaction mixture 0.14 g, 0.62 mmol) was added, and the mixture was refluxed for 3 h. The mixture was concentrated and the residue was was cooled by ice water, water was added slowly till no LiAlH4 remained. Then, a small amount of 20% sulfuric acid was purified by column chromatography (silica gel, benzene; Rf= 1.00, and alumina, hexane; Rf=0.00, chloroform; Rf=1.00) added to dissolve the precipitate, and extracted with diethyl ether.The organic layer was washed with water, dried over to give 0.22 g of 1 as a red-purple liquid crystal. Yield 14%. 1H NMR (CDCl3, TMS) d -2.63 (s. 2H, NH), 0.80 (m, 48H, sodium sulfate, and concentrated. The residue was purified by column chromatography (silica gel, chloroform; Rf=0.44) to CH3), 1.26 (m, 320H, CH2), 3.44–4.10 (m, 32H, OCH2), 6.52–8.24 (m, 36H, Ph), 8.90 (s, 8H, porphyrin).IR (neat) give 1.58 g of 16a as a faintly-brown syrup. Yield 93%. 1H NMR(CCl4, TMS) d 0.90 (m, 12H, CH3), 1.30 (m, 80H, nmax 3320 (NH), 2930, 2860 (CH2), 1600, 1580 (Ph), 1260 cm-1 (ROPh). CH2), 1.70 (s, 1H, OH), 3.43–4.00 (m, 8H, OCH2), 4.60 (s, 2H, PhCH2O), 6.40–7.23 (m, 9H, Ph).IR (neat) nmax 3330 cm-1 (OH). 5,10,15,20-Tetrakis(3,4,3,4-tetraoctyloxy-o-terphenyl )- porphyrin [2; (C8O)16-TTPH2]. The title compound was synthe- 16b: Purified by column chromatography (silica gel, chloroform; Rf=0.21). Pale brown syrup. Yield 90%. 1H sized from aldehyde 17b according to the method described above, and purified by column chromatography (alumina, NMR (CCl4, TMS) d 0.87 (m, 12H, CH3), 1.30 (m, 48H, CH2), 2.26 (s, 1H, OH), 3.30–4.00 (t+t, 8H, OCH2), 4.58 (s, benzene and chloroform; Rf=1.00, and silica gel, hexane; Rf= 0.00 and benzene; Rf=1.00).Red-purple solid. Yield 17%. 1H 2H, PhCH2O), 6.33–7.26 (m, 9H, Ph). IR (neat) nmax 3200 cm-1 (OH). NMR(CDCl3, TMS) d -2.63 (s. 2H, NH), 0.57–1.00 (m, 48H, CH3), 1.00–2.33 (m, 192H, CH2), 3.44–4.17 (m, 32H, 16c: Purified by column chromatography (silica gel, chloroform; Rf=0.38).White solid. m.p. 52 °C. Yield 67%. 1H OCH2 ), 6.47–8.27 (m, 36H, Ph), 8.90 (s, 8H, porphyrin). IR (neat) nmax 3320 (NH), 2930, 2860 (CH2), 1605, 1580, 1510 NMR (CCl4, TMS) d 0.88 (m, 12H, CH3), 1.27 (m, 112H, CH2), 1.63 (s, 1H, OH), 3.33–4.00 (m, 8H, OCH2), 4.55 (s, (Ph), 1250 cm-1 (ROPh). 2H, PhCH2O), 6.27–7.20 (m, 9H, Ph). IR (KBr) nmax 3300 cm-1 (OH). 5,10,15,20-Tetrakis(4,4-didodecyloxy-o-terphenyl )- porphyrin [3; (C12O)8-TTPH2]. The title compound was synthe- 16d: Purified by column chromatography (silica gel, chloroform; Rf=0.40). Pale orange solid. m.p. 47.5 °C. Yield sized from aldehyde 17d according to the method described above, and purified by column chromatography (silica gel, 42%. 1H NMR (CCl4, TMS) d 0.90 (m, 6H, CH3), 1.27 (m, 40H, CH2), 1.93 (s, 1H, OH), 3.80 (t, J=6.0 Hz, 4H, OCH2), chloroform; Rf=1.00, alumina, carbon tetrachloride; Rf=0.00, and benzene; Rf=1.00) and recrystallization (hexane, ethyl 4.53 (s, 2H, PhCH2O), 6.47–7.13 (m, 11H, Ph). IR (neat) nmax 3330 cm-1 (OH). acetate). Purple solid.Yield 15%. 1H NMR (CCl4, TMS) d -2.53 (s, 2H, NH), 0.90 (m, 24H, CH3), 1.67 (m, 160H, CH2), 3.77 (m, 12H, OCH2), 6.40–8.30 (m, 44H, Ph), 8.90 (s, 3,4,3,4-Tetradodecyloxy-o-terphenyl-4¾-carbaldehyde (17a). A mixture of hydroxymethyl 16a (1.54 g, 1.54 mmol) and 8H, porphyrin). IR (film) nmax 3320 (NH), 2930, 2860 (CH2), 1610, 1510 (Ph), 1250 cm-1 (ROPh). pyridinium dichromate (PDC; 0.87 g, 2.31 mmol) in 3 ml of dichloromethane was stirred for 10 h.The reaction mixture was concentrated and the residue was purified by column 5,10,15,20-Tetrakis(3,4,3,4-tetradodecyloxy-o-terphenyl )- porphyrinatocopper(II ) [1-Cu; (C12O)16-TTPCu]. Porphyrin 1 chromatography (silica gel, benzene; Rf=0.70) to give 1.46 g of 17a as a yellowish white solid. m.p. 64–65 °C.Yield 95%. (0.12 g, 2.88×10-2 mmol) and anhydrous cupric chloride (0.04 g, 0.30 mmol) were dissolved in 30 ml of dry N,N- 1H NMR (CCl4, TMS) d 0.88 (m, 12H, CH3), 1.30 (m, 80H, CH2), 3.40–4.13 (m, 8H, OCH2), 6.40–7.85 (m, 9H, Ph), 9.92 dimethylformamide (DMF) and refluxed for 5 h. The reaction mixture was cooled and separated by filtration. The remaining (s, 1H, CHO). IR (neat) nmax 1700 cm-1 (CO). 17b: Purified by column chromatography (silica gel, precipitate was washed by methanol, and purified by column chromatography (alumina, benzene; Rf=1.00) to give 0.11 g chloroform; Rf=0.65). Brownish yellow syrup. Yield 98%. 1H 2648 J. Mater. Chem., 1998, 8, 2637–2650of 1-Cu as a dark red liquid crystal. Yield 90%. IR (neat) nmax Rf=1.00) and recrystallization from ethyl acetate and dichloromethane.Reddish brown solid. Yield 39%. 1H NMR 2930, 2860 (CH2), 1610, 1580 (Ph), 1250 cm-1 (ROPh). (CCl4, TMS) d -3.00 (broad, 2H, NH), 0.83 (m, 12H, CH3), 1.20 (m, 80H, CH2), 3.46–4.40 (m, 8H, OCH2), 6.40–8.00 (m, 4-Dodecyl-4¾-bromobiphenyl (21). A mixture of 4-hydroxy- 4¾-bromobiphenyl 20 (2.00 g, 8.03 mmol) and potassium 22H, Ph), 8.83 (s, 8H, porphyrin), 9.77 (s, 2H, meso-H).IR (KBr) nmax 3300 (NH), 2930, 2860 (CH2), 1610 (Ph), hydroxide (0.90 g, 16.0 mmol) in 15 ml of ethanol was refluxed for 1 h. Then a solution of dodecyl bromide (2.10 g, 1245 cm-1 (ROPh). 8.43 mmol) in 5 ml of ethanol was added, and the mixture was further refluxed for 13 h. After cooling to room tempera- 5,15-Bis(3,4-didodecyloxyphenyl )porphyrin [7; (C12O)4- ture, the reaction mixture was filtered with suction.The BPPH2]. The title compound was synthesized from 3,4-didoderesidual precipitate was washed with water and recrystallized cyloxybenzaldehyde 19 by a similar procedure to that described from ethanol to aVord 1.58 g of 21 as white crystals. above, and the pure product was obtained by column chromam. p. 113 °C. Yield 47%. 1H NMR (CDCl3, TMS) d 0.87 (m, tography (silica gel, benzene; Rf=1.00, and alumina, chloro- 3H, CH3), 1.30 (m, 20H, CH2), 3.90 (t, J=6.0 Hz, 2H, form; Rf=1.00) and recrystallization from acetone. Purple OCH2), 6.67–7.50 (m, 8H, Ph). IR (KBr) nmax 2920, 2850 powder. Yield 33%. 1H NMR (CCl4, TMS) d -3.00 (broad, (CH2), 1600 cm-1 (Ph). 2H, NH), 0.90 (m, 12H, CH3), 1.30 (m, 80H, CH2), 4.13, 4.27 (t+t, 8H, OCH2), 7.30–7.80 (m, 6H, Ph), 9.07, 9.27 4-Formyl-4¾-dodecyloxybiphenyl (22).Under a nitrogen (d+d, 8H, porphyrin), 10.2 (s, 2H, meso-H). IR (film) nmax atmosphere, 1.6 M butyllithium solution in hexanes (2.6 ml, 3285 (NH), 2925, 2855 (CH2), 1505 (Ph), 1246 cm-1 (ROPh). 4.16 mmol) was added slowly to a solution of 21 (1.50 g, 4.09 mmol) in 30 ml of dry benzene and the mixture was 5,15-Bis(4-dodecyloxybiphenyl )porphyrin [8; (C12O)8- stirred for 30 min at room temperature.N,N- BBPH2]. The title compound was synthesized from 4-formyl- Dimethylformamide (DMF; 0.33 g, 4.50 mmol) in 5 ml of 4¾-dodecyloxybiphenyl 22 by a similar procedure to that benzene was added dropwise, and the reaction mixture was described above. However, because of the low solubility of stirred for 2 h at room temperature.The reaction was quenched this compound, the purification was accomplished in the by dilute hydrochloric acid, and the mixture was extracted following manner. The reaction mixture was concentrated, with diethyl ether. The organic layer was washed with water, and the residue was washed with tetrahydrofuran or dichlorodried over sodium sulfate, and concentrated. After column methane and Soxhlet extraction of impurities was performed chromatography (silica gel, benzene; Rf=0.58), 0.49 g of 22 with acetone–ethyl acetate.The residue was recrystallized from was obtained as a white solid. m.p. 87 °C. Yield 36%. 1H chloroform and dichloromethane to give a dark purple powder. NMR (CDCl3, TMS) d 0.70 (m, 3H, CH3), 1.10 (m, 20H, Yield 44%.IR (KBr) nmax 3260 (NH), 2930, 2860 (CH2), CH2), 3.73 (t, 2H, OCH2), 9.58 (s, 1H, CHO). IR (Nujol ) 1600, 1580 (Ph), 1245 cm-1 (ROPh). nmax 1680 cm-1 (CO). 5,15-Bis(3,4,3,4-tetradodecyloxy-o-terphenyl )porphyrin [4; Notes and references (C12O)8-BTPH2]. To a solution of aldehyde 17a (1.43 g, 1 K. Ohta, M. Ando and I. Yamamoto, J. Porphyrins 1.44 mmol) and 2,2¾-dipyrrylmethane44,45 (0.22 g, 1.50 mmol) Phthalocyanines, in press.in 250 ml of dichloromethane, were added seven drops of 2 M. R. Wasielewski, Chem. Rev., 1992, 92, 435; J. P. Collman, Acc. trifluoroacetic acid, and the solution was stirred for 15 h at Chem. Res., 1977, 10, 265; D. Gust and T. A. Moore, Top. Curr. Chem., 1991, 159, 103. room temperature. After p-chloranil (1.42 g, 5.78 mmol) was 3 B.Morgan and D. Dorphin, Struct. Bonding, 1987, 64, 115. added, the mixture was refluxed for 1 h. The reaction mixture 4 J. L. Sessler and K. A. Burrell, Top. Curr. Chem., 1992, 161, 177. was concentrated, and the residue was purified by column 5 For example: J. van Esch, M. F. M. Rocks and R. J. M. Nolte, chromatography (alumina, chloroform; Rf=1.00, benzene; J.Am. Chem. Soc., 1986, 108, 6093; G. A. Schick, I. C. Schreiman, Rf=1.00, carbon tetrachloride; Rf=0.00, and silica gel, chloro- R. W. Wagner, J. S. Lindsey and D. F. Bocian, ibid., 1989, 111, form; Rf=1.00) and recrystallization from ethyl acetate to 1344; J. T. Groves and R. Newmann, ibid., 1989, 111, 2900; B. A. Gregg, M. A. Fox and and A. J. Bard, Tetrahedron, 1989, give 0.48 g of 4 as a reddish brown solid.Yield 30%. 1H NMR 45, 4704. (CCl4, TMS) d -3.00 (broad, 2H, NH), 0.87 (m, 24H, CH3), 6 Y. Suda, K. Shigehara, A. Yamada, H. Matsuda, S. Okada, 1.23 (m, 160H, CH2), 3.50–4.13 (m, 16H, OCH2), 6.47–8.40 A. Masaki and H. Nakanishi, Proc. SPIE-Int. Soc. Opt. Eng., (m, 18H, Ph), 9.23 (s, 8H, porphyrin), 10.1 (s, 2H, meso-H). 1991, 1560 (Nonlinear Opt.Prop. Org. Mater. 4), 75. IR (film) nmax 3300 (NH), 2930, 2860 (CH2), 1610, 1590 (Ph), 7 J. W. Goodby, P. S. Robinson, B.-K. Teo and P. E. Cladis, Mol. 1250 cm-1 (ROPh). Cryst. Liq. Cryst., 1980, 56, 303. 8 B. A. Gregg, M. A. Fox and A. J. Bard, J. Chem. Soc., Chem. Commun., 1987, 1134; J. Am. Chem. Soc., 1989, 111, 3024. 5,15-Bis(3,4,3,4-tetrahexadecyloxy-o-terphenyl )porphyrin 9 B.A. Gregg, M. A. Fox and A. J. Bard, J. Phys. Chem., 1990, [5; (C16O)8-BTPH2]. The title compound was synthesized from 94, 1586. aldehyde 17c by a similar procedure to that described above, 10 P. G. Schouten, J. M. Warman, M. P. de Haas, M. A. Fox and and the pure product was obtained by column chromatography H.-L. Pan, Nature, 1991, 353, 736. (silica gel, chloroform; Rf=1.00, and alumina, chloroform; 11 P.Doppelt and S. Huille, New. J. Chem., 1990, 14, 607. 12 G. Morelli, G. Ricciardi and A. Roviello, Chem. Phys. Lett., 1991, Rf=1.00) and recrystallization from ethyl acetate and 185, 468; F. Lelj, G. Morelli, G. Ricciardi, A. Roviello and dichloromethane. Brown solid. Yield 57%. 1H NMR (CCl4, A. Sirigu, Liq. Cryst., 1992, 12, 941. TMS) d -2.90 (broad, 2H, NH), 0.87 (m, 24H, CH3), 1.30 13 Y.Shimizu, M. Miya, A. Nagata, K. Ohta, A. Matsumura, (m, 224H, CH2), 3.50–4.06 (m, 16H, OCH2), 6.67–8.30 (m, I. Yamamoto and S. Kusabayashi, Chem. Lett., 1991, 25; 8H, Ph), 9.10 (s, 8H, porphyrin), 10.0 (s, 2H, meso-H). IR Y. Shimizu, M. Miya, A. Nagata, K. Ohta, I. Yamamoto and (KBr) nmax 3280 (NH), 2930, 2860 (CH2), 1580 (Ph), S.Kusabayashi, Liq. Cryst., 1993, 14, 795. 14 Y. Shimizu, A. Ishikawa and S. Kusabayashi, Chem. Lett., 1986, 1245 cm-1 (ROPh). 1041. 15 T. Sakaguchi, Y. Shimizu, M. Miya, T. Fukumi, K. Ohta and 5,15-Bis(4,4-didodecyloxy-o-terphenyl )porphyrin [6; (C12- A. Nagata, Chem. Lett., 1992, 281. O)4-BTPH2]. The title compound was synthesized from alde- 16 R. Ramasseul, P. Maldivi, J.-C.Marchon, M. Taylor and hyde 17d by a similar procedure to that described above, and D. Guillon, Liq. Cryst., 1993, 13, 729. the pure product was obtained by column chromatography 17 D. W. Bruce, D. A. Dunmur, L. S. Santa and M. A. Wali, J. Mater. Chem., 1992, 2, 363. (silica gel, chloroform; Rf=1.00, and alumina, chloroform; J. Mater. Chem., 1998, 8, 2637–2650 264918 For example: C. Piechocki, J. Simon, A. Skoulios, D. Guillon and 34 G. Zerbi, R. Magni, M. Gussoni, K. H. Moritz, A. Bigotto and Dirlikov, J. Chem. Phys., 1981, 75, 3175. P. Weber, J. Am. Chem. Soc., 1982, 104, 5245. 35 H. L. Casal, H. H. Mantosh, D. G. Cameron and R. G. Snyder, 19 G. Wenz, Makromol. Chem. Rapid Commun., 1985, 6, 577. J. Chem. Phys., 1982, 77, 2825; G. Unger and N. Masic, J. Phys. 20 H. Strzelecka, C. Jallabert, M. Veber and J. Malthete, Mol. Cryst. Chem., 1985, 89, 1036. Liq. Cryst., 1988, 156, 347. 36 C. Almirante, G. Minoni and G. Zerbi, J. Phys. Chem., 1986, 21 G. W. Gray, B. Jones and F. Marson, J. Chem. Soc., 1957, 393. 90, 852. 22 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, 37 M. Ray-Lafon and T. Hemida, Mol. Cryst. Liq. Cryst., 1990, 178, J. Assour and L. KorsakoV, J. Org. Chem., 1967, 32, 476. 33; W. K. Lee, P.A. Heiney, M. Ohba, J. N. Haseltine and 23 G. H. Barnett, M. F. Hudson and K. M. Smith, J. Chem. Soc., A. B. Smith III, Liq. Cryst., 1990, 8, 839; W. K. Lee, P. A. Heiney, Perkin Trans. 1, 1975, 1401. J. P. McCauley and A. B. Smith III, Mol. Cryst. Liq. Cryst., 1991, 24 A. D. Adler, F. R. Longo and V. Va� radi, Inorganic Synthesis, ed. 198, 273. F. Basolo, McGraw-Hill, New York, 1976, vol. 16, ch. 7, p. 214. 38 D. Chapman, Spectrochim. Acta, 1957, 11, 609; K. Ohta, 25 J. S. Manka and D. S. Lawrence, Tetrahedron Lett., 1989, 30, M. Yokoyama and H. Mikawa, Mol. Cryst. Liq. Cryst., 1981, 6989. 73, 205. 26 S. Seki and H. Suga, Kagaku Sosetsu, No. 5, Non-equilibrium states 39 R. G. Snyder, J. Chem. Phys., 1967, 47, 1316. and relaxation processes, 1974, ch. 9, p. 225. 40 H. Ema, Master Thesis, Shinshu University, Ueda, 1988. 27 N. Ando, Master Thesis, Shinshu University, Ueda, 1992. 41 H. Hasebe, Master Thesis, Shinshu University, Ueda, 1991. 28 M. Ando, Master Thesis, Shinshu University, Ueda, 1993. 42 K. Ohta, T. Watanabe, S. Tanaka, T. Fujimoto, I. Yamamoto, 29 C. Piechocki, J. Simon, J.-J. Andre�, D. Guillon, P. Petit, P. Bassoul, N. Kucharczyk and J. Simon, Liq. Cryst., 1991, 10, A. Skoulios and P. Weber, Chem. Phys. Lett., 1985, 122, 124. 357. 30 H. R. Kricheldorf and G. Schwarz, Polymer, 1990, 31, 481. 43 T. Watanabe, Master Thesis, Shinshu University, Ueda, 1990. 44 H. Rapoport and C. D. Willson, J. Am. Chem. Soc., 1962, 84, 630. 31 B. E. Powell, J. Cryst. Growth., 1973, 18, 307. 45 R. Chong, P. S. Clezy, A. J. Liepa and A. W. Nichol, Aust. 32 G. Lattermann and H. Ho� cker, Mol. Cryst. Liq. Cryst., 1986, 133, J. Chem., 1969, 22, 229. 245, and references therein. 33 K. Ohta, R. Higashi, M. Ikejima, I. Yamamoto and N. Kobayashi, J. Mater. Chem., 1998, 8, 1979. Paper 8/05715J 2650 J. Mater. Chem., 1998, 8, 2637&ndas

