摘要:

MATERIALS CHEMISTRY COMMUNICATION Second harmonic generation of dye aggregates in bentonite clay Thibaud Coradin,a Keitaro Nakatani,b Isabelle Ledoux,c Joseph Zyssc and Rene� Cle�ment*a aL aboratoire de Chimie Inorganique, U.R.A. 420, Universite� Paris-Sud, 91405 Orsay, France bP.P.S.M., Ecole Normale Supe�rieure de Cachan, U.R.A. 1906, avenue du Pdt Wilson, 94235 Cachan, France cFrance T elecom CNET Centre Paris B, L aboratoire de Bagneux, 196, avenue Henri Ravera, 92220 Bagneux, France Intercalation of the dyes was ascertained by powder X-ray diraction, using a Siemens diractometer with a Cu-Ka Intercalation of stilbazolium chromophores in a bentonite clay leads to the formation of dye aggregates exhibiting second anode.The diractograms of the four compounds show a relatively narrow 001 reflection (width ca. 2h=0.5°) indicating harmonic generation properties. a basal spacing of ca. 16A° . Assuming a van derWaals thickness of a clay layer around 9 A° ,10 a value of ca. 7A° can be derived for the thickness of the dye layer, which is consistent with the value found in the MPS3 intercalates. This suggests that the chromophores lie edge-on within the galleries.The amount of The use of organic–inorganic hybrid materials has already inserted dye also compares with the MPS3 analogues [from been extremely fruitful for producing new compounds with elemental analysis, C 11.8%, N 1.5% (by mass) for the non-linear optical (NLO) properties.1–4 We have recently bentonite–DAMS intercalate at maximum loading]. reported that intercalation of stilbazolium chromophores in Fig. 1 shows the evolution of the UV–VIS absorption spectra the hexathiohypodiphosphate MPS3 layered phases can give of the DAMS+ and DAES+ intercalates with increasing rise to NLO-active materials.5,6 A model involving the forma- chromophore concentrations. At low concentrations, both tion of dye J-aggregates in the interlamellar space of the host materials present a broad and slightly asymmetrical band with was then suggested.a maximum absorption around 460 nm, this wavelength being In order to study the influence of the nature of the host very close to the charge transfer band of the organic molecules lattice on the chromophore packing and its possible contri- in aqueous solution. As the amount of inserted cations bution to the NLO properties, we have undertaken the insertion of the same dyes in bentonite, a cation-exchangeable clay.In contrast to MPS3 intercalation chemistry, insertion in clays usually takes place at room temperature and permits monitoring of the concentration of inserted species. The synthesis of the 4-[4-(dimethylamino)-a-styryl]-1- methylpyridinium (DAMS+) iodide, and of the other derivatives (DAZOP+, DAES+, DEMS+) used in this work, has already been reported.6,7 The last three of these present only slight modifications from the DAMS+ skeleton to ensure a similar molecular quadratic hyperpolarisability b.8,9 Bentonite SPV (Comptoir de Mine�raux et de Matie`res Premie`res) with a cation exchange capacity (CEC) of 90 mequiv.per 100 g of the clay was used after equilibration with a sodium chloride solution.Aqueous suspensions with bentonite concentrations from 0.4 to 4 g l-1 and dye concentrations from 10-5 to 10-3 mol l-1 were allowed to stand overnight at room temperature. The strongly Fig. 1 Selected UV–VIS spectra of (a) bentonite–DAMS+ and coloured solids were collected by centrifugation, thoroughly (b) bentonite–DAES+ intercalates in a concentration range of 10-4 (spectrum 1) to 10-2 mol (spectrum 2) of dye per 100 g of clay washed with water and dried.J. Mater. Chem., 1997, 7(6), 853–854 853increases, two dierent behaviours are observed. In the tration dependence and the striking sensitivity to the chromophore structure of the aggregation process suggest a very tight DAMS+ case [Fig. 1(a)], a new band arises around 550 nm, close packing of the organic molecules, consistent with the which grows stronger and narrower than the previous one as nearly 100 nm shift of the charge-transfer band observed for the maximum dye concentration is reached.In contrast, the the intercalates. We are currently studying the photophysical bentonite–DAES+ spectra [Fig. 1(b)] show no equivalent feaproperties of these materials to obtain more information ture, the bandshape remaining essentially the same when concerning the size and structure of these aggregates.concentration is increased. Finally, the DAZOP+ cation presents the same behaviour as DAMS+ whereas DEMS+ seems We thank the Comptoir de Mine�raux et de Matie`res Premie`res to resemble DAES+. As already discussed,6 the strong red- (Paris) for the gift of bentonite. Support by European COST shift of the UV band of intercalated DAMS+ and DAZOR+ Action D4/0001/95 is kindly acknowledged.We are also grate- can be attributed to the formation of J-type aggregates. ful to Dr P. Lacroix (Toulouse) for stimulating discussions. Second harmonic generation (SHG) experiments were carried out on 100 mm sieved samples using the Kurtz–Perry powder technique11 operating at variable fundamental inten- References sity, the harmonic signal from the unknown powder being 1 S.Tomaru, S. Zembutsu, M. Kawachi and M. Kobayashi, J. Chem. plotted with respect to the harmonic emission from a reference Soc., Chem. Commun., 1984, 1207. urea powder.12 The laser source is a ns Nd–YAG pulsed laser 2 V.Ramamurthy and D. F. Eaton, Chem.Mater., 1994, 6, 1128. operating at 1.34 mm. Pure bentonite, bentonite–DAES+ and 3 B. Lebeau, C. Sanchez, S. Brasselet, J. Zyss, G. Froc and bentonite–DEMS+ did not generate any significant signals. In M. Dumont, New J. Chem., 1996, 20, 13. 4 R. Hoss, O. Ko�nig, V. Kramer-Hoss, U. Berger, P. Rogin and contrast, bentonite–DAMS+ and bentonite–DAZOP+ com- J.Hulliger, Angew. Chem., Int. Ed. Engl., 1996, 35, 1664. pounds were found to exhibit SHG signals whose intensity 5 P. G. Lacroix, R. Cle�ment, K. Nakatani, J. Zyss and I. Ledoux, increased with chromophore concentration to reach a maxi- Science, 1994, 263, 658. mum value of 0.25 times urea in the bentonite–DAMS+ case. 6 T. Coradin, R. Cle�ment, P. G. Lacroix and K. Nakatani, Chem.Upon comparison of these results with the previously Mater., 1996, 8, 2153. reported ones concerning MPS3 intercalates,7 the same dis- 7 S. R. Marder, J. W. Perry and C. P. Yakymyshyn, Chem. Mater., 1994, 6, 1137. crimination in UV–VIS spectra and NLO properties was 8 Non L inear Optical Properties of Organic Molecules and Crystals, observed. More precisely, only the intercalates containing ed.D. S. Chemla and J. Zyss, Academic Press, New York, 1987. aggregated dyes gave rise to SHG. The lower eciency, 9 Molecular Non L inear Optics: Materials, Physics and Devices, ed. as compared to MPS3–DAMS+, of the bentonite–DAMS+ J. Zyss, Academic Press, New York, 1994. compound may be attributed, at least in part, to the poor 10 Intercalation Chemistry, ed.M. S.Whittingham and A. J.Jacobson, Academic Press, New York, 1982. crystallinity of the clay samples. 11 S. K. Kurtz and T. T. Perry, J. Appl. Phys., 1968, 19, 3798. In conclusion, this work provides another example of a 12 P. D. Maker, Phys. Rev. A, 1970, 1, 923. host–guest system that exhibits SHG properties even though 13 D. Mo�bius, Adv. Mater., 1995, 7, 437. the host lattice is known to be centrosymmetrical. The nega- 14 R. Cohen and S. Yariv, J. Chem. Soc., Faraday T rans. 1, 1984, tively charged layers appear to favour the formation of highly 80, 1705. positive J-aggregates leading to a non-centrosymmetric arrangement of the dyes.13,14 Moreover, the strong concen- Communication 7/02078C; Received 25thMarch, 1997 854 J. Mater. Chem., 1997,

ISSN:0959-9428    

DOI:10.1039/a702078c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

MATERIALS CHEMISTRY COMMUNICATION Physical stabilization of anatase (TiO2) by freeze-drying Hiroyuki Izutsu,a Padmakumar K. Nairb and Fujio Mizukamib aT aki Chemical Co., L td. 2,Midorimachi, Befu-cho, Kakogawa, 675-01 Hyogo, Japan bNational Institute of Materials and Chemical Research, 1-1 Higashi, T sukuba, 305 Ibaraki, Japan the primary particles of the anatase phase sinter together to The anatase phase of titania has been stabilized without reach the critical nucleus size.10 From circumstantial evidence, chemically modifying the system, by changing the level of it is expected that the critical nucleus size of rutile is at least packing within the aggregates by freeze-drying the water- three times larger than the crystallites present in the anatase washed precipitate obtained by the hydrolysis of titanium phase.11 This means that if sintering of anatase particles is isopropoxide.After calcination at 700 °C for 8 h, freeze-dried retarded by a suitable technique (the probability of reaching samples showed more than 97% anatase phase with a surface the critical nucleus size is lowered), we can retain a high area and porosity of 29 m2 g-1 and 37% respectively. The porosity and surface area as well as retard the transformation oven-dried samples showed a surface area and porosity of 5 m2 to rutile.In this study we have retarded the sintering by g-1 and 10% respectively. eectively decreasing the packing of anatase particles by freeze-drying. Titania powder was prepared by the hydrolysis of titanium isopropoxide (Wako Chemicals, Japan). The alkoxide (0.18 mol) was dissolved in 350 g (5.8 mol) of isopropyl alcohol and The anatase modification of titania is an important material this solution was added dropwise to 350 g of distilled water for catalysis.1 Anatase is a metastable phase and it will under vigorous stirring at room temperature.After separation transform irreversibly to the stable rutile phase.2–5 For many of the precipitated gel by decantation and centrifugation, the applications this transformation is not favoured, for two main precipitate was washed five times with a total of 5 l of deionized reasons: (1) anatase has distinctly better catalytic properties water.This washed precipitate was then divided into two than rutile,1 and (2) this transformation always results in a portions: one portion was dried in an oven at 110 °C for 24 h dense (non-porous) rutile phase, which is not useful as a (designated as WWOD); the other portion was freeze-dried catalyst or as a ceramic membrane material.5,6 It is generally (WWFD). observed that the anatase-to-rutile transformation temperature From the thermal analysis data it was found that both depends on many factors like preparation conditions, nature samples were amorphous in the as-prepared state and on of the precursor, minor impurities, morphology of the primary heating transforms first to anatase and then to rutile.Table 1 particles etc.6 Almost all the attempts to stabilize the anatase gives the DTA transformation temperatures and the textural phase have been based on changing the chemistry of the properties (surface area and porosity) of the oven-dried and system.1,6,7 Even in those studies in which a chemical modifi- freeze-dried samples.As expected, both transformation tem- cation was not the primary aim, the stabilization technique peratures, amorphous-to-anatase and anatase-to-rutile, are ultimately resulted in modifying the chemistry of the system.8,9 higher for the freeze-dried samples. During drying the WWOD However, the degree of modification is thought to be much samples experience a large compressive stress, owing to the smaller than for other chemical methods of stabilization.8,9 In surface tension of the pore fluid, compared to the WWFD this paper we report, for the first time, a purely physical means samples.Therefore the level of packing of primary particles of stabilization of the anatase phase. The major advantage of within the aggregate and also the packing of aggregates this is that unlike chemical modification, this technique will themselves will be higher compared to the WWFD. It should not change the chemistry of the system, which means that the be noted that during freezing, the first step in the freeze-drying catalytic properties are not changed.process, the WWFD samples will also experience compressive The anatase-to-rutile transformation is a nucleation growth stresses similar to drying stresses.12,13 However, this stress will type of transformation and the temperature and rate at which not be acting throughout the sample and, moreover, the it happens, from a physical point of view, depends on how fast possibility for the primary particles to rearrange during freezing is much lower compared to the rearrangement during the Table 1 Eect of drying method on the phase transformation tempera- oven-drying of WWOD.A lower level of packing will lead to ture and BET surface area large porosity (Table 1) and a broad pore size distribution with a higher average pore size.This can be seen from the phase transformation temp./°Ca surface area/m2 g-1 pore size distribution data given in Fig. 1. The average pore size of WWOD samples is lower than that of WWFD. method am.�ana. ana.�rut. 400 °C 700°C Moreover, WWOD samples show a broader pore size distribution with some pores in the microporous (pore radius oven-dried 399 727 116 (51)b 5 (10) <1 nm) range.freeze-dried 416 895 75 (57) 29 (37) A lower level of packing in WWFD samples will result in a aPhase transformation temperaures from amorphous (am.) to anatase lower number of particle–particle contacts and this in turn (ana.) and anatase to rutile (rut.) obtained from exothermic peaks of results in slower particle growth.Therefore WWFD samples DTA curves. bValues in parentheses show porosities (%) evaluated by will transform more slowly than WWOD samples. Fig. 2 shows using total N2 adsorption amounts and densities of titania (3.8g ml-1 XRD patterns of the samples heated at 400 and 700 °C. After for oven-dried and 400 °C heated sample and freeze-dried samples, 4.2g ml-1 for oven-dried and 700°C heated sample).heating at 400 °C for 8 h both the samples show the typical J. Mater. Chem., 1997, 7(6), 855–856 855Fig. 1 Pore size distributions of WWOD and WWFD before heating (a) and after heating to 400 °C (b) and 700 °C (c). Upper traces: freeze-dried; lower traces: oven-dried samples the WWFD sample shows higher porosity indicating a lower level of packing. At 700 °C WWFD has a much higher surface area (29 m2 g-1) and porosity (37%) with more than 97% anatase phase.From the above results it can be seen that freeze-drying is a very eective way to stabilize the catalytically important anatase phase with high surface area and porosity at relatively high temperatures. References 1 K. Foger and J. R. Anderson, Appl. Catal., 1986, 23, 139. 2 R. D.Shannon and J. A. Pask, J. Am. Ceram. Soc., 1965, 48, 391. 3 C. N. R. Rao, Can. J. Chem., 1961, 39, 498. 4 F. Dachille, P. Y. Simens and R. Roy, Am.Mineral., 1968, 53, 1929. 5 K-N. P. Kumar, K. Keizer, A. J. Burggraaf, T. Okubo, S. Morooka and H. Nagamoto, Nature (L ondon), 1992, 358, 48. 6 K-N. P. Kumar, K. Keizer and A. J. Burggraaf, J. Mater. Chem., 1993, 3, 1141. 7 Y-S. Lin, C-H.Chang and R. Gopalan, Ind. Eng. Chem. Res., 1994, 33, 860. 8 K-N. P. Kumar, Jalajakumari Kumar, K. Keizer, T. Okubo, Fig. 2 X-Ray diraction patterns of the titania samples: (a) WWOD M. Sadakata and J. Engell, J. Mater. Sci. L ett., 1995, 14, 1784. heated at 400°C; (b) WWFD heated at 400 °C; (c) WWOD heated at 9 K-N. P. Kumar, Appl. Catal., 1994, 119, 163. 700 °C; (d) WWFD heated at 700°C. A=anatase, R=rutile 10 K-N. P. Kumar, Jalajakumari Kumar and K. Keizer, J. Am. Ceram. Soc., 1994, 77, 1396. 11 K-N. P. Kumar, Scr.Metall.Mater., 1995, 32, 873. anatase pattern [Fig. 2 (a) and (b)], but at 700 °C WWFD 12 G. W. Scherer, J. Non.-Cryst. Solids, 1993, 155, 1. [Fig. 2(d)] practically remains as anatase and WWOD 13 J. Kumar, PhD Thesis, University of Twente, The Netherlands, [Fig. 2(c)] transforms to rutile. 1995. The higher surfarea of WWOD at 400°C is probably Communication 7/01755C; Received 13thMarch, 1997 due to the presence of micropores in the WWOD. However, 856 J. Mater. Chem., 1997, 7(6), 855–856

ISSN:0959-9428    

DOI:10.1039/a701755c

出版商:RSC    

年代:1997

数据来源: RSC

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MATERIALS CHEMISTRY COMMUNICATION Non-classical FeII spin-crossover behaviour leading to an unprecedented extremely large apparent thermal hysteresis of 270 K: application for displays Yann Garcia, Petra J. van Koningsbruggen, Epiphane Codjovi, Rene� Lapouyade, Olivier Kahn* and Louis Rabardel L aboratoire des Sciences Mole�culaires, Institut de Chimie de laMatie`re Condense�e de Bordeaux, UPR CNRS no. 9048, 33608 Pessac, France [Fe(hyetrz)3](anion)2·3H2O [hyetrz=4-(2¾-hydroxyethyl)- 1,2,4-triazole, anion=3-nitrophenylsulfonate] is a novel linear polynuclear FeII spin-crossover compound. The low-spin to high-spin transition accompanied by a pronounced thermochromic eect occurs at 370 K in a very abrupt way. Just before this temperature, the three non-coordinated water molecules are removed.The dehydrated high-spin form remains stable down to ca. 100 K, where it transforms into a new low-spin form, implying that this material shows an apparent thermal hysteresis width of 270 K. Applications of amount of ascorbic acid was heated and added under stirring this material are discussed. to a methanolic solution (10 ml) containing 9.1 mmol (1.03 g) of hyetrz prepared from monoformyl hydrazine, triethylorthoformateand 2-ethanolamine according to the method described by Bayer et al.21 A white precipitate was formed immediately which was filtered, washed with methanol and dried in air.Iron(II) spin-crossover materials have acquired increasing inter- The compound changes from white to pink during the drying est during the last decade.Evidently, the fast developments in process, due to the 1A1g�1T1g d–d transition at 520 nm of the advanced electronic technology may require compounds show- compound in the LS state. The compound changes to white ing bistability behaviour on the molecular scale.1 A fascinating upon heating to ca. 370 K, because the spin-allowed d–d example of molecular bistability is represented by FeII spin- transition of lowest energy of the compound in the HS state, crossover compounds, which show a transition from the high- 5T2g�5Eg, occurs at the limit of the visible and IR regions.spin state (HS, S=2) to the low-spin state (LS, S=0) on Surprisingly, subsequent cooling to room temperature leaves cooling, upon increasing pressure, or by light irradiation.2–9 the white colour of the compound unaected.Since this The use of such materials as molecular-based memory devices compound shows a thermochromic eect, the FeII spin trans- and displays has been investigated.10,11 This type of application ition has been studied optically using a device described requires abrupt spin transitions involving a large thermal previously.7,21 This device records the change in intensity of hysteresis as well as an associated thermochromic the absorption band at 520 nm, and therefore allows one to eect.3,7,9,10,12,13 The occurrence of abrupt transitions involving follow the spin crossover in a remarkably simple and reliable hysteresis is related to cooperativity.Although the mechanism way. The results of the optical measurements displayed in of this cooperativity is not yet fully understood, it is commonly Fig. 1 reveal a very abrupt LS�HS transition taking place at accepted that these interactions may become extremely import- 370 K, after which the compound is further heated to 400 K. ant when the active spin-crossover sites are covalently linked Subsequent cooling shows the HS�LS transition to occur at by conjugated ligands.The cooperativity may even be 100 K, yielding an extremely wide apparent hysteresis of 270 K. enhanced by hydrogen bonding interactions within the crystal lattice.7,9 Indeed, in the linear polynuclear FeII spin-crossover compounds of general formula [Fe(NH2trz)3 ](anion)2·xH2O (NH2trz=4-amino-1,2,4-triazole; anion=NO3-,9,14,15 ClO4-,16 BF4-,10,16 I-,17 Br-,10,16 CH3SO3-18), in which the FeII ions are linked by triple N1,N2-1,2,4-triazole bridges,19 relatively large thermal hysteresis (up to about 35 K) was observed.Within this family of compounds, the derivatives containing tosylate20 and related aromatic sulfonate anions show an exceptionally large apparent hysteresis loop up to 80 K, owing to the synergy between FeII spin-crossover behaviour and a dehydration–rehydration process.Modifying the 1,2,4-triazole ligand yielded a novel polynuclear FeII spincrossover compound showing unprecedented behaviour, and oering a new opportunity to use such compounds in display devices. [Fe(hyetrz)3](anion)2·3H2O [hyetrz=4-(2¾-hydroxyethyl)- 1,2,4-triazole, anion=3-nitrophenylsulfonate] was synthesized Fig. 1 Optical detection of the spin transition for the couple as follows.A methanolic solution (20 ml) containing 3 mmol [Fe(hyetrz)3](3-nitrophenylsulfonate)2·3H2O–[Fe(hyetrz)3 ](3-nitrophenylsulfonate) 2 (1.72 g) of [Fe(H2O)6](3-nitrophenylsulfonate)2 and a small J. Mater. Chem., 1997, 7(6), 857–858 857A second heating experiment reveals a LS�HS transition with by heating the sample as described above, or by secondary pumping at a pressure of 10-6 mbar.TC(=115 K. Additional heating and cooling cycles show that this hysteresis of 15 K is maintained. The unprecedented wide apparent hysteresis loop of 270 K for [Fe(hyetrz)3](3-nitrophenylsulfonate)2·xH2O implies that Thermogravimetry (see Fig. 2) carried out with the same velocity of heating (1 K min-1) as for the optical measurements we are dealing with a compound using its memory eect only once; after it has been addressed by increasing temperature to reveals a continuous loss of mass starting at room temperature.This decrease in mass proceeds rapidly in the temperature the value of TC(, leading to an abrupt LS�HS transition involving a colour change from pink to white, it remains in range 325–340 K, after which it continues in a much smoother fashion.At 370 K the percentage mass lost is in exact agreement this white HS state in the absence of extreme humidity, provided it is not cooled to very low temperature. At room with the removal of all three lattice water molecules from [Fe(hyetrz)3](3-nitrophenylsulfonate)2·3H2O. Consequently, temperature [Fe(hyetrz)3](3-nitrophenylsulfonate)2 in the HS state and under normal atmospheric conditions does not when the spin transition occurs, no lattice water molecules are present in the compound. Upon cooling no change in the mass rehydrate, in contrast to [Fe(NH2trz)3 ](tosylate)2.20 The information induced by the abrupt spin transition is retained. of the sample is observed, which indicates that the compound is not rehydrated. Therefore, this material may be of use in applications in which detection of a specific temperature is required in a very simple The magnetic properties have also been investigated.The results are in good agreement with the optical data of Fig. 1. and accurate way. The spin-crossover material then acts as a thermal sensor giving an optical response only when TC( is In addition, the magnetic data indicate that the LS�HS transition at 370 K for the starting material is essentially reached, for instance as an alert when the temperature exceeds an upper limit.More interestingly, this thermal addressing complete, while the HS�LS transition for the dehydrated compound at 100 K is incomplete; about 15% of the FeII ions accompanied by an abrupt and stable optical response may alsobe used in single-use (orone-shot) displays.Further physical remain in the HS state below 100 K.These results can be interpreted as follows. At room tempera- studies along with detailed exploration of implementation in devices of [Fe(hyetrz)3](3-nitrophenylsulfonate)2·xH2O and ture the thermodynamical stable state for the hydrated compound [Fe(hyetrz)3](3-nitrophenylsulfonate)2·3H2O is the LS related materials are in progress.state. Evidently, this LS state is stabilized by the hydrated nature of this modification. Indeed, studies on mononuclear References FeII spin-crossover compounds have already revealed that the 1 O. Kahn and J. P. Launay, Chemtronics, 1988, 3, 140. low-spin state may be stabilized by interactions with lattice 2 Pding, 1981, 44, 83. water molecules.22–25 Upon heating, the compound loses all 3 J. Zarembowitch and O. Kahn, New J. Chem., 1991, 15, 181. its lattice water molecules, yielding just below 370 K the 4 E.Ko� nig, Prog. Inorg. Chem., 1987, 35, 527. dehydrated [Fe(hyetrz)3 ](3-nitrophenylsulfonate)2 analogue in 5 J. G. Haasnoot, in Magnetism: A Supramolecular Function, ed.a LS state. However, at this temperature this LS state is a O. Kahn, Kluwer Academic Publishers, Dordrecht, 1996, p. 299. 6 P. Gu� tlich, A. Hauser and H. Spiering, Angew. Chem., Int. Ed. metastable state, and transforms in an exceptionally abrupt Engl., 1994, 33, 2024. fashion to the HS state. Further cooling of [Fe(hyetrz)3 ](3- 7 O. Kahn and E.Codjovi, Philos. T rans. R. Soc. L ondon, A, 1996, nitrophenylsulfonate)2 reveals the HS�LS transition for the 354, 359. dehydrated compound taking place at 100 K. Subsequent 8 O. Kahn,MolecularMagnetism, VCH, New York, 1993. heating shows the LS�HS transition with TC(=115 K. This 9 O. Kahn, E. Codjovi, Y. Garcia, P. J. van Koningsbruggen, hysteresis of 15 K is now stable and can be considered as a R.Lapouyade and L. Sommier, in Molecule-Based Magnetic Materials, ed. M. M. Turnbull, T. Sugimoto and L. K. Thompson, genuine hysteresis, whose origin is governed by cooperative ACS Symp. Ser. No. 644, American Chemical Society,Washington interactions. Evidently, the crucial feature allowing the occur- DC, 1996, p. 298. rence of the apparent hysteresis of 270 K results from the 10 O.Kahn, J. Kro�ber and C. Jay, Adv. Mater., 1992, 4, 718. stabilization of the LS state by water molecules, which ceases 11 C. Jay, F. Grolie`re, O. Kahn and J. Kro�ber,Mol. Cryst. L iq. Cryst., only when the water molecules are removed leading to the 1993, 234, 255. formation of the metastable low-spin state of [Fe(hyetrz)3](3- 12 J. Kro�ber, J.-P. Audie`re, R. Claude, E.Codjovi, O. Kahn, J. G. Haasnoot, F. Grolie`re, C. Jay, A. Bousseksou, J. Linare`s, nitrophenylsulfonate)2. The LS [Fe(hyetrz)3](3-nitrophenyl- F. Varret and A. Gonthier-Vassal, Chem.Mater., 1994, 6, 1404. sulfonate)2·3H2O compound, after being cycled once, can be 13 J. Kro�ber, E. Codjovi, O. Kahn, F. Grolie`re and C. Jay, J. Am. reconstructed at room temperature from the HS [Fe(hyetrz)3] Chem.Soc., 1993, 115, 9810. (3-nitrophenylsulfonate)2 compound by placing the latter in a 14 L. G. Lavrenova, V. N. Ikorskii, V. A. Varnek, I. M. Oglezneva very humid (i.e. a water saturated) atmosphere. The reverse and S. V. Larionov, Koord. Khim., 1986, 12, 207. process requires the removal of lattice water molecules either 15 L. G. Lavrenova, V. N. Ikorskii, V.A. Varnek, I. M. Oglezneva and S. V. Larionov, J. Struct. Chem., 1993, 34, 960. 16 L. G. Lavrenova, V. N. Ikorskii, V. A. Varnek, I. M. Oglezneva and S. V. Larionov, Koord. Khim., 1990, 16, 654. 17 L. G. Lavrenova, N. G. Yudina, V. N. Ikorskii, V. A. Varnek, I. M. Oglezneva and S. V. Larionov, Polyhedron, 1995, 14, 1333. 18 R. Bronisz, K. Drabent, P. Polomka and M. F. Rudolf, Conference Proceedings, ICAME95, 1996, 50, 11. 19 A. Michalowicz, J. Moscovici, B. Ducourant, D. Cracco and O. Kahn, Chem.Mater., 1995, 7, 1833. 20 E. Codjovi, L. Sommier, O. Kahn and C. Jay, New J. Chem., 1996, 20, 503. 21 H. O. Bayer, R. S. Cook and W. C. von Meyer, US Pat. 3821 376, 1974. 22 K. H. Sugiyarto, D. C. Graig, A. D. Rae and H. A. Goodwin, Aust. J. Chem., 1994, 47, 869. 23 K. H. Sugiyarto and H. A. Goodwin, Aust. J. Chem., 1988, 41, 1645. 24 M. Sorai, J. Ensling, K. M. Hasselbach and P. Gu�tlich, Chem. Phys., 1977, 20, 197. 25 T. Buchen, P. Gu�tlich, K. H. Sugiyarto and H. A. Goodwin, Chem. Eur. J., 1996, 2, 1134. Fig. 2 Thermogravimetric analysis for [Fe(hyetrz)3 ](3-nitrophenylsulfonate) 2·xH2O Communication 7/01242J; Received 24th February, 1997 858 J. Mater. Chem., 1997,