ISSN:0959-9428    

DOI:10.1039/a805715j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Easy synthesis of liquid crystalline perylene derivatives Peter Schlichting, Ulrike Rohr and Klaus Mu�llen* Max-Planck-Institut fu�r Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany Received 8th June 1998, Accepted 7th September 1998 Mesophase forming chromophores are an important challenge of material science. This article describes the synthesis of new perylene mesogenes 10.The materials were obtained by twofold Diels–Alder reactions of our recently published 151 isomeric mixture of 3,9- and 3,10-dialkylperylenes with N-heptadecyltriazoline-3,5-diones. In contrast to the analogous derivatives 1 published earlier by our group (see reference 3), the new compounds 10 are prepared by a more eYcient synthetic route and on a larger scale.Furthermore the characteristics of the liquid crystalline behavior of both materials are compared. Liquid crystalline chromophores combine the properties of dyes and the characteristics of liquid crystals. This combination is of particular interest for the design of photoconductive and NLO-active materials1 and the construction of light emitting diodes.2 Additional requirements are thermal and photochemical stability, the existence of a stable mesophase over a broad temperature range and of course, ready synthetic accessibility. N N N N N N O O O O CxH2 x+1 CyH2 y+1 CyH2 y+1 CxH2 x+1 P x- y (1) The perylene mesogens Px-y (1) were originally synthesized in our group by twofold Diels–Alder reaction of 3,10-dialkylperylenes 5 with N-alkyltriazolinediones 6.3 Px-y is an abbreviation used for simplicity, with P meaning perylene, x indicating the length of the alkyl chain attached to the perylene core and y the length of the alkyl chain of the urazole unit.The major disadvantage of the Px-y systems (1) was the lengthy synthesis of the 3,10-dialkylperylenes 5, which were used in the subsequent twofold Diels–Alder reaction.Starting from 1-bromonaphthalene (2), the products 5 were obtained through a three-step synthesis in good yields, however the intermediates required tedious purification methods and the reactions were restricted to small scales. An additional problem of this route was the use of highly toxic thallium salts. Herein we describe a new and easy route for the preparation of the new liquid crystalline perylene derivatives 10.Results and discussion The synthesis started with a twofold bromination of perylene. This reaction yielded a 151 isomeric mixture of 3,9- and 3,10- dibromoperylene which could not be separated by column chromatography or HPLC.4 Due to the fact that this isomeric mixture was used in the subsequent Hagihara-coupling, one also obtained an isomeric mixture of 3,9- and 3,10-dialkyl substituted perylenes 9.In our experiments, however, this mixture of isomers showed no significant diVerences in solubility, absorption and reactivity in comparison with the pure N N N N N N R1 R1 C17H35 H35C17 O O O O Br Br Br R1 R1 R1 R1 N N N O O C17H35 1a R1 = C5H11 b R1 = C6H13 c R1 = C8H17 d R1 = C12H25 4,5 a R1 = C5H11 5 12 11 10 9 8 7 6 5 4 3 2 1 K / DME CH3COOH Tl(CH3COO)3 b R1 = C6H13 c R1 = C8H17 d R1 = C12H25 6 4 2 3 R1MgBr 3,10-isomer 5.4 The advantage of this method is the simplicity Scheme 1 of the procedure and its suitability for large-scale synthesis.J. Mater. Chem., 1998, 8, 2651–2655 2651positions, the Pix-y 10 consist of a 151 isomeric mixture of the 3,9- and 3,10-substituted species.Analogous to the 3,9(10)- dibromoperylene (7), all attempts to separate the two isomers of the Pix-y 10 were unsuccessful. Characterization of the Pix-y materials 10 was achieved by field-desorption mass spectrometry (FD-MS), UV-VIS, 1H NMR and 13C NMR spectroscopy and was found to be in good agreement with the structures 10. No trace of side products was observed by the aforementioned characterization techniques or by thin layer chromatography, which is a particularly sensitive method for chromophores.The published liquid crystalline perylenes Px-y (1) are blue solids showing a maximum of absorption of lmax=585 nm. With X-ray diVraction we showed in earlier publications that the majority of Px-y derivatives 1 form discotic phases.3 Through the variation of the alkyl chains at the perylene core and/or the urazole units the characteristics of the mesophase can be controlled.With no or short alkyl chains (x<3) attached to the peri-positions of the perylene core (e.g. P0–17) smectic phases are obtained.3 The transition temperatures are also aVected if one varies the length of the alkyl chains of the 3,5-dioxotriazole units attached to the perylene.All Px-y derivatives 1 form remarkably stable (broad) mesophases (e.g. P12–11 is liquid crystalline in the temperature region between -23 and 373 °C) due to their pronounced form anisotropy shown by deuteron 2H NMR spectroscopy. The results of 2H NMR spectroscopy indicated that the five-membered, heterocyclic ring clearly deviates from a coplanar conformation. This nonplanarity could cause an entanglement between neighboring perylene units, resulting in an increased phase width of the Px-y compounds 1.3 Similar entanglements were found to be the reason for the increased stability of the mesophase formed by ester substituted triphenylenes.5 The new compounds Pix-y 10 show an absorption spectrum with lmax=585 nm (e#20 000 l mol-1 cm-1), which is the same as for Px-y 1.Similar to Px-y 1 the Pix-y derivatives 10 form mesophases, which qualitatively were detected by polarizing microscopy. The materials show birefringence and shearability, N N N N N N C17H35 H35C17 O O O O R2 (R2) R2 Br (Br) Br H R1 R1 R1 R1 R2 (R2) R2 N N N O O C17H35 b R2 = C6H13 c R2 = C8H17 d R2 = C12H25 9,10 a R2 = C5H11 10 6 a R1 = C3H7 b R1 = C4H9 c R1 = C6H13 d R1 = C10H21 9 7 8 H2 / Pd-C Pd(0) Scheme 2 both typical of liquid crystals. The transition temperatures of 10 were determined by calorimetric (DSC) measurements.From comparision of the transition temperatures of the For this reason we used the isomeric mixture 9 for the diVerent Pix-y derivatives 10 (Table 1, right column) it is clear preparation of the new liquid crystalline perylenes 10.that derivatives with the same alkyl chain length at the urazole Analogous to the already mentioned Px-y 1 the new liquid unit ( y=17) show decreasing transition temperatures into the crystalline perylenes are abbreviated as Pix-y 10. The ‘i’ stands mesophase with increasing length of the alkyl chain attached for isomeric mixture of 3,9- and 3,10-substituted dialkylperylto the perylene core.In addition to this trend, the isotropization enes 9. To prepare the Pix-y 10, the 3,9(10)-dibromoperylene temperature increases, i.e. the mesophase range broadens. This 7 was coupled with n-alkynes using a palladium catalyzed trend is exactly the same as in the case of the Px-y reaction in 98–100% yield.4 Subsequent hydrogenation of the compounds 1.triple bonds aVorded the 3,9(10)-dialkylperylenes 9 in quanti- Comparison of the transition temperatures of Pix-y 10 with tative yield.4 As in the case of 3,10-dialkylperylenes 5 these Px-y 1 (Table 1) reveals that the Pix-y 10 have slightly lower were then reacted with N-heptadecyltriazoline-3,5-dione 6 in melting points than the Px-y 1. Isotropization temperatures boiling xylene in a twofold Diels–Alder reaction in both bayare similar, if both classes of compounds have the same alkyl regions of the dialkylperylenes 9 to yield the blue Pix-y 10 chains attached to the perylene core (i.e.same x). The diVer- diaddition products in 95–98% yield.3 The materials show ences in the transition temperatures into the mesophase (Tm) good solubility in organic solvents.The purification steps were are especially pronounced when x is small. For example Pi5–17 much easier than in the case of the Px-y compounds 1, the 10a melts at 47 °C while P5–17 1a shows the transition into dibromoperylene 7 and the dialkyne substituted derivatives 8 the mesophase at 89 °C, a diVerence of 42 °C. In summary, the could be recrystallized and the dialkylperylenes 9 were used fact that the melting temperature Tcreases while the for the next reaction without further purification. Unlike the Px-y derivatives 1, with the alkyl substituents at the 3,10- isotropization temperature Ti is almost the same for the Table 1 Comparison of the phase transition temperatures of Px-y and Pix-y derivatives (Cryst=crystalline, Iso Liq=isotropic liquid ) measured with diVerential scanning calometry (DSC); all data taken from the 2nd heating cycle, scan rate 10 °Cmin-1 x Px-17 Pix-17 5 1a Cryst 89 Colho 226 Iso Liq (°C) 10a Cryst 47 Colho 238 Iso Liq (°C) 6 1b Cryst 76 Colho 245 Iso Liq (°C) 10b Cryst 32 Colho 243 Iso Liq (°C) 8 1c Cryst 57 Colho 288 Iso Liq (°C) 10c Cryst 29 Colho 287 Iso Liq (°C) 12 1d Cryst 16 Colho 316 Iso Liq (°C) 10d Cryst 14 Colho 320 Iso Liq (°C) 2652 J.Mater. Chem., 1998, 8, 2651–2655makes them readily available for diVerent investigations and applications. This was one of the requirements for microwave conductivity detections, which will be presented in a following paper.6 As terminal difunctionalized dialkylperylenes 11 can be synthesized in a similar way to the dialkylperylenes,3 the improved route presented here oVers a possibility for the preparation of functionalized Pix-y derivatives 10 as well, if functionalized alkynes are employed in the coupling reactions.In contrast, the synthesis of 3,10-substituted and terminal functionalized dialkylperylenes starting from 1-bromonaphthalene (2) (Scheme 1) is not possible, since the functional groups are incompatible with the cyclization conditions.The functional Pix-y 10 compounds can then be used to build up liquid crystalline perylene polymers, which is a major goal of our present work. Experimental Measurements 1H NMR: Varian Gemini 200 (200 MHz), Bruker AC 300 (300 MHz), Bruker AMX 500 (500 MHz). 13C NMR: Varian Gemini 200 (50.32 MHz), Bruker AC 300 (75.48 MHz), Bruker AMX 500 (125.80 MHz).UV–VIS: Perkin-Elmer Lambda 9, Perkin-Elmer Lambda 15. FD-MS: ZAB2-SE-FPD (VG Instruments). Melting points (uncorrected): Bu� chi melting point apparatus. Thermal analysis: Mettler DSC 30 diVerential scanning calorimeter. Thin layer chromatography (TLC): Ready-to-use silica gel 60 F254 plates (Merck). Column chromatography: Silica gel, particle size 70–230 mesh (Merck, Fig. 1 Small-angle X-ray diVractograms of P6–17 (1b) at 127 °C and Pi6–17 (10b) at 140 °C. Geduran Si 60) and aluminium oxide (Merck, Geduran AL 90) using the eluents indicated. The argon used was passed through an oxygen scavenger (BTS catalyst, BASF AG), silica corresponding Px-y materials 1, leads to even broader mesogel and KOH pellets. THF, piperidine, DME and DMF were phases for the Pix-y 10.This eVect might be caused by the purified and dried according to standard procedures.7 slightly higher irregularity in the case of the new Pix-y Hydrogen gas was purchased from Linde and used without compounds 10 due to the presence of an isomeric mixture. further purification. The small-angle X-ray diVractograms The mesophases of 10 were characterized by small-angle were measured on a Siemens Kristallflex D-500 diVractometer X-ray scattering.Similar to the corresponding Px-17 com- (beam divergence 0.3), equipped with a hot stage. Cu-Ka pounds 1a–d, all the Pix-17 derivatives 10a–d form discotic radiation was selected by a graphite crystal monochromator. phases with hexagonal superstructure (Colho). Fig. 1 shows the All samples were heated to measurement temperature and kept characteristic scattering peaks of a Colho phase for P6–17 1b at this temperature for 30 min prior to measurement as well as for Pi6–17 10b.(measurement time ~2 h). The intense (100)-reflections at 2h=4.05° (P6–17 1b) and 2h=3.95° (Pi6–17 10b) correspond to an intercolumnar dis- Synthesis tance of approximately 22 A° in both cases.Each derivative shows the (001)-reflection at 2h=25.5° which indicates an 3,9- and 3,10-Dialkylperylenes (151 isomeric mixture). The intracolumnar distance of 3.5 A ° . The hexagonal superstructure diVerent 3,9(10)-dialkylperylenes were prepared according to of both substances was proven from the (110)-reflection our recently published procedure: ‘New synthetic routes to occurring at 2h=7.00° (P6–17 1b) and 2h=6.85° (Pi6–17 10b).alkyl-substituted and functionalized perylenes’.4 N-Heptadecyltriazoline-3,5-dione (6). Heptadecyltriazoline- Conclusions dione 6 was obtained in a five-step reaction starting from The isomeric mixture Pix-y 10 forms very stable liquid stearic acid employing the procedure described by Saville.8 crystalline phases similar to the known Px-y derivatives 1, and therefore, exhibit the same attractive physical properties.Synthesis of Px-y (1) Besides the fact that the mesophases are slightly broader, the 4,4¾-Dibromo-1,1¾-binaphthyl (3). 10 g Thallium trifluoro- new perylene mesogens Pix-y 10 have almost the same liquid acetate and 7.6 g 1-bromonaphthalene were dissolved in 150 ml crystalline properties as the Px-y derivatives 1.Due to the ease trifluoroacetic acid and stirred at room temperature for 3 h. of preparation of the Pix-y derivatives 10, larger amounts of The color of the reaction mixture gradually turned from deep the liquid crystalline chromophores can be synthesized, which purple to gray and the product precipitated. After addition of 150 ml of water the crude product was filtered through a Table 2 Small-angle X-ray scattering-reflections of P6–17 1b at 127 °C Bu�chner funnel, dried under vacuum, recrystallized from diox- and Pi6–17 10b at 140 °C ane and chromatographed over a short column (silica gel– P6–17 1b Pi6–17 10b petroleum ether) The product crystallized as white needles and could be isolated in 38% yield (2.9 g), melting point: 216 °C; (100) 2h=4.05° 2h=3.95° 1H-NMR (200 MHz, CDCl3): d=8.36–8.32 (d; 2 H, 3J=8 Hz, (110) 2h=7.00° 2h=6.85° 2 Ar-H), 7.99–7.95 (d; 2 H, 3J=8 Hz, 2 Ar-H), 7.57–7.53 (m; (001) 2h=25.5° 2h=25.5° 2 H, 2 Ar-H), 7.35–7.24 (m; 6 H, 6 Ar-H); 13C-NMR J.Mater. Chem., 1998, 8, 2651–2655 2653(50 MHz, CDCl3): d=137.72, 133.90, 132.02, 129.49, 128.20, 3J=8.8 Hz, 2 Ar-H), 7.97 (s, 2 H, 2 Ar-H), 7.40–7.10 (m; 2 H, 2 Ar-H), 3.72–3.65 (t; 4 H, 3J=6.7 Hz, CH2-N), 2.72–2.55 127.90, 127.51, 123.00.FD-MS (8 kV): m/z=410.00 (100%) [M+]. (m; 4 H, 2 Ar-CH2), 1.82–1.78 (m; 4 H, 2 CH2), 1.70–1.63 (m; 4 H, 2 CH2), 1.55–1.18 (m; 68 H, 34 CH2), 0.92–0.81 (m; 12 H, 4 CH3). 13C-NMR (125 MHz, C2D2Cl4, 110 °C): d= 4,4¾-Di(n-hexyl )-1,1¾-binaphthyl (4). 8.0 g (12.1 mmol) 4,4¾- Dibromo-1,1¾-binaphthyl (3) and 200 mg Ni(dppe)Cl2 (dppe= 145.02, 144.98, 144.48, 141.18, 129.98, 129.83, 126.39, 125.02, 124.96, 113.82, 113.70, 113.15, 110.98, 41.33, 40.50, 32.86, diphenylphosphinoethane) were suspended in 50 ml of dry ether under an argon atmosphere. 9.16 g (48.40 mmol) 32.20, 32.09, 29.93, 29.53, 29.16, 28.10, 28.03, 27.59, 27.17, 27.13, 26.70, 22.83, 22.69, 13.93. UV (CH2Cl2): lmax (e)= Butylmagnesium bromide in 20 ml ether were added at room temperature with a syringe through a septum.The reaction 585 nm (11252), 539 nm (8542), 503 nm (4465). FD-MS (8 kV): m/z=1091.00 (100%) [M+]. mixture was stirred at room temperature until it began to reflux spontaneously. When the solution started to cool it was heated to reflux for 18 h. The cooled reaction mixture was Synthesis of the Pix–y compounds hydrolyzed by addition of 5 ml of methanol. The solvent was Pi5–17 (10a).Synthesis was performed using Method A: evaporated and the crude product dried under vacuum and 250 mg (0.63 mmol) 3,9(10)-di(n-pentyl )perylene (9a) and purified by chromatography with silica gel and pentane as 1.3 g (3.85 mmol) N-heptadecyltriazolinedione (6) yielded eluent.The yield was 7.95 g (93%) of white crystals, mp: 56 °C. 630 mg (94%) of the deep blue product. DSC: Tm=47 °C, Ti= 1H-NMR (200 MHz, CDCl3): d=8.17–8.14 (d; 2 H, 3J=8 Hz, 238 °C. 1H-NMR (500 MHz, C2D2Cl4, 110 &de: d=8.21–8.16 2 Ar-H), 7.60–7.41 (m; 8 H, 8 Ar-H), 7.36–7.21 (m; 2 H, 2 (m; 2 H, 2 Ar-H), 8.10 (s, 2 H, 2 Ar-H), 7.47–7.40 (m; 2 H, Ar-H), 3.21–3.08 (t; 4 H, 3J=7 Hz, 2 Ar-CH2), 1.98–1.80 (m; 2 Ar-H), 3.71–3.66 (t; 4 H, 3J=6.7 Hz, CH2-N), 2.70–2.55 4 H, 2 Ar-CH2-CH2), 1.56–1.30 (m; 12 H, 6 CH2), 0.99–0.85 (m; 4 H, 2 Ar-CH2), 1.78–1.76 (m; 4 H, 2 CH2), 1.63–1.60 (t; 6 H, 3J=7 Hz, 2 CH3). 13C-NMR (50 MHz, CDCl3): d= (m; 4 H, 2 CH2), 1.50–1.15 (m; 64 H, 32 CH2), 0.89–0.86 (m; 139.22, 137.64, 133.99, 132.52, 128.20, 128.11, 126.00, 125.92, 12 H, 4 CH3). 13C-NMR (125 MHz, C2D2Cl4, 110 °C): d= 125.86, 124.55, 33.81, 32.74, 31.24, 30.09, 23.66, 14.70. IR: n�= 144.69, 144.63, 144.51, 141.10, 130.01, 129.80, 126.43, 125.01, 2961, 1379, 849, 763 cm-1. FD-MS (8 kV): m/z=422.68 [M+]. 124.93, 113.83, 113.67, 113.13, 110.89, 41.23, 40.12, 32.87, 32.21, 32.11, 29.90, 29.51, 29.15, 28.10, 27.98, 27.58, 27.17, 3,10-Di(n-hexyl )perylene (5). 2 g (4.7 mmol) 4,4¾-Bis-n- 27.12, 26.70, 22.83, 22.71, 14.23. UV (CH2Cl2): lmax (e)= hexyl-1,1¾-binaphthyl (4) were dissolved in 50 ml dimethoxy- 585 nm (10593), 539 nm (8912), 503 nm (3876). FD-MS ethane (DME) (dried over potassium) under an argon atmos- (8 kV): m/z=1063.0 (100%) [M+]. phere. 2 g potassium was added in small pieces in an argon stream. The reaction mixture was stirred in the dark at room Pi6–17 (10b).Synthesis was performed using Method A: temperature for 2 days and monitored by thin layer chromatog- 250 mg (0.60 mmol) 3,9(10)-di(n-hexyl )perylene (9b) and raphy. After completion of the reaction the excess potassium 1.2 g (3.57 mmol) N-heptadecyltriazolinedione (6) yielded was removed carefully and the solution was stirred under an 620 mg (95%) of the deep blue product.DSC: Tm=32 °C, Ti= oxygen atmosphere for 1 day. The color changed from deep 243 °C. 1H-NMR (500 MHz, C2D2Cl4, 110 °C): d=8.03–8.01 blue to orange indicating the oxidation of the perylene anions. (d; 2 H, 3J=8.8 Hz, 2 Ar-H), 7.96 (s, 2 H, 2 Ar-H), 7.50–7.20 The DME was removed by distillation and the crude product (m; 2 H, 2 Ar-H), 3.71–3.66 (t; 4 H, 3J=6.7 Hz, CH2-N), purified by column chromatography (silica gel–CH2Cl2), mp: 2.69–2.55 (m; 4 H, 2 Ar-CH2), 1.83–1.78 (m; 4 H, 2 CH2), 131 °C. 1H-NMR (200 MHz, CDCl3): d=8.19–8.17 (d; 2 H, 1.70–1.65 (m; 4 H, 2 CH2), 1.56–1.18 (m; 68 H, 34 CH2), 3J=8 Hz, 2 Ar-H), 8.08–8.05 (d; 2 H, 3J=8 Hz, 2 Ar-H), 0.91–0.83 (m; 12 H, 4 CH3). 13C-NMR (125 MHz, C2D2Cl4, 7.87–7.84 (d; 2 H, 3J=8 Hz, 2 Ar-H), 7.51–7.45 (dd; 2 H, 110 °C): d=145.01, 144.93, 144.21, 141.20, 129.98, 129.80, 3J=8 Hz, 2 Ar-H), 7.31–7.29 (d; 2 H, 3J=8 Hz, 2 Ar-H), 126.35, 125.01, 124.93, 113.80, 113.72, 113.13, 110.89, 41.30, 3.01–2.96 (t; 4 H, 3J=7 Hz, 2 Ar-CH2), 1.80–1.70 (m; 4 H, 2 40.10, 32.81, 32.19, 32.01, 29.91, 29.52, 29.16, 28.10, 28.02, Ar-CH2-CH2), 1.50–1.32 (m; 12 H, 6 CH2), 0.92–0.87 (t; 6 27.58, 27.15, 26.99, 26.68, 22.81, 22.70, 13.90.UV (CH2Cl2): H, 3J=7 Hz, 2 CH3). 13C-NMR (75 MHz, d8-THF): d= lmax (e)=585 nm (10903), 539 nm (8937), 503 nm (4003). 138.32, 132.91, 131.94, 129.57, 128.77, 126.62, 126.05, 123.57, FD-MS (8 kV): m/z=1091.20 (100%) [M+]. 119.83, 33.24, 31.66, 30.45, 29.40, 22.54, 13.95. UV (Dioxan): lmax (e)=451nm (16595), 423nm (12882), 401 nm (5754).Pi8–17 (10c). Synthesis was performed using Method A: FD-MS (8 kV): m/z=420.52 (100%) [M+]. 250 mg (0.52 mmol) 3,9(10)-di(n-octyl )perylene (9c) and 1.06 g (3.14 mmol) N-heptadecyltriazolinedione (6) yielded Twofold Diels–Alder reaction of the dialkylperylenes 5 or 9 560 mg (94%) of the deep blue product. DSC: Tm=29 °C, Ti= with N-heptadecyltriazolinedione 6 (Method A). 250 mg of 287 °C. 1H-NMR (500 MHz, C2D2Cl4, 110 °C): d=8.20–8.15 dialkyl substituted perylene derivative 5 or 9 were dissolved in (m; 2 H, 2 Ar-H), 8.09 (s, 2 H, 2 Ar-H), 7.48–7.40 (m; 2 H, 25 ml of m-xylene and heated to reflux. A fourfold excess of 2 Ar-H), 3.71–3.65 (t; 4 H, 3J=6.7 Hz, 2 CH2-N), 2.82–2.70 N-heptadecyltriazolinedione 6 was added to the solution in (m; 4 H, 2 Ar-CH2), 1.81–1.71 (m; 4 H, 2 CH2), 1.70–1.59 small portions and the reaction monitored by thin layer (m; 4 H, 2 CH2), 1.45–1.18 (m; 76 H, 38 CH2), 0.90–0.78 (m; chromatography until the starting material (yellow) and the 12 H, 4 CH3). 13C-NMR (125 MHz, C2D2Cl4, 110 °C): d= monoadduct (red) vanished. When the reaction was completed 144.98, 144.96, 144.47, 141.21, 130.01, 129.97, 129.85, 126.38, the hot solution was poured into 200 ml of methanol.The 126.36, 125.02, 124.98, 113.81, 113.72, 113.13, 110.91, 41.32, precipitate was collected by filtration, redissolved in dichloro- 40.18, 32.85, 32.18, 32.07, 29.96, 29.87, 29.53, 29.38, 29.16, methane and added dropwise to hot ethanol. The hot solution 28.13, 28.08, 27.63, 27.45, 27.16, 26.73, 22.85, 22.78, 22.70, was filtered and the product isolated as a blue solid which was 14.03.UV (CH2Cl2): lmax (e)=585 nm (10102), 539 nm further purified by chromatography over silica gel with (8946), 503 nm (4203). FD-MS (8 kV): m/z=1146.5 (100%) dichloromethane as eluent. [M+]. P6–17 (1b). Synthesis was performed using Method A: 250 mg (0.60 mmol) 3,10-di(n-hexyl )perylene and 1.2 g Pi12–17 (10d). Synthesis was performed using Method A: 250 mg (0.42 mmol) 3,9(10)-di(n-dodecyl )perylene (9d) and (3.57 mmol) N-heptadecyltriazolinedione (6) yielded 615 mg (94%) of the deep blue product. DSC: Tm=76 °C, Ti=245 °C. 0.86 g (2.55 mmol) N-heptadecyltriazolinedione (6) yielded 492 mg (93%) of the deep blue product. DSC: Tm=14 °C, Ti= 1H-NMR (500 MHz, C2D2Cl4, 110 °C): d=8.04–8.02 (d; 2 H, 2654 J. Mater. Chem., 1998, 8, 2651–26552 T.Christ, B. Glu� sen, A. Greiner, A. Kettner, R. Sander, 320 °C. 1H-NMR (500 MHz, C2D2Cl4, 110 °C): d=8.10–8.00 V. Stu�mpflen, V. Tsukruk and J. H. Wendorf, Adv. Mater., 1997, (m; 2 H, 2 Ar-H), 8.00 (s, 2 H, 2 Ar-H), 7.35–7.10 (broad; 2 9, 48. H, 2 Ar-H), 3.71–3.68 (t; 4 H, 3J=8 Hz, 2 CH2-N), 2.65 3 (a) C. Go� ltner, D. Pressner, K. Mu� llen and H. W. Spieß, Angew. (broad; 4 H, 2 Ar-CH2), 1.82–1.78 (t; 4 H, 3J=8 Hz, 2 CH2), Chem., 1993, 105, 1722; Angew.Chem., Int. Ed. Engl., 1993, 32, 1.64–1.60 (t; 4 H, 3J=7 Hz, 2 CH2), 1.48–1.22 (m; 92 H, 46 1660; (b) D. Pressner, C. Go� ltner, H. W. Spieß and K. Mu� llen, Ber. Busenges. Phys. Chem., 1993, 97, 1362. CH2), 0.89–0.86 (t; 12 H, 3J=6 Hz, 4 CH3). UV (Dioxan): 4 P. Schlichting, U. Rohr and K. Mu� llen, Liebigs Ann./Recl., 1997, lmax (e)=585 nm (11165), 539 nm (9034), 503 nm (4235). 395. FD-MS (8 kV): m/z=1259.00 (100%) [M+]. 5 M. Werth, S. U. Vallerien and H. W. Spiess, Liq. Cryst., 1991, 10, 759. 6 A. M. van de Craats, J. M. Warman, P. Schlichting, U. Rohr and References K. Mu� llen, International Conference on Science and Technology of Synthetic Metals 1998, July 12th–14th, Montpellier, Charge 1 (a) F. Closs, K. Siemensmeyer, T. Frey and D. FunhoV, Liq. Cryst., Transport in Mesomorphic Derivatives of Perylene, Synth. Met., in 1993, 3, 629; (b) H. Bengs, F. Closs, T. Frey, D. FunhoV, the press. H. Ringsdorf and K. Siemensmeyer, Liq. Cryst., 1993, 5, 565; 7 D. D. Perrin, W. L. F. Armarego and D. R. Perrin, Purification of (c) D. Adam, F. Closs, T. Frey, D. FunhoV, D. Haarer, Laboratory Chemicals, 2nd edn., Pergamon Press, Frankfurt, 1987. H. Ringsdorf, P. Schuhmacher and K. Siemensmeyer, Phys. Chem. 8 B. Saville, J. Chem. Soc., Chem. Commun., 1971, 635. Lett., 1993, 70, 457; (d) D. Adam, P. Schuhmacher, J. Simmerer, L. Ha�usling, K. Siemensmeyer, K. H. Etzbach, H. Ringsdorf and D. Haarer, Nature, 1994, 371, 141. Paper 8/04332I J. Mater. Chem., 1998, 8,

ISSN:0959-9428    

DOI:10.1039/a804332i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Room temperature dedoping of conducting poly-3-alkylthiophenes Wu Chun-Guey,* Chan Mei-Jui and Lin Yii-Chung Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, Republic of China. E-mail: T610002@cc.ncu.edu.tw Received 14th July 1998, Accepted 14th September 1998 Thin films of FeCl3 doped polyalkylthiophene (side chain length from 6 to 18) have been automatically dedoped in ambient atmosphere at room temperature.The dedoping rate is dependent upon the side chain length, dopant, ambient lighting and film morphology. The maximum dedoping rate occurred in the first 30 min and dropped oV rapidly after one hour. Dedoping is the reversible process of doping, bipolarons being reduced to polarons and then to the neutral state.The production of Fe2+ and HCl during the dedoping process indicates that moisture acted as the reducing agent. In other words, bipolarons were reduced by H2O to polarons. Polarons subsequently disproportionate to bipolarons and neutral polymer or reduced Fe3+ to Fe2+. Protons, produced from the oxidition of H2O, react with FeCl4- or FeCl42- to produce HCl and iron complexes.polymer chains. Therefore, after doping, the resulting films Introduction may have diVerent dedoping rates. The potential applications of conducting polymers in micro- The applications of conducting P3ATs require that we have electronics have been investigated over the past few decades1–3 a thorough understanding of their properties. In order to and a significant eVort has been made to obtain soluble and understand better the nature of the dedoping phenomenon, processable materials.4 Enhanced solubilization can be we investigated the eVects of structure regularity, alkyl side achieved by grafting long alkyl side chains on a polyaromatic chain length, dopant, solvent, and light on the room temperabackbone as has been demonstrated in polyalkylthiophenes ture dedoping of doped P3ATs.(P3ATs). Polyalkylthiophenes represent a class of conducting polymers that are soluble and processable, and yet retain a Experimental degree of the electrical conductivity of the insoluble parent, polythiophene.5–8 The solubility of polyalkylthiophenes arises Reagents from the decrease of attraction between polymer chains and 3-Bromothiophene (stored over molecular sieves), the introduction of favorable interactions between the substitu- Ni(dppp)Cl2, LDA, Mg, MgBr2, HgO, I2 and bromoalkanes ents and the solvent.Unfortunately, side chain substitution (with chain length ranging from 6 to 18), were purchased from also leads to thermal instability of the doped polymer since in Aldrich Chemical Co. or other commercial sources and used P3AT, the doped state has a higher energy than the neutral as received unless otherwise specified. All solvents are HPLC state.Thermal dedoping appears to be a critical technological grade and distilled over Na or CaH2 prior to used (bromo- problem for the application of P3AT. A considerable number alkanes were distilled over MgSO4). of studies have been made to understand the instability of doped P3AT. It was reported that the dedoping (or conduc- Preparation of P3AT films tivity) decay rate depends on the dopant,9,10 degree of doping and temperature11 as well as the humidity level of the surround- The monomers, 3-alkylthiophenes with a side chain length ing atmosphere.12,13 On the other hand, some studies also ranging from 6 to 18, were prepared by a published procedure20 showed that the dedoping process also depends on the arrange- (Ni catalyzed coupling of the alkyl Grignard with 3-bromoment of alkyl side chains in the polymer backbone.14 A thiophene).The purity of monomers was checked by 1H NMR reduction of the number of alkyl side chains in a regular way and found to be >95%. Regio-random P3ATs were prepared increased the stability towards thermal dedoping. by chemical oxidative coupling of the corresponding monomers The dedoping mechanism in P3AT has been explained by with FeCl3–CHCl3 according to the procedure described by the increasing reactivity of the conducting oxidized state Sugimoto et al.21 Removal of oligomers and impurities from towards reducing species, such as water.9,15 However, the obtained polymers was achieved by Soxhlet extraction Horowitz et al.16 found that the oxidized polymer (in solution) with MeOH.The dark red neutral P3AT was dried under is reduced to the neutral state when acetone was added, but vacuum. Regio-regular polymers were prepared by a literature the exact nature of this reaction is still unknown. Most studies procedure.22 The percentage of HT–HT dyad was measured have centered on the thermal dedoping process of P3ATs by 1H NMR spectroscopy.23 25 mg of dried P3AT was discontaining FeCl4- counter ions.Pei et al. believe that thermally solved in 2.5 ml of solvent and the solutions were cast onto a activated side chain mobility is the cause for dopant removal silicon wafer or a glass slide.All film thicknesses were between from the polymer backbone and that larger dopants will be 4750 and 5250 A° . removed more easily.17 However, Ciprelli et al. discovered that the size of the dopant ions does not appear to be a determining Doping of P3AT films with solutions of FeCl3 or AuCl3 in dry factor in the dedoping process10 and that the electronic propernitromethane ties of the counter anion play a key role in this process.Nevertheless, it was reported by Abdou et al. that for thin Chemical doping was performed by dipping the film (cast on films (<1 mm), photochemical dedoping dominates over ther- substrate) in a nitromethane solution of FeCl3 or AuCl3 for mal dedoping under ambient lighting.18 In addition, solvato- 30 and 60 min, respectively.After oxidation, all films were chromic behavior was observed for polyalkylthiophene.19 The rinsed several times with nitromethane and dried with N2. UV–VIS–NIR absorption spectroscopy was used to monitor solvents used to cast the polymer films aVect the packing of J. Mater. Chem., 1998, 8, 2657–2661 2657Table 1 Molecular weights, Dlmax, HT–HT dyad ratios and average the doping process.Completeness of doping was judged by dedoping rate in the 30 min of P3ATs the total disappearance of the p–p* transition of the neutral polymer. The degree of oxidation was determined by elemen- Side Average dedoping tal analysis. chain Molecular HT–HT rate in the length weight Dlmax b/nm ratio (%) first 30 min Rate of dedoping 6 4 000 39 53 1.86 The dedoping process was monitored by UV–VIS–NIR 7 66 000 32 55 2.88 spectroscopy. 8 100 000 65 67 5.54 8a 4 000 90 96 1.50 10 95 000 28 49 7.77 Physical measurements 12 70 000 34 58 5.86 12a 4 000 85 98 1.60 Fourier transform IR spectra were recorded for films on a Si 14 110 000 35 58 7.08 substrate using a Bio-Rad 155 FTIR spectrometer. The thick- 16 4 000 34 57 6.74 nesses of the polymer films were measured with a Dektak 3 18 3 200 34 48 8.85 surface profile measuring system.The scan length is 5 mm and aRegio-regular polyalkylthiophene. blmax(film)-lmax(CHCl3 solu- the thickness was calculated from the average of the length tion). scanned. The thickness of films was further calibrated by UV–VIS absorption measurements. UV–VIS–NIR spectra were obtained using a Varian Cary 5E spectrometer in the octadecylthiophene). The degree of doping determined from laboratory atmosphere at room temperature. Scanning electron elemental analysis is 0.25 which is similar to that reported in microscopy (SEM) and energy dispersive spectroscopy (EDS) the literature.28–31 The doping time and degree of doping of studies were performed with a Hitachi S-800 apparatus at regio-regular P3ATs are close to those of regio-random poly- 15 kV.X-Ray photoelectron spectroscopy studies were carried alkylthiophenes. out on a Perkin-Elmer PHI-590AM ESCA/XPS spectrometer system with a cylindrical mirror electron (CMA) energy ana- Room temperature dedoping of P3AT lyzer. The X-ray sources were Al-Ka at 600 W and Mg-Ka at The FeCl3 doped P3ATs were stored at room temperature and 400 W.Depth profile secondary ion mass spectra (SIMS) were in ambient lighting. The dedoping of P3AT was monitored by measured with a SIMS Cameca, ims-4f instrument where a UV–VIS–NIR spectroscopy as shown in Fig. 1(a). It was Cs+ ion gun for sputtering was adjusted to 10 kV acceleration found that as the dedoping proceeds, the peak at ca. 1640 nm voltage. Gel permeation chromatography analyses were carried (due to charge-carrying bipolaronic states) decreased and a out on an Eldex model 9600 HPLC with a UV detector and peak at 480 nm (which corresponds to the p–p* transition of 30 cm length columns of Waters HT0&HT4 (molecular weight the neutral polymer) increased.However, the intensity of the range: 100–600 000). Polystyrene with diVerent molecular peaks at 264, 310 and 364 (the absorption peaks of FeCl4-) weights were used as calibration standards and THF was used showed no observable change in the first hour.Interestingly, as an eluent. the peak at ca. 800 nm increased initially [with a slight shift of the absorption maximum, as shown in Fig. 1(b)] then Charge transport measurements decreased as dedoping proceeds.The absorptions of polarons Direct current electrical conductivity measurements of the calculated from a theoretical model were 0.18, 1.23 and films on substrates (1.2 cm×1.2 cm square plate) were per- 1.51 eV.32 The peak at ca. 800 nm (1.7 eV) may be due to the formed in the usual four point geometry.24 The four points absorption of both polarons and bipolarons. At the beginning on the sample surface were in line at an equal spacing of of dedoping, bipolarons were reduced to polarons and 2 mm.Each point was adhered to a gold wire electrode. An although the polarons are also reduced to the neutral state, appropriate current (ranging from 1 nA to 1 mA) was main- the rate of reduction of bipolarons to polarons is higher than tained on the two outer electrodes. The floating potential that of reduction of polarons.Thus, the total concentration across the two inner electrodes was measured to determine the of polarons initially increases. After the concentration of conductivity.25 bipolarons decreased, the production of polarons from bipolarons was slower than the reduction of polarons to the Results and discussion neutral state, and hence the total concentration of polarons decreased.Preparation of P3ATs EVects of the structure and the side chain length on the dedoping Regio-random polyalkylthiophenes (P3ATs) with side chain rate lengths ranging from 6 to 18 were prepared by oxidative coupling of the corresponding monomer using iron(III ) chlor- In order to eliminate the influence of thickness on the dedoping ide as an oxidant. The ratios of HT–HT (head-to-tail to headrate, polymer films with similar thickness (5000±250 A° ) were to-tail ) dyad configuration23 and molecular weights are listed prepared.Since some of the UV–VIS absorption peaks may in Table 1. As shown in Table 1, there is no direct relationship be diYcult to identify during dedoping, the dedoping rate was between side-chain length and dyad ratio or molecular weight.calculated using the absorption peak at 1640 nm [eqn. (1) and Dark red films (thickness: 5000±250 A° ) of neutral polymers (2)]: were cast on glass slides or quartz disks from CHCl3 and THF solutions, then dipped in 0.1 M FeCl3–CH3NO2 for doping. R=(I1640-Ii1640)/I1640×100% (1) After doping, the original broad peak (due to the p–p* n=R/ti (2) transition of the neutral polymer) disappeared, while two broad absorption bands (at lmax ca. 800 and ca. 1640 nm) where R=relative intensity change, n=average dedoping rate within ti h, ti=dedoping time/h, I1640=peak intensity at grew in. These two peaks are believed to be the optical-induced electronic transitions involving charge-carrying bipolaronic 1640 nm immediately after doping and Ii1640=peak intensity at 1640 nm after dedoping for ti h.states.18,26 The peaks at 240, 316 and 368 nm correspond to the absorption of FeCl4- which is the counter anion of doped Typical average dedoping rates vs. dedoping times of polyalkylthiophene are shown in Fig. 2. The average dedoping rate polymers.27 The time required to completely dope the P3ATs is approximately the same (within 30 min), except for poly(3- was very fast in the first 2 h then decreased as dedoping 2658 J. Mater.Chem., 1998, 8, 2657–2661Fig. 1 The UV–VIS–NIR spectra of polyoctadecylthiophene during dedoping: (a) whole spectrum [(I ) just doped; (II ) after 1 h; (III ) after 21 h; (IV) after 250 h], (b) the polaron/bipolaron peak in the first hour. EVects of morphology on the dedoping rate of P3ATs The dedoping rate was aVected not only by side chain length but also by film morphology. It is found that for a given side chain length, the dedoping rate of a polymer film obtained from CHCl3 solution and doped with FeCl3 is higher than that from THF solution and doped with the same oxidant, (Fig. 2) and polyalkylthiophene films cast from diVerent solvents showed diVerent morphologies (Fig. 3). After doping, films obtained from CHCl3 solution had a rather smooth surface, indicating packing of straight polymer chains. By contrast the morphology of doped films obtained from THF solution appear as aggregates of many small polymer balls and fibers. The movement of polymer side-chains and migration of HCl gas (vide infra) are easier for polymers with Fig. 2 The average dedoping rate of FeCl3 doped polyoctadecylthiostraight chains, therefore films cast from CHCl3 solution have phene cast from ($) CHCl3, (+) THF solution. a higher dedoping rate. Furthermore, theoretical calculations have suggested that the stability of doped polythiophenes may proceeds. The maximum average dedoping rates of P3ATs all be maximized by a favored topology of the dopant molecule.36 occurred during the first 30 min and decreased with increasing In other words, the dedoping rate will decrease when the steric time.Table 1 lists the molecular weight, Dlmax (the diVerence arrangement of polymer backbone and dopant are favourable. in absorption maximum between polymer solution and poly- Therefore, the higher stability of doped polyalkthiophene films mer film), HT–HT ratios and average dedoping rate in the made from THF solution may result from the fact that these first 30 min of P3ATs with various side chain lengths.P3ATs polymer films have suitable steric arrangements to accommowith similar regio-regularity have similar absorption maxima date the FeCl4- dopant. In addition, the dissimilar morin solution [except for poly(octadecylthiophene)].The absorp- phology of polymer films obtained from THF and CHCl3 tion maximum for the p–p* transition of polymer solutions is solutions indicated that the interactions between polymer blue shifted with respect to the solid state value. This is due chains of those two types of polymer films are also diVerent. to the change in the planarity of conjugated backbone (solid This was displayed by the diVerent energy of polarons and state packing stabilizes the more planar conformation) which bipolarons in these two types of polymer films as shown in in turn depends on the structure regio-regularity of the poly- Fig. 4. Polymer films obtained from THF solution have lower mers.33–35 We found that the shift of the absorption maximum absorption energies for the polarons and bipolarons and from solution to the solid state film, Dlmax, paralleled the therefore have a lower dedoping rate.structure regio-regularity. However, the maximum dedoping rate is independent of regio-regularity of regio-random P3ATs. EVects of light, dopant and moisture on the dedoping rate The dedoping phenomenon is the process of reduction of the partially oxidized polymer backbone.One can expect that a Photochemical dedoping of FeCl3 doped P3ATs thin films is known18 and it is believed that the photolability of the FeCl4- high degree of conjugation of the polymer backbone (or better stacking of the polymer chains) will lead to a more stable dopant is the cause. We studied the dedoping rate of FeCl3 doped P3AT thin films (ca. 5000 A° ) in the dark and under the doped state, and therefore give a low dedoping (reducing) rate. This is well demonstrated in the dedoping rate between ambient lighting at room temperature. It was found that the dedoping rates follow similar time dependent patterns in both regio-regular and regio-random P3ATs (Table 1). Therefore, the independence of the dedoping rate on structure regio- environments.However, we did not observe the formation of polymer bound alcohol or cross-linked polymer as seen by regularity of regio-random polyalkylthiophene indicated that some other factors may have a large influence on the dedoping Abdou and Holdcroft2 in the photolyses of P3AT in ambient air. Light as well as temperature and humidity14 are known rate of those polymers.As expected, the side chain length plays a major role in to be factors which cause the dedoping of P3ATs. By contrast with the literature report,2 we found that the dedoping rate of determining the dedoping rate of P3ATs. In general, the longer the side chain length the higher the dedoping rate. It is the sample stored in the dark is slightly faster than that in ambient light. The eVects of light on the dedoping rate of the believed18 that the dedoping phenomenon is due to thermally activated side chain mobility, which causes the products (of polymer films were also independent of the film morphology. Replacement of FeCl4- with a less photolabile dopant, the dedoping process) to be removed from the polymer backbone.At room temperature, longer alkyl side chains have a AuCl4-, decreased the dedoping rate.Nevertheless, the dedoping rates are only 4–15 times lower than for samples doped higher ability to remove the dedoping products, and therefore lead to a higher dedoping rate. with FeCl3. This implies that the photolysis of dopant may J. Mater. Chem., 1998, 8, 2657–2661 2659Fig. 3 SEM micrographs of doped (with FeCl3–CH3NO2) polyoctadecylthiophene cast from (a) CHCl3, (b) THF solution.those reported by Abdou et al.18 The released HCl was detected by pH paper or trapped by an active metal film, such as aluminium foil, and the resultant AlCl3 analyzed by EDS. Depth profile SIMS and ESCA spectra of dedoped P3AT showed that the distribution of the elements is fairly homogeneous through the whole film (Fig. 5). This indicates that during dedoping no significant ion migration or aggregation occurred. Moreover, depth profile Auger studies of P3AT during dedoping (after dedoping for 2 h) showed that although the concentration of Cl is higher on the surface, the Fe concentration was the same throughout the film. Reduction of the polymer backbone was also proved by the decrease in the binding energy of C 1s and S 1s.Detailed ESCA and Auger studies of P3ATs during dedoping will be reported elsewhere.37 Moreover, in situ UV–VIS–NIR studies showed that at the beginning of dedoping, the peak intensity at ca. 800 nm increased in the first 30 min and then decreased (vide supra). This indicates that polarons were generated in the dedoping Fig. 4 The UV–VIS–NIR spectra of doped (with FeCl3–CH3NO2) process.Such bipolaron to polaron transformations have been polydodecylthiophene cast from (a) CHCl3, (b) THF solution. observed in the thermal dedoping of thiophene oligomers.38 Both polaron and bipolaron peaks disappeared totally after not be the major factor for the dedoping of polyalkylthiophene dedoping for 3 months. However, the dedoped P3AT has a in ambient light.room temperature conductivity of 10-7 S cm-1, two orders of It was suggested by Ciprelli et al.10 that H2O was the magnitude higher than the neutral polymer. This increased reducing agent during the dedoping of P3ATs. In order to test conductivity may due to a trace amount of polarons and salt the eVect of water molecules on the dedoping rate of polyalkyl- impurity in the polymer film.Scheme 1 shows a simple dedopthiophene, the doped films were stored in a glove box (water ing mechanism derived from the above observations: concentration <1.0 ppm). The dedoping rate of such polymer bipolarons are reduced by H2O to polarons which then dispro- films was much lower than that of samples in the ambient portionate39 to bipolarons and neutral polymer.FeCl4- reacts atmosphere. Unfortunately, since the UV–VIS–NIR spec- with H3O+, produced from the oxidation of H2O, to form trometer was exposed to air, the dedoping of P3AT occurred Fe3+ complexes and HCl. Polarons or neutral polymer may when the UV–VIS–NIR spectra were measured. Reversibility of the doping/dedoping process: compared to the neutral polymer film, the intensity of the p–p* transition absorption decreased slightly (and was slightly blue shifted) after total dedoping.This implied that P3AT film degraded slightly during the dedoping process. Dedoping mechanism Polyalkylthiophenes in the neutral state are thermodynamically more stable than that in the doped state. In the presence of a large amount of good oxidant, however, the polymer backbone is oxidized.After the removal of oxidant, the polymer has the tendency to reduce back to the neutral state and if a reducing agent such as H2O is present, the polymer backbone will be reduced automatically. Nevertheless, some contradictions were observed in various studies.28 In order to understand more about the dedoping mechanism, we studied the products of the dedoping process very carefully.We found that Fe2+ and HCl were produced during the dedoping process (the ESCA spectrum showed no observable Fe2+ peak in the fully doped P3AT film37). The coexistence of Fe2+ and Fe3+ inside the polymer Fig. 5 Depth profile secondary ion mass spectra (SIMS) analysis of polydodecylthiophene after dedoping for 3 months. films was verified by ESCA studies. The results are similar to 2660 J.Mater. Chem., 1998, 8, 2657–26616 M. Leclerc, F. M. Diaz and G. Wegner, Makromol. Chem., 1989, 190, 3105. 7 G. Zerbi, B. Chierichetti and O. Inganas, J. Phys. Chem., 1991, 94, 4646. 8 C. Roux, J. Y. Bergeron and M. Leclerc, Makromol. Chem., 1993, 194, 869. 9 Y. Wang and M. F. Rubner, Synth. Met., 1990, 39, 153. 10 J.L. Ciprelli, C. Clarisse and D. Delabouglise, Synth. Met., 1995, 74, 217. 11 M. T. Loponen, T. Taka, J. Laakso, K. Vakiparta, K. Sunronen, P. Valkeinen and J. E. Osterholm, Synth. Met., 1991, 41, 479. 12 M. C. Magnoni, M. C. Gallazzi and G. Zerbi, Acta Polym., 1996, 47, 228–233. 13 M. R. Andersson, Q. Pei, T. Hjertberg, O. Inganas, O. Wennerstrom and J. E. Osterholm, Synth. Met., 1993, 55, 1227. 14 T. Taka, Synth. Met., 1993, 57, 4985. 15 K. Yoshino, S. Morita, M. Uchida, K. Muro, T. Kawai and Y. Ohmori, Synth. Met., 1993, 55–57, 28. 16 G. Horowitz, A. Yassar and H. J. Von Bardeleben, Synth. Met., Scheme 1 The room temperature dedoping process of poly- 1994, 63, 245. alkylthiophene. 17 Q. Pei, O. Inganas, G. GustaVson, M. Granstrom, M. Anderson, T. Hjerberg, O. Wennerstorm, J.E. Osterholm, J. Laakso and H. Jarvinen, Synth. Met., 1993, 55–57, 1221. also reduce some FeCl4- to FeCl42- which react with H3O+ 18 M. S. A. Abdou and S. Holdcroft, Chem. Mater., 1994, 6, 962. to form HCl and stable Fe2+ complexes. The redox reaction 19 K. Yosghino, P. Love, M. Omoda and R. Sugimoto, Jpn. J. Appl. between water and the polymer backbone and the release of Phys., 1988, 27, 2388.HCl gas could be the rate determination steps. P3ATs with 20 K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato and shorter alkyl side chains form denser films and such films or K. Suzuki, Tetrahedron, 1982, 38, 3347. films with spherical morphology retard the release of HCl and 21 R. Sugimoto, S. Takeda, H. B. Gu and K. Yoshino, Chem. Express, 1986, 1, 635.the diVusion of water out of/in the polymer backbone, resulting 22 (a) R. D. McCullough and R. D. Lowe, J. Chem. Soc., Chem. in a lower dedoping rate. This mechanism also explains why Commun., 1992, 70; (b) R. D. McCullough, R. D. Lowe, at the start of dedoping, the concentration of FeCl4- remains M. Jayaraman and D. L. Anderson, J. Org. Chem., 1993, 58, 904. constant and the concentration of polarons increases. 23 (a) T.-A. Chen, X. Wu and R. D. Rieke, J. Am. Chem. Soc., 1995, 117, 233; (b) R. M. Souto, K. Hinkelmann, H. Eckert and F. Wudl, Macromolecules, 1990, 23, 1269. Conclusions 24 (a) S.-A. Chen and H. T. Lee, Macromolecules, 1993, 26, 3254; (b) G. B. Street, in Handbook of Conducting Polymers, ed. Dedoping of conducting polyalkylthiophene films at room T.A. Skotheim,Marcel Dekker, New York, 1986, vol. 1. p. 224. temperature occurred when the oxidized polymer was reduced 25 F. M. Smiths, Bell System Technical J., 1958, 710. by water. The dedoping rate depends on the polymer side 26 (a) M. S. A. Abdou and S. Holdcroft, Synth. Met., 1993, 60, 93; chain length, film morphology, structure regio-regularity, (b) H. Stubb, E.Punkka and J. Paloheimo, Mater. Sci. Process., dopant and light. During dedoping, some Fe3+ is reduced to 1993, 10, 119; (c) N. Colaneri, D. Nowak, D. Spiegel, S. Hotta and A. J. Heeger, Phys. Rev. B, 1987, 36, 7964. Fe2+ and at the same time HCl is produced. The dedoping 27 (a) H. L. Friedman, J. Am. Chem. Soc., 1952, 74, 5; process involved the conversion of bipolarons to polarons and (b) T.B. Swanson and V. W. Laurie, J. Phys. Chem., 1965, 69, 244. then to the neutral state. However, since polarons have a 28 Y. Cao, P.Wang and R. Qian, Macromol. Chem., 1985, 186, 1903. relatively low oxidation/reduction potential, (or may be 29 G. W. HeVner and D. S. Pearson, Synth. Met., 1991, 44, 341. trapped in defect sites), complete conversion to the original 30 S.Hotta, T. Hosaka, M. Soga and W. Shimotsuma, Synth. Met., neutral state may not occur at room temperature. 1984, 9, 87. 31 H. Neugebauer, G. Nauer, A. Neckel, G. Tourillon, F. Garnier and P. Lang, J. Phys. Chem., 1984, 88, 652. Acknowledgments 32 M. Boman and S. Stafstrom, Synth. Met., 1993, 55–57, 4614. 33 G. Horowitz, B. Bachet, A. Yassar, P. Lang, F. Demanaz, J. Fave This work was supported by the National Science Council of and F. Gariner, Chem.Mater., 1995, 7, 1337. the Republic of China via grant NSC-86-2113-M-008-005. 34 C. Wang, M. Benz, E. LeGoV, J. L. Schindler, T. J. Allbritton, C. R. Kannewurf and M. G. Kanatzidis, Chem. Mater., 1994, 6, 401. References 35 M. D. Curtis and M. D. McClain, Chem. Mater., 1996, 8, 936. 36 M. C. Magnoni, M. C. Gallazzi and G. Zerbi, Acta Polym., 1996, 1 S. X. Cai, J. F. W. Keana, J. C. Nabity and M. N. Wybourne, 47, 228. J. Mol. Electron., 1991, 7, 63. 37 M.-J. Chan and C.-G. Wu, manuscript in preparation. 2 M. S. A. Abdou and S. Holdcroft, Synth. Met., 1992, 52, 159. 38 M. G. Ramsey, D. Steinmuller and F. P. Netzer, Synth. Met., 3 W.-S. Huang, Polymer, 1993, 35, 4057. 1993, 54, 209. 4 (a) R. J. Jensen and J. H. Lai in Polymers for Electronic 39 (a) M. Deussen and H. Bassler, Synth. Met., 1993, 54, 49; Applications, ed. J. H. Lai, CRC Press, Boca Raton, FL, 1989, ch. (b) L. M. Tolbert, Acc. Chem. Res., 1992, 25, 561. 2; (b) J. R. Reynolds, J. Mol. Electron., 1986, 2, 1. 5 K. Yoshino, K. Nakao and R. Sugimoto, J. Appl. Phys., 1989, Paper 8/05462B 28, L490. J. Mater. Chem., 1998, 8, 2657–2661 2661