ISSN:0959-9428    

DOI:10.1039/a701242j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

MATERIALS CHEMISTRY COMMUNICATION Sol–gel transition in CdS colloids Thierry Gacoin,* Laurent Malier and Jean-Pierre Boilot L aboratoire de Physique de laMatie`re Condense�e, URA CNRS 1254 D, E� cole Polytechnique, 91128 Palaiseau Cedex, France the particles in various solvents such as acetone, tetrahydrofuran (THF) and dimethylformamide, with very high concen- We report the preparation of transparent gels from concentrated sols of CdS nanocrystals.The principles of our trations (at least 5 mol l-1, i.e. volumic fraction ca. 15%). Two methods have been adapted from previous studies4,8 for the method can be applied to other systems, enlarging the domain of the inorganic sol–gel process which so far has been synthesis of such concentrated colloids. (1) Colloids from the P-I process were prepared by the growth restricted mainly to oxides.of particles directly in the presence of FPhSH. A solution of deaerated acetone containing H2S (5×10-3 mol l-1), FPhSH (1×10-2 mol l-1) and triethylamine (TEA; 2×10-2 mol l-1) was added dropwise into the same volume of a stirred solution A gel is an open three-dimensional skeleton of aggregated of acetone containing 4×10-3 mol l-1 of Cd(NO3)2.The use of TEA ensured the neutralization of the acidity from H2S and particles, with solvent trapped in its pore network. The formation of an inorganic gel usually requires a well controlled FPhSH. The average size of the particles (ca. 1 nm) was deduced from the absorption spectrum using previously pub- colloidal synthesis, and the successive stabilization and slow destabilization of nanoparticles.The first step, the preparation lished size–gap correlation curves.10 The small size is a consequence of the high thiol content needed to stabilize the of a stable colloid,1 can be achieved by the limited growth of the particles in solution while preventing their agglomeration particles. The flocculation of the particles resulting from complete evaporation of the solvent and subsequent washing with due to van der Waals interactions. In dielectric solvents, particles having surface charges oer repulsive forces which ethanol led to a powder which was dispersed in fresh acetone with a molar concentration.counterbalance the van der Waals interactions. When this electrostatic repulsion between the particles is absent or too (2) In the case of colloids from process P-II, CdS nanoparticles were synthesized within water droplets from a water (2.5 mol weak, their aggregation has to be limited by the presence of molecules which either provide steric hindrance between the l-1)–AOT (0.5 mol l-1)–heptane emulsion [AOT=sodium di- (2-ethylhexyl)sulfosuccinate surfactant].7 The average size of particles or passivate their surface. In any case, the conditions of the stability of colloids give upper limits for the particle size the particles (1–5 nm) was controlled by the initial cadmium concentration in water (0.01–0.15 mol l-1).Excess H2S was and their concentration in the synthesis medium. The second step is the further evolution of the colloid into a gel instead of eliminated by N2 bubbling.Addition of FPhSH and TEA with a concentration equal to 5 times the initial Cd concentration a precipitate. Gelation requires the formation of aggregates with an open structure and only occurs when the number induces flocculation of the particles which can then be recovered as a powder by centrifugation. After washing, the particles and/or the reactivity of the bonding sites at the surface of the particles is low, thus preventing the formation of dense aggre- were dispersed in acetone with a molar concentration. 113Cd NMR spectroscopy was used to study the structure gates.2 This can be induced by addition of a chemical agent to the colloid which slowly increases the reactivity of the particles. andthe surface complexationofCdSparticles(Fig. 1).Following Dance and co-workers,11 the various CdSx(SPhF)4-x contri- So far, the inorganic sol–gel process has been restricted to oxide systems.3 We here report the preparation of non-oxide butions (0×4) can be determined, together with the coordination of the thiolate ligands (either bridging, mSPhF, or concentrated colloids, sols and gels of II–VI semiconductor chalcogenides such as CdS.The elementary CdS particles are terminal, tSPhF). The signals are rather large, which severely limits spectral interpretation. This broadening arises from either nanocrystals resulting from controlled growth in inverted micelles or small clusters prepared in the presence of com- a distribution of Cd chemical shifts corresponding to some variations in the SMCdMS bond lengths and angles.plexing molecules. In both cases, stable and concentrated colloids are obtained by surface complexation of the elementary For the particles prepared by process P-I, we observed a particles with 4-fluorophenylthiol. The destabilization of these colloids, leading to aggregation and gelation, is achieved by progressive decomplexation of the particles. The first step is the synthesis of colloidal II–VI compounds.This problem has been the subject of extensive investigations, 4–8 motivated by the physical properties related to quantum confinement.9 Many synthesis procedures have been developed, which all used the stabilization of the nanoparticles with a complexing agent, e.g. thiol, phosphine, phosphate. The highest colloid concentrations are obtained when the solvent used for the dispersion can also complex the surface of the particles, thus improving their passivation towards aggregation. 6,8 Such passivation prevents gelation.In this work, we looked for both ecient complexation and dispersion in Fig. 1 113Cd NMR spectra performed on CdS concentrated sols in common solvents, together with the possibility of controlled acetone.Chemical shifts are given with reference to Cd(CH3)2. depassivation.We find that 4-fluorophenylthiol (FPhSH), used (a) Typical spectrum for 1 nm particles prepared by the P-I process. (b) Spectrum for 3.4 nm particles obtained by the P-II process. as a strong surface complexing agent, allows the dispersion of J. Mater. Chem., 1997, 7(6), 859–860 859large distribution of Cd environments.The broad bands at d 70 and 50 reveal CdS4 sites, in cubic, zinc-blende-type and hexagonal, wurtzite-type fragments, respectively. The band at d -62 corresponds to Cd(mFPhS)3(tFPhS)1, i.e. Cd complexed with four thiolate ligands, and is relatively narrow as the thiolate groups rotate freely around the Cd ion. The bands at d +30, +10 and -20 probably correspond to the three other environments: CdS3(SPhF)1 , CdS2(SPhF)2 and CdS(SPhF)3 groups, respectively.This large distribution is obviously related to the competition between precipitation and complexation reactions which is inherent to this process. The partial substitution of the tetrahedrally coordinated sulfurs of the zinc blende structure by bridging or terminal thiol groups limits the particle growth.Thiolate species appear as inhibitors for the precipitation and lead to small polymeric particles, i.e. clusters of size 1 nm. For the nanoparticles obtained by the inverted micelle technique (P-II) and complexed by thiolate species, the 113Cd NMR spectrum revealed the presence of CdS4 in a cubic, zinc blende lattice, CdS3(SPhF) and Cd(SPhF)4 groups.The Cd(SPhF)4 groups give the sharp line located at d -62 and form a complexing shell around the particles. No other cadmium environment was detected in these samples, which suggested that these colloids were formed by dense CdS nanoparticles capped with a surface cadmium thiolate complex. It is well known that thiols can be oxidized easily by various oxidizers such as O2 from air, hydrogen peroxide or sodium periodate, to give either dithiol (FPhMSMSMPhF) or sulfonate (FPhMSO3-), depending on the experimental procedure.12 As these compounds are no longer bonded to the surface of Fig. 2 Sol–gel transition performed by thiol oxidation at the surface the particles, they leave reactive sites at the surface and thus of 2 nmCdS crystallites dispersed in acetone (CdS volumic fraction 5%) permit agation. Since the particle surface is slowly activated, random aggregation occurs leading to lacunar aggregates and thus making the sol–gel transition possible. In this scheme of the synthesis is based on the following steps: sense, chalcogenide II–VI colloids complexed with FPhSH and (i) synthesis of the colloid; (ii) preparation of a concentrated dispersed in weakly complexing solvents (e.g. acetone, THF) sol consisting of particles complexed by an organic molecule present a unique opportunity to observe gelation.and dispersed in a neutral solvent; (iii) controlled aggregation Gelation was studied in controlled conditions by adding and gelation through slow depassivation of the surface of the H2O2 to the deaerated CdS sol.This was performed at 0°C particles. The gels may be further processed as transparent under vigorous stirring in order to allow a homogeneous nanostructured monoliths or thin films, the properties of which dispersion of the oxidant in the solution before reaction. After are under investigation. a few minutes, the solution was stored at room temperature. For example, transparent sti gels (Fig. 2) were obtained within References a few minutes for 2 nm crystallites occupying a volume fraction 1 Dispersion of Powders in L iquids, ed. G. D. Parfitt, Applied Science of 5% treated with 0.3 equiv. H2O2 (relative to the thiol Publishers, London, 1981, 3rd edn. concentration). We note that such optically transparent gels 2 P. G. de Gennes, J. Phys. (Paris), 1976, 37, L1; D.Stauer, are obtained for CdS volume fractions higher than 1%, and J. Chem. Soc., Faraday T rans. 2, 1976, 72, 1354. light scattering is increasingly observed as the CdS particle 3 C. J. Brinker and G. Scherer, Sol–Gel Science: T he Physics and Chemistry of Sol–Gel Processing, Academic Press, London, 1990. concentration is decreased. 4 N. Herron, Y. Wang and H. Eckert, J.Am. Chem. Soc., 1990, 112, Concerning the aggregation mechanism, 19F NMR experi- 1322; Y. Nosaka, N. Otha, T. Fukuyama and N. Fujii, J. Colloid ments13 have recently shown that thiol and disulfide molecules Interface Sci., 1993, 155, 23. do not participate directly in the establishment of chemical 5 A. Fojtik, H. Weller, U. Koch and A. Henglein, Ber. Bunsen-Ges. bonding between the particles.This suggests that aggregation Phys. Chem., 1984, 88, 969. 6 C. B. Murray, D. J. Norris and M. G. Bawendi, J. Am. Chem. Soc., between the particles occurs through direct contact between 1993, 115, 8706. CdS particles with no organic link. 7 P. Lianos and J. K. Thomas, Chem. Phys. L ett., 1986, 125, 299. As has already been shown for silica gels, scattering tech- 8 M. L. Steigerwald, A.P. Allivisatos, J. M. Gibson, T. D. Harris, niques are the most appropriate way to study the fractal R. Kortan, A. J. Muller, A. M. Thayer, T. M. Duncan, structures of aggregates and to determine their fractal dimen- D. C. Douglass and L. E. Brus, J. Am. Chem. Soc., 1988, 110, 3046. sion, D, which is related to the aggregation mechanism.14 X- 9 M. G. Bawendi, M.L. Steigerwald and L. E. Brus, Ann. Rev. Phys. Chem., 1990, 41, 477; A. P. Alivisatos, Science, 1996, 271, 933. Ray scattering experiments were carried out using synchrotron 10 Y. Wang and N. Herron, Phys. Rev. B, 1990, 42, 7253. radiation at LURE (Orsay, France). For a CdS gel resulting 11 G. S. Lee, K. J. Fisher, A. M. Vassallo, J. V. Hanna and I. G. Dance, from oxidation of P-I process sol (small polymeric units), the Inorg.Chem., 1993, 32, 66. scattering curve between Q=2×10-2 and 5×10-1 nm-1 exhi- 12 B. J. Evans, J. Takahashi Doi and W. K. Musker, J. Org. Chem., bits a power law corresponding to a fractal dimension of 1.9. 1990, 55, 2337. 13 T. Gacoin, L. Malier and J-P. Boilot, Chem.Mater., submitted. As observed for silica gels, this value is consistent with the 14 D. W. Schaefer and D. Keefer, in Fractals in Physics, ed. fractal dimension of lacunar objects resulting from the cluster– L. Pietronero and E. Tosatti, Elsevier Science Publishers, cluster aggregation model.14 Amsterdam, 1986; R. Vacher, T. Woigner, J. Pelous and In conclusion, we have reported the preparation of trans- E. Courtens, Phys. Rev. B, 1988, 37, 6500. parent gels of CdS. The specific case of chalcogenides (CdS, ZnS, CdSe) is an immediate extension of this work. The general Communication 7/01035D; Received 13th February, 1997 860 J. Mater. Chem., 1997, 7(6), 859–860

ISSN:0959-9428    

DOI:10.1039/a701035d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

MATERIALS CHEMISTRY COMMUNICATION Novel non-aggregated unsymmetrical metallophthalocyanines for second-order nonlinear optics Minquan Tian,a TatsuoWada,*a,b Hiromi Kimura-Sudab and Hiroyuki Sasabea,b aFrontier Research Program, T he Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan bCore Research for Evolution Science and T echnology (CREST), T he Institute of Physical and Chemical Research (RIKEN), 2.1 Hirosawa, Wako-shi, Saitama 351-01, Japan Novel soluble unsymmetrical metallophthalocyanines with twelve 2,2,2-trifluoroethoxy groups as donor substituents and a mono-nitro or an exocyclic conjugated nitro group as an acceptor substituent have been synthesized and characterized.A study of the concentration dependence of UV–VIS absorption spectra showed they were non-aggregated phthalocyanines in solution and in doped polymer films.Second harmonic generation of spin-coated thin films of poly(methyl methacrylate) doped with these metallophthalocyanines was observed after electric poling at 110 °C for 30 min at a fundamental wavelength of 1.064 mm. Phthalocyanines (Pcs) have attracted great research attention for many years because of their two-dimensional p-electron conjugation, great structural variety, high thermal and chemical stability, and unique electrical, optical, magnetic, catalytic, mesogenic and film-formation properties for various applications. 1–3 Up to now, a variety of symmetrical or pseudosymmetrical tetra-, octa- and hexadeca-substituted phthalocyanines have been reported.1–4 However, there have been only a limited number of reports on unsymmetrical phthalocyanines because of their preparative diculty.5 In the last decade, the third-order non-linear optical (NLO) properties of phthalocyanines have been well studied.6 Although it has been pointed out that unsymmetrical phthalocyanines with donor and Scheme 1 Reagents and conditions: i, CF3CH2OH, K2CO3–DMF, acceptor groups should possess second-order NLO properties,7 room temp., 12 h, 94.5%; ii, VCl3 (or ZnCl2), urea, 180–200 °C, 2–5 h; there have been few reports on this research subject.In our iii, H+–water, reflux, 2–4 h; iv, VCl3 (or ZnCl2), urea, 180–200 °C, previous study, we reported the synthesis and second-order 2–5 h; v, H+–water, reflux, 2–4 h; vi, (Ph3P)2PdCl2–CuI, Et3N–THF, 30–40°C, 24 h, 85–95% NLO properties of a Langmuir–Blodgett film of an unsymmetrical phthalocyanine with a nitro group as an acceptor substituent and three tert-butyl groups as donor substituents.8,9 On the other hand, mononuclear species of phthalocyanines trifluoroethoxy)-substituted metallophthalocyanines with a nitro or 4-nitrophenylethynyl group on one of the benzene usually show intermolecular aggregation in common organic solvents at high concentrations and in the solid state.10 We units.There are several reasons why we designed and synthesized such unsymmetrical phthalocyanines. First, we intro- found the molecular aggregation eect has an important influence on the linear and third-order NLO properties of duced twelve trifluoroethoxy groups on three of the benzene units in order to enhance the solubility and suppress the metallophthalocyanines.11 In order to study the influence of molecular aggregation on the second-order NLO properties of intermolecular interaction.Secondly, twelve trifluoroethoxy groups may also be expected to serve as donor groups, and a unsymmetrical phthalocyanines in the condensed state, we are interested in non-aggregated unsymmetrical phthalocyanines nitro group as an acceptor substituent. Thus the target phthalocyanines are two-dimensional conjugated systems containing with conjugated donor–acceptor systems.Here we report the results of syntheses, spectroscopic, and second-order NLO both donor and acceptor.We expect that the extended exocyclic conjugation in 4a and 4b may enhance the molecular second- properties of some novel unsymmetrically substituted metallophthalocyanines (see Scheme 1, compounds 2a, 2b, 4a and order non-linearity.The dierent central metal parts are also of interest because the NLO properties of phthalocyanines 4b) which suppress molecular aggregation even in the solid state. depend strongly on the peripheral and axial substitution patterns.6 Moreover, the target unsymmetrical phthalocyanines The target materials are unsymmetrically dodecakis(2,2,2- J.Mater. Chem., 1997, 7(6), 861–863 861not only can be expected to have second-order NLO properties Fig. 1 shows the absorption spectra for spin-coated poly- (methyl methacrylate) (PMMA) films doped with various but also are third-order NLO materials because of their twodimensional p-conjugated structures.Finally, we expect that concentrations of 2a normalized by the peak value. Mononuclear phthalocyanine generally shows no sign of inter- the target unsymmetrical phthalocyanines may be thermally stable candidates for poled-polymer applications. molecular aggregation in common solvents at concentrations below 1×10-5 M at room temperature.10 At higher concen- The syntheses of the target materials are shown in Scheme 1. 3,4,5,6-Tetrakis(2,2,2-trifluoroethoxy)phthalonitrile 1 was pre- trations, however, intermolecular aggregation can occur. In Fig. 1, the concentration in chloroform solution of 2a is pared by a modification of the published method.4,12 The nucleophilic substitution reaction of 3,4,5,6-tetrafluorophtha- <1×10-5 M and then the spectrum for chloroform solution represents the non-aggregated or ‘monomeric’ state. For 2a, lonitrile with 2,2,2-trifluoroethanol in N,N-dimethylformamide using potassium carbonate as a base at room temperature for the Q-band absorption position does not change with the concentration of doped phthalocyanine.Besides, no significant 12 h gave 1 in 94.5% yield.The statistical condensation of a 155 molar ratio of 1 and 4-nitrophthalonitrile in the presence blue-shift of the Q-band was observed from the comparison of the absorption spectra in chloroform solution and in the solid of an excess of metal salt and dry urea at 180–200 °C produced the desired unsymmetrical metallophthalocyanines 2a and 2b state. These phenomena are contrary to those of aggregated phthalocyanines in the condensed state, such as tetrakis(tert- in 16.3% and 15.0% yield, respectively. Similarly, the new unsymmetrical monoiodinated phthalocy- butyl) metal-free phthalocyanine.15 These results can be explained from the dodecakis(2,2,2-trifluoroethoxy) substi- anines 3a and 3b were synthesized by the mixed condensation of a 153 molar ratio of 1 and 4-iodophthalonitrile13 in 23% tution of the phthalocyanine ring.The strong repulsive eect between electronegative fluorine atoms reduces the possibility and 16% yield, respectively. The cross-coupling reaction between monoiodinated metallophthalocyanines 3a, b and an of severe aggregation between phthalocyanine molecules in the solid state.The aggregation properties of 2b, 4a and 4b in the excess of 4-nitrophenylacetylene14 in triethylamine–tetrahydrofuran (151) with bis(triphenylphosphine)palladium chloride solid state were similar to that of 2a. Therefore, the target compounds 2a, 2b, 4a and 4b can be considered to be non- and copper(I) iodide as catalyst at 30–40 °C under a dry nitrogen atmosphere gave compounds 4a and 4b as dark green aggregated metallophthalocyanines.Thin films of PMMA doped with the target unsymmetrical solids in high yields after purification. All the new unsymmetrical phthalocyanines 2–4 were puri- phthalocyanines 2 and 4 with a thickness of ca. 1.5 mm were obtained on a glass substrate by a spin coating method from fied by column chromatography on silica gel with hexane– ethyl acetate (vol. ratio 451 for 3a, 351 for 2a, 3b and 4a, 351 to 151 for 2b and 4b) several times and then recrystallized from ethyl acetate–hexane.Their structures were identified by UV–VIS, FAB-MS, IR and 1H NMR spectroscopic methods, as well as by elemental analysis.† In the UV–VIS absorption spectra of 2a, 2b, 4a and 4b in 1,4-dioxane, there is a transparent window region between 480 and 580 nm, which is very useful for second harmonic generation research.However, despite the extension of exocyclic conjugation from 2 to 4, no obvious red-shift of the Q-band was observed in the UV–VIS absorption spectra. This may be explained by the reduction of eective conjugation between the phthalocyanine ring and the exocyclic phenyl ring owing to the rotation of benzene ring around the carbon–carbon triple bond.All the new compounds 2–4 show very good solubility in polar organic solvents like diethyl ether, tetrahydrofuran, ethyl acetate and acetone. The thermal stability of the target unsymmetrical phthalocyanines was studied by thermogravimetry Fig. 1 UV–VIS absorption spectra of 2a in solution and in doped (TG).For example, the initial decomposition temperature, PMMA films: i, neat film without polymer; ii, with a concentration of flection temperature and maximum decomposition tempera- 10 mass%; iii, with a concentration of 1 mass%; iv, with a concentration ture for 2a are 313.8, 343.1 and 388.8 °C, while for 4a they are of 0.1 mass%; v, in chloroform solution 178.7, 381.5 and 408.4 °C, respectively.These results indicate that the target materials are suciently thermally stable for some poled-polymer applications. † Selected spectroscopic data for 3b: 1HNMR (270 MHz, CD3COCD3) d 5.18 (m, 12H, 6×OCH2), 5.65 (m, 4H, 2×OCH2), 5.80 (q, 4H, J= 8.58 Hz, 2×OCH2 ), 5.96 (q, 4H, J=8.58 Hz, 2×OCH2 ), 8.33 (d, 1H, J=8.50 Hz, Harom), 8.75 (d, 1H, J=8.50 Hz, Harom), 9.25 (s, 1H, Harom); FAB-MS (m-NBA) m/z 1877.9 (M+-1, 100.0%), 1878.8 (M+, 87.60, 64Zn-3b requires M+ 1878.72), 1879.8 (M++1, 92.04), 1880.8 (M+, 70.46, 66Zn-3b), 1881.8 (M++1/66Zn-3b, M+/67Zn-3b, 70.15), 1882.8 (M+, 37.67), 1883.8 (M++1, 20.12) (68Zn-3b), 1884.8 (M+, 7.97)(70Zn- 3b).For 2a: 1H NMR (270 MHz, CD3COCD3) d 5.28 (m, 12H, 6×OCH2), 5.50–6.50 (br m, 12H, 6×OCH2), 9.30–9.80 (br, Harom); FAB-MS (m-NBA) m/z 1800.9 (M+, 100.0%, requires M+ 1800.77), 1718.0 (M+-CF3CH2 , 25.4); UV–VIS lmax(1,4-dioxane)/nm (log[e/dm3mol-1cm-1]) 730.0 (5.23), 655.5 (4.58), 347.0 (4.76), 267.0 (4.52), 234.0 (4.73).For 4a: yield 95.0%. 1H NMR (270 MHz, CD3COCD3) d 5.29 (m, 12H, 6×OCH2), 5.60–6.50 (br, 12H, 6×OCH2), 8.00–8.90 (br, Harom); FAB-MS (m-NBA) m/z 1901.0 (M+, Fig. 2 SHG Maker fringe data of poled films of 2a and 4a (doped in 100.0%, requires M+ 1900.89), 1818.0 (M+-CF3CH2, 33.4); UV–VIS lmax (1,4-dioxane)/nm (log[e/dm3mol-1cm-1]) 733.0 (5.34), 658.0 PMMA, 5 mass%, film thickness 1.5 mm) on a glass substrate at 1.064 mm (4.65), 350.0 (4.87), 226.0 (5.08). 862 J. Mater. Chem., 1997, 7(6), 861–863Phthalocyanine Research and Applications, CRC Press, Boca their ethyl acetate solutions filtered through a 0.2 mm syringe Raton, Ann Arbor, Boston, 1990.filter, and then dried under high vacuum for 48 h. The orien- 2 Phthalocyanines, Properties and Applications, ed. C. C. Lezno and tation of the chromophores in the polymeric thin films was A. B. P. Lever, VCH Publishers,Weinheim, New York, 1989, 1993, achieved by corona poling at 110 °C for 30 min with an applied 1993, 1996, vol.I, II, III and IV. dc electric field of 13.5 kV cm-1 between a tungsten wire 3 (a) H. Schultz, H. Lehmann, M. Rein and M. Hanack, Struct. electrode and the glass substrate, and subsequently monitored Bonding (Berlin), 1990, 74, 41; (b) M. Hanack and M. Lang, Adv. Mater., 1994, 6, 819. by the second harmonic generation (SHG). The SHG measure- 4 W.Eberhardt and M. Hanack, Synthesis, 1997, 95. ments were performed using a polarized Q-switched Nd–YAG 5 See for example (a) T.G. Linßenand M. Hanack, Chem. Ber., 1994, laser beam (l=1064 nm). A Y-cut quartz crystal plate (second 127, 2051; (b) A. Weitemeyer, H. Kliesch and D. Wo� hrle, J. Org. harmonic coecient d11=0.5 pm V-1) was used as the refer- Chem., 1995, 60, 4900; (c) G.C. Bryant, M. J. Cook, T. G. Ryan ence. The SHG intensity of the target materials was measured and A. J. Thorne, T etrahedron, 1996, 52, 809; (d) A. Sastre, B. del using the standard Maker fringe technique.16 Fig. 2 shows the Rey and T. Torres, J. Org. Chem., 1996, 61, 8591; (e) H. Ali and J. E. van Lier, T etrahedron L ett., 1997, 38, 1157 and refs. therein. typical SHG Maker fringe results of poled thin films of PMMA 6 (a) Z.Z. Ho, C. Y. Ju and W. M. Hetherington III, J. Appl. Phys., doped with 2a and 4a on a glass substrate at a fundamental 1987, 62, 716; (b) T.Wada, Y. Matsuoka, K. Shigehara, A. Yamada, wavelength of 1.064 mm. The success in the observation of A. F. Garito and H. Sasabe, Proc. Mater. Res. Soc. Int. Mtg. on SHG of 2a and 4a demonstrates that non-aggregated metal- Advanced Materials, MRS T okyo, 1989, 12, 75; (c) J.L. Bre�das, lophthalocyanines can be well poled under an electric field C. Adant, P. Tackx and A. Persoons, Chem. Rev., 1994, 94, 243; even in the condensed state. Under the same conditions of (d) N. J. Long, Angew. Chem., Int. Ed. Engl., 1995, 34, 21. 7 D. Q. Li, M. A. Ratner and T.J. Marks, J. Am. Chem. Soc., 1988, thickness and concentration (5 mass%), thin films of 4a showed 110, 1707. larger second-harmonic signals than those of 2a, which may 8 Y. Q. Liu, D. B. Zhu, T. Wada, A. Yamada and H. Sasabe, be attributed to the enhancement of the first-order hyperpolar- J. Heterocycl. Chem., 1994, 31, 1017. izability (b) in the molecules of phthalocyanine 4a with 9 Y.Q. Liu, Y. Xu, D. B. Zhu, T. Wada, H. Sasabe, X. S. Zhao and extended exocyclic p-conjugation. On the other hand, under X. M. Xie, J. Phys. Chem., 1995, 99, 6957. the same poling condition, symmetrical hexadecakis(2,2,2- 10 E. S. Dodsworth, A. B. P. Lever, P. Seymour and C. C. Lezno, trifluoroethoxy)vanadylphthalocyanine [VOPc(TFE)16] J. Phys. Chem., 1985, 89, 5698. 11 T.Wada and H. Sasabe, Proc. SPIE Int. Soc. Opt. Eng., 1994, showed no SHG response. This result indicated that the 2143, 164. observed SHG arose not from an electric-field-induced second- 12 H. Kobayashi, K. Matsumoto and T. Sonoda, Proceedings of the harmonic (EFISH) generation-like c(-2v; v, v, 0) value,6b 2nd International Symposium on the Chemistry of Functional Dyes, but from a non-zero b term. To the best of our knowledge, no Kobe, 1992, Mita Press, Osaka, Japan, abstracts, p. 290. previous results on electric-field-induced alignment of unsym- 13 S. M. Marcuccio, P. I. Svirskaya, S. Greenberg, A. B. P. Lever, metrical phthalocyanines doped in polymer films have been C. C. Lezno and K. B. Tomer, Can. J. Chem., 1985, 63, 3057. 14 S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara, reported. A detailed study on the second-orderNLO properties Synthesis, 1980, 627. of these non-aggregated phthalocyanines is now in progress. 15 S. Yanagi, T. Wada, J. Kumar, H. Sasabe and K. Sasaki, Mol. Cryst. L iq. Cryst., 1994, 255, 167. References 16 J. Jerphagnon and S. K. Kurtz, J. Appl. Phys., 1970, 41, 1667. 1 (a) F. H. Moser and A. L. Thomas, T he Phthalocyanines, CRC Press, Boca Raton, FL, 1983, vol. 1 and 2; (b) A. L. Thomas, Communication 7/01606I; Received 7thMarch, 1997 J. Mater. Chem., 1997, 7(6), 861–863

ISSN:0959-9428    

DOI:10.1039/a701606i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Synthesis and characterization of bis (trialkoxysilymethyl )arenes from related bis (trichlorosilylmethyl )arenes. Comparisons between some organosilicate xerogel materials derived from both Stuart W. Carr,† Majid Motevalli, Duan Li Ou and Alice C. Sullivan Department of Chemistry, QueenMary and Westfield College, Mile End Road, L ondon, UK E1 4NS A series of bis(trialkoxysilylmethyl)aryl compounds 1–17 {[(RO)3SiCH2]2Ar, R=Me, Et, Pr, Bu, Ar=1,4-C6H4; R=Et, Pr, Bu, Ar=1,4-C6H2Me2-2,6; R=Et, Pr, Bu, Ar=1,4-C6Me4-2,3,5,6; R=Et, Pr, Bu, Ar=1,3-C6H4; R=Bu, Ar=1,2-C6H4; R=Et, Pr, Bu, Ar=9,10-C14H8} prepared from the related bis(trichlorosilylmethyl)aryl compounds and characterised by 1H, 13C and 29Si NMR and IR spectroscopy, and high resolution mass spectrometry.The X-ray crystal structures of two of the bis(trichlorosilylmethyl)aryl precursor compounds are reported.Organosilicate xerogels prepared from the precursors 2, 7 and 12 are discussed. These have been studied by a combination of solid state NMR spectroscopy, scanning electron microscopy (one case) and nitrogen sorption porosimetry and their properties compared with those of xerogels derived from related bis(trichlorosilylmethyl)arenes.The idea of tailoring the internal structures of organosilicate from the similarly coloured solid bis(trichlorosilylmethyl)- anthracene. xerogels by inserting organic spacers into the siloxane network through the sol–gel processing of compounds with organo- We previously reported on the molecular structure of bridged trifunctional silyl groups, X3SiMRMSiX3 was originally reported by Shea.1 A number of studies have focused on the relationship between the nature of the organic group and the microarchitecture of the derived glassy xerogel materials.2–4 One of our aims was to gauge the extent to which the nature of the functional groups in such organobridged precursors aect properties such as distribution of T n environments, overall % condensation and surface area in derived gels.We have recently synthesised a series of bis(trichlorosilylmethyl)- arenes,5 from which we prepared and characterised the corresponding monolithic transparent xerogels. In this paper we report on the related series of bis(trialkoxysilylmethyl)arenes, their conversion to xerogels and some of the properties of these materials, e.g.local chemical structure, by 13C and 29Si CP MAS NMR spectroscopy, morphology, by scanning electron microscopy (SEM) and surface area, by nitrogen sorption porosimetry. Results and Discussion There are numerous reported methods for the synthesis of organoalkoxysilane compounds, RSi(OR)3. In addition to direct reactions of organotrichlorosilanes with alcohols6 organylation of alkoxychlorosilanes such as (EtO)3SiCl using lithium7 or sodium8 or Grignard1,7,9 reagents as well as hexachloroplatinic acid promoted organylation2,3 are commonly used.We tried without success to use the p-xylenediyl dianion 1,4-[CH2]2C6H42-, as the Grignard reagent in conjunction with Si(OEt)4 or (Et3O)3SiCl to obtain 1,4- [(EtO)3SiCH2]2C6H4. Only diethyl ether-insoluble polymer like materials were obtained. Direct reaction of bis(trichlorosilylmethyl) arenes5 with alcohol gave the series of bis(trialkoxysilylmethyl) arenes 1–17.The reactions were performed at room temperature and were quantitative. These compounds broadly follow the properties noted for other organotrialkoxysilanes, and are all readily hydrolysed in moist air and soluble in most organic solvents.Unlike the chloride starting materials these compounds are liquids reflecting weaker intermolecular interactions in the alkoxides and are mostly colourless, apart from 6, 11 and 17. They are deep orange–brown, and are derived J. Mater. Chem., 1997, 7(6), 865–872 8652,5-bis(trichlorosilylmethyl)-p-xylene, A,5 and have since com- A, B and C.As with A the CH2SiCl3 groups in B and C are mutually trans about the plane of the arene bridge. Thus there pleted X-ray studies on the related compounds 1,4-bis(trichlorosilylmethyl) benzene, B, and 1,3-bis(trichlorosilylmethyl)- are no obvious structural consequences associated with the additional steric eect of the methyl substituents in A compared benzene, C (molecular structures are shown in Fig. 1 and Fig. 2, along with the corresponding structural data). The bond lengths to B and the dierent substitution pattern in B compared to C. To the best of our knowledge these are the only compounds and angles are all within expected ranges and there are no short inter- or intra-molecular contacts. Both the distances with CH2SiCl3 functions to be structurally characterised.Cl3SiMCH2 and the angles Cl3SiMCH2MC(Ar) are similar in Spectroscopic data for compounds 1–17 Analytical and spectroscopic data for compounds 1–17 (1H, 13C and 29Si NMR, IR and m/z) are assembled in Tables 1–11. The spectroscopic data confirm the expectedstructural features. Correlation data10 were used for the assignment of arene proton and 13C resonances. In the 1H NMR spectra, Tables 1, 4 and 7, the chemical shifts of the methylene protons in the alkoxysilylmethylanthracene derivatives are ca. 1 ppm down- field of the other compounds and the 13C chemical shifts for the methylene carbons in the anthrancene derivatives are 6 ppm upfield of those of the other aralkyl bridges. These relative shifts follow the patterns observed for related xylene and 9,10-dimethylanthracene compounds.11 The 29Si NMR chemical shifts of anthrancene derivatives 6, 11 and 17, Table 10, occurred at lower field than in other aralkyl bridged species.The chemical shifts of the methylene protons in the trialkoxysilylmethylbenzenes were ca. 1 ppm upfield of those of the corresponding trichloride starting materials as expected on Fig. 1 Molecular structure of compound B (ellipsoids at the 50% grounds of likely electronegativity dierences between alkoxy probability level).Selected bond lengths (A° ) and angles (°) for com- and chloride groups. The methylene carbons of the aralkyl pound B: Cl(1)–Si(1) 2.022(1), Cl(2)–Si(1) 2.014(1), Cl(3)–Si(1) bridges were shifted ca. 10 ppm upfield from the corresponding 2.022(1), Cl(4)–Si(2) 2.019(1), Cl(5)–Si(2) 2.018(2), Cl(6)–Si(2) trichlorosilyl compounds.In all of the durene derivatives, the 2.013(2), Si(1)–C(1) 1.842(4), Si(2)–C(5) 1.816(4), C(1)–Si(1)–Cl(2) signals due to the methylene and the methyl protons of the 110.9(2), C(1)–Si(1)–Cl(3) 111.0(2), Cl(2)–Si(1)–Cl(3) 107.67(7), aralkyl fragment were coincident. Changing the aryl bridge C(1)–Si(1)–Cl(1) 111.2(1), Cl(2)–Si(1)–Cl(1) 108.49(7), Cl(3)–Si(1)–Cl(1) 107.43(6), C(5)–Si(2)–Cl(6) 112.4(2), had no eect on the chemical shifts of the alkoxy protons or C(5)–Si(2)–Cl(5) 109.7(2), Cl(6)–Si(2)–Cl(5) 106.59(8), carbons (Tables 1–9) and these were similar to those of the C(5)–Si(2)–Cl(4) 111.4(1), Cl(6)–Si(2)–Cl(4) 108.29(7), corresponding alcohols.12 Similarities between the coupling Cl(5)–Si(2)–Cl(4) 108.28(7), C(2)–C(1)–Si(1) 113.7(3).constants 3JCH3-CH2 and 3JCH2-CH2 greatly simplified the multiplicity associated with protons on the alkyl chains of the alkoxy groups in many cases. Thus the total number of lines seen for any given set of equivalent protons followed from the total number, n, of proton neighbours to which they are coupled10 (see Tables 1, 4, 7). The 29Si NMR chemical shifts, Table 10, were in the range from d-47.54 to -53.36, as expected for MSi(OR)3 containing compounds.13 The 29Si NMR chemical shift of compound 1 occurred at lower field than those of the others.In the IR spectra, the characteristic bands,10,14 of SiMC, SiMOR and C=C, CMH of the phenyl groups were observed. As with the organotrichlorosilane, the SiMC vibrations occured between 1200 and 1262 cm-1 as expected.The SiMOR vibrations of ethoxy compounds appear as two close bands at ca. 1100 cm-1 (ref. 7). The other alkoxy compounds showed one sharp band in this region. Also as with the organotrichlorosilane, no C=C vibrations were observed in durene derivatives. The aromatic ring CMH out of plane deformations generally appeared as a strong band at ca. 800 cm-1. In all of the anthracene derivatives, and the ethoxy compounds, the aromatic CMH out of plane vibrations occurred below 800 cm-1, whilst in the others, including 1,3- and 1,2-disubstitued benzenes, this band appeared above 800 cm-1. Fig. 2 Molecular structure of compound B (ellipsoids at the 50% The mass spectra fragmentation patterns of compounds probability level).Selected bond lengths (A° ) and angles (°) for com- 1–17 are assembled in Table 11. [M]+ and [M-2Si(OR)3]+ pound C: Si(1)–C(1) 1.857(10), Si(1)–Cl(2) 1.993(4), Si(1)–Cl(1) 2.009(5), Si(1)–Cl(3) 2.011(4), Si(2)–C(8) 1.836(10), Si(2)–Cl(5) fragments appear for compounds 1–17. In addition the 1.990(4), Si(2)–Cl(6) 2.003(4), Si(2)–Cl(4) 2.013(4), C(1)–Si(1)–Cl(2) [Si(OR)3]+ fragments were observed for the methoxy com- 109.8(4), C(1)–Si(1)–Cl(1) 111.4(4), Cl(2)–Si(1)–Cl(1) 109.0(2), pound 1, ethoxy compound 4 and all of the propoxy and C(1)–Si(1)–Cl(3) 112.3(4), Cl(2)–Si(1)–Cl(3) 107.0(2), butoxy compounds.[MMSi(OR)3]+ fragments appeared in Cl(1)–Si(1)–Cl(3) 107.3(2), C(8)–Si(2)–Cl(5) 110.7(4), most of the compounds apart from 1, 10, 15, 16, that is those C(8)–Si(2)–Cl(6) 112.0(4), Cl(5)–Si(2)–Cl(6) 107.4(2), compounds where the two trialkoxylsilylmethyl groups occupy C(8)–Si(2)–Cl(4) 111.2(4), Cl(5)–Si(2)–Cl(4) 107.7(2), Cl(6)–Si(2)–Cl(4) 107.5(2), C(2)–C(1)–Si(1) 112.4(7).mutual ortho or meta positions on the phenyl ring. 866 J. Mater. Chem., 1997, 7(6), 865–872Table 1 1H NMR assignments in compounds 1–6 (CDCl3) 1 2 3 CH2Si(OCH2CH3 )3 1 2 3 4 5 6 OCH3 3.49(s, 18H)* CH3 2.23(s, 6H) 2.23(12H) aromatic 7.03(s, 4H) 7.09(s, 4H) 6.90(s, 2H) 7.14–7.28(m, 4H) 7.43–7.55(m, 4H) ring H1 2.18(s, 4H) 2.20(s, 4H) 2.10(s, 4H) 2.23(s, 4H) 2.14(s, 4H) 3.21(s, 4H) H2 3.67–3.93(q, 12H) 3.60–3.86(q, 12H) 3.53–3.80(q, 12H) 3.64–3.89(q, 12H) 3.46–3.73(q, 12H) H3 1.12–1.30(t, 18) 1.07–1.24(t, 18H) 1.04–1.21(t, 18H) 1.08–1.26(t, 18H) 0.94–1.11(t, 18H) Table 2 13C NMR assignments in compounds 1–6 (CDCl3, those for the related xerogel XCl derived from the chlorosilane, 150.90 MHz) in each case reveals an increase (ca. 10%) in the T 2 component at the expense of T 3. The absence of any T 0 peak for X1 and 1 2 3 X3b, both of which were processed in ethanol, is noteworthy. CH2Si(OCH2CH3)3 The overall percentage condensation in each case, Table 13, 1 2 3 4 5 6 was calculated as previously described,4 and is slightly lower OCH3 50.61 than that achieved for the related XCl material.CH3 16.76 16.72 Peak assignments for the 13C and CPMAS NMR spectra C1 18.23 19.55 19.35 19.23 20.47 14.46 are given in Table 14. Peaks associated with the organic bridges C2 58.29 58.42 58.26 58.47 58.54 in the organosilicate framework are close to those previously C3 18.20 17.90 17.32 18.04 17.93 assigned to the XCl xerogel and assignments were confirmed by non-quaternary suppression techniques as previously Table 3 13C NMR assignments of ring carbons in compounds 1–6 described.4 Other peaks present in these spectra are associated (CDCl3, 150.9 MHz)a with residual alkoxy groups both as the alcohol and associated with T n environments.The intensity of these peaks decreased substantially when materials were heated to 200°C at 0.001 Torr for 48 h. The solvent-free xerogels X1–X3 were found to have BET surface areas <2 m2 g-1 when examined by nitrogen sorption porosimetry. This contrasts with the XCl material having the R¢ R¢ 1 1 2 3 4 5 6 same organic bridge but which was microporous with a surface 1 2 3 4 5 6 area 600 m2 g-1 (ref. 4). It is noteworthy that other bis(trialkoxysilyl) arylenes and alkylenes also gave low surface area C1 132.93 133.58 131.49 130.73 136.98 129.29 materials and this was thought to be a consequence of the C2 128.58 128.56 132.42 131.70 129.50 125.02 non-rigidity of the bridging group in these cases.16 The dierent C3 128.58 128.56 130.79 131.70 136.98 126.01 distributions in T n environments compared to those of XCl C4 132.93 133.58 131.49 130.73 125.12 124.10 C5 128.58 128.56 132.42 131.70 127.80 coupled with the presence of residual T n alkoxy groups in C6 128.58 128.56 130.79 131.70 125.12 X1–X3 represent dierences in the local chemical environments which may have eected pore structure although we are not aR¾=CH2Si(OCH3)3; R=CH2Si(OCH2CH3 )3.aware of previous correlations of this type. A high resolution SEM (Fig. 3) on a relatively thick film of X3a cast on a glass Sol–gel processing of 1,4-bis(trialkoxysilylmethyl )arenes slide reveals an apparently more densely packed nanoparticulate surface texture than found for the related XCl material.4 We have already reported on the synthesis and properties of Further work concerning the use of these materials as a range of organosilicate xerogel materials, XCl, derived confinement matrices for a variety of guest species is in hand.through sol–gel processing of 1,4-bis(trichlorosilylmethyl)- This work illustrates that the formationof xerogels is controlled arene compounds,5 and we were interested to compare the by a number of factors and that properties can be adjusted by properties of similar materials derived from related alkoxy altering the nature of the precursors.precursors. The conditions used for sol–gel processing of 1,4- [(RO)3SiCH2]2C6H4 compounds 2 (R=Et), 7 (R=Pr) and 12 (R=Bu) to xerogels X1, X2, X3a and X3b respectively, are Experimental details summarised in Table 12 with further details given in the Experimental section, and involve HCl acid catalysis.The All reactions and manipulations involving moisture sensitive compounds were carried out under purified nitrogen. The molar ratio of SiMOR functions to HCl in these sol–gel mixtures are 40–100 and it is possible that some intermediate bis(trichlorosilylmethyl)arene starting materials were made as previously described.5 The alcohols used were purified by SiMCl is formed (SiMOR/H2O ratios were between 0.5 and 1).Nonetheless times to gelation for the alkoxy compounds distillation from the corresponding magnesium alkoxides. The bis(trialkoxysilylmethyl)arenes were purified by Schlenk flask were generally longer than previously found for the related chlorosilane compounds.A slower rate of hydrolysis is expected to Schlenk flask distillation via a connecting glass tube. A dynamic vacuum was applied through the receiver Schlenk for the alkoxy species.15 In each case a transparent monolith was formed. and, with the distillation Schlenk immersed in an oil bath products were collected at 150–180 °C in the liquid nitrogen The xerogels X1–X3, Table 12, were studied by both 13C and 29Si CPMAS NMR spectroscopy.Chemical shift data are cooled receiver Schlenk and subsequently stored under nitrogen. Solution phase NMR spectra were recorded on Bruker given in Tables 13 and 14. The relative peak areas associated with T n environments (obtained using GAUSSIAN simulation AW-250 (13C, 62.89 MHz; 29Si, 49.66 MHz), Bruker AW-400, Bruker AMX-600 (13C, 150.90 MHz; 29Si, 119.23 MHz) and of the 29Si spectra and where n=0–3 refers to the number of SiMOMSi bonds associated with particular Si sites) in xerogels Bruker WP-80 (1H, 80 MHz) NMR spectrometers. Spectra were recorded on samples dissolved in dried deuteriated CDCl3 X1–X3 are given in Table 13.A comparison of the data with J. Mater. Chem., 1997, 7(6), 865–872 867Table 4 1H NMR assignments in compounds 7–11 (CDCl3). 2 3 4 CH2Si(OCH2CH2CH3)3 7 8 9 10 11 CH3 — 2.25(s, 6H) 2.24(12H) aromatic 7.04(s, 4H) 6.90(s, 4H) 6.90–6.98(s, 4H) 7.43–7.58(m, 4H) ring 8.33–8.46(m, 4H) H1 2.15(s, 4H) 2.10(s, 4H) 2.24(s, 4H) 2.14(s, 4H) 3.21(s, 4H) H2 3.55–3.72(t, 12H) 3.60–3.65(t, 12H) 3.50–3.66(t, 12H) 3.60–3.66(t, 12H) 3.43–3.58(t, 12H) H3 1.40–1.57(sxt, 12H) 1.46–1.61(sxt, 12H) 1.39–1.64(m, 12H) 1.45–1.60(sxt, 12H) 1.29–1.54(m, 12H) H4 0.78–0.96(t, 18H) 0.86–0.93(t, 18H) 0.86–1.11(t, 18H) 0.84–0.90(t, 18H) 0.66–0.82(t, 18H) Table 5 13C NMR assignments in compounds 7–11 (CDCl3, Table 6 13C NMR assignments of ring carbons in compounds 7–11 (CDCl3, 150.90 MHz)a 150.90 MHz) 2 3 4 CH2Si(OCH2CH2CH3)3 7 8 9 10 11 CH3 16.87 16.77 C1 19.42 19.43 19.28 19.97 14.18 C2 64.48 64.45 64.32 64.49 64.42 C3 25.51 25.51 25.48 25.49 25.33 C4 10.08 10.05 11.17 10.06 9.94 and kept under nitrogen atmosphere.All chemical shifts (d in ppm) were referenced to appropriate nuclei in tetramethylsilane. IR spectra were recorded on a Perkin-Elmer FTIR 1720X spectrophotometer, using neat liquids between two KBr plates.Mass spectra were obtained on a Kratos MS 50RF mass spectrometer. The samples were sealed in nitrogen-filled Pyrex capillary tubes. The capillaries were opened and mounted in the probe under a nitrogen atmosphere. A summary of the observed fragmentation patterns is given in Table 11. Elemental analysis (C,H) was obtained from University College London Analytical Service. The samples were sealed under nitrogen in a glass tube.Crystallographic measurements were made using a CAD-4 diractometer in v-2h scan mode, on selected single crystals mounted inside 0.7 mm glass capillaries, which were flame sealed under nitrogen. The structures were solved by direct methods and refined by least-squares analysis. The solid state 13C and 29Si NMR spectra were acquired using cross polarization (CP) magic angle spinning (MAS), and high-power proton decoupling on a Bruker MSL-300 spectrometer.Typical conditions were 2 ms contact time, 1 s recycle delay, a 90° pulse length of 4.07 ms and a spinning speed of 4.5 kHz. The 13C and 29Si frequencies were 75.5 and 59.6 MHz, respectively. All spectra were recorded at room temperature and chemical shifts are quoted relative to SiMe4.Scanning electron micrographs were obtained using a JEOL 7 8 9 10 11 JC6300 Scanning Electron Microscope. C1 133.27 131.78 130.81 137.11 129.22 Surface area measurements were obtained using a C2 128.62 132.46 131.10 129.57 124.63 Micromeretrics ASAP 2400 instrument. C3 128.62 131.35 131.10 137.11 125.97 C4 133.27 131.78 130.81 125.07 123.97 Preparation of 1,4-bis(trimethoxysilylmethyl )benzene 1.C5 128.62 132.46 131.10 127.75 1,4-Bis(trichlorosilylmethyl)benzene (2.30 g, 6.2 mmol) was C6 128.62 131.35 131.10 125.07 dissolved in methanol (40 cm3) and stirred overnight. Removal aR=CH2Si(OCH2CH2CH3)3. of the excess methanol aorded the product as a colourless liquid (1.82 g, yield 85%). dH (80 MHz, CDCl3): 2.18(s, 4H), 3.49(s, 18H), 7.03(s, 4H).dSi (119.23 MHz, CDCl3) -47.54. dC Preparation of 1,4-bis(triethoxysilylmethyl )benzene 2. Prepared as described for 1 from 1,4-bis(trichlorosilyl- (150.9 MHz, CDCl3): 18.23, 50.61, 128.58, 132.93. n/cm-1 (KBr): 2944(s), 2842(s), 1904(w), 1512(s), 1462(m), 1422(m), methyl)benzene (2.00 g, 5.36 mmol) and ethanol (40 cm3); after further distillation, yield, 1.84 g (80%).n/cm-1 (KBr): 2975(s), 1401(m), 1192(s), 1088(s, b), 1023(m), 849(s), 804(s), 747(m), 730(m), 664(w), 641(w), 563(w), 522(m), 478(m). m/z (% relative 2927(s), 2890(s), 1512(m), 1483(w), 1443(w), 1422(w), 1391(m), 1366(w), 1295(w), 1262(w), 1222(m), 1170(s), 1104(s), 1083(s), intensity) theoretical m/z: C14H26Si2O6 , 346.1280(66.2)- 346.1268. C3H9O3Si, 121.0321(100)121.0321. C8H8, 104.0639- 960(s), 839(m), 799(s), 723(w), 565(w), 528(w), 483(w).m/z (% relative intensity) theoretical m/z: C20H38Si2O6, (45.0)104.0626. 868 J. Mater. Chem., 1997, 7(6), 865–872Table 7 1H NMR assignments in compounds 12–17 (CDCl3) 1 2 3 4 5 CH2Si(OCH2CH2CH2CH3)3 12 13 14 15 16 17 CH3 2.21(s, 6H) 2.35(s, 12H) aromatic 7.03(s, 4H) 6.90(s, 2H) 6.90–6.98(m, 4H) 7.05–7.12(m, 4H) 7.45–7.57(m, 4H) ring 8.33–8.45(m, 4H) H1 2.14(s, 4H) 2.09(s, 4H) 2.35(s, 4H) 2.13(s, 4H) 2.27(s, 4H) 3.21(s, 4H) H2 3.65–3.70(t, 12H) 3.61–3.75(t, 12H) 3.65–3.70(t, 12H) 3.58–3.68(t, 12H) 3.48–3.63(t, 12H) H3 1.44–1.55(p, 12H) 1.15–1.59(m, 24H) 1.27–1.71(m, 24H) 1.42–1.55(p, 12H) 1.26–1.69(m, 24H) 1.11–1.57(m, 24H) H4 1.27–1.41(sxt, 12H) 1.26–1.41(sxt, 12H) H5 0.87–0.93(t, 18H) 0.82–1.00(t, 18H) 0.81–1.00(t, 18H) 0.87–0.92(t, 18H) 0.80–0.98(t, 18H) 0.70–0.96(t, 18H) Table 8 13C NMR assignments in compounds 12–17 (CDCl3, 150.90 MHz) Table 9 13C NMR assignments of ring carbons in compounds 12–17 (CDCl3, 150.90 MHz) 1 2 3 4 5 CH2Si(OCH2CH2CH2CH3)3 12 13 14 15 16 17 CH3 16.74 16.06 C1 19.59 19.51 19.44 20.02 20.31 14.30 C2 62.74 62.52 62.42 62.60 62.55 62.59 C3 34.61 34.47 34.47 34.47 34.47 34.20 C4 18.93 18.80 18.81 18.79 18.79 18.69 C5 13.89 13.89 13.83 13.66 13.64 13.62 430.2196(76.2)430.2207.C14H23O3Si, 267.1359(5.4)267.1417. C8H8 , 104.0661(100)104.0626. Calc. for C20H38Si2O6: C, 55.76; H, 8.89. Found: C, 54.68; H: 8.77% Preparation of 2,5-bis( triethoxysilylmethyl)-p-xylene 3. Prepared as described for 1 from 2, 5-bis(trichlorosilylmethyl)- p-xylene (2.60 g, 6.48 mmol) and ethanol (40 cm3).Yield, 2.73 g (92%). n/cm-1 (KBr): 2973(s), 2927(s), 2884(s), 1559(m), 1541(m), 1506(m), 1457(m), 1390(s), 1201(s), 1169(s), 1083(s), 960(s), 885(w), 838(m), 797(s), 761(s), 669(w), 507(w), 471(m). m/z (% relative intensity) theoretical m/z. C22H42Si2O6, 458.2535(36.1)458.2520. C16H27O3Si, 295.1662(8.3)295.1729.C10H12,132.0949(100)132.0939. Preparation of 1,4-bis(triethoxysilylmethyl )durene 4. Prepared as described for 1 from 1,4-bis(trichlorosilylmethyl)- durene (2.4 g, 5.59 mmol) and ethanol (40 cm3). Yield, 2.12 g (78%). n/cm-1 (KBr): 2974(s), 2926(s), 2887(s), 1481(w), 1442(m), 1391(s), 1366(w), 1295(w), 1250(w), 1169(s), 1083(s), 960(s), 855(m), 789(s), 755(w), 554(w). m/z (% relative intensity) theoretical m/z.C24H46Si2O6,486.2829(39.6)486.2833. C18H31O3Si, 323.2012(4.0%)320.2042. C12H16, 160.1264(9.8)- 160.1252. Preparation of 1,3-bis(triethoxysilylmethyl )benzene 5. Prepared as described for 1 from 1,3-bis(trichlorosilylmethyl)- benzene (2.6 g, 6.97 mmol) and ethanol (40 cm3). Yield, 2.52 g (84%). m/z (% relative intensity) theoretical m/z. C20H38Si2O6, 430.2189(2.5)430.2207.C14H23O3Si,267.1437(1.0)267.1417. C8H8 , 104.0600(13.4)104.0626. Preparation of 9,10-bis(triethoxysilylmethyl )anthracene 6. Prepared as described for 1 from 9,10-bis(trichlorosilylmethyl)- anthracene (2.0 g, 4.23 mmol) and ethanol (40 cm3). Yield, 1.91 g (85%). n/cm-1 (KBr): 2974(s), 2926(s), 2888(s), 1457(w), 12 13 14 15 16 17 1447(s), 1389(s), 1367(s), 1294(w), 1261(w), 1168(s), 1083(s), C1 133.44 131.79 130.86 137.14 129.58 129.31 1026(s), 962(s), 870(w), 794(s), 753(s), 664(w), 459(w).m/z (% C2 128.79 132.50 131.10 129.61 135.33 125.00 relative intensity) theoretical m/z. C28H42Si2O6, 530.2514- C3 128.79 130.93 131.10 137.14 135.33 126.03 (100%)530.2520. C22H27O3Si, 367.1655(2.0)367.1729. C16H12, C4 133.44 131.79 130.86 125.07 129.58 124.01 204.0961(8.6)204.0939.C5 128.79 132.50 131.10 127.77 124.44 C6 128.79 130.93 131.10 125.07 124.44 Preparation of 1,4-bis(tripropoxysilylmethyl )benzene 7. aR=CH2Si(OCH2CH2CH2CH3 )3. Prepared as described for 1 from 1,4-bis(trichlorosilylmethyl)- J. Mater. Chem., 1997, 7(6), 865–872 869Table 10 29Si chemical shifts of compounds 1–17 in CDCl3 Table 13 29Si CPMAS chemical shift data (d), relative areas of T n environments and overall % condensation compound chemical shift d % xerogel d,T 0 d,T 1 d,T 2 d,T 3 conden- 1 -17.5l 2 -50.78 sation 3 -51.67 4 -51.69 XCl -18.0, 5.2 -53.5, 5.3 -62.0, 51.3 -71.0, 38.2 74.2 X1 -53.0,8.3 -61.9,73.2 -70.7, 18.6 70.4 5 -50.90 6 -53.36 X2 -17.5, 5.9 -53.9, 9.5 -62.3, 57.9 -70.2, 26.6 68.5 X3a -18.4, 4.3 -53.4, 4.7 -61.7, 61.4 -70.1, 29.6 72.3 7 -51.06 8 -51.00 X3b -53.8, 8.8 -62.2, 66.6 -70.8, 24.6 72.1 9 -51.83 10 -51.18 11 -53.20 Table 14 13C CP MAS chemical shift data and chemical shift assignments 12 -50.68 13 -50.61 14 -50.80 arene MCH2 MCH2 residualxerogel carbons (T 1–T 3) (T0) SiOR/ROH 15 -51.05 16 -50.78 17 -52.16 XCl 129.6, 134.1 22.5 0.8 X1 129.5, 133.9 22.0 58.7, 18.1 X2 129.5, 133.8 22.4 0.5 64.8, 26.1, 10.8 X3a 129.6, 133.8 22.5 1.4 62.7, 35.0, 19.7, 14.3 benzene (1.8 g, 4.83 mmol) and propanol (40 cm3). Yield, 2.36 g X3b 129.5, 134.0 21.9 62.4, 34.9, 19.6, 14.5 (95%).n/cm-1 (KBr): 2962(s), 2936(s), 2877(s), 1512(m), 1463(m), 1422(w), 1391(m), 1261(m), 1221(m), 1171(m), 1154(m), 1088(s,b), 1017(s), 916(w), 899(w), 878(w), 850(s), Preparation of 1,4-bis(tripropoxysilylmethyl )durene 9.Prepared as described for 1 from 1,4-bis(trichloroxylsilylme- 757(m), 567(w), 528(w), 419(m). m/z (% relative intensity) theoretical m/z. C26H50Si2O6, 514.3146(45.3)514.3146. thyl)durene (2.4 g, 5.59 mmol) and propanol (40 cm3). Yield, 2.96 g (93%). dH (80 MHz, CDCl3): 0.86–1.11(t, 18H), C17H29O3Si, 309.1829(4.7)309.1886. C9H21O3Si, 205.1266- (99.4)205.1260.C8H8, 104.0639(100)104.0626. 1.39–1.64(m, 12H), 2.24(s, 16H), 3.50–3.66(q, 12H). n/cm-1 (KBr): 2962(s), 2935(s), 2876(s), 1458(m), 1437(w), 1420(w), 1391(m), 1261(m), 1173(w), 1153(w), 1087(s,b), 1017(s), 899(w), Preparation of 2,5-bis(tripropoxysilylmethyl )-p-xylene 8. Prepared as described for 1 from 2,5-bis(trichlorosilylmethyl)- 863(m), 830(m), 754(m), 555(w). m/z (% relative intensity) theoretical m/z.C30H58Si2O6, 570.3771(100)570.3772. p-xylene (2.60 g, 6.48 mmol) and ethanol (40 cm3). Yield, 2.35 g (90%). n/cm-1 (KBr): 2962(s), 2936(s), 2877(s), 1504(m), C21H37O3Si, 365.2438(5.0)365.2512. C9H21O3Si, 205.0530- (22.6)205.1260. C12H16, 160.1226(3.3)160.1252. 1463(m), 1391(m), 1262(m), 1201(m), 1169(m), 1154(m), 1087(s, b), 1017(s), 885(m), 850(s), 802(w), 767(m), 466(w).m/z (% relative intensity) theoretical m/z. C28H54Si2O6, 542.3481- Preparation of 1,3-bis(tripropoxysilylmethyl )benzene 10. Prepared as described for 1 from 1,3-bis(trichlorosilylmethyl)- (48.1)542.3459. C19H33O3Si, 337.2199(6.0)337.2199. C9H21O3Si, 205.1317(89.3)205.1260. C10H12, 132.0968- benzene (2.60 g, 6.97 mmol) and propanol (40 cm3).Yield, 3.40 g (95%). n/cm-1 (KBr): 2962(s), 2936(s), 2877(s), 1604(w), (100)132.0939. Table 11 Typical fragments in mass spectrum of compounds 1–17 compound typical fragments 1 [M]+, [M-2Si(OR)3]+, [Si(OR)3]+ 2 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+ 3 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+ 4 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 5 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+ 6 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+ 7 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3]+ 8 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 9 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 10 [M]+, [M-2Si(OR)3]+, [Si(OR)3]+ 11 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 12 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 13 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3 ]+ 14 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [Si(OR)3]+ 15 [M]+, [M-2Si(OR)3]+, [Si(OR)3]+ 16 [M]+, [M-2Si(OR)3]+, [Si(OR)3]+ 17 [M]+, [M-2Si(OR)3]+, [M-Si(OR)3]+, [M-Si(OR)3 ]+, [Si(OR)3 ]+ Table 12 Conditions for formation of xerogels solvent time to xerogel precursor(mass/g) (volume/cm3) catalyst gelation/d XCl 1,4-{Cl3SiCH2}2C6H4 (1.0) THF(10) 0.11 cm3 of 0.1 M HCl 1 X1 1,4-{(EtO)3SiCH2 }2C6H4 (2.0) EtOH(10) 0.4 cm3 of 0.1 M HCl 6 X2 1,4-{(PrO)3SiCH2}2C6H4 (1.89) PrOH(10) 0.35 cm3 of 0.1 M HCl 60 X3a 1,4-{(BuO)3SiCH2}2C6H4(2.35) BuOH(10) 1.0 cm3 of 0.1 M HCl 21 X3b 1,4-{(BuO)3SiCH2}2C6H4(2.1) EtOH(5) 0.35 cm3 of 0.1 M HCl 4 870 J.Mater. Chem., 1997, 7(6), 865–872654.4712(4.7)654.4711. C24H43O3Si, 407.2929(13.3)407.2982. C12H27O3Si, 247.1688(30.3)247.1729. C12H16, 160.1231- (100)160.1252.Preparation of 1,3-bis(tributoxysilylmethyl )benzene 15. Prepared as described for 1 from 1,3-bis(trichlorosilylmethyl)- benzene (2.60 g, 6.97 mmol) and butanol (40 cm3). Yield, 3.96 g (95%). n/cm-1 (KBr): 2959(s), 2933(s), 2874(s), 1604(m), 1585(w), 1465(s), 1386(s), 1300(w), 1261(w), 1235(w), 1170(w), 1152(w), 1093(s) 1041(s), 1010(w), 988(s), 930(m), 899(s), 835(w), 806(s), 736(m), 702(w), 455(w).m/z (% relative intensity) theoretical m/z C32H62Si2O6, 598.4080(14.0)598.4085. C12H27O3Si, 247.1653(100)247.1729. C8H8, 104.0636(56.1)- 104.0626. Calc. for C32H62Si2O6 : C, 64.16; H, 10.43. Found: C, 63.04; H: 10.38%. Fig. 3 Scanning electron micrograph showing nanoparticulate surface Preparation of 1,2-bis(tributoxysilylmethyl )benzene 16. of film of X3a Prepared as described for 1 from 1,2-bis(trichlorosilylmethyl)- benzene (2.50 g, 6.70 mmol) and butanol (40 cm3).Yield, 3.73g (93%). n/cm-1 (KBr): 2959(s), 2873(s), 2741(s), 1601(m), 1559(w), 1507(w), 1474(w), 1458(m), 1438(w), 1392(m), 1576(w), 1488(s), 1465(s), 1434(w), 1387(s), 1300(s), 1265(m), 1260(m), 1170(m), 1154(m), 1087(s,b), 1017(s), 930(w), 899(w), 1234(w), 1222(m), 1167(s), 1093(s), 1040(s), 1010(w), 988(s), 847(s), 800(m), 755(w), 703(w), 472(w).m/z (% relative inten- 957(w), 938(w), 898(s), 801(s), 776(w), 758(m), 728(m), 673(m), sity) theoretical m/z. C26H50Si2O6, 514.3142(20.1)514.3146. 616(s), 562(w), 595(s), 471(s), 417(s). m/z (% relative intensity) C9H21O3Si, 205.1252(100),205.1260. C8H8, 104.0613(6.6)- theoretical m/z C32H62Si2O6, 598.4083(8.0)598.4085. 104.0626. C12H27O3Si, 247.1641(100)247.1729. C8H8 , 104.0641(26.2)- 104.0626. Preparation of 9,10-bis(tripropoxysilylmethyl ) anthracene 11. Prepared as described for (1) from 9,10-bis(trichlorosilyl methyl)anthracene (2.00 g, 4.23 mmol) and propanol (40 cm3). Preparation of 9,10-bis(tributoxysilylmethyl )anthracene 17. Yield, 2.39 g (92%). n/cm-1 (KBr): 2961(s), 2934(s), 2876(s), Prepared as described for 1 from 9, 10-bis(trichlorosilylmethyl)- 1473(w), 1457(m), 1387(w), 1369(m), 1261(m), 1169(m), anthracene (2.00 g, 4.23 mmol) and butanol (40cm3).Yield, 1087(s,b), 1018(s), 881(m), 840(m), 808(m), 746(s), 670(w), 2.80 g (95%). m/z (% relative intensity) theoretical m/z 420(w). m/z (% relative intensity) theoretical m/z. C34H54Si2O6, C40H66Si2O6, 698.4403(100)698.4398.C28H39O3Si, 614.3434(41.9)614.3459. C25H33O3Si, 409.2172(1.7)409.2199. 451.2728(10.8)451.2669. C12H27O3Si, 247.1726(57.8)247.1729. C9H21O3Si, 205.1145(100)205.1260. C16H12, 204.0897(16.1)- C16H12, 204.0936(37.9)204.0939. 204.0939. General procedure for the preparation of xerogels X1, X2, Preparation of 1,4-bis(tributoxysilylmethyl )benzene 12. X3a, X3b. In general a clear solution of the alkoxy compound, Prepared as described for 1 from 1,4-bis(trichlorosilylmethyl)- 1,4-bis(RO3SiCH2)2C6H4 (R=Et, Pr, Bu) in the appropriate benzene (4.00 g, 10.72 mmol) and butanol (50 cm3).After solvent (see Table 12) was prepared under nitrogen in a Pyrex further distillation 5.45 g (85%) colourless liquid was obtained. round-bottomed flask and subsequently treated with aqueous dC (62.90 MHz, CDCl3): 13.89, 18.93, 19.59, 34.61, 62.74, 128.79, HCl (0.11 cm3).This mixture was vigorously stirred to a clear 133.44. n/cm-1 (KBr): 2959(s), 2934(s), 2874(s), 1512(m), sol, and left to gel in a static nitrogen atmosphere. No 1465(m), 1385(m), 1301(w), 1262(w), 1222(w), 1171(w), 1093(s), precipitation was observed and clear transparent gels sub- 1041(s), 988(m), 899(m), 841(m), 801(m), 746(w), 567(w), sequently formed. Gelation occured within 1–60 d.The wet 532(w). m/z (% relative intensity) theoretical m/z. C32H62Si2O6, gels were left to age for a further 24 h after which drying 598.4085(100)598.4085. C20H35O3Si, 351.2366(1.3)351.2356. commenced through two small (diameter ca. 1 mm) pin-holes C12H27O3Si, 247.1708(48.5)247.1729. C8H8, 104.0633 for several days.Subsequently, the whole sample was exposed (19.7)104.0626. Calc. for C32H62Si2O6: C, 64.16; H, 10.43. to air for further slow drying for three weeks. The dried Found: C, 63.13; H: 10.70. xerogels were obtained as transparent orange coloured monoliths. Precise experimental quantities used are given in Table 12. Preparation of 2,5-bis(tributoxysilylmethyl )-p-xylene 13.Prepared as described for 1 from 2,5-bis(trichlorosilylmethyl)- p-xylene (2.60 g, 6.48 mmol) and butanol (40 cm3). Yield, 3.49 g X-Ray crystallography (86%). n/cm-1 (KBr): 2959(s), 2933(s), 2874(s), 1559(w), 1541(w), 1506(s), 1459(s), 1386(s), 1261(s), 1234(w), 1201(w), Crystal data for compound B, C8H8Cl6Si2, M=373.02, monoclinic space group P21/c; with a=8.9956(10), b=13.035(2), 1168(s), 1093(s,b), 1041(s), 988(s), 898(s), 837(w), 801(s), 734(w), 462(w), 442(w).m/z (% relative intensity) theoretical m/z: c=13.460(2) A° , b=103.85(1)°, V=532.3(4) A° 3 , Z=4, Dc 1.617 g cm-3, F=1.249 mm-1, (000)=744, 3087 reflections C34H66Si2O6, 626.4395(41.0)626.4397. C22H39O3Si, 379.2733- (6.4)379.2668. C12H27O3Si, 247.1721(34.2)247.1729.C10H12, were measured using Mo-Ka (l=0.71069 A° ) radiation. 2684 independent reflections were measured, h range 2.21 132.0937(82.4)132.0939. <h<24.97°. The structure was solved by direct methods and dierence Fourier technique (SHELXS-86).17 Refinement Preparation of 1,4-bis(tributoxysilylmethyl )durene 14. Prepared as described for 1 from 1,4-bis(trichlorosilylmethyl)- was carried out with full-matrix least-squares analysis on F2(SHELXL-93)18.R=.|Fo-Fc|/.Fo=0.0406 [1710 durene (2.4 g, 5.59 mmol) and propanol (40 cm3). Yield, 3.44 g (94%).n/cm-1(KBr): 2959(s), 2933(s), 2874(s),1464(s),1433(w), reflections with I>2s(I )]. wR2={.[w(Fo2-Fc2)2] .[w(Fo2)2]}1/2=0.0928; w=1/[s2(Fo2)+(0.0458P)2 +0.0.34P] 1384(s), 1298(w), 1262(m), 1235(w), 1172(w), 1093(s,b), 1041(s), 1010(w), 987(s), 900(s), 831(w), 798(m), 773(w), 735(s), 428(w).where P=(Fo2+2Fc2)/3, and residual electron density 0.411/-0.327 e A° 3. m/z (% relative intensity) theoretical m/z: C36H70Si2O6, J. Mater. Chem., 1997, 7(6), 865–872 8713 R. J. Corriu and D. Leclercq, Angew. Chem., Int. Ed. Engl., 1996, Crystal data for compound C, C8 H8 Cl6 Si2 , M=373.02, 35, 1420.triclinic, space group P1�; with a=9.895(1), b=10.305(1), 4 P. J. Barrie, S. W. Carr, D. L. Ou and A. C. Sullivan, Chem.Mater., c=15.778(2) A° , a=89.6(1), b=101.98(2), c=91.29(1)°, 1995, 7, 265. V=1573.4(3) A° 3, Z=4, Dc=1.617 g cm-3, m=1.216 mm-1, 5 M. Motevalli, D. L. Ou, A. C. Sullivan and S. W. Carr, F(000)=744, 4774 reflections were measured using Mo-Ka J.Organomet. Chem., 1993, 445, 35. (l=0.71069 A° ) radiation. 4378 independent reflections were 6 D. A. Armitage, in Comprehensive Organometallic Chemistry, ed. measured, h range 1.98° <h <22.99°). The structure was G. Wilkinson, F. G. A. Stone and E. Abel, Pergamon Press, Oxford, 1982, vol. 2, p. 6. solved by direct methods and dierence Fourier technique 7 K. J.Shea, D. A. Loy and O. Webster, J. Am. Chem. Soc., 1992, (SHELXS-86).13 Refinement was carried out with full-matrix 114, 6700. least-squares analysis on F2(SHELXL-93).14 R=./Fo-Fc 8 C. C. Chappelow, Jr., R. L. Elliott and J. T. Goodwin, Jr., J. Org. Fo=0.0824 [2198 reflections with I>2s(I)]. wR2= Chem., 1960, 25, 435. {.[w(Fo2-Fc2)2].[w(Fo2 )2]/}1/2=0.0928; w=1/[s2(Fo2)+ 9 J.Pola, V. Chvalovsky�, Collect. Czech. Chem. Commun., 1973, 38, (0.1546P)2+0.00P] where P=(Fo2+2Fc2 )/3, and residual elec- 1674. tron density 0.489/–0.369 e A° 3. 10 W. Kemp, Organic Spectroscopy, 2nd edn, Macmillan, London, 1987. Atomic coordinates, thermal parameters, and bond lengths 11 V. R. Stosser, M. Graf and H. Koppel, J. Prakt. Chem. 1975, and angles have been deposited at the Cambridge 317, 591. Crystallographic Data Centre (CCDC). See Information for 12 W. Bremser, L. Ernst and B. Franke, Carbon-13 NMR Spectral Authors, J. Mater, Chem., 1997, Issue 1. Any request to the Data, Verlag Chemie,Weinheim, 1978. CCDC for this material should quote the full literature citation 13 H. Marsmann, NMR Basic Principles and Progress, Springer and the reference number 1145/33. Verlag, 1981, pp. 198–205. 14 G. Socrates, Inf ra-red Spectra of Complex Molecules, 2nd edn, Wiley, New York, 1994. D.L.O. and A.C.S. thank Unilever for support, and the Airey 15 C. Eaborn, Organosilicon Compounds, Butterworths Publications, Neave Trust for financial assistance (to D.L.O.). We thank London, 1960. Peter Cook and Greg Coumbarides (QMW) for mass spectra 16 J. H. Small, K. J. Shea and D. A. Loy, J. Non-Cryst. Solids, 1993, and NMR spectra; we thank Peter Haycock, Harold Toms 160, 234; R. J. P. Corriu, J. J. E. Moreru, P. Thepot and M. Wong and Patrick J. Barrie of the University of London Chi Man, Chem. Mater, 1992, 4, 1217; G. Cerveau, R. J. P. Corriu Intercollegiate NMR Research Facilities at Queen Mary and and N. Costa, J. Non-Cryst. Solids, 1993, 163, 226. Westfield College and University College London, for NMR 17 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. spectra. 18 G. M. Sheldrick, SHELXL93, Program for the Refinement of Crystal Structures, University of Go�ttingen, Germany. References Paper 6/07633E; Received 11th November, 1996 1 K. J. Shea, D. A. Loy and O. Webster, Chem.Mater., 1989, 1, 572. 2 D. A. Loy and K. J. Shea, Chem. Rev., 1995, 95, 1431. 872 J. Mater. Chem., 1997, 7(6), 865&nda