ISSN:0959-9428    

DOI:10.1039/a805462b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Poly[3,3¾-dialkyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene)]: electrically conducting and fluorescent polymers incorporating a rigid acetylenic spacer Siu-Choon Ng,*a Teng-Teng Onga and Hardy S. O. Chana,b aDepartment of Chemistry, National University of Singapore, Singapore 119260. †E-mail: chmngsc@leonis.nus.edu.sg bDepartment of Material Science, National University of Singapore, Singapore 119260 Received 27th July 1998, Accepted 2nd September 1998 A series of poly[3,3¾-dialkyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene)]s, comprising a rigid carbon–carbon triple bond between two bithiophene repeating units, were synthesized.The improved rigidity of the polymer backbone led to an increased fluorescent quantum yield in comparison to poly(3-alkylthiophene)s.A generic trend depicting decreasing Stokes shift in the fluorescence spectra with increasing pendant alkyl chain length was observed. The incorporation of the acetylenic spacer also resulted in a significant red shift in the absorption spectra in comparison to poly(3-alkylthiophene)s, corresponding to an increase in eVective conjugation over the entire series of polymers.These polymers, upon doping with iodine or ferric chloride, gave electrical conductivity in the range of 100 to 10-4 S cm-1. Thermochromism studies showed a blue shift in absorption peak as the temperature changes from 25 to 180 °C. The influence of alkyl chain length and the acetylenic spacer on the conductivity and UV–VIS absorption is also discussed.In situ electrochemical doping studies were monitored using UV–VIS–near infrared absorption spectroscopy and showed the evolution of polaron bands at around 1.4 eV. Poly(3-alkylthiophene)s remain attractive candidates for ophene) polymers. We report here our eVorts on the synthesis, characterization and properties of these materials. research studies on account of their good chemical stability, processability and high conductivity in the doped state.1–3 Recently, numerous reports on the light emitting properties of poly(3-alkylthiophene)s4–8 have aroused our interest in this burgeoning field of research.An ideal organic polymer light emitting diode (LED) should as a first requirement exhibit high fluorescence quantum yields, charge mobility, injection barriers and eVective p–conjugation.9–11 Whilst short chain oligomers are known to limit delocalization by diminishing the eVective conjugation, they are nevertheless more rigid, which can result in reducing relaxation from the excited states through non-radiative process with consequently enhanced S R S R R = C12H25 PEBT PDBEBT PDHEBT PDOEBT PDDEBT x R = H R = Bu R = C6H13 R = C8H17 fluorescence.12 Although numerous polythiophene derivatives with high fluorescent quantum yield (>50%)13 have been reported, there has been relatively little research into thio- Experimental phene-based polymers incorporating rigid acetylene spacers.14 In conjunction with our ongoing research on structure–prop- Synthesis of monomers erty correlation of functional and conducting polymers, we Monomer syntheses were carried out in accordance with the have synthesized a series of symmetrical 3,3¾-dialkyl-2,2¾- generic approach depicted in Scheme 1. 3-Alkylthiophenes II (ethyne-1,2-diyl )bis(thiophene) monomers which upon chemiwere synthesised from 3-bromothiophene I by a nickel cata- cal oxidative polymerization with FeCl3 aVorded polymers lysed Grignard cross-coupling approach.18 Bromination of II that exhibited both electrical conductivity and enhanced at the 2-position was eVected using 1 equiv.of N-bromosuc- fluorescence on comparison with polythiophenes. cinimide to aVord 2-bromo-3-alkylthiophene III in nearly The incorporation of the acetylenic spacers into the quantitative yield.19 Thereafter a one-pot reaction of III with polythiophene backbone is anticipated to oVer several distinct 2-methylbut-3-yn-2-ol in the presence of Pd(PPh3)4 as advantages.Thus, they can act as rigid conjugative spacers catalyst20 aVorded the symmetrical monomer IV. linking two bithiophene repeating units through the 2,2¾- positions on the same plane. The resulting polymer can be 2,2¾-( Ethyne-1,2-diyl )bis(thiophene) (EBT) expected to aVord a more planar conformation through diminished steric eVects so that a maximum degree of delocalization A mixture of 2-bromothiophene (2.05 g, 12.6 mmol), of the p-electrons is achieved.15 In addition, the rigid spacer 2-methylbut-3-yn-2-ol (1.06 g, 12.6 mmol), tetrakis(triphenylwhich helps to minimize neighboring ring interactions in this phosphine)palladium(0) (0.15 g, 0.333 mmol), benzyltriethylseries should result in a bathochromic shift in the UV–VIS ammonium bromide (0.099 g, 0.363 mmol) and cuprous iodide absorption maxima with correspondingly reduced bandgap (0.097 g, 0.509 mmol) in 10 ml of benzene was deareated with energy when compared to polythiophene or polyalkylthi- N2 for 15 min.Thereafter, aq. NaOH (5.5 M, 10 ml ) was ophene analogues.16,17 In regard to these favorable factors added.The resulting reaction mixture, which turned brown– which an acetylenic spacer oVers, we have successfully synthe- black, was heated at reflux under a nitrogen atmosphere for 18 h, whence a second portion of 2-bromothiophene (2.08 g, sized a series of 3,3¾-dialkyl-2,2¾-(ethyne-1,2-diyl )bis(thi- J. Mater. Chem., 1998, 8, 2663–2669 2663(24H, m), 0.86 (6H, t, J=7.0 Hz); m/z 414 (M+, 100%), 329 (20), 217 (55) (Found: C, 75.1; H, 8.7; S, 15.4.Calc. for C26H38S25C, 75.3; H, 9.2; S, 15.5%). 3,3¾-Didodecyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene) (DDEBT) 31% yield; dH(300 MHz, CDCl3), 7.18 (2H, d, J=5.0 Hz), 6.88 (2H, d, J=5.0 Hz), 2.74 (4H, t, J=7.5 Hz), 1.66–1.25 (40H, m), 0.87 (6H, t, J=7.5 Hz); m/z 526 (M+, 100%), 385 (20), 217 (50) (Found: C, 78.0; H, 10.3; S, 11.7.Calc. for C34H54S25C, 77.5; H, 10.3; S, 12.1%). Electrochemistry Polymer films were grafted onto a platinum or an indium tin S Br S R S R Br S R S R S R S R I II III IV V iv iii ii i x oxide (ITO) glass electrode via spin-coating using chloroform Scheme 1 Reagents and conditions: i, RMgBr, Et2O, Ni(dppp)Cl2 as solvent. Cyclic voltammetry of the polymers was conducted (cat.); ii, N-bromosuccinimide, chloroform, acetic acid, 30 min, 0 °C; in a three-electrode single compartment electrochemical cell iii, Pd(PPh3)4, 2-methylbut-3-yn-2-ol, benzene, reflux, 48 h; iv, FeCl3, consisting of platinum foil as the working electrode, a platinum CHCl3, 0°C.wire as the counter electrode and Ag/AgNO3 (0.1 M using dry acetonitrile as solvent) as the reference electrode (0.34 V vs.SCE). CVs of polymers were studied under argon atmos- 12.8 mmol) in benzene (10 ml ) was added into the reaction phere using tetra-n-butylammonium fluoroborate (0.1 M) as mixture. After heating at reflux for a further 16 h, the reaction electrolyte. mixture was allowed to cool, followed by addition of aq. NH4Cl (5.5 M, 50 ml ); it was then stirred for 3 h at room Chemical polymerization temperature.The crude product was extracted with benzene and purified by flash chromatography to aVord white needle General procedure. A solution of the monomer (0.1 M) in shaped crystals in 54% yield; mp 99 °C ( lit.,20 99.5–101 °C); dry chloroform was added dropwise into a reaction vessel dH(300 MHz, CDCl3) 7.30 (2H, dd, J2,4=1.1 Hz, J3,4= containing 4 equiv.of anhydrous ferric chloride at 0 °C for 5.1 Hz), 7.26 (2H, dd, J2,4=1.1 Hz, J3,4=3.6 Hz), 7.00 (2H, 1 h. Thereafter, polymerisation was terminated by adding an dd, J3,4=3.6, J2,3=5.1); m/z 190 (M+, 100%), 145 (50) excess amount of methanol. The resulting polymer was sub- (Found: C, 63.3; H, 3.4; S, 33.0. Calc. for C10H6S25C, 63.1; jected to Soxhlet extraction with methanol and then acetone H, 3.2; S, 33.6%).in turn for 24 h each. The resulting polymer was dedoped by stirring the polymer powder in hydrazine hydrate–water (151 3,3¾-Dibutyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene) (DBEBT) v/v) for 24 h to aVord a deep red polymer powder which was dried in vacuo. The dedoped polymer was further extracted Representative procedure.To a mixture of 2-methylbut-3-ynwith chloroform for 4 h to obtain the soluble portion (ca. 2-ol (4.20 g, 50 mmol), 2-bromo-3-butylthiophene (11.03 g, 10%) of the bulk polymer. The soluble portion was adopted 50 mmol), benzyltriethylammonium bromide (0.22 g, for characterisation studies such as solution UV–VIS, fluores- 1.02 mmol), cuprous iodide (0.22 g, 1.15 mmol) and tetrakis cence and nuclear magnetic resonance (NMR) spectroscopy (triphenylphosphine)palladium (1.50 g, 1.28 mmol) in benzene and gel permeation chromatography (GPC).(80 ml ) under a nitrogen atmosphere was added aq. sodium hydroxide (5.5 M, 80 ml ). The resulting black mixture was Chemical doping heated under reflux for 72 h whence a second portion of 2- bromo-3-butylthiophene (11.10 g, 50.0 mmol) in benzene Iodine doping of pressed pellets of dedoped polymers was (5 ml ) was added and heating continued for another 48 h.eVected by placing them in an iodine chamber for 1 week in Upon cooling, aq. ammonium chloride (100 ml ) was added the dark. The iodine uptake was monitored by progressive and the mixture stirred 3 h at room temperature. The organic weight gain and increasing electrical conductivity. Solution phase is separated whilst the aqueous phase is extracted with doping was eVected by stirring polymer powder (ca. 50 mg) in benzene (2×80 ml ). The combined organic phases were 0.1 M ferric chloride solution (ca. 50 ml ) in anhydrous nitrowashed with deionised water (3×100 ml ) and then dried methane under nitrogen for 1 h.Polymer pellets were observed (MgSO4), whereupon after removal of the solvent the crude to turn from deep red to deep green when doped. compound was obtained as a dark brown viscous liquid which was purified by vacuum distillation; [bp 168–170 °C Instrumentation (0.5 mmHg)] as a pale yellow liquid in 40% yield; dH(300 MHz, CDCl3) 7.18 (2H, d, J=5.1 Hz), 6.88 (2H, d, J=5.1 Hz), 2.75 Elemental analysis of all monomer and polymer samples was (4H, t, J=7.5 Hz), 1.69–1.32 (4H, m), 0.94 (6H, t, J=7.5 Hz); performed at the NUS Microanalytical Laboratory on a m/z 302 (M+, 100%), 217 (97), 273 (60) (Found: C, 71.2; H, Perkin-Elmer 240C elemental analyser for C, H, N and S 7.2; S, 21.2.Calc. for C18H22S25C, 71.5; H, 7.3; S, 21.2%). determination. Halogen determinations were done either by ion chromatography or the oxygen flask method. FT-IR 3,3¾-Dihexyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene) (DHEBT) spectra were recorded for monomer and polymer dispersed in KBr disks using a Perkin-Elmer 1600 spectrometer.UV–VIS 35% yield; bp 180–185 °C (0.2 mmHg); dH(300 MHz, CDCl3) spectra were obtained for dilute solutions or thin polymer 7.20 (2H, d, J=5.2 Hz), 6.88 (2H, d, J=5.2 Hz), 2.74 (4H, t, films deposited onto indium tin oxide coated glass plates on a J=7.4 Hz), 1.70–1.24 (12H, m), 0.87 (6H, t, J=7.4 Hz); m/z Perkin-Elmer Lamda 900 spectrophotometer. 1HNMR spectra 358 (M+, 100%), 301 (50), 217 (85) (Found: C, 73.8; H, 8.1; were recorded on a Bruker ACF 300 FT-NMR spectrometer S, 18.4. Calc. for C22H30S25C, 73.7; H, 8.3; S, 17.8%). operating at 300 MHz, while 13C NMR spectra were recorded at 62.9 MHz.Deuterated solvents were used as indicated and 3,3¾-Dioctyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene) (DOEBT) tetramethylsilane (TMS) was used as the internal reference. Mass spectra were obtained using a Micromass VG 7035E 40% yield; dH(300 MHz, CDCl3), 7.19 (2H, d, J=5.6 Hz), 6.89 (2H, d, J=5.6 Hz), 2.73 (4H, t, J=2.7 Hz), 1.67–1.25 mass spectrometer at a source temperature of 200 °C and an 2664 J.Mater. Chem., 1998, 8, 2663–2669ionising voltage of 70 eV. Thermogravimetric analyses (TGA) of polymer powders were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric analyser. A heating rate of 10 °Cmin-1 with an air flow of 75 ml min-1 was used. The runs were conducted from room temperature to 800 °C.Conductivity measurements were carried out on polymer pellets of known thickness using a fourpoint probe connected to a Keithley constant current source. Conductivities were calculated from at least 10 pairs of consistent readings taken at diVerent points of the pressed pellet. Fluorescence measurements were conducted on a Shimadzu RF5000 spectrofluorophotometer using a xenon lamp as the light source.Standard polymer solutions dissolved in dry chloroform (10-5 M) were used for analysis and Coumarin (Aldrich) was used as the calibration standard. In situ electrochemical doping studies of polymers were carried out using an EG&G 263A potentiostat together with UV–VIS–near infrared spectrophotometer.GPC analyses were carried out using a Perkin-Elmer Model 200 HPLC system with PhenogelTM MXL and MXM columns (300 mm×4.6 mm ID) calibrated using polystyrene standards and THF as eluent. Results and discussion Physical properties and structural characterization Elemental composition of the neutral polymers as determined from microanalyses showed good agreement between the expected and calculated empirical formulae, with low iron and chloride contents (Table 1).Table 1 also summarizes the number average molecular weights (Mn) for the dedoped polymers as determined via GPC. These polymers have a polydispersity index (PDI) ranging from 1.3 to 1.8 and Mn values in the range 5400 to 6800, corresponding to the existence of 10–18 monomeric repeat units. As the molecular weights obtained from the soluble portion of the bulk polymers possibly represent only the lower molecular weight fractions, Fig. 1 FTIR of 3,3¾-dibutyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene) and the insoluble fractions are expected to have higher molecular its corresponding polymer, PDBEBT: (a) monomer, (b) dedoped weights.21 This series of polymers was found to be partially PDBEBT and (c) I2 doped PDBEBT.soluble (ca. 10%) in common organic solvents like chloroform, THF, DMF and DMSO. Purification of these polymers was carried out by first dissolving the polymer in solvent followed CH2 groups. A weak rocking bend due to CH2 group at 718 cm-1 is also observed. The COC group manifests as a by precipitation from cold methanol. Although the soluble portion of these polymers only represents the lower molecular very low intensity stretching band at 2196 cm-1.The thiophene ring depicts C–H stretching at 3101 cm-1 and C–H in-plane weight fractions, uniform solid thin films could be grafted onto ITO glass plates easily from chloroform solution and deformation at 1085 and 1237 cm-1, whilst ring vibrational modes are seen at 1377, 1460, 1517 and 1598 cm-1.The used for UV–VIS absorption, cyclic voltammetry, fluorescence spectroscopy and electrochemical doping studies. Currently, monomer also depict vibrational bands at 721 and 837 cm-1 which are ascribable respectively to the C–Ha and C–Hb out- we are investigating ways of deriving a suitable polymerization route so as to synthesize higher molecular weight polymers of-plane bending modes of the thiophene rings.22 In contrast, neutral PDBEBT shows a strong b-CH out-of-plane bend at that have good solubility in common organic solvents.The chemical structure of the monomers and bulk polymers 826 cm-1, whilst the a-CH out-of-plane bend is relatively insignificant, suggesting that predominant a–a¾ coupling of the were studied in detail using FT-IR spectroscopy.The FT-IR spectra of the representative 3,3¾-dibutyl-2,2¾-(ethyne-1,2-diyl )- thiophene ring is inherent in this polymer. Thiophene ring stretches at 1376, 1429, 1528, 1654 and 1718 cm-1 remain bis(thiophene) and its corresponding polymer PDBEBT both in its neutral and doped forms are shown in Fig. 1. The unchanged with respect to the monomer. The presence of two intense bands at 2852 and 2920 cm-1 suggests that the alkyl presence of the butyl pendants in the monomer is evident from C–H stretching at ca. 2850 and 2950 cm-1 due to CH3 and chain remains intact after polymerization. A weak stretching Table 1 Physical properties of polymers PEBT, PDBEBT, PDHEBT, PDOEBT, PDDEBT including GPC, elemental analysis and conductivity results GPC results Elemental analysis Conductivity Polymer Pn PDI Mn (I2 doped)/S cm-1 Empirical formula Found PEBT 8 1.5 1523 1.5 C10.0H4.0S2.0 C10H4.1S2.0 PDBEBT 18 1.8 5500 0.03 C18.0H20.0S2.0 C18.0H20.4S2.1 PDHEBT 18 1.4 6500 0.002 C22.0H28.0S2.0 C22.0H27.9S2.1 PDOEBT 17 1.3 6900 0.001 C26.0H36.0S2.0 C26.0H36.5S2.1 PDDEBT 11 1.3 5400 0.0002 C34.0H52.0S2.0 C34.0H51.3S2.0 J.Mater. Chem., 1998, 8, 2663–2669 2665attributed to the COC group is also observed at 2210 cm-1.reference solutions and Ir and Is are the corresponding relative integrated fluorescence intensities. Table 2 summarises the The FT-IR spectrum of iodine-doped PDBEBT exhibits dramatic changes in the 1035 to 1438 cm-1 region. Here the IR electronic absorption and emission maxima and the respective polymer fluorescent quantum yields relative to Coumarin 334 bands are intensified and overlap to constitute a broad band.This broad band is assigned to doping-induced bands attri- laser dye. There is generally little diVerence in the UV absorption maximum between the parent polymer PEBT and the buted to the vibrational modes in the anion-doped (charged transferred) thiophene rings.23 The low intensity broad band alkyl-substituted polymers in their solutions UV–VIS spectra.All polymer solutions depicted absorption maxima at ca. at 3000 to 3800 cm-1 is characterized as weakly bonded O–H stretching due to absorbed moisture from the atmosphere. 476 nm, which is red-shifted in comparison to that of polythiophene at 450 nm.27 This observation is consistent with enhanced ring conjugation in the polymers attributed to Conductivity of doped polymers reduced steric eVects imposed by alkyl pendants with the The dedoped polymers upon doping with iodine or ferric introduction of an acetylenic spacer between the thiophene chloride yielded electrical conductivity ranging from 100 to rings.This assumption also correlates well with our experimen- 10-4 S cm-1.The graphical representation of the variation of tal data whereby the UV–VIS absorption of PEBT and the conductivity with iodine uptake for the typical polymer PEBT alkyl-substituted polymers remain fairly unchanged. is shown in Fig. 2. As summarised in Table 1, the conductivity When the alkyl-substituted polymers PDBEBT, PDHEBT, of the unsubstituted polymer PEBT is highest followed by a PDOEBT and PDDEBT are spin-coated on ITO glass from trend of diminishing conductivity with increasing pendant chloroform solutions to aVord thin polymer films, a red shift alkyl chain length on going from PDBEBT to PDHEBT, of only 20–60 nm with respect to the polymer solution resulted.PDOEBT and PDDEBT. These results are consistent with This bathochromic shift is somewhat less than that observed earlier reports by Kaeriyama et al.24 in their study of polyalkyl- for poly(3-alkylthiophene)s at between 60–100 nm28 on going thiophene.It is observed experimentally that with increasing from the solution to the condensed phase, suggesting that the alkyl chain length, the rate of iodine uptake reflected from acetylene spacer has imparted a significant amount of rigidity percentage weight change also decreases.This phenomenon is to the polymer backbone. The electrochemically synthesized attributed to the increasing size of the alkyl group, which unsubstituted polymer PEBT, on the other hand, is obtained takes up more of the weight of the polymer, therefore the as a deep red–violet film with an absorption maximum at amount of iodine absorbed is correspondingly smaller.The 519 nm, which is red-shifted from the 496 nm of rate of iodine uptake was found to be progressively slower polybithiophene.29 from PDBEBT to PDDEBT, although the doping period (4 The band gap energies of these polymers (Table 2) can be days) was kept consistent for all samples, implying that the deduced from the energy absorption edge of the UV–VIS doping eYciency was diminished.Elemental analysis of iodine- spectrum according to the approach of Johnson et al.30 A doped polymers showed that the concentration of I3- dopant reduced band gap energy of 1.7–1.9 eV is observed in this also decreased on going from PDBEBT to PFHEBT, PDOEBT series of polymers in comparison to polythiophene (2.1 eV).31 and PDDEBT. This reduction in rate of doping is largely Although PDBET (535 nm, 1.7 eV) depicted enhanced ring assigned to significant steric hindrance towards the dopant conjugation compared to PEBT (519 nm, 1.8 eV), the longer molecules, which inhibits charge carrier formation during the alkyl chain polymers PDHEBT, PDOEBT and PDDEBT on doping process.25 the contrary do not exhibit significant red shifts with respect to PEBT.Electronic (UV–VIS) and fluorescence spectroscopy The fluorescence excitation/emission studies of these polymers from PEBT to PDDEBT showed a green emission Standard polymer solutions of 10-5 M concentration in in chloroform solution (10-4 M) when the polymers were chloroform were used for UV–VIS and fluorescence spectroexposed to ultraviolet radiation. These polymers gave an scopic measurements.Fluorescence measurements were comemission peak between 540 and 573 nm with an accompanying pared with Coumarin 334 laser dye (Aldrich) which absorbs decreasing Stokes shift as the chain length of the alkyl substitu- at 450 nm and emits at 490 nm. The calculation of fluorescence ent increases. The progressively smaller Stokes shift from quantum yield of a solution sample (Ws) relative to a reference PEBT to PDDBET implies that the polymer backbone sample of known quantum yield (Wr) is related to eqn.(1),26 becomes more rigid32,33 as the alkyl chain length is increased. Ws=Wr [(Ar/As)×(Is/Ir)] (1) The increasing rigidity of these polymers must have contributed to the increase in overall fluorescent quantum yield by reducing where As and Ar are the absorbencies of the sample and the extent of non-radiative losses.As the Stokes shift diminishes, the quantum yield becomes progressively higher in the order PEBT<PDBEBT<PDHEBT but decreases again in going to PDDEBT. From the Mn values presented in Table 1, whilst the polymer chains of PDBEBT, PDHEBT and PDOEBT contain a fairly consistent number of monomeric repeat units (17–18) in their soluble fractions, PDDEBT has a significantly smaller degree of polymerisation (DPn) with only 11 repeat units.Previously, it has been shown with thiophene oligomers that a trend of diminishing fluorescent quantum yields can be correlated with a reduced number of conjugated repeat units in the oligomers.34 Consequently, arising from this, PDDEBT has a reduced fluorescence quantum yield even though its Stokes shift is the smallest among this series of polymer.Thermochromism eVects The temperature dependency in the optical absorption spectra Fig. 2 Conductivity plot of PEBT against uptake of iodine (wt%). of alkyl substituted polymers PDBEBT to PDDEBT were 2666 J. Mater. Chem., 1998, 8, 2663–2669Table 2 UV–VIS absorption and fluorescence emission data and band gap of various polymers in chloroform solution at 25 °C lmax/nm Fluorescence/nm Quantum Stokes Band Polymer Solution Film Excitation Emission yield shift gapa/eV PEBT 476 519 476 573 22 97 1.8 PDBEBT 475 535 478 568 27 90 1.7 PDHEBT 470 491 470 549 39 79 1.9 PDOEBT 475 492 475 550 37 75 1.9 PDDEBT 471 493 470 540 29 70 1.9 aBand gap is derived from UV–VIS spectrum of polymer film coated on ITO glass.studied. Solid polymer samples spin-coated from chloroform twisting of the polymer chain, reducing the extent of interring conjugation. However, the extent of twisting and conse- solution onto ITO-coated glass were used in these studies. These polymers undergo a colour change from red to orange quently the magnitude of blue shift is significantly reduced in comparison to poly(alkylthiophene)s,36 due to the eVect of upon heating. This is accompanied by a blue shift in the absorption maxima from 535 to 466 (PDBEBT), 491 to 452 the spacer unit on the polymer chain, which helps diminish the repulsive intrachain steric interactions exerted by the alkyl (PDHEBT), 493 to 458 (PDOEBT) and 493 to 468 nm (PDDEBT).It is diYcult to identify any intermediate phases pendant groups. Moreover, experimental fluorescence spectroscopy results also show decreasing Stokes shift values in formed in this series as no clear isosbestic point is observed in the UV–VIS spectra (Fig. 3).35 Only a gradual blue shift is the same order. This corroborates the assumption that substitution with longer alkyl pendants aVords polymers with a observed in these polymers upon heating, which is indicative of a decrease in conjugation. The magnitude of the blue shift more rigid structure.This thermochromic behaviour is fully reversible, regaining the initial absorption state upon cooling. diminishes with increasing chain length of the pendant alkyl group, with PDDEBT<PDOEBT<PDHEBT<PDBEBT.Electrochemistry The blue shift is ascribed to heat-induced disorder in the side chain leading to accentuated steric interaction and concomitant The cyclic voltammograms of various polymers are shown in Fig. 4. The electrochemical oxidation of PEBT is compared with polythiophene (PT) and polybithiophene (PBT). A generally lower monomer oxidation potential (1.43 V) in comparison to PT (1.65 V)38 is required for generation of PEBT when a current density of 1 mA cm-2 is used.PEBT is highly electroactive showing excellent reversibility of its p-doping redox states when subjected to repeated electrochemical cycling between -1.0 to 0.9 V (vs. SCE). The p-doped polymer PEBT has a deep green colour which turned red–brown upon electrochemical dedoping.The polymer oxidation potential of PEBT is comparable to polybithophene (1.0 V)37 but is significantly lower than pristine polythiophene (1.3 V).38 The eVect of lowering the oxidation potential is advantageous as this would prevent over-oxidation of the polymer film when a high oxidising (positive) potential was applied. The film formation process for alkyl-substituted polymers is diYcult to achieve as these polymers are slightly soluble in acetonitrile. Therefore electrochemical analysis of these polymers was conducted on chemically polymerized samples which were spin-coated onto platinium electrodes. The p-doping of PDBEBT, PDHEBT, PDOEBT and PDDEBT was observed to be stable, with clearly defined anodic and cathodic peaks.When these polymers were scanned repeatedly using cyclic voltammetry, no significant overoxidation or degradation of the polymer films was observed.The ratio of polymer oxidation potential (Epa) to reduction potential (Epc) showed a slight deviation from unity, suggesting that the doping/dedoping process of these polymers is not absolutely reversible. On varying the scan rates from 20 to 80 mV s-1, the peak current densities of these polymers were observed to scale linearly with increasing scan rates, implying that the doping/undoping processes are non-diVusion controlled reactions.39 The Epa values of alkyl-substituted polymers were found to increase with increasing alkyl chain length, whilst the corresponding Epc values shifted towards lower potential.This phenomenon was also observed by Tanaka et al.24 and Yamabe et al.40 in poly(3-alkylthiophene)s.Our findings indicate that the electron donating eVect attributed to the butyl groups in PDBEBT (Epa=0.92 V) leads to a lowering of Epa compared to PEBT (Epa=0.94 V) and PBT (Epa=1.01 V),37 as well as Fig. 3 Variation of absorption maxima in UV–VIS spectra of PT (Epa=1.30 V).38 In PDHEBT, PDOEBT and PDDEBT (a) PDBEBT and (b) PDOEBT upon heating in solid state from 25 to 180 °C.on the other hand, the Epa values shows a gradual increase J. Mater. Chem., 1998, 8, 2663–2669 2667Fig. 5 In situ electrochemical doping studies of various polymers: (a) PDBBT, (b) PDHEBT, (c) PDOEBT and (d) PDDEBT. infrared region. The position of this polaron band occurs at 880, 860, 840 and 840 nm for PEBT, PDHEBT, PDOEBT and PDDEBT, respectively, which correspond to about 1.4 eV.Therefore when polymers are in lightly doped states within the potential range 0.0 to 1.0 V, two electronic bands corresponding to the p–p* interband transition as well as the polaron band were observed. When the extent of doping was increased through applying a potential greater than 1.25 V, the polaron band continued to grow in intensity whilst the p–p* band diminished in intensity until a negative deviation formed.The polymer film appears to be deep blue in this heavily doped state. The calculated electrochemical bandgaps of these polymers were determined from the position where the isosbestic point occurs in the optical spectrum obtained during in situ electrochemical doping studies.It has been mentioned by several Fig. 4 Cyclic voltammograms of various polymers at scan rate of 20 mV s-1: (a) PEBT, (b) PDBEBT, (c)PDHEBT, (d) PDOEBT and authors41 that the relative electrochemical band gap energy (d)PDDEBT. can be estimated from the position of the isosbestic point in the optical spectrum using eqn. (2), with reference to PEBT.The electro-oxidation process involves E (eV )=hn=hc/l=1240/l (nm) (2) the removal of one electron from the neutral polymer and the resulting polymer aquires a single positive charge on the sulfur where h is Plank’s constant, l is wavelength in nm and c is the speed of light, and E denotes the band gap energy of the heteroatom. This positively charged species is stabilised electrochemically in the presence of solvated counter anions.It was polymer. From Table 3, the evaluated electrochemical band gap energies of PDBEBT, PDHEBT, PDOEBT and PDDEBT anticipated that with increasing alkyl chain length, the bulky alkyl group is likely to slow down the rate of mobility of are found to be 1.8, 1.9, 1.9 and 1.9 eV, respectively. These readings correlate well with the experimentally determined counter anions into and out of the polymer surface, thus resulting in higher oxidation potential.optical band gap energies. In summary, the polymer oxidation potentials for this series of polymers lie between 0.92 to 1.30 V, which is comparatively Thermal stability of neutral and doped polymers lower than the oxidation potential of polythiophene.Reductive The thermal properties of polymers in both their neutral and n-doping studies of these polymers were also examined in the doped states were studied in air over a temperature range of potential range 0 to -2.5 V vs. SCE. However, no significant 25 to 800 °C. The neutral polymer, PEBT, depicted a single n-doping peaks were observed. weight-loss step in the temperature range 300 to 500 °C, corresponding to the thermal oxidative degradation of the In situ electrochemical doping studies of polymers polymer backbone.All the alkyl-substituted polymers PDBEBT to PDDEBT depicted a two-step weight loss. The The UV–VIS-near infrared absorption shifts of doped polymers during electrochemical doping are depicted in Fig. 5. first step occurring in the temperature range 220 to 370 °C, corresponded to cleavage of the alkyl chain.42 The next weight Usually, a low potential of 0.0 V vs.SCE was applied to first obtain an undoped polymer spectrum. At this potential, only loss step, which took place in the temperature range 370 to 800 °C, was attributed to the degradation of the polymer one main potential corresponding to the p–p* interband transition is observed at 526, 495, 493 and 494 nm for chain.In most cases, a small residue content of less than 5% was left behind. PDBEBT, PDHEBT, PDOEBT and PDDEBT, respectively. As the applied potential was gradually increased from 0.00 to The iodine-doped polymers depict diVerent TGA spectra to those of the undoped polymers. The first step, occuring at 100 0.95 V, the intensity of the p–p* interband transition decreased slightly with evolution of a new polaronic band in the near to 200 °C, is attributed to the expulsion of molecular iodine 2668 J.Mater. Chem., 1998, 8, 2663–26699 M. Sato, S. Tanaka and S. Kaeriyama, Makromol. Chem., 1987, from the polymer surface. The second weight-loss step, from 188, 176. 200 to 800 °C, due to degradation of polymer chain adopts a 10 T.J. Kang, J. Y. Kim, C. Lee and S. B. Rhee, Synth. Met., 1995, gradual weight loss pattern. The thermal dedoping process 69, 377. occurring in the temperature range 100 to 200 °C in doped 11 M. Feldhues, G. Kampf, H. Litterer, T. Mecklenburg and PDBEBT was closely monitored using FT-IR spectroscopy. P. Wegener, Synth. Met., 1989, 28, C487. 12 M. T.Vala and J. Haebig, J. Chem. Phys., 1965, 43, 886. These results showed decreasing intensity of the doped induced 13 J. K. Tai, Y. K. Jae, J. K. Kyung, J. L. Chang and B. R. Suh, bands from 1054 to 1458 cm-1 as the dopant is expelled at Synth. Met., 1995, 69, 377. temperatures ranging from 50 to 250 °C. Thus, application of 14 S. C. Ng, S. O. Chan, H. H. Huang, T. T. Ong, A. Sarkar, heat can lead to the recovery of the dedoped polymer.K. Kumura, Y. Mazaki and K. Kobayashi, J. Mater. Sci. Lett., 1996, 15, 1684. 15 H. Hotta, T. Hosaka and W. Shimotsuma, J. Chem. Phys., 1984, 80, 954. Conclusion 16 A. Bolognesi, C. Botta, Z. Geng, C. Flores and L. Denti, Synth. A series of conducting polymers having a rigid backbone Met., 1995, 71, 2191. 17 X. C. Li, F. Cacialli, M.Grumer, R. H. Friend, A. B. Holmes and through incorporation of an acetylenic spacer, poly[3,3¾- S. C. Yong, Adv. Mater., 1995, 7, 898. dialkyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene)], was synthesized 18 M. K. Richard, A. P. Schaap, E. T. Harper and H. Wynberg, via FeCl3 chemical oxidative polymerization of the respective J. Org. Chem., 1968, 33, 2902. monomers. Polymerization occurred predominantly a–a¾, with 19 R.L. Elsenbaumer, K. Y. Jen and R. Oboodi, Synth. Met., 1986, the doped polymers displaying electrical conductivity in the 15, 169. 20 C. Adriano, A. Lessi and R. Rossi, Synthesis, 1994, C571. range of 10-4 to 10-2 S cm-1. A trend of decreasing Stokes 21 I. Catellani, S. Luzzati and F. Speroni, Synth. Met., 1993, 55, shift in the fluorescence spectra as the alkyl chain length 1188.increases indicates an improvement of rigidity of the polymer 22 S. Hasoon, M. Galtier and L. Sauvajol, Synth. Met., 1989, 28, backbone, which helps to enhance the fluorescence quantum C317. yield. A green emission at 500–570 nm was observed in this 23 Y. Cao, D. Guo, M. Pang and R. Qian, Synth. Met., 1987, 18, 189. series of polymers. The eVective conjugation in these polymers 24 S.Kaeriyama, M. Sato and S. Tanaka, Synth. Met., 1987, 18, 233. 25 M. R. Anderson, Q. Pei, T. Hjertherg, O. Inganas, was red-shifted as compared to polythiophene. This suggested O. Wennwestrom and J. E. Osterholm, Synth. Met., 1993, 55, a smaller twist angle between the neighbouring rings in 1227. poly[3,3¾-dialkyl-2,2¾-(ethyne-1,2-diyl )bis(thiophene)]s com- 26 A.P. Davey, E. Simon, O. Orla and B. Werner, J. Chem. Soc., pared to pristine polythiophene. Due to the enhanced rigidity Chem. Commun., 1995, 1433. and coplanarity of these polymers, thermochromic studies 27 J. Roncali, Chem. Rev., 1992, 92, 711. 28 O. Inganas, W. R. Salaneck, J. E. Osterholm and J. Laakso, Synth. reveals that the extent of blue shift depicted in their UV–VIS Met., 1988, 22, 395.spectra was much less than poly(3-alkylthiophene)s when they 29 R. Claudine and L. Mario, Chem. Mater., 1994, 6, 620. were heated from 25 to 200 °C. These polymers displayed 30 E. G. Johnson, R. Willardson and A. C. Beer, in Semiconductors thermal dedoping behaviour at temperatures ranging from 100 and Semimetals, Academic Press, New York, 1967, vol. 3, p. 153. to 250 °C due to explusion of dopants from the surface of the 31 K. Iwasaki, H. Fujimoto and S. Matsuzaki, Synth. Met., 1994, bulk polymer. Degradation of the polymer chain in air showed 63, 101. 32 S. Heun, H. Bassler, U. Muller and K. Mullen, J. Phys. Chem., an onset at 220 °C, the polymer being completely degraded 1994, 98, 7355. at 600 °C. 33 M. Leclerc, C. Roux and J. Y. Bergeron, Synth. Met., 1993, 55, 287. 34 W. R. Salaneck, O. Inganas, B. Thenmans, J. O. Nilsson, We thank the National University of Singapore for financial B. Sjogren, J. E. Osterholm and S. Stevensson, J. Chem. Phys., support through the research grant RP960613. T. T. Ong is 1988, 89, 4613. grateful to NUS for the award of a research scholarship as 35 T. Kohji, O. Keiko, M. Yasuhisa and M. Kobayashi, J. Polym. well as to ICI for scholarship top-up funding. Sci., Part B: Polym. Phys., 1991, 29, 1223. 36 C. Roux, J. Y. Bergeron and M. Leclerc, Makromol. Chem., 1993, 194, 669. 37 T. Yamamoto, K. Sanachika and A. Yamamoto, Bull. Chem. Soc. References Jpn., 1983, 56, 1497. 1 M. A. Sato, T. Shimizu and A. Yamauchi, Synth. Met., 1991, 38 S. O. Chan, S. C. Ng, S. H. Seow and J. G. Marc, J. Mater. Chem., 1992, 2, 1135. 41, 551. 39 E. Genies, G. Bidan and A. F. Diaz, J. Electroanal. Chem., 1983, 2 T. Kawai and M. Nakazono, J. Mater. Chem., 1992, 2, 903. 149, 113. 3 T. A. Chen and R. D. Rieke, Synth. Met., 1993, 60, 175. 40 S. Wang, H. Takahashi, K. Yoshino, K. Tanaka and T. Yamabe, 4 S. A. Chen and C. S. Liao, Synth. Met., 1993, 55, 4930. Jpn. J. Appl. Phys., 1990, 29, 772. 5 Y. Ohmori, M. Uchida and K. Yoshino, Jpn. Appl. Phys., 1991, 41 M. Onoda, T. Iwasa, Y. Kawai and K. Yoshino, J. Phys. D: Appl. 10, 1938. Phys., 1991, 24, 2076. 6 H. Fujimoto, K. I. Iwasaki and S. Matsuzaki, Synth. Met., 1994, 42 B. Themans, W. R. Salaneck and J. L. Bredas, Synth. Met., 1989, 69, 99. 28, C359. 7 D. A. Santo, C. Quattrochi, R. H. Friend and J. L. Bredas, J. Chem. Phys., 1994, 100, 3301. 8 J. Mouton and P. Smith, Polymer., 1992, 33, 4611. Paper 8/05840G J. Mater. Chem., 1998, 8, 2663–2669 2669