ISSN:0959-9428    

DOI:10.1039/a607633e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Poly(isothianaphthene) from 2,5-bis(trialkylsilyl )isothianaphthenes: preparation and spectroscopic characterization M. Lapkowski,a,b R. Kiebooms,c J. Gelan,c D. Vanderzande,c A. Pron,d,e T. P. Nguyen,f G. Louarnf and S. Lefrantf aDepartment of Chemistry, Silesian T echnical University, 44 100 Gliwice, Poland bDepartment of T extile Engineering and Environmental Sciences, T echnical University of £odz, Bielsko-Biala Campus, 43 300 Bielsko-Biala, Plac Fabryczny 1, Poland cL imburg University, Instituut voorMateriaalonderzoek (IMO), Department BSG, Universitaire Campus, B-3590 Diepenbeek, Belgium dDepartment ofMaterials Science and Ceramics, Academy of Mining and Metallurgy, 30 059 Krako�w, Mickiewicza 30, Poland eDepartment of Chemistry, T echnical University of Warsaw, 00 664 Warszawa, Noakowskiego 3, Poland fL aboratoire de Physique Cristalline, IMN, Universite� de Nantes, UMR 110, 2, rue de la Houssinie`re, 44072 Nantes Ce�dex 03, France A new method for the preparation of poly(isothianaphthene) is proposed, namely electropolymerisation of bis(tertbutyldimethylsilyl) isothianaphthene (BTBDMS)ITN.The advantage oered by this method is based on the fact that (BTBDMS)ITN is a stable monomer at ambient conditions whereas unsubstituted isothianaphthene is unstable and must be prepared prior to the polymerisation. Poly(isothianaphthene) (PITN) prepared from (BTBDMS)ITN shows an average polymerisation degree of 20 and spectral and spectroelectrochemical characteristics similar to classical PITN.FT Raman spectroelectrochemical studies show that during oxidative doping PITN undergoes similar changes to poly(alkylthiophenes) and poly(alkoxythiophenes).In modern molecular electronics significant research eort is which, in contrast to isothianaphthene, is a stable monomer directed towards the preparation of low band-gap conjugated and can be stored for extended times in a bottle in laboratory polymers due to several possible industrial applications of such conditions.In addition to the description of the electrochemical systems. Poly(isothianaphthene) (PITN) initially synthesized behaviour of PITN prepared from (BTBDMS)ITN we characby Wudl et al.1 exhibits the lowest band-gap of all polyconju- terize the obtained polymer by UV–VIS–NIR, XPS and Raman gated systems studied to date.Both PITN and its C6 ring spectroscopies. substituted derivatives can be prepared by electrochemical oxidative polymerisation of isothianaphthene or its deriva- Experimental tives.1–5 However the monomers used for these syntheses are rather unstable at ambient conditions and must be freshly For the synthesis of the monomer 2,5(tert-butyldimethylsilyl)- prepared prior to the polymerisation.In order to avoid the isothianaphthene the procedure described by Okuda et al. was inconveniences associated with electropolymerisation, chemical used.13 Electropolymerisation was carried out in a reaction oxidation procedures have been suggested involving the medium consisting of NBu4BF4 and (BTBDMS)ITN dissolved oxidation of dihydroisothianaphthene with FeCl3, O2,6 or in nitrobenzene.The concentrations of the electrolytic salt and N-chlorosuccinimide.7 the monomer were 0.2 and 0.1 M respectively. The reaction PITN can also be prepared by dehydrogenation of the PITN was performed in a three-electrode electrochemical cell with a precursor, namely poly(dihydroisothianapthene) (PDHITN) platinum counter electrode and Ag/AgCl wire as the reference with such dehydrogenation agents as SO2Cl2,8 or tert-butyl electrode.Three types of working electrodes were used, plati- hypochlorite.9 This last method is especially interesting because num, gold and ITO, dependingon the subsequent spectroscopic dehydrogenation of PDHITN in solution leads to a stable studies of the deposited polymer film. The polymerisation was PITN solution.Thus films of PITN can be prepared on an performed at a constant potential of 1.4 V vs. Ag/AgCl. appropriate substrate by casting. Here, we propose a new In addition to the deposition of the polymer on the working method for the preparation of PITN via electropolymerisation electrode, the formation of soluble oligomers took place which of disilyl derivatives of ITN. Silicon directed reactions have was manifested by a change of the colour of the electrolyte been widely used in organic chemistry with the goal of improv- solution in the vicinity of the working electrode.The deposition ing the selectivity of carbon–carbon bond formation.10 Recently of a homogeneous film required electrolysis times exceeding they have been applied to the preparation of polythiophene11 5 min.and poly(3-alkylthiophene).12 In order to prepare PITN we The electropolymerised film was then reduced electrochemi- have used 2,5-bis(tert-butyldimethylsilyl)isothianaphthene cally at E=-0.6 V vs. Ag/AgCl to give the neutral polymer (BTBDMS)ITN: of a distinct blue colour. The electrode with the film deposited on it was then carefully rinsed with pure nitrobenzene and then with acetonitrile in order to remove all oligomeric species.All operation were carried out in a dry nitrogen atmosphere. Cyclic voltammetry Cyclic voltammograms were recorded in a monomer free 0.2 M NBu4BF4 solution in acetonitrile using a PAR 273 potentiostat/ J. Mater. Chem., 1997, 7(6), 873–876 873galvanostat. The working electrode consisted of a layer of for the polymerisation reaction.The polymerisation carried out after 2 months using the same batch of ITN gave identical poly(isothianaphthene) deposited on a platinum foil. As in the electropolymerisation experiments a Pt counter electrode and polymer. In the neutral (i.e. reduced at E=-0.6 V) PITN film, XPS spectroscopy shows the presence of carbon, sulfur an Ag/AgCl reference electrode were used. and a small amount of oxygen in addition to the already mentioned silicon. The C 1s peak is located at 284.7 eV with UV–VIS–NIR spectroelectrochemistry a skewed arc at the high energy side and a full width at half UV–VIS–NIR spectroelectrochemical studies were performed maximum of 2 eV.The S 2p line shows a peak at 163.5 eV in the same electrolyte solutions as in the cyclic voltammetry with a widened base at low binding energy.These features are studies, using the same counter and reference electrodes. similar to those observed for polythiophene except that some Poly(isothianaphthene) was deposited on an indium tin oxide carbon atoms are aected by the silyl end groups.14 transparent electrode (ITO). Cyclic voltammograms of PITN prepared from (BTBDMS)ITN are shown in Fig. 1. We restricted ourselves FT Raman spectroelectrochemistry to oxidative (p-type) doping although there are literature reports of p- and n-type doping of PITN.15,16 The Raman spectra were recorded with a near-IR excitation Oxidative doping of PITN synthesized from the disilyl line (1064 nm) on a FT-Raman Bruker RFS spectrometer derivative of ITN gives rise to two broad strongly overlapping working in a back scattering geometry.For Raman studies the oxidation peaks (due to anion doping) and two reduction film of PITN was deposited on a Pt electrode. The same peaks associated with undoping. The shape of the current– electrolyte, counter and reference electrodes as in cyclic voltamvoltage curves is essentially the same as that reported by metry were used.Higgins et al.17 for poly(benzo[c]thiophene) cycled in NBu4X–acetonitrile electrolyte. XPS studies In the case of PITN the shape of the current–voltage curve The XPS measurements were performed on a Leybold LH 12 depends on the history of the sample and, more precisely, on analyser (CNRS Universite� de Nantes) using an Mg-Ka X-ray whether the scan range has been extended to n-doping prior source in a UHV system.The pressure of the chamber was to p-doping. In such case a pre-peak is observed.15 Onada kept in the 10-9 mbar range during experiments. The polymer et al.16 have ascribed the existence of these additional peak to film were deposited on ITO substrates and no charging eect the diculty in the removal of all negative charge upon due the beam radiation was observed.The binding energy was oxidapreviously n-doped polymer. The release of this referenced to the Au 4f7/2 line (84 eV) from a gold probe residual charge gives rise to this additional ‘pre-oxidation evaporation on the surface of the sample holder. The collected peak’. We do not observe this peak, in agreement with other data were treated by a computer program with satellite back- authors,16,17 in the experiments where PITN was not previously ground subtraction.Semi-quantitative determination of the n-doped. composition of the analysed surface was performed from It should be stressed here than our PITN has a very good the obtained spectra taking account of the sensitivity of the cycling stability. In addition the oxidative doping of our PITN elements present.seems to be more reversible than that reported in ref. 18. UV–VIS–NIR spectra registered for increasing electrode potentials are shown in Fig. 2. In the reduced polymer (E= Results and Discussion -400 mV) the dominant peak ascribed to the p–p* transition (BTBDMS)ITN readily polymerises electrochemically to give in the conjugated backbone shows a maximum at 690–700 nm, PITN.However, as has been stated before, the preparation of i.e. it is blue shifted by ca. 50 nm as compared to the PITN homogeneous films on the electrode requires higher concen- spectrum reported in ref. 15, and by ca. 90–100 nm in compari- trations of the silylated monomer as compared to unsubstituted son to the spectra recorded in refs. 9 and 16.Since the position isothianaphthene. In addition longer electrodeposition times of the p–p* transition band can be taken as a measure of are required. This may imply that in the case of (BTBTMS)ITN conjugation we conclude that PITN obtained from the electropolymerisation mechanism is significantly dierent (BTBDMS)ITN is less conjugated. This eect may be associ- than in the case of unsubstituted ITN.There is a low electro- ated with the influence of the silyl end groups taking into polymerisation yield and the presence of the oligomeric species in the vicinity of the electrode is only one of several electrooxidation products. Studies of the polymerisation mechanism are in progress. Due to the presence of the leaving silyl groups in the monomer the polymerisation degree in the polymer can be conveniently determined by end group analysis, and more precisely from the analytically determined S/Si molar ratio.XPS studies of the poly(isothianaphthene) film deposited on the ITO electrode show that this ratio is close to 10 which gives an average polymerisation degree equal to 20. Thus the trialkylsilyl groups are eciently eliminated during the electrochemical oxidation according to Scheme 1 It should be stressed that, in contrast to ITN, its silylated derivatives can be stored for extended times before their use Fig. 1 Cyclic voltammograms of PITN recorded in 0.1 mol dm-3 Scheme 1 (n#20) NBu4BF4 solution in acetonitrile 874 J. Mater. Chem., 1997, 7(6), 873–876Fig. 2 In situ UV–VIS absorbance curves of PITN recorded for selected electrode potentials (vs.Ag/AgCl): (a) -400; (b) 200; (c) 300; (d) 400; (e) 500; (f) 600; (g) 900; (h) 1000 mV account that the polymerisation degree in our polymer is rather low (average polymerisation degree of ca. 20). In conjugated polymers oxidative doping is usually manifested by bleaching of the p–p* transition peak with simultaneous growth of a peak (peaks) in the near-IR part of the spectrum.Qualitatively the same behaviour is observed for the PITN studied in this research. HoweverUV–VIS–NIR spectroelectrochemistry gives evidence of two distinctly dierent doping stages. Up to potentials E=0.6 V, which is in the vicinity of the maximum of the oxidative doping peak, two isosbestic points are observed at 365 and 430 nm.This means that only two optically dierent phases are present in the Fig. 3 Raman spectra with lex=1064 nm of PITN recorded during system. At E=0.6 V the polymer is only partially doped as the oxidative process (potentials vs. Ag/AgCl): (a) -300; (b) 300; (c) 600; (d) 1000 mV judged from a rather high absorbance at 690–700 nm. Complete doping manifested by total bleaching of the p–p* peak requires electrode polarization at potentials exceeding 0.9 V.In the second oxidation step no isosbestic points are even if minute amounts of dopant are present. A recently published PITN spectrum20 is very similar to that reported observed. It seems therefore plausible that during the first oxidation step polarons (radical cations) are formed which here; however, it contains one additional peak between the modes at 1301 and 1166 cm-1 which is absent in our spectrum.then recombine to bipolarons (dications) at higher potentials. Such a transformation clearly explains the existence of the Careful spectroscopic analysis of PITN and model compounds by Raman21 and NMR21,22 spectroscopies seems to indicate isosbestic points at the beginning of the oxidation and their absence at the end of the oxidative doping.that in the neutral state this polymer adopts the quinonoid sequence of bonds. Such a conclusion is also supported by This conclusion is also supported by the ellipsometric and FTIR results of Christiansen et al.19 who also claimed two- theoretical calculations.23 However, as has been pointed out by Kiebooms,24 the step oxidativedoping of PITN.However additional verification by joint cyclic voltammetry and EPR studies is required; such energy dierence between the quinonoid and aromatic states is very small (2.4 kcal mol-1, 1 cal=4.184 J) so the structure studies are in progress. We have also undertaken Raman spectroelectrochemical studies of PITN. In general Raman of the neutral polymer may be influenced by the nature of the end groups in the monomer used for the synthesis.Since studies of polyconjugated systems are complicated by resonance eects which result in a strong dependence of the Raman (BTBDMS)ITN monomer should favour the aromatic sequence of bonds in the resulting polymer it is highly probable line intensities (and sometimes their shape and positions) on the excitation wavelength energy.In addition the resonance that in PITN prepared from the disilyl derivative the aromatic structure is adopted in the neutral state; thus the doping conditions are altered significantly in the course of the doping reaction due to the doping induced changes in the electronic should lead to the quinonoid structure. This hypothesis is based on the close similarity of the Raman spectroelectro- spectra of conjugated polymers.We have selected the near-IR excitation line (lex=1064 nm) chemical behaviour of PITN and regioregular poly(3-alkylthiophenes) 25 and poly(dialkoxybithiophenes).26 In the last mainly because its position is very close to the maximum of the doping induced electronic transition. In addition at this two cases oxidative doping causes the transformation of the aromatic structure into the quinonoid one.wavelength we are also within the p–p* transition peak of the neutral form of PITN and asmall but not negligible absorbance As probed by Raman spectroscopy, doping induced spectral changes start at potentials E>0 V vs. Ag/AgCl. However is registered at 1064 nm for this compound. FT Raman spectra registered for increasing electrode poten- between 0.1 and 0.6 V the spectra are essentially the same showing the features of the doped sample.The main changes tials are shown in Fig. 3. The Raman spectrum of neutral (E= -0.3 V) PITN prepared from the disilyl derivative is dierent occurring upon doping can be characterized as follows. (i) The band at 1462 cm-1 in neutral PITN ascribed to CaMCb from that reported by Hoogmartens et al.18 In fact, the spectrum published in ref. 18 is essentially identical to our stretchings shifts to lower wavenumber (1417 cm-1) and decreases in intensity with respect to other bands. Identical spectrum of slightly doped PITN, i.e. that recorded at E= 0.3 V. Taking into account that lex=1064 nm almost matches behaviour has been observed for poly(3-alkylthiophenes)23 and poly(alkoxythiophenes).24 (ii) The band at 1440 cm-1 in the the maximum of the electronic absorption in the doped polymer, strong resonant enhancement of vibrations characteristic neutral PITN ascribed to the vibrations of the benzene ring condensed with the thiophene ring is essentially unaected by of the doped structure is expected.It is therefore highly probable that the features of the doped polymer may appear the doping. (iii) A band at 1195 cm-1 appears which can be J. Mater. Chem., 1997, 7(6), 873–876 8753 G. King, S. J. Higgins, S. E. Garner and A. R. Hillman, Synth.Met., interpreted as originating from the CaMCa¾ inter-ring 1994, 67, 241. vibrations of the quinonoid structure. 4 G. King and S.J. Higgins, J. Chem. Soc., Chem. Commun., 1994, At E>0.6 V further spectral changes occur which support 825. the hypothesis of the quinonoid structure formation upon 5 G. King and S. J. Higgins, J. Mater. Chem., 1995, 5, 447. doping. In particular the peak at 1301 cm-1 in the neutral 6 K. Jen and Elsenbaumer, Synth. Met., 1986, 16, 379. 7 I. Hoogmartens, D. Vanderzande, H.Martens and J. Gelan, Synth. polymer and ascribed to CbMCb¾ stretching broadens and Met., 1992, 47, 367. shifts to slightly higher wavenumber whereas the peak due to 8 T. L. Rose and M. C. Liberto, Synth.Met., 1989, 31, 395. CaMCb stretchings continues to shift towards lower wave- 9 S. A. Chen and C. C. Lee, Synth.Met., 1995, 75, 187. lengths (from 1462 cm-1 in the neutral polymer to 1400 cm-1 10 E.W. Colvin, in Silicon in Organic Synthesis, Butterworth, for the quinonoid CaMCa¾ sequence of bonds). The inter-ring Guildford, 1981. 11 J. L. Sauvajol, C. Chorro, J. P. Le`re-Porte, R. J. P. Corriu, J. J. E. stretching peak continues to grow. Moreau, P. The�pot and M. W. C. Man, Synth.Met., 1994, 62, 233. It should be stressed once more that these changes are 12 M.Bouachrine, J. P. Le`re-Porte, J. J. E. Moreau and M. W. C. qualitatively the same as those observed for poly(3-alkylthio- Man, J. Mater. Chem., 1995, 5, 797. phenes)25 and poly(alkoxythiophenes).26 The comparison with 13 Y. Okuda, M. V. Laksmikantham and M. P. Cava, J. Org. Chem., poly(3,3¾-dibutoxy-2,2¾-bithiophene) should be instructive. For 1991, 56, 6024. 14 G. Morea, C.Malitesta, L. Sabbatini and P. G. Zambonin, both polymers the near-IR excitation line (lex=1064 nm) is J. Chem. Soc., Faraday T rans., 1990, 86, 3769. located in the vicinity of the doping induced absorption 15 S. M. Dale, A. Glidle and A. R. Hillman, J. Mater. Chem., 1992, maximum and both polymers undergo very similar changes in 2, 99. the Raman spectra upon electrochemical doping. 16 M. Onoda, H. Nakayama, S. Morita and K. Yoshino, J. Electrochem. Soc., 1994, 141, 338. 17 S. J. Higgins, C. Jones, G. King, K. H. D. Slack and S. Petidy, Synth. Met., 1996, 78, 155. Conclusions 18 I. Hoogmartens, P. Adriaensen, R. Carleer, D. Vanderzande, M. Martens and J. Gelan, Synth. Met., 1992, 51, 219. We have demonstrated that electropolymerisation of bis(tert- 19 P. A.Christiansen, J. C. H. Kerr, S. J. Higgins and A. Hamnett, butyldimethyl)silylisothianaphthene (BTBDMS)ITN leads to Faraday Discuss. Chem. Soc., 1989, 88, 261. poly(isothianaphthene) with an average polymerisation degree 20 G. Zerbi, M. C. Magnoni, I. Hoogmartens, R. Kiebooms, R. Carleer, D. Vanderzande and J. Gelan, Adv. Mater., 1995, 7, of 20. The obtained polymer shows spectral features similar 1027. but not identical to poly(isothianaphthene) prepared by classi- 21 I. Hoogmartens, P. Adriaensen, D. Vanderzande, J. Gelan, cal methods. The main advantage of the procedure proposed C. Quattrocchi, R. Lazzaroni and J. L. Bredas, Macromolecules, here relies on the fact that (BTBDMS)ITN is a stable monomer 1992, 25, 7347. and can be stored for extended times whereas isothianaphthene 22 I. Hoogmartens, P. Adriaensen, D. Vanderzande and J. Gelan, Anal. Chim. Acta, 1993, 283, 1025. must be synthesized prior to the electropolymerisation. 23 L. Cu, M. Kertesz, J. Geisselbrecht, J. Ku�rti and H. Kuzmany, Synth. Met., 1993, 55, 564. 24 R. Kiebooms, PhD Thesis, University of Limburgs, 1995. 25 M. Trznadel, M. Zago�rska, M. Lapkowski, G. Louarn, S. Lefrant References and A. Pron, J. Chem. Soc., Faraday T rans., 1996, 92, 1387. 26 A. Pron, G. Louarn, M. Lapkowski, M. Zago�rska, I. Glo�wczyk- 1 F. Wudl, M. Kobayashi and A. J. Heeger, J. Org. Chem., 1984, Zubek and S. Lefrant, Macromolecules, 1995, 28, 4644. 49, 3382. 2 H. Yashima, M. Kobayashi, K. B. Lee, D. Chung, A. J. Heeger and F.Wudl, J. Electrochem. Soc., 1987, 134, 46. Paper 6/06868E; Received 7th October, 1996 876 J. Mater. Chem., 1997, 7(6), 873