ISSN:0959-9428    

DOI:10.1039/a805840g

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Photochromic reaction in a molecular glass as a novel host matrix: the 4-dimethylaminoazobenzene–4,4¾,4-tris[3- methylphenyl(phenyl )amino]triphenylamine system Kazuyuki Moriwaki, Mitsushi Kusumoto, Keiichi Akamatsu, Hideyuki Nakano and Yasuhiko Shirota* Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565–0871, Japan.E-mail: shirota@ap.chem.eng.osaka-u.ac.jp Received 22nd July 1998, Accepted 16th September 1998 For the purposes of clarifying the properties of a molecular glass as a novel host matrix and gaining information on the microstructure of the molecular glass, the photochromic behavior of 4-dimethylaminoazobenzene (DAAB) in a novel molecular glass of 4,4¾,4-tris[3-methylphenyl(phenyl )amino]triphenylamine (m-MTDATA) was investigated, and compared with its behavior in a polystyrene glass matrix and a benzene solution. It was found that the fraction of the photoisomerized cis-isomer of DAAB at the photostationary state is smaller in the m-MTDATA glass matrix than in the polystyrene matrix and the benzene solution, and that the apparent initial rate constant for the backward cisAtrans thermal isomerization of DAAB is much larger in the m-MTDATA glass than in the polystyrene matrix and the benzene solution. These results suggest that the average size of local free volume in the molecular glass of m-MTDATA is smaller than that in the polystyrene glass.Amorphous glasses serve as excellent host matrices because of matrices in comparison with those of amorphous polymers.their excellent film formation, transparency, isotropic proper- In addition, studies of photochromic reactions in the molecular ties, and homogeneous properties owing to the absence of glass are expected to provide information on the microstructure grain boundaries. Inorganic sol-gel glasses have been widely of the molecular glass as the host matrix. used as host matrices, embedding a variety of functional In the present study, we have investigated photochromic materials.Organic polymers have also been widely used as reactions in a molecular glass of 4,4¾,4-tris[3-methylphematrices for embedding functional materials. For example, nyl(phenyl )amino]triphenylamine (m-MTDATA) in order to molecularly-doped polymer systems where photoconducting elucidate the properties of the molecular glass as a novel host materials are dispersed in an amorphous polymer such as matrix and to gain information on the microstructure of the polycarbonate have been put to practical use as photoreceptors molecular glass.An azobenzene derivative was chosen as a in electrophotography. Photochromic reactions of low molecu- photochromic compound because azobenzenes have been most lar-weight organic compounds dispersed in a polymer matrix extensively studied.Since the m-MTDATA film shows an have also been studied extensively, and microenvironmental electronic absorption band in the near UV region, we selected eVects on photochromic reactions have been discussed in terms 4-dimethylaminoazobenzene (DAAB) as a photochromic of their molecular motions associated with glass transition and probe compound, which shows an absorption spectral change the free volume of host polymer matrices.1–11 due to trans<cis isomerization in the visible region.The In contrast to polymers, low molecular-weight organic photoisomerization behavior and the kinetics for the backward compounds tend to crystallize readily.We have been making cisAtrans thermal isomerization of DAAB in the molecular studies of the creation of low molecular-weight organic com- glass of m-MTDATA are investigated in the temperature pounds that readily form stable amorphous glasses above region below and above the Tg. The results are discussed in room temperature, which we refer to as ‘amorphous molecular comparison with those in a polystyrene matrix and a benzene materials’ or ‘molecular glasses’, considering the following solution.Preliminary results have been reported as a aspects. Amorphous molecular materials are expected to con- communication.37 stitute a novel family of organic functional materials that exhibit glass-transition phenomena usually associated with Experimental polymers.Creating such amorphous molecular materials is of interest and significance not only for technological applications Materials but also from a scientific viewpoint, opening up a new field of organic materials science that deals with ‘molecular glasses’. m-MTDATA was prepared according to the method described We have created several novel families of molecular glasses in our previous paper.12 trans-DAAB was obtained commerwith relatively high glass-transition temperatures (Tgs), which cially (Tokyo Chemical Industry, Co., Ltd.) and purified by include 4,4¾,4-tris(diphenylamino)triphenylamine (TDATA) sublimation (at ca. 80 °C and at 0.15 mmHg). Polystyrene was and its derivatives,12–16 substituted 1,3,5-tris(diphenylamino)- commercially available (Wako Pure Chem.Ind., Ltd.) and benzenes (TDABs),17–24 4,4¾,4-tris(diphenylamino)triphenyl- purified by repeated reprecipitation from benzene into benzene (TDAPB) and its derivatives,25 and others.26–31 They methanol (Mw=1.9×105, Mw/Mn=1.7). readily form uniform amorphous films by vacuum deposition, spin coating or solvent casting and have found successful Preparation of glass samples for DSC measurement application as materials for organic electroluminescent Glass samples for the determination of Tg by diVerential devices.14–16,32–36 Like polymers, molecular glasses are also scanning calorimetry (DSC) were prepared as follows.expected to function as novel host matrices for embedding Appropriate amounts of m-MTDATA and trans-DAAB with functional materials such as photochromic materials.It is of interest to elucidate the properties of molecular glasses as host molar ratios of m-MTDATA5DAAB=351, 551, 1051 and J. Mater. Chem., 1998, 8, 2671–2676 2671Fig. 1 DSC curve of a glass obtained by cooling the melt of a mixture of m-MTDATA and DAAB with a molar ratio of m- MTDATA5DAAB=351. Results and discussion Glass formation of DAAB—m-MTDATA mixtures It was found that the mixtures of varying amounts of m-MTDATA and DAAB form homogeneous, amorphous glasses, as confirmed by DSC, X-ray diVraction, and polarizing microscopy.Fig. 1 shows a DSC curve of a glass obtained by cooling the melt of the mixture of a molar ratio of m- MTDATA5trans-DAAB=351. When the sample was heated, a glass-transition phenomenon was observed at 60 °C, which was 15 °C lower than the Tg of m-MTDATA itself.The result that only one glass-transition phenomenon was observed suggests that the DAAB molecules are homogeneously dispersed in the m-MTDATA glass matrix. On further heating, an N N N N H3C CH3 CH3 N N N H3C H3C N N N H3C H3C m-MTDATA trans-DAAB cis-DAAB hn D exothermic peak due to crystallization of both m-MTDATA and DAAB was observed at ca. 129 °C, followed by a broad endothermic peak due to melting at around 193 °C. The Xray diVraction (XRD) pattern of a glass with a molar ratio 10051, were placed in a glass sample tube, and then the tube of m-MTDATA5trans-DAAB=351 is shown in Fig. 2. No was sealed oV. After the sample melted on heating in the appreciable diVerence in the XRD pattern was observed among sample tube, it was allowed to cool to room temperature to the glasses with varying molar ratios of m-MTDATA and give a homogeneous glass of m-MTDATA containing DAAB.DAAB. Table 1 lists the Tgs of the glasses of the mixtures of Photochromic reaction in amorphous films Amorphous films of m-MTDATA containing trans-DAAB were prepared on a transparent glass substrate by spin coating from a benzene solution containing appropriate amounts of m-MTDATA and DAAB.The film was dried overnight under reduced pressure before use. The resulting film was confirmed to be amorphous by X-ray diVraction and polarizing microscopy. Polystyrene films containing DAAB were also prepared by spin coating from a benzene solution. Photoisomerization of DAAB in the amorphous films of m-MTDATA and polystyrene was carried out by irradiation Fig. 2 X-Ray diVraction pattern of a glass obtained by cooling the with 400 nm light with a bandwidth of 10 nm from a 500 W melt of a mixture of m-MTDATA and DAAB with a molar ratio of Xenon lamp (UXL-500D, USHIO) through an interference m-MTDATA5DAAB=351. filter (IF-S 400, Vacuum Optics Co.) and an optical fiber.Photochromic reactions were analyzed from the change in the Table 1 Glass-transition temperatures (Tgs) of the glasses of mixtures electronic absorption spectra. of m-MTDATA and DAAB Sample Tg/ °C Apparatus m-MTDATA 75 m-MTDATA5DAAB=10051a 71 Tg values were determined by DSC with a Seiko DSC220C. m-MTDATA5DAAB=1051a 63 Electronic absorption spectral change were measured with a m-MTDATA5DAAB=551a 60 Hitachi U-3200 spectrophotometer.The sample was kept at a m-MTDATA5DAAB=351a 60 constant temperature by using a temperature controller aMolar ratio. (TM-105, Toho Electronics Inc.) with a tungsten heater. 2672 J. Mater. Chem., 1998, 8, 2671–2676Table 2 The cis-fraction (Y) of DAAB at the photostationary state upon irradiation with 400 nm light at 30 °C in m-MTDATA films Reaction system Y 10051-m-MTDATA film 0.26 1051-m-MTDATA film 0.48 551-m-MTDATA film 0.54 351-m-MTDATA film 0.54 than those for the polystyrene film and the benzene solution indicates that a number of trans-DAAB molecules remain unchanged in the m-MTDATA amorphous film, probably because the local free volume around the remaining trans- DAAB molecules is not large enough to allow the isomerization of DAAB from its trans-form to the cis-form in the m- MTDATA glass matrix.It is suggested that the average size of local free volume in the m-MTDATA glass is smaller than that in the polystyrene glass. The increase in the Y value with increasing concentration of DAAB in the m-MTDATA glass matrix indicates that the addition of DAAB into the m- MTDATA glass causes a change in the microstructure of the Fig. 3 Electronic absorption spectral change of 351-m-MTDATA film: glass, e.g. the size and distribution of the local free volume. It (a) before irradiation; (b)–(e) irradiated with 400 nm light for (b) 2, is suggested that the fraction of the local free volume that (c) 5, (d ) 10 and (e) longer than 30 min (photostationary state).allows the photoisomerization of DAAB increases with Electronic absorption spectra of ( f ) an amorphous film of increasing concentration of DAAB. m-MTDATA alone and (g) DAAB in a benzene solution Next, the backward cisAtrans thermal isomerization of (1.0×10-5 mol dm-3). DAAB in the m-MTDATA glass was examined. The ratio of the concentration of cis-DAAB at the initial state and at time m-MTDATA and DAAB.It was found that the Tg decreases t was determined from the absorbance at 410 nm according to as the concentration of DAAB increases. eqn. (2), Photochromism of DAAB in the m-MTDATA glass matrix [cis]0 [cis]t = A0-A2 At-A2 (2) The amorphous film with a molar ratio of m- MTDATA5DAAB=n51 prepared on a transparent glass sub- where [cis]0 and [cis]t represent the concentration of cis-DAAB strate by spin coating from a benzene solution is hereafter at the initial state and at time t, respectively, and A0, A2, and referred to as the n51-m-MTDATA film (n=3, 5, 10, 100).At are the absorbances of the film at 410 nm at the initial and The reversible transAcis and cisAtrans photoisomerizations infinite time, and at a time t, respectively. If the reaction and thermal isomerizations of DAAB took place in the n51- follows first-order kinetics, the plots of ln([cis]0/[cis]t) vs.time m-MTDATA amorphous film. Fig. 3 shows the electronic will be linear and the slope of the straight line represents the absorption spectral change for the 351-m-MTDATA film rate constant for the reaction. Fig. 4 shows the first-order together with the electronic absorption spectra of an amorph- plots for the cisAtrans thermal isomerization of the 351- and ous film of m-MTDATA alone, prepared on a glass substrate 10051-m-MTDATA films at 30 °C after the reaction sysby spin coating from a benzene solution, and trans-DAAB in tem has reached the photostationary state by irradiation a benzene solution.Upon irradiation with 400 nm light, the with 400 nm light.The results for a benzene solution absorbance of the film at around 410 nm decreased due to the photoisomerization of trans-DAAB to the cis-form. When irradiation was stopped after the reaction system had reached a photostationary state, the absorption spectrum of the film gradually began to recover to give the original one due to the backward thermal isomerization of cis-DAAB to the transform.The m-MTDATA film was stable to 400 nm light irradiation under the same conditions. The cis-fraction (Y) of DAAB in the n51-m-MTDATA film at the photostationary state can be determined from eqn. (1), Y=Aet+neh et-ec BAAint-Apss Aint B (1) where et, ec and eh are the molar extinction coeYcients of trans-DAAB (et=2.9×104 M-1 cm-1 at 405 nm),38 cis-DAAB (ec=2.0×103 M-1 cm-1 at 405 nm),38 and the m-MTDATA host matrix (eh=6.2×102 M-1 cm-1 at 405 nm), and Aint and Apss are the absorbances of the film at the initial and photostationary states, respectively.Table 2 shows the Y values for the n51-m-MTDATA films at 30 °C. It was found that the cisfraction Y of DAAB in the m-MTDATA glass is smaller than Fig. 4 First-order plots for the cisAtrans thermal isomerization of those (ca. 0.85) for a polystyrene glass and a benzene solution DAAB in (a) 351-m-MTDATA film, (b) 10051-m-MTDATA film and and that the Y value increases when the concentration of (c) 351-m-MTDATA film prepared under irradiation of 400 nm light, DAAB increases in the DAAB—m-MTDATA system. The (d) polystyrene film and (e) benzene solution.Solid lines are fitting curves based on eqn. (3) for (a) and eqn. (4) for (b), (d) and (e). result that the Y value for the m-MTDATA glass is smaller J. Mater. Chem., 1998, 8, 2671–2676 2673Table 3 Kinetic parameters based on eqn. (4) for the thermal (3.3×10-4 mol dm-3) and a polystyrene glass matrix containcisAtrans isomerization of DAAB at 30 °C ing the same DAAB concentration as that in the 10051-m- MTDATA film (0.28 wt%) are also shown in Fig. 4. It was k1/min-1 f1 k2/min-1 f2 found that the cisAtrans thermal isomerization of DAAB in the m-MTDATA and polystyrene films did not follow first- 10051-m-MTDATA film 0.083 0.54 0.003 0.46 Polystyrene matrix 0.062 0.12 0.003 0.88 order kinetics and that the apparent rate constant for the Benzene solutiona — — 0.003 1.00 cisAtrans thermal isomerization in the m-MTDATA glass is initially much larger than those in the polystyrene matrix and aSingle component.the benzene solution, gradually approaching the same value as that in the solution. This result suggests that there exist cisisomers trapped in strained conformations in the host matrix, large as that of the slower component.The rate constant of which go back faster to the trans-isomers than the structurally the slower component for the 10051-m-MTDATA and polyrelaxed cis-isomers. In order to verify this idea, the 351-m- styrene films was found to be the same as for solution. It is MTDATA film was prepared by spin coating under 400 nm suggested that the faster and the slower components are light irradiation and the backward cisAtrans thermal isomeriz- attributed to the reactions of the strained cis-isomer and the ation was examined. As a result, the first-order plot for the structurally relaxed one, respectively. It is noteworthy that the 351-m-MTDATA film prepared under irradiation showed less fraction of the faster component ( f1) is considerably larger deviation from the linear plot [Fig. 4(c)] than the film prepared for the 10051-m-MTDATA film ( f1=0.54) than for the polyin the dark [Fig. 4(a)]. This result indicates that the amount styrene matrix film ( f1=0.12). This leads to a larger apparent of the strained cis-DAAB in the film prepared under irradiation rate constant at the initial stage for the 10051-m-MTDATA is smaller than that prepared in the dark.Similar phenomena film than for the polystyrene film. These results indicate that have also been reported for polymer film systems.3,8 the ratio of the number of the strained cis-isomers to the relaxed cis-isomers at the photostationary state is much larger Kinetic analysis of the cisAtrans thermal isomerization of for the 10051-m-MTDATA film than for the polystyrene film. DAAB in m-MTDATA films The reason why the cisAtrans thermal isomerization of DAAB both in the 10051-m-MTDATA film and in the polystyrene Since the cisAtrans thermal isomerization did not follow film can be analyzed in terms of the first-order kinetics for a simple first-order kinetics, the Kohlrausch–Williams–Watts two component system rather than the Gaussian model is that (KWW) function ([cis]t/[cis]0=exp[-(t/t)b]),39 the Gaussian both the 10051-m-MTDATA film and the polystyrene film Model,40 and first-order kinetics for a two component system involve the reaction of the relaxed cis-isomer to the extent of were applied.As a result, the cisAtrans thermal isomerization 46% and 88%, respectively. of DAAB in the 351-m-MTDATA film was successfully ana- The larger apparent rate constant for the cisAtrans thermal lyzed by the Gaussian Model, which assumes a Gaussian isomerization in the m-MTDATA film relative to the poly- distribution of the free energy of activation.In terms of this styrene film also suggests that the average size of the local free model, the ratio of the concentration of the cis-isomer at a volume in the m-MTDATA glass is smaller than that in the time t to that at the initial time, [cis]t/[cis]0, is given by polystyrene glass.eqn. (3), The results of a larger cis-fraction at the photostationary state and a larger ratio of the strained cis-isomer to the relaxed [cis]t [cis]0 = 1 p1/2 P+2 -2 exp(-x2)exp[-kAVt exp(cx)]dx (3) one for the 351-m-MTDATA film relative to the 10051-m- MTDATA film are ascribed to the diVerence in the size and where x is the stochastic variable of a Gaussian distribution, distribution of the local free volume between the 351-m- kAV is the mean rate constant, and c is the spread of the MTDATA and 10051-m-MTDATA films.It is thought that Gaussian distribution of the free energy of activation. The free trans-DAAB can be isomerized to cis-DAAB when the local energy of activation is represented as DG‡=DG‡AV-cxRT, free volume around the molecule is larger than V0; however, where DG‡AV is the mean free energy of activation.photogenerated cis-DAAB is trapped in a strained confor- The cisAtrans thermal isomerization of the 351-mmation in the host matrix when the local free volume is smaller MTDATA film was found to fit eqn.(3) with the parameters than V1. The comparison of the cis-isomer fraction (Y) at the of kAV=0.034 min-1 and c=1.8. The value of kAV is much photostationary state and the ratio of the strained cis-isomer larger than the first-order rate constant (0.003 min-1) of the to the relaxed one between the 351- and 10051-m-MTDATA cisAtrans thermal isomerization of DAAB in benzene solution.films suggests that the fraction of the free volume larger than These results suggest that most cis-isomers photochemically V0 is larger for the 351-m-MTDATA film than for the 10051-m- generated in the 351-m-MTDATA film take strained confor- MTDATA film, but that the size of the local free volume is mations and their free energies are subject to the Gaussian smaller than V1 for the 351-m-MTDATA film, whereas a distribution.local free volume larger than V1 is available for the 10051- In the case of the 10051-m-MTDATA film, the cisAtrans m-MTDATA film. thermal isomerization of DAAB could not be analyzed by the Gaussian Model but instead could be analyzed by first-order Temperature dependence of the kinetic parameters for the kinetics for a two component system [eqn.(4)], 10051-m-MTDATA film [cis]t [cis]0 =f1 exp(-k1t)+f2 exp(-k2t) (4) The temperature dependence of the kinetic parameters for the cisAtrans thermal isomerization were investigated with regard to the 10051-m-MTDATA film, the reaction of which was where fi and ki are the fractions and the rate constants for the faster (i=1) and the slower (i=2) components, respectively. analyzed by first-order kinetics for a two component system according to eqn.(4). Fig. 5 shows the first-order plots for the Likewise, the cisAtrans thermal isomerization of DAAB in the polystyrene film was analyzed by first-order kinetics for a cisAtrans thermal isomerization of the 10051-m-MTDATA film at various temperatures below Tg. The apparent rate two component system. Table 3 lists the kinetic parameters for the reactions in the 10051-m-MTDATA film, the polystyrene constant of the reaction increased with rising temperature. The kinetic parameters in eqn.(4) obtained for the 10051-m- film, and the benzene solution at 30 °C. The rate constant of the faster component for the 10051-m-MTDATA film and the MTDATA film are summarized in Table 4. The results show that the values of f1 and f2 are almost constant irrespective of polystyrene film was found to be ca. 27 and ca. 21 times as 2674 J. Mater. Chem., 1998, 8, 2671–2676isomerization of the 10051-m-MTDATA supercooled liquid film in the temperature region above Tg, at 75 and 77 °C, was found to follow simple first-order kinetics, as shown in Table 4 and Fig. 6.43 The rate constant is comparable to that predicted from the Arrhenius plots for the slower reaction component below Tg.This result suggests that the photogenerated cisisomer can take a relaxed conformation in the supercooled liquid state, probably because molecular motion is not restricted in the supercooled liquid state. Summary The photochromic behavior of DAAB dispersed in a molecular glass of m-MTDATA was investigated in order to elucidate the properties of the molecular glass as a novel host matrix and to gain information on the microstructure of the molecular glass.The m-MTDATA glass was found to function as a host matrix, homogeneously embedding the photochromic molecule DAAB. It was shown that the fraction of the photoisomerized Fig. 5 First-order plots for the cisAtrans thermal isomerization of cis-isomer at the photostationary state in the m-MTDATA DAAB in 10051-m-MTDATA film at various temperatures: (a) 30, matrix is smaller than that in the polystyrene matrix and that (b) 40, (c) 50 and (d) 60° C.Solid lines are fitting curves based on eqn. (4). the apparent rate constant at the initial stage for the backward cisAtrans thermal isomerization of DAAB in the m-MTDATA glass matrix is considerably larger than those in a polystyrene Table 4 Kinetic parameters based on eqn.(4) for the cisAtrans matrix and in a benzene solution. These results indicate that thermal isomerization of DAAB in 10051-m-MTDATA film at various temperatures there is a large diVerence in the size and distribution of local free volume between the molecular glass of m-MTDATA and T/ °C k1/min-1 f1 k2/min-1 f2 the polystyrene matrix.That is, the local free volume in the molecular glass of m-MTDATA is suggested to be smaller 30 0.083 0.54 0.003 0.46 than that in the polystyrene glass. The present study presents 40 0.11 0.54 0.011 0.46 the first example of photochromic behavior in a molecular 50 0.16 0.54 0.029 0.46 60 0.37 0.53 0.061 0.47 glass as a novel host matrix and can be extended to other 75a — — 0.346 1.00 photochromic compounds and other molecular glasses to gain 77a — — 0.382 1.00 further information on the properties of molecular glasses as aSingle component.a novel class of host matrix and on the microstructure of molecular glasses. the temperature, whereas the rate constants k1 and k2 increase References with rising temperature. Fig. 6 shows the Arrhenius plots for both k1 and k2. The activation energies for the reactions of 1 Photochromism, Molecules and Systems, ed. H. Du� rr and the faster and the slower components were determined to be H. Bouas-Laurant, Elsevier, 1990. 41 and 84 kJ mol-1, respectively. The activation energy for 2 Applied Photochromic Polymer Systems, ed.C. B. McArdle, Blackie & Son, 1992. the slower reaction component is similar to that for solution 3 C. Paik and H. Morawetz, Macromolecules, 1972, 5, 171. (ca. 88 kJ mol-1),41,42 but the activation energy for the faster 4 C. D. Eisenbach, Makromol. Chem., 1978, 179, 2489. reaction component is almost half of that of the slower reaction 5 C. D. Eisenbach, Ber. Bunsenges.Phys. Chem., 1980, 84, 680. component. It is thought that the slower and the faster 6 J. G. Victor and J. M. Torkelson, Macromolecules, 1987, 20, 2241. reactions are attributed to the cisAtrans thermal isomerization 7 W-C. Yu, C. S. P. Sung and R. E. Robertson, Macromolecules, reactions from the relaxed cis-isomer and from the cis-isomer 1988, 21, 355. 8 I. Mita, K. Horie and K.Hirao, Macromolecules, 1989, 22, 558. trapped in strained conformations in the m-MTDATA host 9 G. S. Kumar and D. C. Neckers, Chem. Rev., 1989, 89, 1915. matrix, respectively. On the other hand, the cisAtrans thermal 10 T. Naito, K. Horie and I. Mita, Macromolecules, 1991, 24, 2907. 11 S. Xie, A. Natansohn and P. Rochon, Chem.Mater., 1993, 5, 403. 12 Y. Shirota, T. Kobata and N.Noma, Chem. Lett., 1989, 1145. 13 A. Higuchi, H. Inada, T. Kobata and Y. Shirota, Adv. Mater., 1991, 3, 549. 14 Y. Kuwabara, H. Ogawa, H. Inada, N. Noma and Y. Shirota, Adv. Mater., 1994, 6, 677. 15 Y. Shirota, Y. Kuwabara, D. Okuda, R. Okuda, H. Ogawa, H. Inada, T. Wakimoto, H. Nakada and Y. Yonemoto, J. Lumin., 1997, 72–74, 985. 16 H. Ogawa, H. Inada and Y. Shirota, Macromol.Symp., 1997, 125, 171. 17 W. Ishikawa, H. Inada, H. Nakano and Y. Shirota, Chem. Lett., 1991, 1731. 18 W. Ishikawa, H. Inada, H. Nakano and Y. Shirota, Mol. Cryst. Liq. Cryst., 1992, 211, 431. 19 W. Ishikawa, H. Inada, H. Nakano and Y. Shirota, J. Phys. D: Appl. Phys., 1993, 26, B94. 20 W. Ishikawa, K. Noguchi, Y. Kuwabara and Y. Shirota, Adv. Mater., 1993, 5, 559. 21 E. Ueta, H.Nakano and Y. Shirota, Chem. Lett., 1994, 2397. Fig. 6 Arrhenius plots for the cisAtrans thermal isomerization 22 H. Kageyama, K. Itano, W. Ishikawa and Y. Shirota, J. Mater. Chem., 1996, 6, 675. reaction of 10051-m-MTDATA film: ($) faster reaction component below Tg, (&) slower reaction component below Tg, and (+) above Tg. 23 K. Katsuma and Y. Shirota, Adv. Mater., 1998, 10, 223. J.Mater. Chem., 1998, 8, 2671–2676 267524 H. Nakano, E. Ueta and Y. Shirota, Mol. Cryst. Liq. Cryst., 1998, 34 T. Noda, H. Ogawa, N. Noma and Y. Shirota, Appl. Phys. Lett., 1997, 70, 669. 313, 241. 25 H. Inada and Y. Shirota, J. Mater. Chem., 1993, 3, 319. 35 T. Noda, H. Ogawa, N. Noma and Y. Shirota, Adv. Mater., 1997, 9, 720. 26 A. Higuchi, K. Ohnishi, S. Nomura, H. Inada and Y. Shirota, J. Mater. Chem., 1992, 2, 1109. 36 K. Itano, H. Ogawa and Y. Shirota, Appl. Phys. Lett., 1998, 72, 636. 27 H. Inada, K. Ohnishi, S. Nomura, A. Higuchi, H. Nakano and Y. Shirota, J. Mater. Chem., 1994, 4, 171. 37 H. Nakano, K. Akamatsu, K. Moriwaki and Y. Shirota, Chem. Lett., 1996, 701. 28 S. Nomura, K. Nishimura and Y. Shirota, Thin Solid Films, 1996, 273, 27. 38 E. Fischer and Y. Frei, J. Chem. Phys., 1957, 27, 328. 39 G. Williams and D. C.Watts, Trans. Faraday Soc., 1970, 66, 80. 29 M. Yoshiiwa, H. Kageyama, F. Wakasa, M. Takai, K. Gamo and Y. Shirota, Appl. Phys. Lett., 1996, 69, 2605. 40 W. J. Albery, P. N. Bartlett, C. P. Wilde and J. R. Darwent, J. Am. Chem. Soc., 1985, 107, 1854. 30 T. Noda, I. Imae, N. Noma and Y. Shirota, Adv. Mater., 1997, 9, 239. 41 D. Schulte-Frohlinde, Liebigs Ann. Chem., 1958, 612, 138. 42 N. Nishimura, T. Sueyoshi, H. Yamanaka, E. Imai, S. Yamamoto 31 J. Sakai, H. Kageyama, S. Nomura, H. Nakano and Y. Shirota, Mol. Cryst. Liq. Cryst., 1997, 296, 445. and S. Hasegawa, Bull. Chem. Soc. Jpn., 1976, 49, 1381. 43 The reaction in the higher temperature region above 77 °C could 32 Y. Shirota, Proc. SPIE—Int. Soc. Opt. Eng., 1997, 3148, 186 and references cited therein. not be carried out due to crystallization of the reaction system. 33 Y. Shirota, Y. Kuwabara, H. Inada, T. Wakimoto, H. Nakada, Y. Yonemoto, S. Kawami and K. Imai, Appl. Phys. Lett., 1994, Paper 8/05735D 65, 807. 2676 J. Mater. Chem., 1998, 8, 2671–2676

ISSN:0959-9428    

DOI:10.1039/a805735d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Reversibly thermochromic systems based on pH-sensitive spirolactone-derived functional dyes Stephen M. Burkinshaw, John GriYths and Andrew D. Towns* Department of Colour Chemistry, University of Leeds, Leeds, UK LS2 9JT. E-mail: ccdadt@leeds.ac.uk Received 30th July 1998, Accepted 9th October 1998 Composites formulated from pH-sensitive colour formers mixed with fatty acid co-solvents and acidic developers have been prepared and their thermochromic properties investigated.Possible explanations for the thermochromic eVect have been considered and evidence is presented in support of a mechanism based on phase changes occurring within the compositions during heating and cooling. Introduction Colour formers that are pH-sensitive have been utilised commercially in the production of thermographic recording materials for around thirty years.The main outlet for such technology is facsimile paper in which the colour formers are designed to change irreversibly from colourless to coloured states on the application of heat.1,2 However, thermochromic systems are known which utilise colour formers in order to produce thermally-triggered reversible switching between coloured and colourless states.3 In addition to a pH-sensitive colorant, these systems also contain a readily fusible solid cosolvent and a colour developer.The co-solvent is a relatively low-melting hydrophobic compound that acts as a medium in which the colour former and developer can interact; the material typically has a long chain aliphatic character and may be a fatty acid, amide or alcohol.Provided that the mixture is formulated correctly, a striking colour change from and phenolic developers. From the observed influence of coloured to colourless occurs upon heating the composition molecular structure of the developer on thermochromism, and above its melting point, the original colour returning when also the significance of fractional composition on the eYcacy the material solidifies through cooling.Reversibly thermo- of thermochromism, a mechanism for the process has been chromic systems based on acidic developers and spirolactone proposed. colour formers are typical of the formulations encountered in the literature: an example of the latter component is Crystal Results and discussion Violet lactone (1), which in its lactone form, 1a, is colourless, but on ring-opening (Scheme 1) converts to the intense blue Synthesis and properties of the colour formers species 1b.The ring-opening may be induced by the addition The colour formers employed in this investigation are typical of a proton or through an increase in the polarity or hydrogenof the classes of colorant used industrially: diarylphthalide bonding ability of the host environment.The reaction is fully (1), fluoran (2), vinylphthalide (3) and fluorene (4). Crystal reversible. Violet lactone, 1, is readily available commercially. The fluoran 2 was prepared by condensation of the benzoylbenzoic acid 5 with 4-acetylaminophenol (6a) followed by hydrolysis to give fluoran 7, the primary amino group of which was then dibenzylated (Scheme 2).6 Scheme 1 Despite the many patent applications concerning thermochromic materials based on co-solvent/developer/colour former compositions, little has been published that addresses the mechanism of the thermochromic eVect.3–5 This paper describes the behaviour of thermochromic compositions formulated with fatty acids, spirolactone colour formers (1–4) © British Crown Copyright 1998/MOD.Published with the permission Scheme 2 of the Controller of Her Britannic Majesty’s Stationery OYce. J. Mater. Chem., 1998, 8, 2677–2683 2677The phthalide 3 was synthesised by condensing Michler’s compositions, some coloured solid remained, which dissolved at higher temperatures to complete the colour loss.Reducing ethylene (8) with the tetrachloro-substituted benzoylbenzoic acid 9 (Scheme 3).7 the proportions of co-solvent to developer and colour former from 505251 to 505151 and 255151 made little diVerence to the initial colour intensity, but raised the temperature at which complete colour loss occurred (Table 2). However, in all cases, the onset temperature coincided with the start of melting of the composition, which was little diVerent from that of stearic acid itself (mp 67–69 °C).Compositions were prepared from the colour formers and Bisphenol A using fatty acids other than stearic acid. Onset of colour loss was again observed to be related to the melting Scheme 3 point of the co-solvent. For example, 505251 (fatty acid5Bisphenol A51) compositions prepared using lauric acid, While 4 has been obtained from an aminospirolactone by myristic acid and palmitic acid as the co-solvent component diazotisation and intramolecular coupling8 or treatment with exhibited colour loss onset temperatures of 45 °C, 52 °C and sodium sulfite in concentrated sulfuric acid followed by 62 °C, respectively, which correspond well with the melting addition of copper powder,9 a method involving an intramol- points of the co-solvents (42–46 °C, 51–53 °C and 61–63 °C ecular Friedel–Crafts reaction10 was chosen owing to the respectively).12 For a given co-solvent, varying the mixture availability of the starting material, 1 (Scheme 4).ratio of the components had little eVect on the point at which the composition started to melt or change colour and the switching temperature was determined solely by the temperature at which each formulation began to melt.The colour change was found in all cases to be fully reversible: no colour loss was noted on repeated heating and cooling of the samples. For example, when the composition (505251) based on 2 was subjected to thirty cycles of heating to 90–100 °C and allowing to cool below 40 °C, no significant Scheme 4 diVerences in reflectance minima were noted.Each colour former showed strong infrared absorption in the 1750–1760 cm-1 range characteristic of phthalides.11 In its Mechanism of the thermochromic eVect solid form, 3 displayed photochromism in that the initially green crystals turned darker and more yellow in sunlight, While the mechanism of irreversible thermochromism of spiroreturning to their original colour in the dark.lactone-based thermographic materials that change from a The lactones, when examined by thin layer chromatography, colourless to a permanently coloured state on heating is well rapidly became coloured on contact with alumina or silica, as understood,13 little is known about the mode of operation of was expected with such polar media: 2, 3 and 4 gave dark the reversible coloured-to-colourless compositions described green, turquoise and pale green spots, respectively.The colour above, despite the volume of patent material which has of the spots paralleled the absorption maxima of the derivatives appeared and the widespread use of such compositions (in in acetic acid solution (Table 1). microencapsulated form) in textile and novelty goods.Theories involving steric considerations3 or phase separa- Preparation and properties of the compositions tion3–5 have been put forward in an attempt to explain why these compositions have only slight colour, if any, when Thermochromic compositions were prepared from each colour molten, and yet are intensely coloured in the solid state. One former 1–4 in the following manner: stearic acid, Bisphenol A theory proposes that steric factors determine the generation and colour former in the ratio 505251 were mixed and heated and loss of colour, whereas another explains the phenomenon above the melting point of the fatty acid to produce weakly in terms of temperature-driven phase changes within the coloured or colourless solutions, which were then rapidly composition.However, direct experimental evidence support- cooled by the addition of cold water causing simultaneous ing either mechanism is surprisingly lacking. It is useful first solidification and coloration of the wax. The reflectance to summarise the two mechanisms and then describe our own minima of the dried, powdered compositions accorded well observations which strongly support the second mechanism.with the absorption maxima of the corresponding colour former in acetic acid. Sterically-induced mechanism of thermochromism. In this Each composition exhibited reversible thermochromism. At premise, it is argued that the existence of the coloured species the onset of melting of the composition, colour loss started to (e.g. 1b, Scheme 1) is more favourable sterically in the solid occur and within a few degrees above the melting point, the matrix of the composition compared to that for the colourless majority of the colour had been lost. Depending on the form (e.g. 1a). Whereas the more restricted environment of fractional composition and colour former, the diVerence in the solid composition favours the coloured, relatively planar temperature between the onset of colour loss and complete ring-opened structure over the tetrahedral colourless spirolac- loss of colour varied from only a few degrees to over 40 °C tone structure, in the molten composition, the smaller steric (Table 2).At 75 °C, the melts of the 505251 (stearic requirement of the coloured species is less important and acid5Bisphenol A5dye) samples based on 2 and 3 were almost conversion to the lactone (and thus colour loss) can take place colourless, although it was observed that after melting of the more readily.The argument is based on the supposition that steric factors regulate the position of the ring-opening equilib- Table 1 Absorption maxima of the colour formers in acetic acid (99%) rium: cooling and solidification of the composition, which Colour former lmax/nm when molten contains the colour former predominantly in the colourless form, moves the equilibrium towards the coloured 2 609, 464, 437 form since the planar geometry of the latter structure is more 3 706 favourable in the solid. 4 915, 836, 621 However, X-ray diVraction data and molecular modelling 2678 J.Mater. Chem., 1998, 8, 2677–2683Table 2 Temperatures of melting, colour loss onset and completion for compositions of stearic acid/Bisphenol A/colour former Colour Mixture Onset of colour End point of former ratio Melting point/°C loss/°C colour loss/°C 2 505151 67–68.5 67 72 2 505251 67–69 67 ca. 83 2 255151 67–68.5 67 90 3 505251 67–69 67 ca. 110 cast doubt on this theory. While X-ray crystallography has confirmed the non-planar nature of the spirolactone colour formers, like fluorans,14 the ring-opened coloured species have also been found to be non-planar. Thus: (1) the aromatic rings of Crystal Violet Lactone cation (1b) complexed with metal iodides have a propeller-like orientation;15 (2) the cation from benzofluoran 10 complexed with metal iodides has a near-planar xanthene component, although the carboxy-substituted ring is almost perpendicular to it;16 (3) Scheme 5 suYciently high degree for satisfactory colour development.Conversely, too little co-solvent will prevent complete dissolution on melting and inhibit colour loss. The consequence of a the ring-opened hydrochloride salt of the anilinofluoran 11 system lacking any co-solvent, or the use of one that does not was found to have a structure in which the pendant phenyl melt in the temperature range of interest, would be that the ring is at right angles to, and the anilino substituent twisted colour change would be more gradual and less complete.There out of plane of, the xanthene structure.17 will be no sudden removal of material into solution and Molecular modelling reproduced the non-planar features of consequent rapid colour loss.the structures in the first two examples listed above. Other The eVectiveness of a developer can therefore be anticipated ring-opened species were predicted to be significantly non- to depend not only on its acidity, but also on its solubility in planar, for example, the structure of 3, in which none of the the co-solvent.In order to verify this suggestion and to test aromatic rings were co-planar because of the crowded nature the validity of the phase separation theory, a series of Nof the molecule. From the X-ray studies and molecular modelling, it is clear that the coloured species are not planar and do not possess significantly smaller steric requirements over the corresponding colourless lactone forms.Thus a mechanism based on sterically- driven thermochromism seems unlikely. acylaminophenols 6 (R=CH3 to C7H15, C17H35) of varying hydrophobicity, and thus solubility, has been synthesised. Phase separation mechanism of thermochromism. A more attractive theory for the mechanism of the thermochromic Each member has been used as a developer in stearic acidbased compositions in conjunction with a variety of colour eVect assumes that phase separation plays a major role.Thus little or no colour generation occurs in the molten composition formers, and the eVect of developer structure on thermochromism measured. because the colour former and acidic developer are dissolved in the co-solvent; the average environment experienced by the The consequences of using diVerent ratios of components have also been examined.In addition to giving rise to a chromogenic compound is therefore relatively non-polar, which encourages lactonisation, so that the equilibrium is well dilution eVect, a high ratio of co-solvent to developer and colour former should, in terms of the phase separation theory, over to the ring-closed, colourless spirolactone side.On cooling, the solubilities of the colour former and developer fall, so inhibit precipitation of the solutes, leading to a low degree of colour development, whereas too little co-solvent should pre- that eventually a proportion of these two components separates from the bulk monodisperse solution phase on solidification.vent complete dissolution on melting and restrict colour loss. To examine these eVects, a series of compositions of diVering The developer precipitates, bringing colour former with it (or vice versa). In this phase, the colour former experiences a more mixture ratios based on stearic acid and incorporating the developers 6 were prepared. polar environment and intimate contact with the developer, resulting in ring-opening and generation of colour.On heating, All the developers 6a–h caused colour development, but to varying degrees depending not only on the colour former used, the two phases merge and the colour former returns to its colourless spirolactone form. A simplified diagrammatic rep- but also on the structure of the developer, the ratio of the components and the age of the composition (see following resentation of the phase changes is shown in Scheme 5.This explanation of the mechanism has many implications. Sections). In addition to having the correct balance of acidity of the developer and basicity of the colour former, a balance must EVect of developer structure. The colour intensity of each composition in the solid state was determined by measuring also be struck between the solubilities and solvating powers of the components in the composition. The theory suggests the reflectance of the powdered material at the lmax of the colour former.The results are summarised in Fig. 1–3. All that the developer must be soluble enough to dissolve in the molten fatty acid, but not so soluble that it does not precipitate showed a similar pattern of colour development.Thus developers with short alkyl chains (6a, 6b) conferred relatively pale when the composition solidifies. Also, if too much co-solvent is present in the system, the solutes will not precipitate to a colours; inserting one or two methylene fragments into the J. Mater. Chem., 1998, 8, 2677–2683 2679in conjunction with 3 (Fig. 3); reflectance values of compositions containing 6c or 6d approached those achieved with Bisphenol A. While colour development decreased with the employment of developers of longer chain length, the colour yields were significantly greater than without any developer. Both the visible and near infrared absorption of compositions formulated with 4 exhibited a strong dependence on the structure of the developer (Fig. 4). All these findings conform to the predictions of the phase separation theory. The developers with short alkyl chains (6a, 6b) are polar and not very soluble in the co-solvent (stearic acid), so that they conferred only pale colours when the compositions solidified on cooling, because much of the developer did not dissolve in the melt during composition prep- Fig. 1 Reflectance of powdered 505151 stearic acid–6–1 compositions aration. On the other hand, the developers with long alkyl at 610 nm. chains (6f–h) were found to be very soluble in the molten compositions, but gave only weakly coloured waxes, presumably because their high solubility inhibited phase separation on cooling. The developers possessing alkyl chains of intermediate length (6c, 6d) seemed to have the required balance of satisfactory solubility in the molten stearic acid and poor solubility in the cold wax, so that in these cases, the highest amount of phase separated material was produced and colour development was greatest.EVect of fractional composition on thermochromism. The influence of the mixture ratio on the colour strengths of solid stearic acid56a–g51 compositions of ratio 2551:1, 5051:1 and 10051:1 is depicted in Fig. 5. Increasing the ratio of co-solvent to developer and colour former generally lowered colour strength of the solids as anticipated. In addition to diluting Fig. 2 Reflectance of powdered 255151 stearic acid–6–2 compositions the colour, the increased proportion of co-solvent reduces at 605 nm.colour development by inhibiting precipitation of the components on solidification of the molten composition. Consequently, while the pattern of colour strength in relation to developer chain length as described above for the 505151 series (see Section above) was generally reproduced in the 255151 and 1005151 formulations, the average colour strength Fig. 3 Reflectance of powdered 505251 stearic acid–6–3 compositions at 720 nm. chain of the latter to give 6c–d caused deepening of the colour of the compositions, but further lengthening of the alkyl residue decreased the colour intensity. Fig. 4 Reflectance of powdered 505251 stearic acid–6–4 compositions In the case of the 505151 stearic acid5developer51 composi- at 655 nm and 910 nm.tions, addition of 6a or 6b brought a reduction in minimum reflectance of around 20% compared to the formulation lacking developer (Fig. 1); use of the propyl and butyl analogues led to a further lowering of the minimum, while the colour yield with 6e was close to the level obtained with 6a and 6b. The developers with the longest chains produced the highest reflectances (weakest colours), the formulation containing 6g having a reflectance approaching that corresponding to the residual colour of 1 in stearic acid alone, i.e.a composition with no developer at all. A similar pattern was shown by the series based on 2 (Fig. 2). Colour development was generally greater than in the previous series; even the long chain developers produced significantly lower reflectances than the mixture containing the Fig. 5 Reflectance of powdered 255151, 505151 and 1005151 stearic acid–6–1 compositions at 610 nm. colour former alone. The developers were particularly eVective 2680 J. Mater. Chem., 1998, 8, 2677–2683of the former series was stronger than that of the 505151 displayed by the analogous range of 505151 formulations shown in Fig. 6. compositions, whereas the average minimum reflectance of the latter series was higher. Wax constituting a 1005151 mixture Week-old compositions were generally more weakly coloured than freshly prepared material. In certain cases, the of stearic acid56g51 was almost as pale as the corresponding material lacking developer, suggesting that the acylamino- colour change occurred suYciently rapidly to be perceptible to the naked eye; for example, molten 255151 and 505151 phenol in the former composition had little tendency to separate from the stearic acid phase and/or form a separate stearic acid56g51 compositions gave dark blue waxes when first quenched, which, over a few seconds, faded to pale blue.phase with 1. The compositions containing 6b did not conform to the The corresponding 505251 composition based on 3 lost colour over the course of a few minutes, while changes in the colours typical pattern: colour yield slightly increased on raising the proportion of co-solvent from 505151 to 1005151, presumably of 255151 stearic acid56f–g51 and 505251 stearic acid56f–g51 formulations were noticeable after a few hours.because more developer can go into solution and consequently separate with colour former on cooling.The phenomenon can be explained in terms of phase separation: rapid cooling of the molten mixture brings about brief colour development through the initial co-separation of devel- EVect of ageing on the solid composites. Whereas all the coloured solid compositions containing Bisphenol A remained oper and colour former; secondary separation then takes place, whereupon colour former crystallises out of the developer (or intensely coloured over long periods of time, the compositions formulated with the 4-acylaminophenols tended to lose their vice versa) so that colour is lost as the former is no longer intimately associated with the latter.When the incompatibility initial colour on standing with varying degrees of rapidity (Fig. 6–8). The series of 255151 and 1005151 stearic acid5651 between colour former and developer is particularly great, separation occurs rapidly enough for the colour of the wax to compositions exhibited a similar pattern of colour loss to that fade perceptibly over the course of several seconds or minutes. Thus not only is the solubility of the developer in the cosolvent an important factor, but the solubility of the colour former in the developer (or association between them) is of major relevance.Experimental Thin layer chromatography was performed using alumina plates (DC Alufolien Aluminiumoxid 150 F254 neutral type T, Merck). Melting points were determined on an Electrothermal melting point apparatus and are uncorrected. Thermal, FTIR and elemental analyses were performed on a DuPont 2000 diVerential scanning calorimeter, using a Perkin-Elmer 1740 spectrophotometer and in the Department of Chemistry of the Fig. 6 Time dependence of reflectance of powdered 505151 stearic acid–6–1 compositions at 610 nm. University of Leeds, respectively. Reflectance measurements were obtained by means of a Perkin-Elmer Lambda 9 UV/visible/NIR spectrophotometer.Preparation of the colour formers and developers Fluoran colour former 2. 4-Acetylaminophenol 6a (4.98 g, 33 mmol) and 2-(4-N,N-diethylamino-2-hydroxybenzoyl )benzoic acid 5 (8.91 g, 28 mmol) were added portionwise to stirred sulfuric acid (98%, 15 ml ) over 20 min so that the temperature remained under 45 °C. The mixture was heated and stirred at 55 °C for 22 h, water (15 ml ) added, maintaining the temperature below 85 °C, and then heated with stirring for 3 h at 90–95 °C.The intense red solution was cooled to room temperature and poured into a solution of sodium hydroxide (18 g) in water (130 ml ) at such a rate that the temperature Fig. 7 Time dependence of reflectance of powdered 255151 stearic did not exceed 80 °C; aqueous ammonia (32%, ca. 8 ml) was acid–6–2 compositions at 605 nm. added to make the pH of the purple suspension weakly alkaline. The solid was collected, washed with very dilute aqueous ammonia and dried to give crude 2¾-amino-6¾-N,Ndiethylaminofluoran 7. Crude 7 (8.00 g, 21 mmol) was added to sodium carbonate (5.71 g, 54 mmol), benzyl chloride (98.5%, 6.75 ml, 58 mmol) and water (20 ml ), before heating to 90 °C overnight to give a dark green mixture.This was cooled to room temperature, the aqueous phase decanted oV and the residual dark green tarry product washed several times with water. Stirring with ethanol (20 ml ) at 65 °C for 30 min furnished a green suspension which was cooled to room temperature and filtered. The collected solid was washed with a little ethanol (5 ml, twice) and then butanone (5 ml ) to give crude 2 as a pale green powder (10.04 g, 86% crude yield).A portion (1.00 g) of this material was recrystallised twice (ethanol–DMF, 1551) aVord- Fig. 8 Time dependence of reflectance of powdered 505251 stearic acid–6–3 compositions at 720 nm. ing analytically pure, pale beige crystals (0.58 g, mp J. Mater.Chem., 1998, 8, 2677–2683 2681172.5–174 °C). Microanalysis found C, 80.5; H, 6.1; N, 5.0% 10.15% (C26H27N3O2 requires C, 75.52; H, 6.58; N, 10.16%). DSC indicated reasonable purity, analysis revealing a small (C38H34O3N2 requires C, 80.5; H, 6.0; N, 4.9%). DSC and TLC (alumina, 951 toluene–ethyl acetate) indicated purity, endotherm at 248.4 °C and a sharp, major endotherm at 261.7 °C, with decomposition occurring at around 316 °C.TLC showing a sharp endotherm at 172.3 °C and a single dark green spot respectively. FTIR (KBr)/cm-1: 1752 (lactone (alumina, 951 toluene–ethyl acetate) revealed a single green CLO). spot of Rf 0.57. FTIR (KBr)/cm-1: 1752 (lactone CLO). Vinylphthalide colour former 3. Magnesium (98%, 4.2 g, Developers 6a–h. Apart from the readily available 6a, the 0.17 mol ) and diethyl ether (20 ml ) were stirred under nitrogen developers 6 were synthesised from 4-aminophenol by the as iodomethane (99%, 25.0 g, 0.17 mol) was added dropwise methods of Fierz-David and Kuster.20 The 4-propionyl ana- over 20 min at such a rate as to maintain a continuous logue 6b was obtained using propionic anhydride, whereas the exotherm and gentle refluxing.The mixture was gently refluxed longer alkyl chain derivatives (R=C3H7 to C7H15) were for 25 min by which time almost all of the magnesium had synthesised from the corresponding acid chlorides, while the dissolved. The reaction mixture was protected from light and stearoyl derivative 6h was prepared by condensation with a solution of Michler’s ketone (98%, 9.0 g, 33 mmol) in toluene stearic acid.(280 ml ) at room temperature was run in. The mixture was stirred under nitrogen in the absence of light at ambient temperature for 22 h, before cautiously quenching with water Preparation of the compositions (200 ml ) to give a light blue emulsion, which was stirred for 15 min. A solution of ammonium chloride (30 g) and acetic Formulations of 5051:1 stearic acid (2.00 g), developer 6 acid (99%, 15 ml ) in water (150 ml ) was added and the whole (Table 3) and 1 (0.040 g) were prepared by heating the mixture stirred for 3.5 h.The aqueous phase was washed twice with to 100–105 °C and stirring until dissolution was complete, or toluene (50 ml ) and the extracts combined with the organic until no more dissolution occurred, and quenching with the phase, from which the solvent was removed by rotary evapor- addition of ca. 20 ml of cold water. The solidified wax was ation after drying overnight with magnesium sulfate. The pale filtered oV, allowed to air-dry overnight and powdered. blue-green residue (8.59 g, 98% crude yield, mp 116–120 °C) Series of compositions of ratio 255151 and 1005151 were was recrystallised in ethanol, furnishing Michler’s ethylene (8) also prepared in a similar manner.Formulations containing 2 as a pale blue lustrous solid (7.15 g, mp 121–123 °C, lit.,18 (255151), 3 (505251) and 4 (505251) were made by the same 121–122 °C). procedure, except that the mixtures were heated to 95–100 °C, A mixture of 8 (1.33 g, 5.0 mmol), 2-(4-N,N-dimethylamino- 105–110 °C and 100–105 °C, respectively.The ratios strictly benzoyl )-3,4,5,6-tetrachlorobenzoic acid 919 (2.04 g, only apply to compositions containing 6a; the amounts of 5.0 mmol) and acetic anhydride (7.5 ml ) was stirred and developer listed in Table 3 are equimolar so that, within a heated to reflux for 20 min. The dark green mixture was particular series of compositions, each member of the range allowed to cool and poured into a mixture of toluene (50 ml ), consists of a fixed molar ratio of developer to colour former ice (50 ml ) and aqueous ammonia (32%, 10 ml ).The emulsion and co-solvent. was destroyed by addition of a little dichloromethane; the The procedure for measuring the reflectance of the powdered organic phase was collected and the aqueous phase extracted formulations involved packing the material into a glass-fronted with more dichloromethane.The combined extracts were cylindrical cell comprising two close-fitting components. The washed several times with water, dried (magnesium sulfate) composition was compressed in the cell by insertion of the and rotary evaporated to dryness, giving a dark yellow- cylinder and the reflectance measured (scan speed brown solid (2.94 g, 90% crude yield, mp 220–222 °C). 240 nm min-1); the powder was displaced and re-compressed Recrystallisation (methoxyethanol, methoxyethanol–DMF before taking a second measurement. The technique was found 1251 twice) furnished 3 as green needle-like crystals (1.03 g, to yield consistent results. mp 227.5–229 °C), which darken in sunlight, but return to their original colour in the dark.Microanalysis found C, 61.9; Molecular modelling H, 4.8; N, 6.1; Cl, 20.8% (C34H31N3O2Cl4 requires C, 62.3; H, 4.8; N, 6.4; Cl, 21.6%). DSC indicated reasonable purity, The ‘Hyperchem’ software package (Release 3 For Windows, showing a single endotherm at 226.6 °C. TLC (alumina, 951 Autodesk Inc.) was used in an attempt to visualise the geometry toluene–ethyl acetate) revealed one blue-green spot.FTIR of the ring-opened colour former molecules. The procedure (KBr)/cm-1: 1758 (lactone CLO). involved optimising the geometry by using molecular mechanical methods, conducting the iterative energy-minimising rou- Fluorene colour former 4. Aluminium chloride (96%, 50.0 g, tines to the desired energy gradient (0.01 kcal A° -1 mol-1) 0.36 mol ), urea (7.5 g, 0.12 mol) and aluminium chloride with the Polak–Ribiere algorithm. The MM+ force field was hexahydrate (99%, 0.75 g, 3.1 mmol) were stirred and heated used as it was deemed the most appropriate for relatively to 125 °C.Crystal Violet Lactone (1) (97%, 5.2 g, 12 mmol) small molecules like the colour formers. For the sake of was added and the mixture stirred at 135–140 °C for 4 h.simplicity, the colour formers were assumed to ring open to Heating was continued for another 18 h by which time the give a free carboxylic acid group, i.e. the nature of the reaction mixture had become a solid mass. The reaction was developer and the type of association was not considered in quenched by gradual addition of water (400 ml ) to give a the modelling.blue-green suspension, which was treated with hydrogen peroxide (30%, 1.2 ml ) and stirred for 1.5 h. The suspension was extracted several times with dichloromethane; the combined extracts were washed and dried over magnesium sulfate. Table 3 Masses of developers 6 used in 505151 compositions Removal of the drying agent and solvent furnished a dull green solid (4.43 g, 89% crude yield).Three recrystallisations Developer Mass/g Developer Mass/g (toluene/charcoal ) gave 4 as buV crystals (1.20 g, mp 6a 0.0400±0.0004 6e 0.0549±0.0005 225–227.5 °C). Repeated recrystallisation of 0.40 g of this 6b 0.0438±0.0004 6f 0.0586±0.0005 material from toluene and ethanol aVorded analytically-pure 6c 0.0475±0.0004 6g 0.0623±0.0005 pale cream crystals (0.07 g, mp 237–242 °C, lit.,8 244–246 °C, 6d 0.0512±0.0005 6h 0.0995±0.0005 lit.,10 240–245 °C).Microanalysis found C, 75.3; H, 6.7; N, 2682 J. Mater. Chem., 1998, 8, 2677–2683the reverse of that observed for the three-component com- Conclusions posites discussed above. Presumably the b-estradiol assumes Thermochromic systems have been prepared which deliver the roles of both developer and co-solvent as not only does it sharp reversible changes from coloured to colourless states have a phenolic residue, typical of the first component, but it when heated above their melting points. A mechanism for the also has a hydrophobic alkyl skeleton, characteristic of the phenomenon based on steric considerations was rejected on second.In the molten composite, the colorant is ring-opened the basis of X-ray crystallographic data and molecular model- and thus coloured, because it is dissolved in, and can interact ling predictions.An explanation in terms of phase changes with, the b-estradiol, whereas on solidification, the colorant was investigated by preparing compositions from developers separates from the bulk phase, ring-closes and the formulation of diVering hydrophobicity.The findings lent weight to such loses its colour. a theory, although more direct evidence of the existence of the Within the framework of the proposed mechanism, it would proposed phases and phase changes is necessary for confir- appear that another approach to produce coloured-to-colourmation of its validity. less formulations comprising only two components is possible: Several influences on colour yield were identified; for in these, a colorant of a design which combines the functions example, developer structure had a significant eVect.The of both colour former and developer, for example a spirolacdevelopers with short alkyl chains were polar and not very tone bearing phenolic residues, is formulated with a co-solvent.soluble in the co-solvent, so that they conferred only pale Provided the colorant is readily soluble in the melt, separates colours when the compositions solidified on cooling, whereas from the bulk phase on solidification and has the correct the developers with long alkyl chains were found to be very balance of basicity and acidity, the composition will be reversisoluble in the molten compositions, but gave only weakly bly thermochromic: in the molten composition, lactonisation coloured waxes, presumably because their high solubility will be favoured, while cooling will lead to separation of a inhibited phase separation on cooling.The developers pos- colorant phase in which intermolecular interaction between sessing alkyl chains of intermediate length seemed to have the the lactone and phenolic elements can occur causing ringrequired balance of satisfactory solubility in the molten stearic opening and colour generation.acid and poor solubility in the cold wax, so that in these cases, the highest amount of phase separated material was produced Acknowledgement on solidification and colour development was greatest.As anticipated, colour strengths were observed to be dependent The authors wish to thank the Defence Clothing and Textiles on mixture ratio: increasing the ratio of co-solvent to developer Agency (Colchester, UK) for the funding and support of and colour former generally lowered colour yields. However, this work. in certain cases, an increase in the proportion of co-solvent relative to developer improved colour development as more References of the latter could be dissolved and consequently separate with colour former on cooling.While formulations containing 1 F. Jones, Rev. Prog. Coloration, 1989, 19, 20. Bisphenol A have not been observed to change colour over 2 A. R. Katritzky, Z.-X. Zhang, H.-Y. Lang, N. Jubran, L. M. Leichter and N. Sweeny, J.Mater. Chem., 1997, 7, 1399. time, compositions prepared from the N-acylaminophenol 3 D. Aitken, S. M. Burkinshaw, J. GriYths and A. D. Towns, Rev. developers were found to fade to diVerent extents with varying Prog. Coloration, 1996, 26, 1. degrees of rapidity from over the course of seconds to weeks. 4 K. Naito, Appl. Phys. Lett., 1995, 67, 211. The phenomenon may arise through phase separation of the 5 J.GriYths, in ChemiChromics 95 Conference Papers, Manchester, colour former and developer from each other after the initial 1995. 6 J. Schofield, personal communication. separation of the developer together with the colour former 7 NCR Corp., US Pat. 4 119 776 (1978). on cooling. 8 Yamamoto Kagaku Gosei, Eur. Pat. 124 377 (1984). If, as suggested by the above findings, the explanation of 9 Kanzaki Paper Manufacturing Co.Ltd., Eur. Pat. 209 259 (1986). the thermochromism lies in phase separation, there are a 10 Yamamoto Kagaku Gosei, Eur. Pat. 278 614 (1988). number of conclusions that can be drawn concerning the 11 D. H. Williams and I. Fleming, Spectroscopic methods in organic design and optimisation of compositions based on co-solvent/ chemistry, 3rd edn., McGraw-Hill, 1980. 12 D. Aitken, unpublished work. developer/colour former combinations. The developer must 13 J. GriYths, J. Soc. Dyers Colour., 1988, 104, 416. possess just enough solubility in the molten co-solvent to cause 14 M. Kubata, H. Yoshioka, K. Nakatsu, M. Matsumoto and complete dissolution and yet have suYciently poor solubility Y. Sato, in Chemistry of Functional Dyes, ed. Z. Yoshida and in the cooled composition to maximise phase separation. In Y. Shirota, Mita Press, Tokyo, 1989, p. 223. addition to the colour former having satisfactory solubility in 15 G. Rihs and C. D. Weis, Dyes Pigm., 1991, 15, 107. the co-solvent and the correct basicity for colour changes of 16 G. Rihs and C. D. Weis, Dyes Pigm., 1991, 15, 165. 17 J. Sueyoshi, M. Kubata, H. Yoshioka, K. Nakatsu and Y. Hatano, high contrast, the colorant must be compatible with the in Chemistry of Functional Dyes, ed. Z. Yoshida and Y. Shirota, developer, otherwise phase separation between these two com- Mita Press, Tokyo, 1992, vol. 2, p. 34. ponents will occur after the initial separation from the co- 18 P. PfeiVer and R. Wizinger, Ann., 1928, 461, 132. solvent, resulting in loss of colour after solidification of the 19 A. Haller and H. Umbgrove, C.R. Hebd. Seances Acad. Sci., 1899, composition. 129, 90. Phase separation can also explain the thermochromism of a 20 H.E. Fierz-David and W. Kuster, Helv. Chim. Acta, 1939, 22, 82. two-component system based on 1 and b-estradiol that gives a change from colourless to coloured on melting,4 which is Paper 8/05994B J. Mater. Chem., 1998, 8, 2677–2683 2683