ISSN:0959-9428    

DOI:10.1039/a606868e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Temporal stability of second-order optical non-linearities depending on non-linear optically active groups of polyesters Masaaki Tsuchimori,* OsamuWatanabe and Akane Okada T oyota Central Research and Development L aboratories, Inc., 41-1 Yokomichi, Nagakute, Nagakutecho, Aichigun, Aichi, 480-11, Japan Four types of non-linear optical (NLO) polyesters with the same main chain and with dierent NLO-active groups have been synthesized.Second-order NLO properties of the corona-poled polyesters are studied by the second-harmonic generation (SHG) method. The structure of the NLO-active group aects not only the magnitude of the SHG coecient (d33) but also the temporal stability of d33. Though all the polyesters show nearly the same glass transition temperature, the polyesters having NLO-active groups with larger dipole moments show better temporal stability, suggesting that the dipole moment has a significant eect on temporal stability.Non-linear optical (NLO) polymers have been studied to develop electro-optic devices.1,2 The NLO polymers usually include NLO-active groups having dipole moments, and show second-order optical non-linearity only when the NLO-active groups are aligned.Although the alignment of NLO-active groups can be achieved by an electricpoling method, relaxation of the alignment can occur, especially at elevated temperature. Many attempts have been made to restrain the relaxation, and the temporal stability of the dipolar orientation has been improved, for example with side-chainNLO polymers,3–5NLO polymers whose main chains include dialkylamino groups in the NLO-active groups,6–8 introducing hydrogen-bonding groups in the main chain,9 crosslinking,7,10–12 and imidization. 13–15 Most of the above attempts have improved the relaxation by modifying the structures of the polymer matrix or the links between the main chain and the NLO-active group.There have been few reports investigating the dependence of the relaxation on the NLO-active groups, except that Kitipichai et al.have reported the influence of sizes of NLOactive groups.7 A study of this dependence is useful in order to obtain NLO polymers with improved temporal stability. Here we report the dependence for NLO polyesters whose main chains include dialkylamino groups in the NLO-active groups.Four types of polyesters with the same main chain and with dierent NLO-active groups were synthesized by polycondensation between 4,4¾-biphenyldicarbonyl chloride Scheme 1 and an NLO-active diol. NLO properties of the polyesters were studied by the second-harmonic generation (SHG) method, and were compared with one another. The magnitude washed with water, and dried in vacuo.The crude product and temporal stability of the SHG coecient (d33) are discussed (14.3 g) was recrystallized twice from ethanol and dried in in terms of the hyperpolarisability and the dipole moment of vacuo to give 11.0 g (74%) of compound 1: mp 159°C; the NLO-active group. dH[(CD3)2SO] 2.6 (s, 3H, CH3 ), 3.6 (s, 8H, CH2), 4.9 (s, 2H, OH), 6.6–6.8 (br, 2H, aromatic), 7.6–8.1 (m, 5H, aromatic); n/cm-1 (KBr) 1510, 1600 (aromatic C), 2230 (CN), 2930 (CH2 ), Experimental 3430 (OH). 4-N,N-Bis (2-hydroxyethyl)amino-4¾-cyano-2- methylazobenzene (1) 4-N,N-Bis(2-hydroxyethyl )amino-4¾-cyano-2-methyl-3¾- trifluoromethylazobenzene (2) 4-Cyanoaniline (5.91 g) was dissolved in a mixture of 36% hydrochloric acid (45 ml) and water (100 ml), and diazotized A mixture of 5-amino-2-cyanobenzotrifluoride (5.05 g) and 36% hydrochloric acid (25 ml) and water (55 ml) was stirred with sodium nitrite (3.80 g in 20 ml of water) at 4°C.To this solution, m-tolyldiethanolamine (9.06 g) dissolved in a mixture at room temp. for 20 min, and was cooled to 4°C. Sodium nitrite (2.06 g in 10 ml of water) was gradually added to the of water (125 ml) and 36% hydrochloric acid (7.5 ml) was added dropwise at 4°C within 45 min.After the addition was mixture. After stirring for 2 h, ethanol (80 ml) was added and stirred another 20 min at 4°C. To this solution, m-tolyldiethan- completed, the mixture was stirred for another 90 min at room temp. Potassium hydroxide solution was then added to neu- olamine (5.30 g) dissolved in a mixture of water (70 ml), ethanol (20 ml) and 36% hydrochloric acid (4.0 ml) was added tralize the mixture.The precipitate was separated by filtration, J. Mater. Chem., 1997, 7(6), 877–881 877dropwise at 4°C within 30 min. After the addition was com- P3 (yield 69%): n/cm-1 (KBr) 1130, 1180, 1320 (CF3 ), 1360, 1540 (NO2), 1510, 1600 (aromatic C), 1720 (CNO), 2900–3000 pleted, the mixture was stirred for 20 min at 4°C and was stirred for another 60 min at room temp.Potassium hydroxide (CH2, CH3). P4 (yield 66%): n/cm-1 (KBr) 1140, 1180 (CF3), 1320–1360 solution was then added to neutralize the mixture. The precipitate was separated by filtration, washed with water, and dried (CF3, NO2 ) , 1530 (NO2), 1510, 1600 (aromatic C), 1720 (CNO), 2900–3000 (CH2, CH3). in vacuo. The crude product (10.0 g) was recrystallized from ethanol–hexane, and dried in vacuo to give 7.6 g (71%) of Characterization compound 2: mp 167°C; dH[(CD3)2SO] 2.6 (s, 3H, CH3), 3.6 (s, 8H, CH2 ), 4.9 (s, 2H, OH), 6.6–6.8 (br, 2H, aromatic), 1H NMR spectra were obtained using a JEOL JMNFX-90-Q 7.6–8.3 (m, 4H, aromatic); n/cm-1 (KBr) 1135, 1170, 1330 spectrometer (J values in Hz).FTIR spectra were recorded on (CF3), 1510, 1600 (aromatic C), 2230 (CN), 2950 (CH2), a JASCO FT/IR-5M spectrometer.Melting points and glass 3300 (OH). transition temperatures (Tg) were determined by thermal analyses using a Perkin-Elmer DSC-7 dierential scanning calor- 4-N,N-Bis (2-hydroxyethyl)amino-2-methyl-2¾-nitro-4¾- imeter with a heating rate of 10°C min-1. UV–VIS spectra of trifluoromethylazobenzene (3) polymer films were taken with a Shimazu UV-2100 spectrometer.Intrinsic viscosities ([g]) were measured in N-methyl- 4-Amino-3-nitrobenzotrifluoride (10.31 g) was dissolved in a 2-pyrrolidone (NMP) at 30°C using a Ubbelohde viscometer. mixture of 36% hydrochloric acid (45 ml) and water (100 ml), Refractive indices in the visible range were determined using and diazotized with sodium nitrite (3.80 g in 18 ml of water) a Rudolph S2000 ellipsometer.Refractive indices in infrared at 4°C. To this solution, m-tolyldiethanolamine (9.06 g) dis- range were extrapolated using the Cauchy’s equation. solved in a mixture of water (125 ml) and 36% hydrochloric acid (7.5 ml) was added dropwise at 4°C within 20 min. After Molecular orbital calculations the addition was completed, the mixture was stirred for 30 min at 4°C and was stirred for another 60 min at room temp.Dipole moments (m) and hyperpolarisabilities along m (b) are Potassium hydroxide solution was then added to neutralize important properties for NLO-active groups, because the the mixture. The precipitate was separated by filtration, values of d33 for electric-poled polymers depend on mb.2 washed with water, and dried in vacuo.The crude product Moreover, m is considered to aect the temporal stability of (13.9 g) was recrystallized from ethanol–hexane, and dried in d33 through electrostatic interactions. When m of an NLOvacuo to give 5.1 g (25%) of compound 3: mp 124 °C; active group is large, electrostatic interactions acting on the dH[(CD3)2SO] 2.6 (s, 3H, CH3), 3.6 (s, 8H, CH2 ), 4.9 (s, 2H, NLO-active group are considered to be strong.OH), 6.6–6.8 (br, 2H, aromatic), 7.5–8.4 (m, 4H, aromatic); The m and static b of NLO-active groups were calculated n/cm-1 (KBr) 1140, 1170, 1330 (CF3), 1350, 1540 (NO2), 1510, by the semi-empirical AM1 molecular-orbital (MO) method,16 1600 (aromatic C), 2850–3000 (CH2, CH3), 3100–3400 (OH).using the MOPAC program.17,18 Geometry was fully optimized in the calculations. The b was calculated by a coupled 4-N,N-Bis (2-hydroxyethyl)amino-2-methyl-4¾-nitro-2¾- Hartree–Fock method implemented in the program.19 trifluoromethylazobenzene (4) Non-linear optical measurements 2-Amino-5-nitrobenzotrifluoride (10.31 g) was dissolved in a mixture of 36% hydrochloric acid (45 ml), ethanol (300 ml) Thin films of the polyesters were prepared on glass substrates and water (100 ml), and diazotized with sodium nitrite (3.80 g by spin-coating. 1,2-Dichloroethane and chloroform were used in 18 ml of water) at 4°C. To this solution, m-tolyldiethanol- as solvent. The film thickness was monitored using a Dektak amine (9.76 g) dissolved in a mixture of water (100 ml) and II profiler.The films were corona-poled in air using a needle 36% hydrochloric acid (7.5 ml) was added dropwise at 4°C electrode under following conditions: interelectrode distance, within 15 min. After the addition was completed, the mixture 15–30 mm; voltage, 10–20 kV; poling time, 2–5 min; and cool- was stirred for 10 min at 4°C and was stirred for another ing time, 20 min.Negative voltage was applied to the needle 60 min at room temp. Potassium hydroxide solution was then electrode in the poling. SHG coecients (d33) were determined added to neutralize the mixture. The precipitate was separated by the Maker-fringe technique.20 A Continuum NY-81 by filtration, washed with water, and dried in vacuo. The crude Nd5YAG laser (pulse width=8 ns, 10 Hz repetition) was used product (8.1 g) was recrystallized from butan-1-ol–hexane, and as an s-polarized fundamental source, and p-polarized second dried in vacuo to give 3.6 g (18%) of compound 4: decomposed harmonic wave was detected.The value of d33 was assumed to around 180°C; dH[(CD3)2SO] 2.6 (s, 3H, CH3), 3.6 (s, 8H, be three times as large as d31.2 Absorbing eects of second- CH2), 4.9 (s, 2H, OH), 6.7–6.9 (m, 2H, aromatic), 7.7 (d, J 9.1, harmonic waves on d33 were allowed for through absorption 1H, aromatic), 7.9 (d, J 9.1, 1H, aromatic), 8.5–8.6 (m, 2H, coecients at the second-harmonic wavelength.21 A Y-cut aromatic); n/cm-1 (KBr) 1150, 1170 (CF3), 1320–1360 (CF3, quartz sample was used as a reference, d11=0.5 pm V-1.NO2), 1500–1540 (aromatic C, NO2), 1600 (aromatic C), 2850–3000 (CH2, CH3), 3200–3500 (OH).Results and Discussion Synthesis Polymerization All polyesters were prepared by the same procedure. One Four types of NLO-active diols 1–4 were synthesized via a diazo coupling reaction between substituted aniline and m- example for P1 is detailed here. The compound 1 (0.581 g) and 4,4¾-biphenyldicarbonyl chloride (0.500 g) were dissolved tolyldiethanolamine.The structures of diols 1–4 are shown in Scheme 1. The diols are dierent in the structures of acceptor in a mixture of 1,2-dichloroethane (15 ml) and pyridine (3 ml). This solution was heated to reflux for 2.5 h under a nitrogen groups, and their volumes are nearly the same. NLO polyesters were synthesized through polycondensation between the diol atmosphere, and was poured into ethanol (500 ml).The polymer precipitate was collected by filtration, and dried in vacuo and 4,4¾-biphenyldicarbonyl chloride (Scheme 1). All the NLO polyesters are the same in the structure of the main chain, to give 0.78 g (72%) of polymer P1: n/cm-1 (KBr) 1510, 1600 (aromatic C), 1720 (CNO), 2230 (CN), 2900–3000 (CH2, CH3). while they dier in the structures of the NLO-active groups.In the FTIR spectra of the polyesters, carbonyl absorption P2 (yield 78%): n/cm-1 (KBr) 1140, 1170, 1320 (CF3), 1505, 1600 (aromatic C), 1720 (CNO), 2230 (CN), 2900–3000 peaks appeared at 1720 cm-1, indicating formation of ester groups. The absorption peaks due to acceptor groups in NLO- (CH2, CH3). 878 J. Mater. Chem., 1997, 7(6), 877–881Table 4 Refractive indices of polyesters active groups, namely cyano group of polyester P1, cyano and trifluoromethyl groups of polyester P2, and nitro and trifluoro- Refractive index methyl groups of polyesters P3 and P4, were observed in the spectra.The values of [g] of the polyesters were around 0.1 dl Polyesters 532 nm 1064 nm g-1, and the values of Tg of all the polyesters were nearly the P1 1.92 1.65 same (Table 1).P2 1.99 1.68 P3 2.01 1.67 Molecular orbital calculations P4 1.85 1.70 To estimate NLO properties of the NLO-active groups, MO calculations were performed. Since the NLO properties of the interelectrode distance, 30 mm; voltage, 12 kV; poling time, monomer diols were considered to be a reasonable represen- 5 min; and cooling time, 20 min.The optimum poling tempera- tation of those of the NLO-active groups, the properties of the tures are considered to depend on two properties. One is the diols were calculated. The results are listed in Table 2. The mobility of the NLO-active groups, and the other is the calculated values of mb of diols 2 and 4 were nearly the same, conductivity of the material.22,23 At temperatures lower than and were larger than those of diols 1 and 3.These calculations the optimum poling temperatures, the mobility is too low to predict that the values of d33 of polyesters P2 and P4 are align NLO-active groups suciently, while at temperatures larger than those of polyesters P1 and P3. The calculated higher than the optimum, the conductivity reduces the eective result for m of the diols suggests that electrostatic interactions poling electric field in the polyester film.The optimum poling acting on NLO-active groups in polyesters P2, P4, P3 and P1 temperatures of polyesters P1, P2 and P3 were the higher than decrease that order. their Tg by ca. 15°C, whereas that of polyester P4 was higher than its Tg by ca. 40°C (Table 5).If the Tg corresponds to the Linear optical properties of polyesters motion of NLO-active groups, the dierence in the optimum The UV–VIS absorption peaks (lmax) of the polyester films poling temperature can be interpreted in terms of a dierence ranged from 455 to 508 nm owing to their NLO-active groups. in the temperature dependence of conductivity. The observed lmax and absorption coecients (a) at 532 nm The maximum values of d33 measured shortly after poling are given in Table 3.The values of a at 532 nm were above are listed in Table 5. The values of d33 of polyesters P2 and P4 5 mm-1. These large values suggest that an absorption correc- were larger than those of polyesters P1 and P3. This agrees tion is necessary to determine d33 at a 1064 nm fundamental with the MO calculations qualitatively, though values of wavelength for the polyesters.calculated b are static values. Fig. 1 shows the temporal The observed refractive indices of the polyesters at 532 and behaviour of d33 at room temperature. The value of d33 of 1064 nm are listed in Table 4. For each polyester, the refractive polyester P1 decayed rapidly to less than 10% of its initial index at 532 nm was larger than that at 1064 nm, owing to the value, and that of polyester P3 decayed more slowly.Polyesters absorption of the NLO-active groups. P2 and P4 showed fairly stable d33 at room temperature. The temporal behaviour was fitted well with the stretched Non-linear optical properties of polyesters exponential function [eqn. (1)]24,25 Films of synthesized polyesters were corona-poled under vari- d33(t) d33(0)=exp C-Att BnD(0<n1) (1) ous poling conditions, and their d33 values were measured using a 1064 nm fundamental wave.Each polyester was found to have an optimum poling temperature, which led to a where t is the characteristic relaxation time at which d33 maximum value of d33 under standard poling conditions: decayed to 1/e of its initial value, and n describes the breadth Table 1 Intrinsic viscosity [g] and glass transition temperatures Tg of Table 5 Optimum poling temperatures Tp and d33 of polyesters.d33 polyesters values were measured shortly after poling at a 1064 nm fundamental wavelength Polyesters [g]/dl g-1 Tg/°C Polyesters Tp/°C d33/pm V-1 P1 0.10 115 P2 0.09 118 P1 130 57 P3 0.09 113 P2 130 230 P4 0.10 119 P3 130 76 P4 160 170 Table 2 Calculated dipole moments m and hyperpolarisabilities along the dipole moments b of diols Diols m/10-18 esu b/10-30 esu mb/10-48 esu 1 5.5 13.0 72 2 8.3 15.8 131 3 6.3 8.9 56 4 7.4 17.2 127 Table 3 UV–VIS absorption peaks (lmax) and absorption coecients a at 532 nm of polyesters Polyesters lmax/nm a/mm-1 P1 455 5.3 P2 469 8.2 Fig. 1 Temporal behaviour of d33 at room temperature for ($) P1, P3 465 5.3 (&) P2, (#) P3 and (1) P4. Solid lines represent the fit with the P4 508 10.0 stretched exponential expression. J. Mater. Chem., 1997, 7(6), 877–881 879of the distribution in relaxation times. The fitted temporal the NLO-active group from changing its orientation in the material. parameters are listed in Table 6.The temporal behaviour of d33 at 100 °C was also observed for polyesters P2 and P4 to distinguish their stability (Fig. 2). Conclusion The temporal behaviour at 100 °C also fitted well with the The temporal stability of d33 was studied for the NLO poly- stretched exponential function. The fitted temporal parameters esters with dierent NLO-active groups. Though all the poly- are listed in Table 7. The stability of polyester P2 was better esters showed nearly the same Tg, the polyester having NLO- than that of polyester P4.These observations about the active groups with larger dipole moments showed better tem- temporal behaviour at both room temperature and 100 °C poral stability, suggesting that the dipole moment has a indicate that the temporal stability of d33 for the polyesters significant eect on the temporal stability.Such a dependence decreases in the order P2, P4, P3 and P1. This order of of the temporal stability on the dipole moment is expected to temporal stability of the polyesters agreed with the order of apply to other NLO polymers. It is important to study the the calculated dipole moment; the polyester having NLOdependence for other NLO polymers, as well as advanced active groups with larger dipole moments showed better teminvestigation for the NLO polyesters.poral stability. The temporal stability of d33 has been considered to depend We acknowledge Mr Hiromitsu Tanaka, Mr Naohiko Kato on various factors:2 for example Tg,26 free volume,27–30 local and Mr Yoshiharu Hirose in our laboratory for their help and molecular dynamics,31 hydrogen bonding,28,32–34 packing of useful discussions in various measurements. polymer chains,35 liquid crystalline phase,36 dipole–dipole interaction between an chromophore and a matrix,37 sizes of NLO-active groups7 and trapped charge.38 For the polyesters References studied in the present paper, the observed dierence in the 1 Nonlinear Optical Properties of Organic Molecules and Crystals, ed.temporal stability is considered to be independent of Tg, D. S. Chemla and J. Zyss, Academic Press, Orlando, vol. 1 and hydrogen bonding, packing of polymer chains, and sizes of 2, 1987. NLO-active groups. The correlation between the calculated 2 D. M. Burland, R. D. Miller and C. A. Walsh, Chem. Rev., 1994, dipole moment of the NLO-active group and the temporal 94, 31.stability of the polyesters seems to suggest that the dipole 3 K. D. Singer, M. G. Kuzyk, W. R. Holland, J. E. Sohn, S. J. Lalama, R. B. Comizzoli, H. E. Katz and M. L. Schilling, Appl. moment has a significant eect on the temporal stability. One Phys. L ett., 1988, 53, 1800. possible role of the dipole moment is as follows.Each NLO- 4 A. Nahata, C. Wu, C. Knapp, V. Lu, J. Shan and J. T. Yardley, active group experiences forces from other NLO-active groups Appl. Phys. L ett., 1994, 64, 3371. through dipole–dipole interactions. Since movement of one 5 C.-S. Kang, H.-J. Winkelhahn, M. Schulze, D. Neher and NLO-active group changes the forces acting on other NLO- G. Wegner, Chem.Mater., 1994, 6, 2159.active groups, the motion of each NLO-active group depends 6 M. Chen, L. Yu, L. R. Dalton, Y. Shi and W. H. Steier, Macromolecules, 1991, 24, 5421. on the motion of the other NLO-active groups. The dependence 7 P. Kitipichai, R. L. Peruta, G. M. Korenowski and G. E. Wnek, increases with increasing dipole moment of the NLO-active J. Polym. Sci. Part A, 1993, 31, 1365. group.Such dipole–dipole interactions are assumed to prevent 8 K.-J. Moon, H.-K. Shim and K.-S. Lee, Mol. Cryst. L iq. Cryst., 1994, 247, 91. Table 6 Temporal stability parameters of d33 with the stretched 9 M. Tsuchimori, O.Watanabe, S.Ogata and A. Okada, Jpn. J. Appl. exponential expression [eqn. (1)] at room temp. for polyesters Phys., 1996, 35, L444. 10 M. Eich, B. Reck, D. Y. Yoon, C.G. Willson and G. C. Bjorklund, Polyesters n t/h J. Appl. Phys., 1989, 66, 3241. 11 M. Chen, L. R. Dalton, L. P. Yu, Y. Q. Shi and W. H. Steier, P1 0.31 30 Macromolecules, 1992, 25, 4032. P2 0.66 >10000 12 Y. Shi, P. M. Ranon, W. H. Steier, C. Xu, B.Wu and L. R. Dalton, P3 0.27 1400 Appl. Phys. L ett., 1993, 63, 2168. P4 0.14 >10000 13 K. Y. Wong and A. K.-Y. Jen, J. Appl.Phys., 1994, 75, 3308. 14 W. Sotoyama, S. Tatsuura and T. Yoshimura, Appl. Phys. L ett., 1994, 64, 2197. 15 P. Pre�tre, P. Kaatz, A. Bohren, P. Gu�nter, B. Zysset, M. Ahlheim, M. Sta�helin and F. Lehr,Macromolecules, 1994, 27, 5476. 16 M. J. S. Dewar, E. G. Zoebisch, E. F. Healy and J. J. P. Stewart, J. Am. Chem. Soc., 1985, 107, 3902. 17 J. J. P. Stewart, MOPAC 6.0 QCPE#455, Quantum Chemistry Program Exchange, Indiana Univ., USA, 1990. 18 J. J. P. Stewart, J. Comput.-Aided Mol. Des., 1990, 4, 1. 19 H. A. Kurtz, J. J. P. Stewart and K. M. Dieter, J. Comp. Chem., 1990, 11, 82. 20 J. Jerphagnon and S. K. Kurts, J. Appl. Phys., 1970, 41, 1667. 21 G. D. Boyd, H. Kasper and J. H. McFee, IEEE J. Quantum Electron., 1971, QE-7, 563. 22 G. S’heeren, A. Persoons, H. Bolink, M.Heylen, M. Van Beylen and C. Samyn, Eur. Polym. J., 1993, 29, 981. 23 K.-J. Moon, H.-K. Shim, K.-S. Lee, J. Zieba and P. N. Prasad, Macromolecules, 1996, 29, 861. Fig. 2 Temporal behaviour of d33 at 100°C for (#) P2 and ($) P4. 24 G. Williams and D. C. Watts, T rans. Faraday Soc., 1970, 66, 80. Solid lines represent the fit with the stretched exponential expression. 25 S.H. Chung and J. R. Stevens, Am. J. Phys., 1991, 59, 1024. 26 C. A. Walsh, D. M. Burland, V. Y. Lee, R. D. Miller, B. A. Smith, R. J. Twieg and W. Volksen,Macromolecules, 1993, 26, 3720. Table 7 Temporal stability parameters of d33 with the stretched 27 H. L. Hampsch, J. Yang, G. K. Wong and J. M. Torkelson, exponential expression [eqn. (1)] at 100°C for polyesters Macromolecules, 1990, 23, 3648. 28 G. T. Boyd, C. V. Francis, J. E. Trend and D. A. Ender, J. Opt. Soc. Polyesters n t/h Am. B, 1991, 8, 887. 29 H.-T. Man and H. N. Yoon, Adv. Mater., 1992, 4, 159. P2 0.30 400 30 N. Tsutsumi, O. Matsumoto, W. Sakai and T. Kiyotsukuri, P4 0.36 160 Macromolecules, 1996, 29, 592. 880 J. Mater. Chem., 1997, 7(6), 877–88131 C. W. Dirk, S. Devanathan, M. Velez, F. Ghebremichael and 36 B. Park, S. Y. Eom, S.-D. Lee, D. H. Choi, S. Y. Park and N. Kim, M. G. Kuzyk,Macromolecules, 1994, 27, 6167. Opt. Quant. Electron., 1995, 27, 337. 32 Y. Karakus, D. Bloor and G. H. Cross, J. Phys. D: Appl. Phys., 37 R. Meyrueix and G. Mignani, Mater. Res. Soc. Symp. Proc., 1990, 1992, 25, 1014. 173, 619. 33 F.Wan, G. O. Carlisle, K. Koch and D. R. Martinez, J.Mater. Sci.: 38 M. A. Pauley, H. W. Guan and C. H. Wang, J. Chem. Phys., 1996, Mater. in Electron., 1995, 6, 228. 104, 6834. 34 C. Y. S. Fu, H. S. Lackritz, D. B. Priddy, Jr. and J. E. McGrath, Chem.Mater., 1996, 8, 514. 35 M. E. Wright, E. G. Toplikar, H. S. Lackritz and J. T. Kerney, Paper 6/07525H; Received 5th November, 1996 Macromolecules, 1994, 27, 3016. J. Mater. Chem., 1997, 7(6), 877–8