ISSN:0959-9428    

DOI:10.1039/a805994b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials An investigation into the deacidification of paper by ethoxymagnesium ethylcarbonate Robin J. H. Clark,*a Peter J. Gibbsa and Raik A. Jarjisb aChristopher Ingold Laboratories, University College London, 20 Gordon Street, London, UK WC1H 0AJ bNuclear Physics Laboratory, University of Oxford, Keble Road, Oxford UK OX1 3RH Received 12th June 1998, Accepted 5th October 1998 Aspects of the procedure used since 1995 by the British Library whereby paper is deacidified with ethoxymagnesium ethylcarbonate (EMEC) in hexamethyldisiloxane (HMDS) have been studied using scanning electron microscopy (SEM) along with energy dispersive X-ray analysis (EDAX), X-ray fluorescence (XRF) spectrometry and particleinduced X-ray emission (PIXE).The treatment was applied to three types of test paper, and the analytical results compared with those for similar samples treated using a method which mimicked as closely as possible the library’s previous deacidification procedure; this involved the use of the now-banned solvent trichlorofluoroethane.The amount of EMEC distributed over the whole paper sample was fairly consistent for each paper type, but microscopically it was found to be congealed into large deposits, possibly hydrolysed by moisture in the paper, and not distributed as evenly among the paper fibres as is either desirable or possible.The depth of penetration of the EMEC particles obtained by spraying only one side of the paper is found to be poor for paper of heavy gauge and high moisture content, the thinnest samples retaining little alkaline buVer.The results obtained by the newer procedure were similar to those obtained by the older one, and no HMDS either reacted with, or remained in, the paper despite the relatively long drying time. The principal cause of the deterioration of cellulose-containing microscopy (SEM) and associated energy dispersive X-ray analysis (EDAX), and particle-induced X-ray emission materials, especially paper, was identified in the 1950s to be sulfuric acid generated by the hydrolysis of the common sizing (PIXE) to establish the uniformity of distribution and depth of penetration of the deacidification agent EMEC among agent aluminium sulfate1 (referred to, somewhat misleadingly, as ‘paper makers’ alum’).Aluminium sulfate is used in conjunc- paper fibres.Due to the large number of documents to be treated in the tion with natural wood resins to control water penetration in paper. Traditionally it was used to deposit saponified resins BL, a deacidification solution must be priced reasonably and, moreover, it must also penetrate each book uniformly in a onto the surface of paper fibres during manufacture so as to moderate period of time, and provide a suYcient alkaline achieve the desired firmness and to prevent the blurring of reserve for prolonged performance.10 Over the past two dec- dyes and inks.2 Other causes of acidity include the oxidation ades, the trend has been towards using non-aqueous solvents of lignin and cellulose and the absorption of atmospheric to deliver the deacidification agent, some of which involved pollutants;3 indeed, any acidic environment, regardless of the CFC chemicals that have now been phased out due to environ- source of the acidity, aVects paper in the same way, initiating mental legislation.In 1995, the BL changed their delivery ageing processes that aVect the lengths of the cellulose chains, solvent from trichlorofluoroethane to polydimethylsiloxane, resulting in brittleness and fragility.2 The library and museum but the latter was found to be slow to dry causing inks to be community are obliged to preserve printed matter that was fugitive and even tide-mark stains to develop. prepared on poor-quality (acidic), mass-produced paper; such The new paper preservation technique is based upon ethoxy- items, for example newspapers or the scribbled first drafts of magnesium ethylcarbonate (EMEC, 1), which is the deacidifi- now famous manuscripts, were often intended to be ephemeral cation agent, and the siloxane solvent, hexamethyldisiloxane but now have a high cultural value.The deacidification of (HMDS, 2).20 these items to preserve them for future generations is a major The EMEC reacts with the acid in the paper (in this concern of librarians and archivists world-wide.2–17 However, example, sulfuric acid) in a similar way to that discussed for the mass deacidification of paper is also controversial.The other organometallic deacidification agents [Scheme 2(a)].21 current method of evaluating the ‘pH of paper’ is known to MgO formed from the primary hydrolysis product be flawed, as it is really the pH of the solution used to moisten [Scheme 2(b)]21 reacts with CO2 to form the desired buVer, the paper surface that is being measured by a conventional MgCO3. The source of the CO2 may be the hydrolysis of the pH probe; there is thus the real possibility that millions of ethylcarbonate ligand, but comparison with the similar Batelle folios are being treated needlessly because they are being deemed, incorrectly, to be too acidic.This controversy will continue until a method is devised to measure the pH of moisture trapped inside the actual paper fibres, thereby yielding the true ‘pH of the paper’.18,19 The research reported here is an investigation into the eVectiveness of the delivery procedure of the mass deacidifi- cation agent EMEC used in the British Library (BL). Many C2H5OCO2MgOC2H5 H3C Si O CH3 CH3 Si CH3 CH3 CH3 2 1 treated and untreated samples have been examined by X-ray Scheme 1 Ethoxymagnesium ethylcarbonate (EMEC, 1) and hexamethyldisiloxane (HMDS, 2).fluorescence (XRF) spectrometry, scanning electron J. Mater. Chem., 1998, 8, 2685–2690 2685process2 (vide infra) suggests that it is probably atmospheric.Scanning electron microscopy and energy dispersive X-ray analysis C2H5OCO2MgOC2H5+H2SO4AMgSO4+CO2+2C2H5OH A study of 66 samples and 12 standards was performed on a (a) JEOL JSM-6400 scanning electron microscope with an accelerating voltage of 5 kV and an EDAX attachment. The samples C2H5OCO2MgOC2H5+H2OAMgO+CO2+2C2H5OH were mounted on 40 mm aluminium discs and sputter-coated with a 5–10 nm film of gold and palladium. MgO+CO2AMgCO3 (b) Scheme 2 (a) An example of EMEC deacidification and (b) a proposed X-Ray fluorescence spectrometry mechanism for the formation of the desired buVer.21 48 samples and 12 standards were analysed by XRF spectrometry using a Philips PW 1480 sequential X-ray spectro- There are three questions of interest: first, whether the photometer.The radiation source was a rhodium lamp with HMDS solvent permits a more uniform distribution of the wide-band excitation operating at 60 kV and 40 mA. The EMEC than does the CFC solvent; second, whether the crystals used were InSb (Si analysis) and thallium HMDS detaches from the cellulose fibres after application; azide phthalate (Mg analysis) and the number of counts was and third, whether the depth of penetration of the EMEC measured by a flow counter.Both sides of the samples were particles could be determined (the solution is normally applied studied and, for each, six recordings and background counts to one side of the paper only, and thus the EMEC particles (collection time=40 s) were performed for the Mg analysis, may not penetrate through to the other side before the solvent and four recordings and background counts (collection time= evaporates).Hereinafter, all Mg-containing particles related 16 s) were performed for the Si analysis. to EMEC will be described as EMEC particles; this is used as a generic term and no distinction is made as to whether the Particle-induced X-ray emission compound has reacted with acid, been hydrolysed, or perhaps not reacted, as only the presence of a magnesium-containing Elemental depth profiling was carried out by detecting X-rays compound is determinable.generated as a result of scanning a focused beam of 3.0 MeV The deacidification agent and the bulk solvent both contain protons over the cross-sections of the paper samples.The the elements Mg and Si not associated normally with organic results produced in the form of maps and line-scan plots were materials such as the cellulose fibres of paper, although they obtained using the scanning proton microprobe facility at the are associated with sizes, loads and impurities, and therefore University of Oxford. The experiments were performed using control samples were used extensively.Elemental analysis a 1 mm wide proton beam spot, and the X-rays produced were targeting these two elements in particular was considered to detected using a conventional Si(Li) detector. Further details about the experimental arrangements and new developments be the most perceptive approach to this project, via XRF in the application of ion-beam analysis (IBA) to historical spectrometry, SEM, EDAX analysis and PIXE techniques.materials (including paper) are presented elsewhere.23,24 A novel experimental procedure was developed for this study and will be published subsequently. Experimental Results and discussion Preparation of paper samples Scanning electron microscopy and energy dispersive X-ray Three diVerent types of paper studied: 20th century newsprint analysis (mechanical wood fibres, 50–60 g m-2, 6–9% moisture content, calliper 0.08 mm); general 1920s print (chemical/mechan- At a relatively high magnification (×6000) it was possible ical wood fibres, 80–90 g m-2, 5% moisture content, calliper among the paper fibres to detect white particles, which were 0.13–0.14 mm); and 18th century handmade (rag linen rarely greater than 1 mm in diameter and often much smaller: fibres, 100–120 g m-2, 5–8% moisture content, calliper an example of the type of image observed is shown in Fig. 1(a). 0.20–0.25 mm). The BL provided over 70 paper samples The particles were almost spherical and analysis using EDAX (9 cm×9 cm), including untreated controls, 27 samples treated revealed that they contained magnesium.The particles were with EMEC in HMDS, and 27 samples treated with EMEC small and of regular shape and their presence in all of the in the solvent 1,1-dichloro-2,2,2-trifluoroethane (DCTFE). As EMEC samples treated, their magnesium content, and the lack it is now impossible to obtain CFC solvents in the UK, of any other element with a relative atomic mass >23, proves DCTFE, which itself will be banned early next century, was that they are derived from the EMEC deacidification agent.substituted for trichlorofluoroethane. The samples were treated Other particles were found amongst the paper fibres but, in-house by the BL following their usual deacidification pro- due to their shape, size and analysis by EDAX, they could cedure. They were cut to size and then placed on a wire-mesh not be confused with the EMEC particles.The results of the treatment screen and held in place by a suction motor (air EDAX analysis are listed in Table 1. velocity ca. 1.4 m s-1). The freshly prepared deacidification Apart from the EMEC, the most important particles to be solution, propelled by nitrogen at a pressure of 3.85 kg cm-2, identified in the general and newsprint samples were irregular was sprayed by hand from approximately 10 cm in a sweeping crystals with both a high Al and, importantly, high Si content; motion until ‘full saturation’ was achieved.22 they are probably an aluminosilicate clay.The high Si content Sixteen 2 cm×2 cm sub-samples were removed from each of these particles will have an important bearing on the of 33 of the 9 cm×9 cm samples, including 6 controls, and interpretation of the results of the PIXE and XRF the positions of the sub-samples in the original samples were spectrometric analysis (vide infra).recorded. Four 40 mm circular sub-samples were removed In the test samples examined, there were generally signifi- from each of the remaining treated samples and six controls cantly more EMEC particles on the sprayed side than on the to take advantage of the optimum sampling area (XRF unsprayed side.An extreme example is illustrated in Fig. 1(a) spectrometry); the original positions of the sub-samples were and (b): one side of a general print/HMDS sample [the again recorded. In total there were 660 samples available for sprayed side, Fig. 1(a)] was well covered in what was, for this analysis, representing equally each paper type and each delivery study, a well above average number of EMEC particles, but on the reverse [unsprayed side, Fig. 1(b)] such particles are solvent, and with suYcient standard samples. 2686 J. Mater. Chem., 1998, 8, 2685–2690Fig. 1 Electron micrographs of (a) EMEC particles on a general print samples ×6000, (b) EMEC particles on the reverse of general print samples in (a) ×6000, (c) ‘strings’ of EMEC particles ×6000, (d) ‘bunches’ of EMEC particles ×6000.represented, but on a much lesser scale. This was generally paper is well covered in EMEC particles, there are many fewer EMEC particles on the reverse. true for all of the samples examined, regardless of whether the deacidification agent was delivered in the DCTFE or The conclusions drawn above are dependent in a large way on how many particles were deposited on the sprayed side of siloxane solvent.Using SEM/EDAX it is not possible to judge the depth of the paper samples in the first place. The type of coverage illustrated in Fig. 1(a), for which the sample had been sprayed penetration of the particles but only possible to examine each side of a sample to see whether EMEC particles are rep- with the siloxane-based solvent, was greater than that of any other sample examined, and in most cases it was much greater.resented. By this method, the following conclusions could be made as to the eVectiveness of the penetration of the particles More representative examples are shown in Fig. 1(c) and (d), which show isolated groups of EMEC particles in paper for the diVerent paper types: (1) some EMEC particles were always observed on both sides of the newsprint samples, but samples treated with the siloxane solvent. Generally, for all paper types and both solvent delivery systems, these groups for the thicker handmade paper very few if any penetrated to the reverse side.Newsprint paper is thin, and this is the likely of particles were few and far between. Two significant observations can be made from the images reason for the better penetration; (2) in the case of the general print samples, EMEC particles were always observed on both observed in this experiment: (1) even on the samples (those with the sides sprayed) with the most EMEC particles, the sides, but Fig. 1(a) and (b) indicate the relative ineVectiveness of the penetration to the reverse. Furthermore, the presence distribution is very uneven for all of the paper types, with isolated groups of particles dotted around the samples; (2) the of ink on the sprayed side of the samples blocks the penetration of the deacidification agent.particle size is generally larger on all of the newsprint, handmade samples and the general print samples examined which Generally, therefore, the depth of penetration achieved by spraying on one side of the paper depends only upon the had been treated with the DCTFE-based agent, than it is for the general print samples treated with the HMDS-based solu- thickness of the paper and whether or not there is ink on the sprayed side.However, even where one side of the thinnest tion [Fig. 1(a)–(d) are all at the same magnification, ×6000]. Table 1 EDAX analysis of crystals found between the paper fibres Elements identified (relative atomic mass <23) Identity of compound Paper typea and notes Mg EMEC or magnesium salt product Treated G, H & N Ca and S Gypsum,CaSO4·2H2O G and H.Probably added as a load Ca Chalk, CaCO3 G Fe, K and S Alum, AlK(SO4)2·12H2O G. Probably added as a size Al and Si Aluminosilicate clay G & N. Probably added as a load aG=1920s general print, H=18th century handmade and N=20th century newsprint. J. Mater. Chem., 1998, 8, 2685–2690 2687It was common for the EMEC particles to form either ‘strings’ general print standards is about three times more than on the newsprint standards, and over 40 times that detected on the [Fig. 1(c)] or ‘bunches’ [Fig. 1(d)] on the samples that displayed larger EMEC particles (the ‘string’ between the particles handmade samples. From the EDAX analysis, it is known that aluminosilicate clays are present in significant quantities in Fig. 1(c) is formed by the EMEC). The smaller particles in some general print examples treated with the HMDS-based in the general print samples, and to a lesser degree in the newsprint samples: they are probably added deliberately to fill solution do also coagulate, but they tend to distribute much more widely.the paper, and are the source of the high Si content. The very low relative amounts of Si on the handmade paper indicates The particles on most of the paper samples examined are up to ten times the diameter of the smallest observed on the that little or no Si-containing compounds were added deliberately at manufacture.general print samples treated with the siloxane-based solution. The smaller particles obviously give better coverage where Higher levels of Mg were detected on all of the treated paper samples relative to the standard samples.For the general they are deposited, although they can still be spread inconsistently across the general print samples treated with the HMDS. print samples, there was a higher level of Mg on the sprayed side, but considerable amounts were detected on the unsprayed The large particle size and ‘bunching’ of the EMEC particles on all of the other sample types reinforces the poor distribution sides as well.There was little diVerence between the average amounts of Mg detected whether the EMEC was delivered in of the deacidification agent. A possible cause is that the EMEC/HMDS solution is very water sensitive, and a white the HMDS or DCTFE. The range of the relative amounts of Mg detected does suggest that the EMEC/HMDS has slightly product, MgCO3, drops out of solution if the deacidification solution is contaminated with moisture.22 A similar problem better penetration, which would be explained by the smaller particle size.was noticed in the development of the Battelle process, employed by the Deutsche Bibliothek,2 which uses the same For the handmade samples, there was a vast diVerence between the amount of Mg detected on the sprayed and solvent as the BL but a diVerent deacidification agent, Mg(OC2H5)2.This alkoxide also hydrolyses to the desired unsprayed sides. On average, more Mg was detected on the sprayed sides of the samples treated with EMEC/DCTFE than buVer, MgCO3, but this can occur rapidly in humid conditions, aVecting the uniformity of distribution.2 The Battelle process those sprayed with EMEC/HMDS.The most important observation, however, is that the amount of Mg detected on the therefore includes a pre-drying of the samples from their stored humidity of 5–7% by weight to a water content of less reverse of the handmade samples was very low, comparable to that on untreated samples. In agreement with the SEM than 1%.2 The BL do not pre-dry their samples, and this may be the observations, this suggests that very little EMEC penetrates the thick-gauged handmade paper, regardless of the carrying reason for the clumping of particles observed generally in the handmade and newsprint samples, both of which have a solvent.The relatively high moisture content of the handmade paper may also contribute to this observation due to the relatively high moisture content.The general print samples, however, have the lowest moisture levels, as is expected for EMEC particles being hydrolysed before they can penetrate deeply into the paper. mechanical papers of such an age with degraded cellulose fibres. It is possible that the good spread of EMEC particles The most surprising observation was the relatively low levels of Mg detected on the treated newsprint samples.The amounts in some of the general print samples examined is attributable to a lack of moisture, implying that pre-drying will assist the were higher than detected on the untreated standards, but not by as much as had been expected. Similar amounts of Mg distribution and so the eVectiveness of the deacidification agent.It seems that the distribution of the EMEC particles were detected on the sprayed and unsprayed sides, suggesting that the thin gauge of the paper aided the even distribution of among the paper fibres is typically less eYcient than is either desirable or achievable. the particles; but, as the samples of the three papers were treated identically, the thin gauge of the newsprint does seem to inhibit its potential to retain a suYcient alkaline reserve X-Ray fluorescence spectrometry before becoming saturated. Both sides of four circular sub-samples, 40 mm diameter, The mean of the number of counts (minus the background count) for Si and Mg was calculated and a standard deviation were examined for each 9 cm×9 cm original.The samples covered 62% of the whole area of each sprayed sheet.Strikingly obtained for each sample. The normality of distribution of the number of counts for each sample set was established for both variable relative amounts of Mg were sometimes found in sub-samples from the same original (e.g. a ratio of the Mg and Si analysis (3s error test). However, the mean number of counts between similar samples (e.g.the unsprayed 0.4250.5150.8351.0 on four diVerent samples from the sprayed side of one general print/HMDS sample), but the relatively sides of EMEC/HMDS general print samples) were always found to diVer significantly using the statistical technique of low readings in this sample were extreme. The variations tended to be greater between original samples than within the analysis of variance (ANOVA, P=0.05) whereby the variance of each element within the same sample group and between same sample.Overall, the least amount of Mg detected was rarely less than half the maximum amount detected on similar similarly treated samples is compared. In other words, the amount of Mg and Si detected in samples treated identically sub-samples, and this suggests that the spraying technique with either solvent is depositing the EMEC fairly evenly on a varies significantly.As the number of counts is relative for each sample, it is macro-scale; but as the SEM analysis revealed, the distribution on a micro-scale within the paper fibres is poor. possible to determine the range of the relative amounts of each element detected on samples treated in an identical way Hexamethyldisiloxane has a relatively low boiling point (100 °C), a relatively high vapour pressure (20 mbar at 20 °C) (Table 2).Though there is no statistical similarity between the relative amounts of each element detected on similar samples, and a low enthalpy of vaporization (186 kJ kg-1), which means that treated papers will dry fairly quickly.However, the tabulated data convey important information regarding the distribution of each element in the paper samples. Thus this solvent dries much more slowly than the trichlorofluoroethane used previously, giving rise to concern that the pro- the amount of Mg present in the standard (untreated) samples is consistently low for each type of paper, and probably results longed exposure of the paper to the siloxane solvent may have adverse eVects and that the solvent may even react with species from impurities that entered the paper during manufacture, rather than from substances added deliberately.By contrast, within the paper or the paper fibres themselves, depositing unknown silicon-containing compounds within the paper. the level of Si detected in the standard samples varies considerably for the three paper types.The level of Si detected on the The results of the XRF analysis displayed in Table 1 suggest 2688 J. Mater. Chem., 1998, 8, 2685–2690Table 2 Range and weighted mean of relative number of counts determined from similar samples for Si and Mg by XRF spectrometry Range of relative number of counts and weighted mean (in parentheses) Deacidification Sprayed (S) or Paper type solution solvent unsprayed (U) side Si Mg General print HMDS U 21.5–32.9 (28.7) 0.17–0.36 (0.26) S 29.7–44.5 (37.6) 0.19–0.49 (0.39) DCTFE U 22.1–30.6 (28.1) 0.16–0.28 (0.24) S 21.9–40.3 (33.3) 0.32–0.46 (0.41) Standard 28.4–31.9 (29.9) 0.06–0.09 (0.08) Handmade HMDS U 0.45–0.59 (0.49) 0.02–0.04 (0.03) S 0.41–0.82 (0.54) 0.14–0.20 (0.17) DCTFE U 0.31–0.42 (0.37) 0.08–0.09 (0.09) S 0.50–0.67 (0.60) 0.42–0.55 (0.48) Standard 0.67–0.80 (0.71) 0.07–0.09 (0.08) Newsprint HMDS U 8.63–12.66 (10.1) 0.06–0.08 (0.07) S 8.60–12.71 (10.1) 0.06–0.08 (0.07) DCTFE U 8.01–10.97 (9.71) 0.06–0.09 (0.08) S 8.21–11.52 (9.53) 0.07–0.10 (0.08) Standard 10.1–12.42 (11.2) 0.02–0.04 (0.03) that the HMDS solvent is not retained by the treated paper.There is no significant diVerence between the ranges of the amounts of Si detected, regardless of whether the paper types were standard samples, or ones treated with either the siloxanebased or the DCTFE solution. This is particularly apparent in the handmade samples, which already contain a relatively low amount of Si, and where those samples treated with EMEC/HMDS actually contained the lowest average amount of Si.Particle-induced X-ray emission spectrometry The similar profiles of the line-scan plots obtained for Al and Si from general print and newsprint samples treated with EMEC/HMDS [e.g. Fig. 2(a) and (b)] confirm that they predominantly co-exist, which corresponds to the observation by SEM/EDAX that aluminosilicate clays are present. This supports the observation that Si present on the paper samples is due neither to the HMDS solvent nor to any reaction products, but to additives or impurities in the manufacturing process.The similar profiles of the plots obtained for Ca and S [e.g. Fig. 2(c) and (d)] from the handmade and general print also confirm that these elements co-exist as gypsum.The depth profile of the distribution of Mg, as illustrated by line-scan spectra, show that the maximum concentration of Mg is at a depth of roughly 50–70 mm (i.e. about one-third to one-half the way through) into the paper for the general print samples [e.g. Fig. 2(e) and (f )]. This observation is similar for the handmade papers which, due to their thicker gauge, means that less of the paper is protected. As an immediate result of this study, the BL has altered its procedure to include spraying each page from both sides to ensure maximum protection.The Library is now considering whether reducing the moisture content of the paper to aid Fig. 2 PIXE line-scan plots (150 mm) of (a) Al and (b) Si on a general distribution of the agent is practical and desirable.print sample treated with EMEC/HMDS, (c) Ca and (d) S on a general print sample treated with EMEC/HMDS, (e) and (f ) Mg on Conclusions two diVerent samples treated with EMEC/HMDS indicating the lack of penetration through the paper. The amount of EMEC distributed over the whole paper sample was fairly consistent for each paper type, but microscopically, however, the EMEC was found to be congealed in large deposits, possibly hydrolysed by moisture in the paper, and reacted with, or remained in, the paper despite the relatively long drying time.not distributed as evenly among the paper fibres as is either desirable or possible. The depth of penetration of the EMEC particles obtained by spraying only one side of the paper is Acknowledgements poor for heavy gauged papers and those with a high moisture content, and the thinnest samples retained a relatively low We are indebted to the Leverhulme Trust for the award of a fellowship (PJG), to ULIRS and the von Clemm foundation amount of alkaline buVer.The results obtained with the new method of application were similar to those for the previous for financial support, to Dr G.Mariner at Royal Holloway and Bedford New College (XRF), to the electron microscope method, and there was no evidence that the HMDS either J. Mater. Chem., 1998, 8, 2685–2690 268912 A.-C. Brandt, Mass Deacidification of Paper: A Comparative Study unit at The Queen’s University of Belfast, and to Shad Mehmet of Existing Processes, Bibliothe`que Nationale, Paris, 1992. and Dr.Mirjam Foot at the British Library. 13 E. M. Kaminska and H. D. Burgess, Natl. Libr. News, 1994, 26, 11. 14 R. Areal Guerra, J. M. A. Gibert Vives, J. M. A Daga` Monmany References and J. Fernandez Garrido, Restaurator, 1995, 16, 175. 1 W. J. Barrow, Manuscripts and Documents: Their Deterioration 15 V. D. Daniels, Chem. Soc. Rev., 1996, 25, 179. and Restoration, University of Virginia Press, Charlottesville, 16 M. C. Sistach Anguera, Restaurator, 1996, 17, 117. 1955. 17 S. R. Middleton, A. M. Scallan, X. Zou and D. H. Page, Tappai, 2 J. Wittekind, Restaurator, 1994, 15, 189. 1996, 79, 187. 3 L. R. Green and M. Lesse, Restaurator, 1991, 12, 147. 18 A. Kennedy and K. R. Seddon, personal communication. 4 J. S. Arney, A. J. Jacobs and R. Newman, J. Am. Inst. 19 V. Bukovsky�, Restaurator, 1997, 18, 25. Conservation, 1979, 19, 34. 20 PDTA solution from Particle Technology Limited, Hatton, UK. 5 M. Hey, The Paper Conservator, 1979, vol. 4, p. 66. Solvent includes 10% ethanol to assist solution. 6 R. D. Smith, Can. Libr. J., 1979, 325. 21 A. N. MacInnes and A. R. Barron, J. Mater. Chem., 1992, 2, 1049 7 D. Mihram, Restaurator, 1986, 7, 81. and references therein. 8 D. Mihram, Restaurator, 1986, 7, 99. 22 S. Mehmet, personal communication. 9 L. Santucci, V. Grosso, M. Hey and L. Rossi, in New Directions in 23 R. A. Jarjis, in Application of Particle and Laser Beams in Paper Conservation, Institute of Paper Conservation, Leigh, 1986, Materials Technology, ed. P. Misalides, Kluwer Academic D68–D69. Publishers, Dordrecht, 1995, pp. 443–461. 10 G. B. Kelly, in Conservation of Library and Archive Materials and 24 R. A. Jarjis, in Conservation and Preservation of Islamic the Graphic Arts, ed. G. Petherbridge, Institute Of Paper Manuscripts, ed. Y. Ibish and G. Atiyeh, Al-Furqan Publications, Conservation/Society Of Archivists, London, 1987, pp. 117–123. London, 1996, pp. 93–117. 11 P. Schwerdt, in Sauvegarde et Conservation des Photographies, Dessins, Imprime�s et Manuscrits, ARSAG, Paris, 1991, pp. 213–216. Paper 8/04453H 2690 J. Mater. Chem., 1998, 8, 2685–