ISSN:0959-9428    

DOI:10.1039/a607525h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Hydrogen bonded liquid crystals from nitrophenols and alkoxystilbazoles Daniel J. Price,‡b Kimberley Willis,b Tim Richardson,b Goran Ungarb and Duncan W. Bruce*a aDepartment of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD Fax:+44 1392 263434. Email: d.bruce@exeter.ac.uk. bCentre for MolecularMaterials, Dainton Building, University of Sheeld, Sheeld, UK S3 7HF Three series of hydrogen bonded adducts have been formed between 4-alkoxy-4¾-stilbazoles† and the nitrophenols 4-nitrophenol, 3-nitrophenol and 2,4-dinitrophenol. Each series is mesomorphic displaying both nematic and smectic A phases, in sharp contrast to the behaviour of the individual components.The binary phase behaviour of mixtures of 3-nitrophenol and 4-octyloxystilbazole is reported, and gives conclusive evidence for the formation of a one-to-one hydrogen bonded adduct.Electronic spectroscopy of 2,4-dinitrophenol/decyloxystilbazole was very informative and showed that the higher energy, ionic hydrogen bonded state, corresponding to proton transfer, was significantly populated through the mesophase, and that the mesophase provides an additional stabilisation for this state.phenol and 2,4-dinitrophenol. Each of these complexes will be Introduction referred to by the abbreviated format X-Nn; where X refers to In the field of liquid crystals, hydrogen bonding has long been the position of substitution on the phenol and n is the length recognised as crucial to mesophase formation in certain sys- of the carbon chain on the stilbazole (thus, 2,4-N6 would tems.An early, and now classic, example is that of the represent the complex between hexyloxystilbazole and 2,4- alkoxybenzoic acids,1 where dimerisation of the molecules dinitrophenol). gives enhanced structural anisotropy. Another class of hydro- The proposed structures of these complexes are shown gen bonded mesogen are the alkylsilanediols,2 the aggregation below; variation of the alkyl chain length, n, of the stilbazole of which has been the subject of investigation.3 The silanediols gave three homologous series.The mesomorphism of these are in turn related to the large class of mesomorphic poly- materials was studied by optical microscopy and dierential alcohols, characterised by periodicity within the mesophase scanning calorimetry (DSC).The phase behaviour, transition structure, and including compounds from the straight chain temperatures and associated thermal parameters are given in a,b,y-alkanetetraols,4 to carbohydrates.5 In the latter case, Tables 1–3. mesophase formation is driven by a microphase separation The behaviour of these adducts is very dierent to that of dierent parts (polar and non-polar) of the molecules.shown by the individual components. For example, the alkoxy- More recently, the results of studies of complementary stilbazoles14 show a narrow range of smectic B and crystal heteromeric hydrogen bonded systems have been reported.6 smectic E phases, typically between 80 and 90°C, while the 4- Lehn and co-workers7 demonstrated induced mesomorphism nitro-, 3-nitro- and 2,4-dinitro-phenols simply melt at 113, 96 in ‘pseudo’ main-chain polymers and low molecular mass and 108 °C, respectively. materials self-assembled from complex, complementary parts.On a similar theme but at a structurally simpler level Yu,8 Grin,9 ourselves10 and particularly Kato,11 and their respective co-workers, have described many mesomorphic materials based on the adducts formed between substituted pyridines and carboxylic acid groups.Alongside work based on this carboxylic acid pyridyl interaction, we have examined liquid crystalline systems where the proton donor is a phenol. We demonstrated monotropic mesomorphism in complexes of 4-cyanophenol with 4-alkoxystilbazoles, 12 and, more recently, enantiotropic nematic and smectic A phases in complexes of 3-cyanophenol with 4- alkoxystilbazoles,13 showing how structural anisotropy, and hence mesophase stability, can be simply controlled in these complexes.It was also clear that the phenol–stilbazole hydrogen bond was suciently strong to allow the formation of mesophases from the complexes. Having studied these cyanophenols, we then turned our attention to nitrophenols as other examples of phenols bearing polarisable groups, and three series of complexes containing nitrophenols were prepared.Mesomorphism of the Complexes Hydrogen bonded adducts were formed between 4-alkoxystil- Complexes of 4-nitrophenol with 4-alkoxystilbazole (4-Nn) bazole and the following nitrophenols: 4-nitrophenol, 3-nitro- This series has the phase behaviour shown in Fig. 1. Monotropic nematic phases are seen for homologues from † Stilbazole=styrylpyridine; 4¾-stilbazole denotes attachment at the methoxy (4-N1) to octyloxy (4-N8). The nonyloxy derivative 4-position of the pyridine ring. (4-N9) sees the onset of smectic behaviour, with both nonyloxy ‡ Current address: School of Chemical Sciences, University of East Anglia, University Plain, Norwich, UK NR4 7TJ.(4-N9) and decyloxy (4-N10) derivatives showing monotropic J. Mater. Chem., 1997, 7(6), 883–891 883Table 1 Mesomorphism, and associated enthalpies and entropies for Table 2 Mesomorphism, and associated enthalpies and entropies for the 3-Nn series; monotropic transitions are indicated by parentheses the 4-Nn series of hydrogen bonded adducts; monotropic transitions are indicated by parentheses DH DS complex transition t/°C /kJ mol-1 /J K-1 mol-1 DH DS complex transition t/°C /kJ mol-1 /J K-1 mol-1 3-N1 Crys–I 98 33.0 89 (N–I) (97) (1.01) (2.7) 4-N1 Crys–I 118 35.2 91 (N–I) 88 —a 3-N2 Crys–I 114 37.2 96 (N–I) (99) —a 4-N2 Crys–I 101 31.8 85 (N–I) 85 0.68 1.9 3-N3 Crys–I 90 33.2 92 (N–I) (83) (0.82) (2.3) 4-N3 Crys–I 100 32.2 98 (N–I) (70) (0.4) (1.2) 3-N4 Crys–N 66 35.5 105 (Crys¾–N) (60) (24.8) (75.0) 4-N4 Crys–I 93 27.6 75.5 (N–I) (79) (0.4) (1.1) N–I 89 0.93 2.6 3-N5 Crys–N 60 28.5 86 4-N5 Crys–I 82 36.6 103 (N–I) (71) (0.41) (1.2) N–I 84 0.54 1.5 3-N6 Crys–N 79 44.6 126 4-N6 Crys–I 97 42.2 115 (N–I) (77) (0.4) (1.0) N–I 88 0.7 1.8 3-N7 Crys–N 81 41.5 118 4-N7 Crys–I 92 47.8 131 (N–I) (77) (0.42) (1.2) N–I 86 0.55 1.5 3-N8 Crys–N 75 41.9 120 4-N8 Crys–I 99 51.7 139 (N–I) (80) (0.85) (2.4) (Crys¾–N) (74) —a N–I 90 0.84 2.3 4-N9 Crys–I 93 52.3 143 (Crys¾–N) (79) (41.9) (122) 3-N9 Crys–N 71 44.2 129 (Crys¾–N) (70) —a (SA–N) (70) b (N–I) (82) (1.07) (3.0) N–I 86 0.77 2.2 3-N10 Crys–SA 78 51.8b 148b 4-N10 Crys–I 97 57.4 155 (SA–N) (84) b SA–N 79 N–I 90 1.11 3.1 (N–I) (86) (-0.83)c (-2.3) 4-N11 Crys–I 90 56.3 155 3-N11 Crys–SA 77 54.1 155 SA–N 87 0.22 0.61 (Crys¾–SA) (80) —a SA–I 89 2.50 6.9 N–I 90 1.25 3.4 3-N12 Crys–SA 80 56.5 160 4-N12 Crys–SA 80 36.4 103 (Crys¾–SA) (74) —a (Crys¾–SA) (66) —a SA–I 92 2.92 8.0 SA–I 91 2.98 8.2 4-N13 Crys–SA 88 54.9 152 3-N13 Crys–SA 79 64.6 184 (Crys¾–SA) (70) —a SA–I 95 3.50 9.5 SA–I 93 4.04 11 aDenotes a transition not seen in the DSC experiment.bIndicates a second order transition.cIndicates where monotropic transitions could aDenotes a transition not seen in the DSC experiment. bIndicates combined enthalpies of transition where a baseline resolution was not be seen or resolved as part of a heating cycle, and therefore the cooling cycle was used. not obtained. Fig. 1 The phase behaviour of the 4-Nn series: (%) K–, (1) SA–, Fig. 2 Plot of nematic–isotropic transition temperature vs. chain (#) N–I length for complexes of stilbazoles with nitro- and cyano-phenols: (%) 4-Nn, (#) 3-Nn, (1) 2,4-Nn, (Z) 4-Cn, (C) 3-Cn smectic A and nematic phases. The 4-N11 has just a monotropic smectic A phase, while for the 4-N12 and 4-N13 nematic phase at longer chain lengths, and in the nitro derivatives, this is a gradual change, with intermediate chain homologues, the combination of the continued destabilisation of the crystal phase and the increased stability of the smectic A lengths showing both nematic and smectic A phases.In contrast, there is a sudden switch from nematic to smectic A in phase resulted in enantiotropic behaviour. This series of adducts can be compared with the analogous the analogous cyano derivatives. Thus, extensive supercooling of the nematic phase of 4-C9 never revealed a smectic phase, complexes formed between 4-cyanophenol and alkoxystilbazoles, 13 (4-Cn—this abbreviation refers to the analogous yet 4-C10 showed only a smectic A structure.There are also similarities in the melting behaviour of both complexes with 4-cyanophenol).First, in the 4-Nn series the mesophases are more thermally stable (Fig. 2) by some series. After initially decreasing from the high melting methoxy and ethoxy derivatives, an odd–even eect is seen in both 10–20°C, which we tentatively attribute to enhanced antiparallel correlations induced by the nitro group in these systems. cases, although this is more pronounced in the 4-Nn complexes.In both 4-Nn and 4-Cn complexes, we also noted the existence In both series, the smectic A phase is seen to replace the 884 J. Mater. Chem., 1997, 7(6), 883–891Table 3 Mesomorphism, and associated enthalpies and entropies for showing, in addition, a smectic A phase. The 4-N12 and 4- the 2,4-Nn series; monotropic transitions are indicated by parentheses N13 homologues show only the smectic A phase between ca. 80 and 93°C. In this series, a normal odd–even eect is clearly DH DS seen at the nematic-to-isotropic phase transition. complex transition t/°C /kJ mol-1 /J K-1 mol-1 For the 3-Nn series, two comparisons can be made; first, 2,4-N1 Crys–I 150 43.2 102 with the structurally analogous cyano derivatives already (Crys¾–I) (148) —a described,13 and secondly with the 4-Nn series to assess the (N–I) (80) —a relative merits of meta and para substitution.Comparison of 2,4-N2 Crys–I 157 44.8 104 the 3-Nn series with the analogous 3-cyanophenol–alkoxystil- (Crys¾–I) (120) —a bazole (3-Cn) complexes revealed (Fig. 2) that the thermal (N–I) (72) —a stability of mesophases for the 3-Nn complexes was again 2,4-N3 Crys–I 139 47.8 117 (Crys¾–I) (121) —a typically 10–20 °C higher than that of their cyano counterparts.(N–I) (55) —a As with the 4-Nn series, the onset of the smectic behaviour 2,4-N4 Crys–I 114 41.9 103 was gradual, with intermediate derivatives being polymeso- (Crys¾–I) (100) —a morphic. This is in contrast to the sudden change seen for the (N–I) (69) —a 3-Cn complexes, where 3-C12 shows only a nematic phase and 2,4-N5 Crys–I 114 49.3 127 3-C13 only a smectic A phase. (Crys¾–I) (111) —a (N–I) (72) —a Comparison of the phase behaviour of the 3-Nn series with 2,4-N6 Crys–I 113 42.8 112 that of the 4-Nn series shows the dramatic eect of structural (SA–I) (85) —a isomerism.The fact that the 3-Nn complexes have a higher 2,4-N7 Crys–I 101 36.5 99 mesophase stability than their corresponding 4-Nn analogues (Crys¾–I) (95) —a indicates the importance of structural anisotropy.In the 3-Nn (SA–I) (94) (2.53) (7.0) series, meta substitution counters the ‘kink’ induced in the 2,4-N8 Crys–SA 95 37.4 103 SA–I 104 3.33 8.9 structure by the hydrogen bond to the phenol. This explains 2,4-N9 Crys–SA 98 48.2 130 the greater stability of the nematic phase (TNI is at least 10°C SA–I 111 4.06 10.6 higher than in 4-Nn complexes) and the more pronounced 2,4-N10 Crys–SA 97 44.7 121 odd–even eect (Fig. 2). The occurrence of the smectic A phase SA–I 117 4.50 11.5 in both series is very similar appearing at about the same 2,4-N11 Crys–SA 101 59.2 159 temperatures for given chain lengths. SA–I 121 4.94 12.5 2,4-N12 Crys–SA 97 47.2 129 SA–I 125 5.32 13.4 Complexes of 2,4-dinitrophenol with 4-alkoxystilbazole 2,4-N13 Crys–SA 97 45.2 122 (2,4-Nn) SA–I 126 4.63 11.6 These complexes were bright yellow in contrast with all other aDenotes a transition not seen in the DSC experiment.series previously described, which were cream coloured. The phase behaviour is displayed in Fig. 4 and again, only nematic and smectic A phases were observed, although this time the of a second, metastable crystal polymorph which typically phase diagram was of a dierent form.Thus, for short homol- melted at some 10–20 °C lower than the more stable state. ogues (from 2,4-N1 to 2,4-N5), a monotropic nematic phase Finally, it was curious to note that the stability of the nematic was seen at temperatures much lower than the melting points.phase of these complexes is higher than that of the related Increasing the alkyl chain length saw a sudden transition to 3-cyanophenol complexes, despite the more advantageous smectic behaviour, and from the 2,4-N6 to the 2,4-N13 deriva- structural anisotropy in the latter series. tive, a smectic A phase was observed. This was stabilised with increasing alkyl chain length, becoming enantiotropic from Complexes of 3-nitrophenol with 4-alkoxystilbazole (3-Nn) 2,4-N8 and reaching a thermal stability of 126°C in 2,4-N13.The phase behaviour of this series of complexes is shown in The mesomorphism of the 2,4-Nn complexes can be com- Fig. 3. All derivatives with the exception of 3-N1, 3-N2 and pared with both that shown by the 4-Nn and 3-Nn systems. 3-N3 display enantiotropic mesomorphism.This series shows Although the thermal stability of the nematic phase does not the largest thermal range of liquid crystal phases yet seen in vary much within any given series, the stability is seen to complexes based on the phenol–pyridyl interaction. The increase in the order 2,4-Nn<4-Nn<3-Nn (Fig. 2). This paral- nematic phase is seen for all homologues up to the 3-N9, after lels the increase in structural anisotropy, and is consistent with which both the 3-N10 and 3-N11 derivatives are polymorphic Fig. 4 The phase behaviour of the 2,4-Nn series: (%) K–, (1) SA–I, Fig. 3 The phase behaviour of the 3-Nn series: (%) K–, (1) SA–, (#) N–I (#) N–I J. Mater. Chem., 1997, 7(6), 883–891 885Table 4 Small angle X-ray scattering data complex T /°C t/Tcl phase d/A° dcalc/A° a d/dcalc 4-N12 85 0.93 SA 45.7, 4.5 29.0 1.46 3-N12 85 0.92 SA 43.0, 4.4 32.3 1.33 2,4-N12 105 0.84 SA 47.2, 23.2, 4.4 31.3 1.5 3-N10 85 0.94 N 40.0, 4.5 29.0 1.37 2,4-N8 102 0.98 SA 40.0, 19.3, 11.1, 4.4 26.0 1.54 aMolecular components calculated using CHEM 3DTM and hydrogen bonded distance from ref. 13. the idea that formation of the nematic phase is related to the an interdigitated bilayer structure.However, the nematic cannot be interdigitated as it is not layered and so we must structural and polarisability anisotropies of the rigid core. The stability of the smectic A phase as a function of chain conclude here that we have the predicted antiparallel dimers as illustrated in Fig. 6. On this basis, we would assume that length is shown in Fig. 5. In all series, the transition temperatures are seen to increase rapidly with increasing chain length this arrangement existed in the SA materials and was the cause of the increased layer spacing there, too. beginning to ‘level o ’ at longer homologues. The stability is clearly much greater in the 2,4-Nn series than in both 4-Nn and 3-Nn complexes, which are similar to one another.In Thermodynamic Properties addition, we note that smectic behaviour can be induced by a hexyloxy chain for the 2,4-Nn series, whereas nonyloxy or From plots of entropy change as a function of chain length, n, decyloxy chains are needed in the 4-Nn and 3-Nn series. That for a particular transition in a given series, certain trends can is, in these cases, much longer alkyl chains are required to be seen.In all cases crystal-to-isotropic liquid or crystal-toproduce the microphase separation of constituent parts that is mesophase transitions can be grouped together, as dierences the smectic A phase. in entropy of the transition are typically much larger than the Despite the high acidity of 2,4-dinitrophenol (pKa=3.96),15 dierences found between the isotropic liquid and mesophase.the complex is still expected to exist predominantly in the non- For all series we can see a general increase in DS with increasing ionic hydrogen bonded form,16 on account of the small value homologue superimposed by a small parity dependence. of DpKa [the dierence between the pKa of the conjugate acid However, as these values depend on factors, such as crystal of the stilbazole (ca. 5–6), and the pKa of the phenol]. Although structure, which have not been evaluated, then no meaningful the complex is non-ionic (at least in the ground state17—vide comparison is possible here. inf ra), the increased acidity of the phenol strengthens the For the nematic-to-isotropic transition, enthalpies could hydrogen bond, and increases its polarisability.Thus, the only be obtained for the 4-Nn and 3-Nn series. Both series combination of increased polarisation due to having two nitro show no general trend with values in the range 1.0 to groups and increased polarisability (the hydrogen bond) that 3.4 J K-1 mol-1. The 3-Nn series shows an odd–even eect, gives an additional stabilisation to the core–core interactions, where even homologues show larger transition temperatures disfavouring core–chain interactions, resulting in the predomi- (TNI ) and larger entropies (DSNI).That no great variation was nance of the smectic A phase in the 2,4-Nn complexes. observed is in agreement with the idea that increasing the alkyl chain length does nothing to stabilise or increase the order in the nematic phase, and that the origin of this phase X-Ray Scattering Studies derives primarily from the rigid core.In our studies of the related 3-cyanophenol complexes,13 we For the smectic A-to-isotropic transition, in all cases we see had in one case performed X-ray scattering experiments which a clear increase in the entropy with increasing chain length. clearly demonstrated that the SA phase in question was inter- The data for the 4-Nn, 3-Nn and 2,4-Nn series are shown digitated.X-Ray scattering studies were therefore carried out graphically in Fig. 7. Unlike the nematic phase which has only in the present case to obtain similar information. The data are one type of order—defined by the order parameter and related collected in Table 4. to the orientational distribution of molecules about the What the data clearly show is that the layer spacing in the director—the smectic A phase has two.First, it has, like the SA phase and the apparent molecular length in the nematic nematic, a director and associated ‘order parameter’. Secondly, phase (3-N10 only) are significantly greater than the calculated there exists a one-dimensional periodicity giving it its layered molecular length.In the case of the SA phase, this points to structure. In liquid crystals, this positional ordering varies between two extremes. The most disordered case is a loose association that gives layers where the periodicity is best described by a sinusoidal distribution function. This is the case for many thermotropic liquid crystals, especially immediately below a nematic phase.At the other end, the lamellar structure can be very well defined, where the layers are much more ‘rigid’ and the periodicity approaches a series of Gaussian functions. This is typically the case found in lyotropic phases. The similar structuresof these complexes mean that comparison of their entropies is valid. So, first we make the assumption that the dierence between entropies of the isotropic states, either within or between 2,4-Nn, 4-Nn and 3-Nn complexes, is insignificant.This done, the changes in entropy of transition can be attributed to changes in the nature of the smectic A phases. Given that the entropies of the nematic-to-isotropic transition are more or less independent of alkyl chain length, no eect on the order parameter of the smectic A phase is expected for an increase in chain length.Thus, lower entropies Fig. 5 The thermal stability of the smectic A phase (T SAI and T SAN) for complexes of (1) 4-Nn, (#) 3-Nn and (%) 2,4-Nn correspond to a more sinusoidal distribution function, while 886 J. Mater. Chem., 1997, 7(6), 883–891Fig. 6 The antiparallel structure adopted by the hydrogen bonded complexes or 3-N12 derivatives.It can also be said that smectic A-toisotropic transitions with similar entropies will also have similar distribution functions. Thus, since 2,4-N7 and 4-N11 are almost isoentropic, they probably have similar phase structures. These conclusions are further supported by the Xray data presented in Table 4 in which it is clearly seen that it is the two dinitrophenol complexes which show second and third order reflections for the lamellar spacings, again suggesting a more Gaussian distribution.Binary Mixture Studies of 3-N8 Binary mixtures of various compositions were formed from 3-nitrophenol and 4-octyloxy-4¾-stilbazole by a melt synthesis procedure. The phase behaviour of these mixtures was studied as a function of temperature using optical microscopy and Fig. 7 The variation in entropy of the smectic A–isotropic transition DSC experiments. The results are shown in Fig. 8 as a binary for various homologues of the (%) 4-Nn, (1) 3-Nn and (#) 2,4- phase diagram. The complexity of the phase behaviour is so Nn series great that even with the 15 compositions studied it is not possible to determine unambiguously the detailed structure of higher values represent a greater deviation toward a Gaussian the phase diagram.The lines delimiting phase boundaries, distribution. eutectic and ‘peritectic’ like behaviour serve to highlight the Changes in the distribution function which describes the gross behaviour, and are most likely the correct interpretation periodicity of the layers are solely a consequence of changes of the data.in the intermolecular interactions. By dividing molecules into The congruent melting behaviour observed at 50% 3-nitro- two parts (the aromatic, polarisable core and the aliphatic chain), this system can be considered as containing only three types of pairwise interaction. These are core–core, chain–chain or core–chain interactions.In a rigidly layered system where cores are separated from chains, we have only core–core and chain–chain interactions. In a non-layered system, core–chain interactions would also be present. When the energy of the core–chain interaction is too ‘costly’—that is when the dierence between interaction energies exceeds a certain threshold—the amount of core–chain interactions is reduced by forming a layered structure.Further increase in the ‘cost’ of this interaction causes a deviation from a purely sinusoidal distribution function towards a Gaussian one. These changes in distribution can be related to the entropy of the phase. Thus, through the nature of the distribution function, a larger value of DS can be related to a higher ‘cost’ of core–chain interactions. In this way we can see that changing the alkyl chain length, in a homologous series, can only eect chain–chain and core–chain interactions, and that the increase in DS with increasing homologue, n, reflects the stabilisation of chain–chain (or core–core) interactions above core–chain interactions.For the 2,4-Nn series we see that each additional carbon atom to the alkyl chain adds between 1 and 2 J K-1 mol-1 of order to the phase.Comparison of the 2,4-Nn, 4-Nn and 3-Nn series shows the structurally isomeric 4-Nn and 3-Nn complexes to have very similar behaviour, whereas the addition of an extra nitro group in the 2,4-Nn complex massively changes the order of the Fig. 8 The binary phase behaviour of mixtures of 3-nitrophenol and phase.The smectic A phase of the 2,4-N12 derivative has an 4-octyloxy-4¾-stilbazole: (%) K–, (1) K+N–, (#) K+I–, (') E–, (Z) E+N–, (2) E+I–, (C) SB–, (() N–, (D) N+I– additional 5 J K-1 mol-1 (ca. 60%) of order than the 4-N12 J. Mater. Chem., 1997, 7(6), 883–891 887phenol (percentages are given as mole fractions of the two complexes in decreasing wavenumber such that 3-C8>4- C8>3-N8>4-N8.This suggests that the hydrogen bonding is components) is conclusive evidence for the formation of a oneto- one adduct. This, and the increased thermal stability in the strongest in the nitro derivatives, and that the 4-substitution gives a stronger hydrogen bond than 3-substitution. This is crystal and nematic phases at the 50% composition, implies complex formation is strongly favoured over the reverse reac- anticipated given the eect of these substituents upon the proton donating ability (which can be related to pKa) of these tion.It is consequently legitimate to treat the diagram as two separate halves: from 0 to 50% 3-nitrophenol, which in reality phenols. The order is primarily attributed to the stronger electron-withdrawing properties of the nitro group over that corresponds to a binary phase diagram of 4-octyloxy-4¾-stilbazole with the complex 3-N8; and from 50 to 100% 3-nitrophe- of the cyano group, and secondarily the fact that any 3- substituted derivatives, unlike the 4-substituted, are not conju- nol, which is the phase diagram of 3-N8 with 3-nitrophenol.For the right hand side of the diagram (50–100% 3-nitrophe- gated to the phenolic oxygen.The broad nOH band at ca. 2500 cm-1 suggests a ‘weak’ single minimum potential. This is nol) the behaviour is that of two components whose isotropic liquid phases are completely miscible but do not form solid anticipated for the monosubstituted adducts on the basis of the DpKa values. However, with the increased acidity of the solutions.Here the eutectic point is formed at about 67% 3-nitrophenol with a melting point at ca. 65°C. The nematic 2,4-dinitrophenol, an unsymmetric double minimum potential may be expected in the 2,4-Nn complexes. phase, is quickly destabilised becoming monotropic just above 60% 3-nitrophenol, and biphasic behaviour is seen at this When compared to 3-Cn, 4-Cn, the nitro-substituted adducts show additional bands.In the 3-N8 and 4-N8 complexes a clearing transition. On the left hand side (0–50% 3-nitrophenol) the diagram broad band with a vibrational fine structure, centred at ca. 1800 cm-1, is observed. This is more intense in the 4-N8 shows the behaviour of mixtures of 4-octyloxy-4¾-stilbazole and 3-N8. This is much more complicated than the right hand derivative than the 3-N8, and is not seen at all in the analogous cyano complexes. In 2,4-N8 two additional bands at 2116 and side.It arises not only because now both of the components are mesomorphic, but also because dierent phases show 2022 cm-1 are seen. Although the hydrogen bond strength in 2,4-N8 is expected to be comparable with carboxylic acid– diering degrees of miscibility. In particular while both crystal phases are immiscible, the smectic E phase shows a limited pyridyl adducts, no similarity in the IR spectra is observed. Complexes of carboxylic acids and pyridyl moieties are miscibility for a range of compositions.This is seen at the Estilbazole+I�I transition, where a near flat phase boundary described as forming intermediate to strong hydrogen bonds, and give rise to ‘type i’ spectra as defined by Hadzi,19 showing occurs at about 77°C for compositions 85 to 80% stilbazole.This implies that the composition of the smectic E phase here a trio of bands, A–C at typically 2800, 2500 and 1800 cm-1. The additional bands observed in 2,4-N8 are probably over- is between 90 and 85% stilbazole, while the isotropic phase is relatively enriched in the complex 3-N8.tones and combinations of other stretches. Other noticeable changes are more subtle. Generally we see It is not surprising that the crystal smectic E phase of the stilbazole is rather more tolerant of 3-N8 impurity than the pyridyl nCN stretch increase from 1590 cm-1 by ca. 10 cm-1 upon complexation. Similarly, the predominantly phenolic nCO the crystal phase.Given the more disordered nature of the smectic E phase, such behaviour is understandable. For these increases by ca. 20 cm-1 to 1250 cm-1. The magnitude and direction of each of these changes is as expected for the change compositions the first transition on heating occurs at about 66°C, and it is likely that the corresponding eutectic composi- in the environment for these groups.20 The cOH and dOH, ‘outof’ and ‘in-plane’ deformations of the pure phenols are not tion is at about 70% stilbazole.A final point worth noting is the overall stability of the nematic phase. The delimiting line, seen in the spectra of the adducts. These vibrations are believed to be responsible for the increase in background absorption21 representing its uppermost thermal stability is unsymmetric across the whole phase diagram.The phase is tremendously below 1300 cm-1. destabilised by the non-mesogenic 3-nitrophenol, on the other Variable temperature IR studies hand, as one might expect, the mesogenic stilbazole impurity is quite well tolerated with relatively little depreciation in the Studies were performed on a sample of 3-N5.The sample was phase stability. heated under an argon atmosphere and spectra were recorded every 5°C from room temperature (23°C), to the isotropic phase at 140°C. Other than ageneral loss of spectral resolution, Spectroscopic Investigations two major changes were observed. The first was an unsym- Infrared studies metric broadening of the nOH band at ca. 2500 cm-1, and a shift in position of the band maximum to higher frequencies.IR spectroscopy was used to examine the hydrogen bonding This shift and broadening of the nOH is consistent with a in these complexes. Samples were run as KBr discs and were lengthening of the hydrogen bond, and an increased polaris- examined between 4000 and 450 cm-1. We acknowledge the ability, reflecting the increased number of possible environ- suggestion18 that KBr may not be an inert matrix for these ments of this bond.Part of this region of the spectra is hydrogen bonded adducts, as the possibility of a hydrogen obscured by various nCH stretches, which are unaected by the bonded interaction with the bromide ion exists. However, changes in temperature. identical spectra were obtained for a sample of solid 3-N5 and The second, and most impressive change was the complete this adduct in a KBr disc.We also note that the hydrogen and sudden loss of the band at ca. 1800 cm-1 upon melting. bonded complexes of Yu and co-workers8 prepared as Nujol This broad, medium-intensity band, is present in the crystal at mulls gave identical spectra to those in KBr discs. We believe 60°C, but disappears completely at 65°C when the adduct has that the changes in homologue and core structure of our melted into the nematic phase.From this observation we can complexes are unlikely to cause a change in the interaction say that the band is in some way related to a lattice mode. with KBr. The most obvious changes upon complexation are observed Solid state NMR studies in the nOH region above 1700 cm-1.The nOH band in the phenol at ca. 3200 cm-1 is replaced by a broad band in the The timescale and sensitivity of the NMR experiment should reveal information about the average state of the hydrogen complex centred at ca. 2500 cm-1 showing some substructure. This is indicative of the formation of a stronger hydrogen bonding, by changes in the chemical shifts of the atoms in the proximity of the interaction.Preliminary solid state MAS 13C bond in the complex than in the pure phenol. Comparison of the spectral positions of the nOH stretching bands ranks the spectra were obtained for the complex 3-N8 at ambient tem- 888 J. Mater. Chem., 19, 7(6), 883–891perature (23°C) in the crystal phase, at 94°C in the nematic state, and at 99°C in the isotropic liquid.No discernible change was seen in these spectra, suggesting that in this complex the isotropisation is not driven by a dissociation of the complex into its constituent parts. Further, and more detailed studies are already underway. Electronic spectroscopy of 2,4-N10 Unlike all of the other hydrogen bonded systems we have examined, the 2,4-Nn complexes are golden yellow.This is also in stark contrast to the components, the stilbazoles being cream coloured; lmax(THF) 326 nm, and 2,4-dinitrophenol is a pale yellow; lmax(THF) 295, sh 340 nm. The nature of the Scheme 1 Proton transfer between (a) the normal state of hydrogen bonding in the adduct and (b) the ionic hydrogen bonded form hydrogen bond greatly aects the electronic states in each conjugated chromophore. The large shift in the position of the absorption maxima experienced by both parts makes these that in the absence of more appropriate data such comparisons complexes ideal for investigations by UV spectroscopy.Indeed are acceptable. the results of our preliminary studies have already been The fact that isosbestic behaviour is observed up to 121 °C reported.17 implies only one pair of species, and that no significant The electronic spectra of 2,4-N10—whose mesomorphism is dissociation is seen up to this point.That is, isotropisation is Crys·97·SA·117·I, was recorded every 0.33 °C at 90–126 °C. driven by the structural anisotropy and properties of the Reproducible spectra were obtained once the material had complex as a whole, and not by the dissociation into constitu- been allowed to crystallise.Fig. 9 shows a heating run from ent parts. It is informative to plot the intensities of the key 90–118°C; glass was used as a substrate giving a ‘cut-o ’ transitions as a function of temperature and state; this is done point of ca. 310 nm. Fortunately, all major transitions are well in Fig. 10. Thus, bands B and D are seen initially to increase above this value. In order to assign the spectra, it is useful to at the expense of band A. The transition C is apparently seen make comparison with certain fragments. In addition to the to increase, as it is not deconvoluted from bands B and D. components (vide supra), we find that, decyloxystilbazolium Above 121 °C, we see the beginning of a general broadening chloride is bright yellow having a lmax(THF) at 368 nm, and of the spectra, a deviation from isosbestic behaviour, and a potassium 2,4-dinitrophenoxide is bright orange, lmax(THF) decrease in the intensities of all transitions.This is attributed 363 and 424 nm. to the dissociation of the complex from both ionic and non- There are four bands in the spectra, A–D, and we have ionic hydrogen bonded states.Dissociation from both of these assigned each of these to the lowest energy transitions in 4- states would lead to the observed hypsochromic and batho- decyloxy-4¾-stilbazole, 4-decyloxy-4¾-stilbazolium, 2,4-dinitro- chromic shifts in the spectra. This would support the proposal phenol and 2,4-dinitrophenate, respectively. The observed from Kato22 that dissociation does not occur until the isotropic isosbestic behaviour at 90–121 °C shows that only two species state is reached and that, indeed, the fact that the hydrogen are present, which we identify as the non-ionic and ionic bonded complex is in a mesophase (particularly in the case of hydrogen bonded states (Scheme 1) and which shows that an smectic phases) may serve to stabilise the hydrogen bond.increase in temperature populates the (excited) ionic state. A final point to note concerns the relative populations of Thus, the hydrogen bond clearly has an unsymmetric double the two states. As both stilbazole and stilbazolium have similar minimum potential. That the non-ionic state is the ground extinction coecients (30600 and 33000 dm3 cm mol-1, state is also supported by the low value of the DpKa between respectively), we can say that a near 50% population is stilbazolium and 2,4-dinitrophenol, which is between 1 and 2.obtained above ca. 114 °C. However, a further increase in Lindemann and Zundel16 suggest that usually a value of 4 is temperature above the clearing point sees a relative decrease required to eect 50% proton transfer.Although comparisons in the population of the ionic hydrogen bonded state. To of solution with solid state spectra, and predictions based on aqueous acidities, must be viewed with some caution, we feel Fig. 9 Electronic spectra of the adduct 2,4-N10 at 90–118 °C, as it Fig. 10 The variation of the key transitions as a function of passes from the crystal through the smectic A phase and into isotropic state temperature: (%) 348 (A), (1) 368 (B), (#) 400 (C) and (') 426 nm (D) J.Mater. Chem., 1997, 7(6), 883–891 889account for this deviation from a normal thermal population in good yield by coupling 4-methylpyridine and the corresponding 4-alkoxybenzaldehyde, followed by an acid-catalysed of the ionic excited state, we propose that the environment of the smectic A phase, where there is a lamellar microphase elimination to convert the intermediate secondary alcohol into the product.The procedure is described for the butoxy deriva- separation of alkyl chains from the aryl cores, provides an additional stabilisation of the ionic hydrogen bonded state, as tive. Analogous procedures were employed for all other homologues.All components gave satisfactory characterisation. The here the hydrogen bond is predominantly surrounded by polarisable (aryl groups) and polarised (nitro groups) func- behaviour of the stilbazoles was identical to that of authentic samples.14 tionalities. Thus, we re-emphasise the important conclusion that significant dissociation from the hydrogen bonded complexes does not occur until the isotropic state is reached and General sample preparation that isotropisation is not driven by a breakdown of the Complexes were formed by dissolving exactly equimolar hydrogen bonded complex, indeed the mesophase may act to amounts of the components in tetrahydrofuran and removing stabilise the hydrogen bond.the solvent on a rotary evaporator.The compromise to purity that mixing brings is estimated to be not more than 1%. Experimental Mixture preparation Instrumentation Homogeneous mixtures were formed from solutions of the The components were characterised by microanalysis, percomponents, by removing the solvent (tetrahydrofuran) at ca. formed at Sheeld University, and by 1H and 13C NMR on a 60°C, then heating the mixture while stirring with a magnetic Bruker WM250 spectrometer. Chemical shifts are quoted follower, at up to ca. 120 °C, where only a single isotropic relative to an internal standard, and all coupling constants are phase is present, and then cooling quickly. given in Hz. 13C NMR data were obtained from J-modulated spectra. All components gave satisfactory characterisation. Routine IR spectroscopy was performed, unless otherwise 1-(4-Butoxyphenyl )-2-(4-pyridyl )ethanol.A solution of diiso- specified, as KBr discs on a Perkin Elmer 1600 series FTIR. propylamine (3.757 g, 37.2 mmol), in dry tetrahydrofuran Variable temperature IR studies were performed using a (200 cm3; freshly distilled from sodium benzophenone ketyl), Perkin Elmer 1710 FTIR equipped with an Infrared Associates was cooled under a nitrogen atmosphere to -78°C.Ltd NO 161373 liquid nitrogen cooled detector, working to a Butyllithium (23.5 cm3, 1.6 mol dm-3 solution in hexanes, resolution of 4 cm-1.The sample was deposited by evaporation 37.6 mmol) was added dropwise over a period of 40 min. The from a diethyl ether solution onto a silicon rod, within a reaction was allowed to stir for a further 30 min while a pressure cell.The cell was filled with argon to a pressure of 1 temperature of -78 °C was maintained. After this time a atmosphere at room temperature (23°C) and sealed. The cell solution of 4-methylpyridine (3.459 g, 37.2 mmol) in tetrawas then equipped with a heater and thermocouple and a hydrofuran(30 cm3) was added dropwise over 1 h. The reaction temperature controlled to an accuracy of ±5°C.Attenuated mixture, which became bright orange, indicating the formation total reflectance FTIR spectra were obtained every 5 K, of the carbanion, was stirred for a further 40 min. Subsequent through crystal, nematic and isotropic phases at dropwise addition of 4-butoxybenzaldehyde (6.0 g, 33.7 mmol) 4000–200 cm-1. in tetrahydrofuran (30 cm3) over 30 min was accompanied by Tetrahydrofuran (THF) was refluxed under nitrogen over a colour change of the reaction mixture from orange to pale lumps of sodium and benzophenone until the solution became yellow.The mixture was stirred for 30 min and then allowed purple and was freshly distilled immediately prior to use. to warm to room temp. over 3 h. The excess pyridyl carbanion Solution state electronic spectra were recorded on a Phillips was quenched with water (20 cm3), upon which the reaction PU8720 UV–VIS scanning spectrophotometer. The variable became instantly colourless, the mixture was then neutralised temperature ‘solid’ state electronic spectroscopy was performed with dilute aqueous hydrochloric acid.All of the solvents were in transmission, with a Photal Otsuka Electronics Deuterium removed under reduced pressure on a rotary evaporator.The Lamp, MC-962A and Spectromultichannel Photo Detector, solid was partitioned between dichloromethane (200 cm3) and MCPD-100. The sample was heated on a Mettler hot stage water (3×200 cm3) and washed once with saturated brine with an FP90 control processor. Heating rates of 1 and solution (1×200 cm3).The organic phase was dried over 4 K min-1 were employed and spectra were taken every 0.33 anhydrous magnesium sulfate, filtered and the solvent removed or 1 K. Samples were prepared by placing a saturated solution on a rotary evaporator, giving the crude product as an oil of the material in tetrahydrofuran onto a glass microscope which crystallised upon standing.Recrystallisation from hep- slide, covering with a coverslip and allowing the solvent to tane gave the product (yield 4.95 g, 18.3 mmol, 54%). mp 87°C evaporate at ca. 60°C. (found: C, 75.1; H, 7.8; N, 5.2. C17H21NO2 requires: C, 75.3; The mesomorphism was characterised by heated stage polar- H, 7.8; N, 5.2%); nmax cm-1 (KBr) nO–H 3202 br vs; dH ising optical microscopy, using a Zeiss Labpol microscope (250 MHz; CDCl3) 0.97 (3H, Ha, t, 3Jac 9.4), 1.40–1.58 (2H, fitted with a Linkam TH600 hot stage and a PR600 tempera- Hb, m), 1.68–1.82 (2H, Hc, m), 2.93 (1H, Hj, dd, J 16.9, 6.9), ture controller.Enthalpies of transitions were recorded by a 3.03 (1H, Hj, dd, J 16.9, 10.0), ca. 3.0 (1H, Hn, br s), 3.94 (2H, Perkin Elmer DSC 7 instrument, at heating and cooling rates Hd, t, 3Jcd 8.1), 4.85 (1H, Hi, dd, J 10.0, 6.9), 6.84 (2H, Hf, of between 5 and 10 K min-1 were employed.AA¾XX¾, J 10.6), 7.05 (2H, Hl, AA¾XX¾, J 7.5), 7.20 (2H, Hg, X-Ray diraction patterns were recorded with an Image AA¾XX¾, J 10.6) and 8.35 (2H, Hm, AA¾XX¾, J 7.5); dC (63 MHz; Plate area detector (MAR Research) using graphite-monochro- CDCl3) 13.9 Ca, 19.6 Cb, 31.3 Cc, 45.1 Cj, 67.7 Cd, 74.0 Ci, matised Cu-Ka pinhole collimated radiation.The samples, in 114.4 Cf, 125.0 Cl, 127.1 Cg, 135.6 Ch, 147.8 Ck, 149.3 Cm and glass capillaries, were held in a temperature-controlled cell. 158.8 Ce. The beam path was flushed with helium. Components 3-Nitrophenol (BDH) was crystallised from water. 2,4- Dinitrophenol (BDH) was dried under high vacuum and 4- nitrophenol (Hopkin and Williams Ltd) was used without further purification. 4-Alkoxy-4¾-stilbazoles were synthesised 890 J. Mater. Chem., 1997, 7(6), 883–891J. W. Goodby and G. W. Gray, J. Chem. Soc., Faraday T rans. 1, trans-4-Butoxy-4¾-stilbazole {trans-4-[2-(4-butoxyphenyl) 1982, 713. ethenyl]pyridine}. To a solution of 1-(4-butoxyphenyl)-2-(4- 4 F.Henrich, S. Diele and C. Tschierske, L iq. Cryst., 1994, 17, 827. pyridyl)ethanol (4.921 g, 18.15 mmol) in toluene (300 cm3) was 5 For reviews of this subject see: G. A. Jeery and L. M. Wingert, added toluene-p-sulfonic acid (10.021 g, 56.26 mmol) and pyri- L iq. Cryst., 1992, 12, 179; G. A. Jeery, Acc. Chem. Res., 1986, dine (4.430 g, 56.08 mmol). The reaction mixture was heated 19, 168. 6 C. Paleos and D. Tsiourvas, Angew. Chem., Int. Ed. Engl., 1995, under reflux overnight and a Dean–Stark apparatus was used 34, 1696. to remove the water produced by azeotropic distillation. 7 M. Kotera, J.-M. Lehn and J.-P. Vigneron, J. Chem. Soc., Chem. After cooling, a solution of potassium hydroxide (3.614 g, Commun., 1994, 197; M.-J. Brienne, J. Gabard, J.-M. Lehn and 64.42 mmol) in a mixture of water (200 cm3) and ethanol I.Stibor, J. Chem. Soc., Chem. Commun., 1993, 420. (5 cm3) was added, and the reaction stirred for a further 12 h. 8 L. J. Yu, J. M.Wu and S. L.Wu, Mol. Cryst. L iq. Cryst., 1991, 198, The phases were separated and the organic layer washed with 407; L. J. Yu and J. L. Pan, L iq. Cryst., 1993, 14, 829; L. J. Yu, L iq. Cryst., 1993, 14, 1303.water (5×200 cm3) and saturated brine (1×200 cm3). The 9 C. M. Lee, C. P. Jarwala and A. C. Grin, Polymer, 1994, 35, 4550. toluene solution was then dried over anhydrous magnesium 10 D. J. Price, PhD thesis, Sheeld University, 1995; H. Kihara, sulfate, filtered and the solvent removed under reduced press- T. Kato, T. Uryu, S. Ujiie, K. Iimura, U. Kumar, J. M. J. Fre� chet, ure.Crystallisation from hot acetone gave the product, trans- D. W. Bruce and D. J. Price, L iq. Cryst., 1996, 21, 25; D. J. Price, 4-butoxy-4¾-stilbazole (yield 3.371 g, 11.21 mmol, 62%). mp H. Adams and D. W. Bruce, Mol. Cryst. L iq. Cryst., 1996, 289, 127; 95°C (lit.,14 95°C) (found: C, 80.34; H, 7.56; N, 5.57. C21H19ON K. Willis, J. E. Luckhurst, D. J. Price, J. M. J.Fre� chet, H. Kihara, T. Kato, G. Ungar and D. W. Bruce, L iq. Cryst., 1996, 21, 585. requires: C, 80.60; H, 7.56; N, 5.53%); dH (250 MHz; CDCl3) 11 T. Kato and J. M. J. Fre� chet, J. Am. Chem. Soc., 1989, 111, 8533; 0.97 (3H, Ha, t, 3Jab 7.5), 1.49 (2H, Hb, m), 1.77 (2H, Hc, m), T. Kato and J. M. J. Fre� chet, Macromolecules, 1989, 22, 3818; 3.98 (2H, Hd, t, 3Jdc 6.4), 6.77 (1H, Hj, d, 3Jij 16.2), 6.83 (2H, U.Kumar, T. Kato and J. M. J. Fre� chet, J. Am. Chem. Soc., 1992, Hg, AA¾XX¾, J 8.4), 7.15 (1H, Hi, d, 3Jij 16.2), 7.22 (2H, Hl, 114, 6630; T. Kato, H. Kihara, T. Uryu, A. Fuijishima and AA¾XX¾, J 6.1), 7.38 (2H, Hf, AA¾XX¾, J 8.4) and 8.46 (2H, J. M. J. Fre� chet, Macromolecules, 1992, 25, 6836; T. Kato, Hm, AA¾XX¾, J 6.1); dC (63 MHz; CDCl3) 13.9 Ca, 19.2 Cb, H. Kihara, U. Kumar, T. Uryu and J. M. J. Fre� chet, Angew. Chem., Int. Ed. Engl., 1994, 33, 1644; T. Kato, P. G. Wilson, A. Fuijishima 31.3 Cc, 67.8 Cd, 114.8 Cf, 120.6 Cl, 123.6 Cj, 128.4 Cg, 128.7 and J. M. J. Fre� chet, Chem. L ett., 1990, 2003; T. Kato, Ch, 132.8 Ci, 145.0 Ck, 150.1 Cm and 159.8 Ce. J. M. J. Fre� chet, P. G. Wilson, T. Saito, T. Uryu, A. Fuijishima, C. Sin and F. Kaneuch, Chem. Mater., 1993, 5, 1094; T. Kato, A. Fuijishima and J. M. J. Fre� chet, Chem. L ett., 1990, 912; M. Fukumassa, T. Kato, T. Uryu and J. M. J. Fre� chet, Chem. L ett., 1993, 65; T. Kato, H. Kihara, T. Uryu, S. Ujiie, K. Iimura, J. M. J. Fre� chet and U. Kumar, Ferroelectrics, 1994, 148, 1303. 12 D. W. Bruce and D. J. Price, Adv. Mater. Opt. Electron., 1994, 4, 273. 13 H. Adams, D. W. Bruce, D. J. Price, G. Ungar and K. Willis, J. Mater. Chem., 1995, 5, 2195. We would like to thank the EPSRC for a studentship to 14 D. W. Bruce, D. A. Dunmur, E. Lalinde, P. M. Maitlis and D. J. P., Dr David Apperly (EPSRC Solid State NMR service, P. Styring, L iq. Cryst., 1988, 3, 385. Durham) for his invaluable assistance with solid state MAS 15 CRC Handbook of Chemistry and Physics, ed. D. R. Lide, 75th edn., CRC Press Inc., Boca Raton, Florida. NMR and Dr Tony Haynes (Sheeld) for his assistance with 16 R. Lindemann and G. Zundey T rans. 2, variable-temperature infrared studies. We wish to thank 1972, 68, 979;R. Lindemann and G. Zundel, J. Chem. Soc., Faraday Professor Gu�nter Lattermann (Bayreuth) for suggesting the T rans. 2, 1977, 73, 788. potential benefits of a nitro group in these systems. 17 D. J. Price, T. Richardson and D. W. Bruce, J. Chem. Soc., Chem. Commun., 1995, 1911. 18 K. R. Seddon, personal communication, 1995. References 19 D. Hadzi, Pure Appl. Chem., 1965, 11, 435. 20 D. W. Brown, A. J. Floyd and M. Sainsbury, Organic Spectroscopy, 1 D. Vorla�nder, Z. Phys. Chem., 1923, 105, 211; G. M. Bennett and Wiley, Bath, 1988. B. Jones, J. Chem. Soc., 1939, 420. 21 S. L. Johnson and K. A. Rumon, J. Phys. Chem., 1965, 69, 74. 2 C. Eaborn, J. Chem. Soc., 1952, 2840; A. Polishchuk, 22 T. Kato, personal communication. T. V. Timofeeva, N. N. Makarova, M. Yu. Antipin and Yu. T. Struchov, L iq. Cryst., 1991, 9, 433. 3 J. D. Bunning, J. E. Lydon, C. Eaborn, P. M. Jackson, Paper 7/00575J; Received 24th January, 1997 J. Mater. Chem., 1997, 7(6), 883–891