ISSN:0959-9428    

DOI:10.1039/a804453h

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Crystal structure of the mixed conductors phases, Li0.5–3xLa0.5+x+yTi1–3yM3yO3 (M=Mn, Cr) with x=0.133 and y=0.20 Manuel Morales,a Lourdes Mestres,a Maja Dlouha�,b Stanislav Vratislavb and Maria-Luisa Martý�nez-Sarrio�n*a aDept. Inorganic Chemistry, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain. *E-mail: mluisa@kripto.qui.ub.es bDept.of Solid State Engineering, Czech Technical University in Prague, Bøehova� 7, 115 19 Prague 1, Czech Republic Received 23rd June 1998, Accepted 14th September 1998 Perovskite-like solid solutions of general formula Li0.5–3xLa0.5+x+yTi1–3yM3yO3 (M=Mn, Cr) show three polymorphs; A, b and C. The crystal structure of the C polymorphs in manganese– and chromium–lanthanum systems, determined from powder neutron diVraction using Rietveld refinement, are of the ordered perovskite type.The structures of both phases are similar, containing a three dimensional framework of corner-sharing MO6 (M=Ti or Mn/Cr) octahedra in which the structures are partially collapsed as a result of a cooperative tilting and rotation of octahedra. Orthorhombic unit cell, M=Mn: a=5.5411(11) A° , b=7.8120(14) A° , c=5.4924(10) A° ; M=Cr: a=5.5014(9) A° , b=7.7735(15) A° , c=5.4729(9) A° ; space group Pnma (no. 62). Ionic conductivity takes place by a hopping mechanism between Li+-occupied and empty A-sites, while electronic conductivity is along octahedra. The family of Li+ ion-conductors with perovskite-like structure of general formula Li0.5–3xRE0.5+xTiO3 (RE=La, Pr, Nd, Sm) has been extensively studied because of their high Li-ion conductivity.The maximum bulk ionic conductivity is found in the lanthanum system with a value of 1.1×10-3 S cm-1 for x=0.07.1–4 A few years ago, phase diagrams of La, Pr and Nd systems were reported,5,6 which show two polymorphs in the lanthanum system, labelled A and b, and three polymorphs, A, b and C, in the praseodymium and neodymium systems.All of these have a perovskite-related structure. Polymorph A is a simple cubic perovskite, while b is a tetragonal perovskite with ao=bo#ac and co#2ac, and C is an orthorhombic distortion of A with ao=Ó2ac+d, bo#2ac and co=Ó2ac-d, where ac is the parameter of a cubic perovskite. Recently, the study of titanium substitution by manganese and chromium in lanthanum and praseodymium systems have led to compounds of general formula RE0.5+x+y- Li0.5–3xTi1–3yMn3yO3 (RE=La, Pr and M=Mn, Cr)7,8 with large regions of perovskite-like solid solutions.These compounds showed both electronic and Li-ion conductivity. The ionic conductivity was similar in manganese and chromium systems while the electronic conductivity was much higher in the manganese system.Polymorph C appeared for the first time in lanthanum systems when titanium was substituted by manganese or chromium. The aim of the present work was to obtain the crystal structure of this polymorph in lanthanum systems. Experimental Samples were prepared in 10 g quantities from La2O3 (99.9% Fluka), TiO2 (Aldrich 99+%), MnO2 (>99% Fluka) or Cr2O3 (>99% Fluka) and Li2CO3 (Aldrich >99%). La2O3 and TiO2 were dried overnight at 900 °C prior to weighing.These chemicals were weighed, mixed in an agate mortar with acetone, dried and heated at 650 °C for 2 h to drive oV CO2. Fig. 1 Phase diagrams along joins: a) La0.538Li0.25TiO3–LaMnO3 and b) La0.538Li0.25TiO3–LaCrO3. After grinding, samples were pressed into pellets and covered J.Mater. Chem., 1998, 8, 2691–2694 2691Table 1 Crystallographic data for La0.833Li0.10Ti0.40Mn0.60O3 a Atom Site x/a y/b z/c Uiso/10-2 A° 2 Occupancy La 4c 0.0067(12) 0.25 0.9968(14) 1.2(5) 0.832(5) Li 4c 0.388(4) 0.25 0.439(5) 2.1(6) 0.11(4) Ti 4b 0.5 0.0 0.0 1.1(5) 0.395(5) Mn 4b 0.5 0.0 0.0 1.1(5) 0.605(5) O(1) 4c 0.5156(9) 0.25 0.0134(8) — 1.00 O(2) 8d 0.2541(6) 0.0413(6) 0.7374(8) — 1.00 Anisotropic temperature factors/10-2 A° 2 Atom U11 U22 U33 U12 U13 U23 O(1) 9.8(5) 0.8(9) 3.2(8) 0.00 -5.1(9) 0.00 O(2) 0.6(7) 1.4(6) 3.6(8) -0.25(8) -0.24(7) -2.1(7) Bond lengths and angles La coordination M coordination La–O(1) 2.710(7) M–O(1) ×2 1.956(5) La–O(1) 2.604(7) M–O(2) ×2 1.945(4) La–O(2) ×2 2.542(7) M–O(2) ×2 1.987(4) La–O(2) ×2 2.913(8) La–O(2) ×2 2.616(8) O(1)–M–O(1) 180 La–Li 0.699(1) O(1)–M–O(2) ×2 80.1(8) Li coordination O(1)–M–O(2) ×2 99.9(8) Li–O(1) 2.442(8) O(1)–M–O(2) ×2 95.9(8) Li–O(1) 2.079(7) O(1)–M–O(2) ×2 84.1(7) Li–O(2) ×2 2.426(7) O(2)–M–O(2) ×2 180 O(2)–M–O(2) ×2 89.0(7) O(1)–Li–O(1) 114.1(8) O(2)–M–O(2) ×2 90.9(7) O(1)–Li–O(2) 67.2(8) O(1)–Li–O(2) 137.3(9) O(2)–Li–O(1) 84.4(9) aSpace group: Pnma (no. 62); ao=5.5411(11) A° , bo=7.8120(14) A° , co=5.4924(10) A° ; Rwp=8.13%, Rp=6.04%.Fig. 2 Observed, calculated (upper curve) and diVerence ( lower curve) Fig. 3 Polymorph C structure of La0.833Li0.10Ti0.40Mn0.60O3; neutron profiles for a) La0.833Li0.10Ti0.40Mn0.60O3 and b) octahedra, MO6 (M=Ti/Mn); black balls, La; and gray balls, Li. La0.833Li0.10Ti0.40Cr0.60O3. 2692 J. Mater. Chem., 1998, 8, 2691–2694Table 2 Crystallographic data for La0.833Li0.10Ti0.40Cr0.60O3 a Atom Site x/a y/b z/c Uiso/10-2A° 2 Occupancy La 4c 0.0067(16) 0.25 0.9910(12) 0.63(10) 0.830(5) Li 4c 0.355(8) 0.25 0.433(7) 1.8(8) 0.10(4) Ti 4b 0.5 0.0 0.0 0.88(17) 0.402(5) Cr 4b 0.5 0.0 0.0 0.88(17) 0.588(5) O(1) 4c 0.5043(8) 0.25 0.0124(8) — 1.00 O(2) 8d 0.2593(7) 0.0378(6) 0.7424(8) — 1.00 Anisotropic temperature factors/10-2 A° 2 Atom U11 U22 U33 U12 U13 U23 O(1) 8.9(9) 1.0(5) 3.2(7) 0.00 -1.2(8) 0.00 O(2) 1.2(7) 1.4(4) 2.3(6) -0.46(5) 0.72(7) -1.8(8) Bond lengths and angles La coordination M coordination La–O(1) 2.588(6) M–O(1) ×2 1.946(5) La–O(1) 2.815(6) M–O(2) ×2 1.942(4) La–O(2) ×2 2.555(6) M–O(2) ×2 1.984(4) La–O(2) ×2 2.883(8) La–O(2) ×2 2.625(8) O(1)–M–O(1) 180 La–Li 0.866(11) O(1)–M–O(2) ×2 81.2(9) Li coordination O(1)–M–O(2) ×2 98.8(9) Li–O(1) 2.447(7) O(1)–M–O(2) ×2 95.7(9) Li–O(1) 2.001(6) O(1)–M–O(2) ×2 84.3(8) Li–O(2) ×2 2.444(6) O(2)–M–O(2) ×2 180 O(2)–M–O(2) ×2 89.1(8) O(1)–Li–O(1) 120.5(8) O(2)–M–O(2) ×2 90.8(8) O(1)–Li–O(2) 70.8(8) O(1)–Li–O(2) 137.4(9) O(2)–Li–O(1) 84.9(9) aSpace group: Pnma (no. 62); ao=5.5014(9) A° , bo=7.7735(15) A° , co=5.4729(9) A° ; Rwp=7.32%, Rp=5.18%.with powder of the same composition to avoid loss of lithium Samples of composition La0.833Li0.10Ti0.40M0.60O3 (M=Cr or Mn) were synthesized and annealed at 1000 °C and were during thermal treatment. The pellets were fired at 1100 °C for 8 h giving green products which were reground, repelleted and studied by powder neutron diVraction, since they were clearly located in the polymorph C region for this temperature and fired at 1200 and 1250 °C for 12 h.Phase purity was checked by X-ray powder diVraction using composition. a Siemens D-500 diVractometer. Stoichiometries were obtained by ICP with a JOVIN IVON apparatus. Crystal structure Phase diagram studies vs. temperature were carried out for The structures were refined initially using the parameters of joins La0.583Li0.25TiO3–LaMO3 where M=Cr or Mn. Small the polymorph C in the system Pr0.5+xLi0.5–3xTiO310 with La pelleted samples were wrapped in platinum foil envelopes, and Li placed on the larger A sites of the perovskite structure placed in a furnace and annealed isothermally for 15 min in (ABO3) and Ti and Mn or Cr on the octahedral B sites.order to reach equilibrium.Finally they were droliquid Occupancies for La/Li and Ti/Mn or Cr were constrained at nitrogen to quench the phase. Samples for neutron diVraction the values 0.83/0.10 and 0.40/0.60 respectively, which were were pressed in several pellets, annealed at 1000 °C for 15 min obtained by ICP. In the first stage, lithium coordinates were and quenched in liquid nitrogen. Powder neutron diVraction fixed and lanthanum, titanium and manganese or chromium data were collected on the KSN-2 diVractometer located at coordinates and temperature factors were refined.Finally the LVR-15 research reactor near Prague. The crystal struclithium coordinates, isotropic thermal parameters and occu- tures were refined by the Rietveld method with the program pancies were refined.GSAS,9 using data collected at l=0.1362 nm, between 10 and Final refined atomic coordinates, temperature factors, bond 85° in 2h and taking into consideration the absorption correcangles and lengths for La0.833Li0.10Ti0.40Mn0.60O3 and tion for the natural mixture of the lithium isotopes. La0.833Li0.10Ti0.40Cr0.60O3 are given in Tables 1 and 2, respectively, with fitted neutron diVraction profiles for Results manganese– and chromium–lanthanum compounds [Fig. 2(a) and 2(b)].Phase diagrams The structure (Fig. 3) contains a three dimensional framework of corner-sharing MO6 (M=Ti or Mn/Cr) octahedra in Polymorphs A, b and C were identified along both joins [Fig. 1(a) and (b)]. Polymorphs A and C only form at high which the structure is partially collapsed in all three directions as a result of a cooperative tilting and rotating of octahedra. temperatures (T800 °C), although they can be preserved at room temperature by quenching.Polymorph C spreads over Although polymorphs C in the manganese– and chromium– lanthanum systems show similar features to those in praseo- a large region for y0.133 while polymorph b extends along the whole range of composition at low temperatures.dymium and neodymium systems, there are some diVerences. J. Mater. Chem., 1998, 8, 2691–2694 2693For instance, rare earth elements are placed close to the Acknowledgements theoretical A-site in all of these systems, however, Pr and This work was partially sponsored by financial support from Nd10,11 are clearly displaced from this site by 0.098 and CICYT MAT95–0218 and from 1997SGR 00265 and from 0.141 A° , respectively, which allows them to adopt a distorted GAE`R 202/97/K038.eight-coordination for RE–O, while La is closer to theoretical A-site with distances of 0.041 and 0.061 A° for manganese and chromium systems, giving a distorted 12-coordination with References La–O distances in the range 2.555–2.883 A° in the lanthanum– 1 M.Itoh, Y. Inaguma, W. Jung, L. Chen and T. Nakamura, Solid chromium system. This behaviour could be associated to rare State Ionics, 1994, 70/71, 203. earth size, since it is more diYcult for a large element to move 2 H. Kawai and J. Kuwano, J. Electrochem. Soc., 1994, 141, L78. oV the cell centre. 3 Y. Inaguma, L. Chen, M. Itoh and T.Nakamura, Solid State On the other hand, Li+ in manganese– and chromium– Ionics, 1994, 70/71, 196. lanthanum systems is clearly oV-centre with a displacement of 4 Y. Inaguma and M. Itoh, Solid State Ionics, 1996, 86–88, 257. 5 A. D. Robertson, S. Garcý�a Martý�n, A. Coats and A. R. West, 0.7053 and 0.8382 A° , respectively, cf. 0.5260 A° in the praseo- J. Mater. Chem., 1995, 5, 1405.dymium system. This displacement allows lithium to adopt a 6 M.Morales and A. R. West, Solid State Ionics, 1996, 84, 33. distorted tetrahedral coordination. 7 I.Moreno, M. Morales and M. L. Martý�nez Sarrio� n, J. Solid State MO6 (M=Ti or Cr/Mn) octahedra are more distorted than Chem., 1998, 140, in the press. in Pr and Nd systems with M–O distances between 1.945 and 8 M. Morales and M. L. Martý�nez Sarrio� n, J. Mater. Chem., 1998, 1.987 A° in the manganese system and 1.942–1.984 A° in the 8, 1583. 9 A. C. Larson, R. B. Von Dreele, GSAS Generalized Crystal chromium system. The distance M–O(1) is slightly larger in Structure Analysis System, Los Alamos National Laboratory, Los the manganese than in the chromium system probably due to Alamos, New Mexico, 1994. electronic eVects. 10 J. M. S. Skakle, G. C. Mather, M. Morales, R. I. Smith and A. R. These phases show both Li+-ion and electronic conductivity. West, J. Mater. Chem., 1995, 5, 1807. From the structure, it is presumed that ionic conductivity 11 R. I. Smith, J. M. S. Skakle, G. C. Mather, M. Morales and A. R. takes place by a hopping mechanism among Li+-occupied West, Mater. Sci. Forum, 1996, 228–231, 701. and empty A-sites, while electronic conductivity is along octahedra. Paper 8/04764B 2694 J. Mater. Chem., 1998, 8, 269

ISSN:0959-9428    

DOI:10.1039/a804764b

出版商:RSC    

年代:1998

数据来源: RSC