ISSN:0959-9428    

DOI:10.1039/a700575j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Cholesteric helix inversion: investigations on the influence of the terminal group on the inversion of the helical pitch in trioxadecalins Volkmar Vill,a H. Markus von Mindena and Duncan W. Bruceb aInstitute of Organic Chemistry, University of Hamburg, Martin-L uther-King-Platz 6, D-20146 Hamburg, Germany bDepartment of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD Synthesis and mesogenic properties of new liquid crystals, bearing a chiral trioxadecalin system, are described.As cholesteric helix inversions in trioxadecalin systems bearing a terminal cyano or nitro group have previously been observed, the terminal group has been changed systematically to elucidate its influence on the occurrence of inversions of the helical pitch. Chirality has become one of the most important and complex topics in liquid crystal research, since molecular asymmetry imparts form chirality to the liquid crystalline phases.1 Most of the chiral liquid crystals investigated possess only one chiral centre in the flexible side chain.2 However, the use of carbohydrates enables us to introduce a chiral trioxadecalin ring system directly into the molecular core.3 In this way it is possible to locate the chirality in that part of the molecule which determines the general mesogenic properties, and many of our compounds show interesting and unusual behaviour.Previously, we reported trioxadecalins with terminal cyano or nitro groups showing a cholesteric helix inversion.4,5 One of Scheme 2 these nitro compounds has presented a nearly double inversion of the helical twist sense, for the first time as far as we are aware. The aim of this work was to examine the influence of the synthesis of compounds with the trioxadecalin system at a terminal group on the helix inversion.We synthesized a dierent position to that for compounds 13b–23b (Scheme 3), homologous series of compounds with terminal halogen and was obtained by a modified Ferrier reaction.6 The dimethyl pseudo halogen groups, as well as molecules with small non- acetals and the corresponding aldehydes were synthesized polar head groups.Also the eect of the position of the chiral using standard methods in the cases where these aldehydes trioxadecalin system in the molecule has been examined by were not commerically available.synthesizing compounds in which the position of the molecular core was changed. Experimental The diols 12a–c were synthesized according to the previously described procedure starting from commercially available tri- Techniques O-acetyl-D-glucal.3 The diols can easily be combined with aldehyde dimethyl acetals giving the trioxadecalin structure TLC was performed on silica gel (Merck GF254), and detection was eected by UV absorbance, and spraying with a solution (Scheme 1).The diol 27 (Scheme 2), the starting point for the 1 XNH 12a RNC6H13 13b XNH, RNC8H17 2 XNF b RNC8H17 14a XNF, RNC6H13 3 XNCl c RNC10H21 14b XNF, RNC8H17 4 XNBr 15b XNCl, RNC8H17 5 XNI 16a XNBr, RNC6H13 6 XNN3 16b XNBr, RNC8H17 7 XNNCS 16c XNBr, RNC10H21 8 XNMe 17a XNI, RNC6H13 9 XNPri 17b XNI, RNC8H17 10 XNMe3SiCOC 18b XNN3, RNC8H17 11 XNHCOC 19b XNNCS, RNC8H17 20b XNMe, RNC8H17 21b XNPri, RNC8H17 22b XNMe3SiCOC, RNC8H17 23b XNHCOC, RNC8H17 Scheme 1 J.Mater. Chem., 1997, 7(6), 893–899 89328 XNH17C8OC6H4 27 33 XNH17C8OC6H4 29 XNH17C8OC6H4CO2 34 XNH17C8OC6H4CO2 30 XNH13C6OC6H4CO2 35 XNH13C6OC6H4CO2 31 XNH17C8OC6H4OCO 36 XNH17C8OC6H4OCO 32 XNH13C6OC6H4OCO 37 XNH13C6OC6H4OCO Scheme 3 of ethanol–sulfuric acid (951), followed by heating.Column H-3, H-5), 6.87 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.48 (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 chromatography was performed on silica gel 60 (230–240 mesh, Merck). Optical rotations were recorded using a Perkin- (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, Elmer 241 polarimeter.The NMR spectra (1H: 400 MHz, 13C: 100.6 MHz) were recorded on a Bruker AMX-400 spectrometer H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 4H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J3¾,F;5¾,F 8.8, with SiMe4 as internal standard (mc=centred multiplet). J values in Hz.An Olympus BH optical polarizing microscope 4J2¾,F;6¾,F 5.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.6, 3J1,6 8.9, 3J1,10eq 4.8; equipped with a Mettler FP 82 hot stage and a Mettler FP 80 cental processor was used to identify thermal transitions and dC (CDCl3 ) 163.1 (C-4), 158.8 (C-4¾), 133.78 (C-1), 133.5 (C- 1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 115.2 (C-3, C-5), characterize anisotropic textures.For further verification of the textures, a contact preparation with N4 (4-butyl-4¾-meth- 114.5 (C-3¾, C-5¾), 101.1 (C-3), 79.7 (C-8), 78.3 (C-6), 74.0 (C- 1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.3, 29.2, oxyazoxybenzene, K 16 N 76 I) was carried out. Analysis by DSC was carried out on a Perkin-Elmer DSC7 instrument 26.0, 22.7 (CH2), 14.1 (CH3); 1J4¾,F 163.1, 2J3¾,F;5¾,F 21.6, 3J2¾,F;6¾,F 8.6, 4J1¾,F 3.3.using heating and cooling rates of 5 K min-1. General reaction conditions for the synthesis of the Synthesis of (1S,3R,6R,8R)-3-(4-fluorophenyl)-8-(4¾-octyltrioxadecalin structure oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (14b) A flask with 40 mg of the diol, the para-substituted benzal- General reaction conditions using 4-fluorobenzaldehyde dehyde dimethyl acetal (1.2 equiv.) and toluene-p-sulfonic acid dimethyl acetal were followed.Yield 40 mg (76%); colourless (monohydrate) (5 mg) in abs. N,N-dimethylformamide was crystals; mp 113.8 °C; [a]D20+23.6 (c 0.93, CHCl3); dH (CDCl3) fitted to a rotatory evaporator.The mixture was heated at 7.50 (dd, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H¾6), 7.05 (dd, 2H, reduced pressure (29–33 hPa) in a water-bath of 60°C, in order H-3, H-5), 6.87 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.48 to remove the formed methanol, until TLC revealed complete (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 reaction. The solvent was removed in vacuo (10 hPa) at a (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 water-bath temperature of 75°C.The solid residue was washed (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, with saturated aqueous sodium hydrogen carbonate, filtered, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc 8H, washed with water and cold ethanol and then recrystallized CH2), 0.89 (t, 3H, CH3 ); 3J2¾,3¾;5¾,6¾ 8.9, 3J3¾,F;5¾,F 8.8, from ethanol. 4J2¾,F;6¾,F 5.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.6, 3J1,6 8.9, 3J1,10eq 4.8; Synthesis of (1S,3R,6R,8R)-3-phenyl-8-(4¾-octyloxyphenyl )- dC (CDCl3 ) 163.1 (C-4), 158.8 (C-4¾), 133.78 (C-1), 133.5 (C- 2,4,7-trioxabicyclo[4.4.0]decane (13b) 1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 115.2 (C-3, C-5), 114.5 (C-3¾, C-5¾), 101.1 (C-3), 79.7 (C-8), 78.3 (C-6), 74.0 (C- General reaction conditions using benzaldehyde dimethyl 1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, acetal were followed.Yield 16.0 mg (31%); colourless crystals; 29.2, 26.0, 22.7 (CH2), 14.1 (CH3); 1J4¾,F 163.1, 2J3¾,F;5¾,F 21.6, mp 105.8°C; [a]D20+23.8 (c 9.87, CHCl3); dH (CDCl3) (=3- 3J2¾,F;6¾,F 8.6, 4J1¾,F 3.3.phenyl ring; ¾=8-octyloxyphenyl ring) 7.51 (dd, 2H, H-2, H- 6), 7.36 (mc, 3H, H-3, H-4, H-5), 7.26 (d, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.60 (s, 1H, H-3), 4.48 (dd, 1H, H-8), Synthesis of (1S,3R,6R,8R)-3-(4-chlorophenyl )-8-(4¾-octyloxyphenyl)- 2,4,7-trioxabicyclo[4.4.0]decane (15b) 4.32 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.79 (dd, 1H, H-5ax), 3.67 (ddd, 1H, H-1), 3.59 (ddd, 1H, H-6), 2.21 (mc , 1H, H- General reaction conditions using 4-chlorobenzaldehyde 10eq), 2.03 (mc, 1H, H-9eq), 1.86 (mc, 2H, H-9ax, H-10ax), 1.75 dimethyl acetal were followed. Yield 16.8 mg (31%); colourless (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc, 8H, CH2), 0.89 crystals; mp 128.8 °C; [a]D20+25.4 (c 0.72, CHCl3); dH (CDCl3) (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 7.5 3J2¾,4¾;6¾,4¾ 1.5, 3J2¾,3¾;5¾,6¾ 8.2, 7.45 (d, 2H, H-2, H-6), 7.34 (d, 2H, H-3, H-5), 7.26 (d, 2H, 3J8,9ax 10.2, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 137.8 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, (C-1), 133.6 (C-1¾), 129.0 (C-3, C-5), 128.3 (C-4), 127.2 (C- 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 2¾, C-6¾), 126.2 (C-2, C-6), 114.5 (C-3¾, C-5¾), 101.8 (C-3), 79.7 (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, (C-8), 78.4 (C-6), 74.1 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 10), 31.8 (C-9), 29.4, 29.3, 26.1, 22.7 (CH2), 14.1 (CH3). 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, Synthesis of (1S,3R,6R,8R)-3-(4-fluorophenyl )-8-(4¾-hexyl- 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 136.3 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (14a) (C-1), 134.8 (C-4), 133.4 (C-1¾), 128.5 (C-3, C-5), 127.7 (C- 2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 100.9 (C-3), 79.7 General reaction conditions using 4-fluorobenzaldehyde dimethyl acetal were followed.Yield 41.6 mg (77%); colourless (C-8), 78.4 (C-6), 74.0 (C-1), 69.5 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 26.0, 22.7 crystals; mp 119.3°C; [a]D20+23.3 (c 0.91, CHCl3); dH (CDCl3) 7.50 (dd, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H¾6), 7.05 (dd, 2H, (CH2), 14.1 (CH3 ). 894 J. Mater. Chem., 1997, 7(6), 893–899Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-hexyl- 10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.75 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, 4H, CH2), 0.90 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16a) (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq General reaction conditions using 4-bromobenzaldehyde 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.9, 3J1,6 8.9, dimethyl acetal were followed.Yield 42.1 mg (68%); colourless 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 137.4 (C-3, C-5), 133.4 crystals; mp 144.9°C; [a]D20+23.2 (c 0.92, CHCl3); dH (CDCl3) (C-1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 101.0 (C-3), 94.9 (C-4), 79.7 (C-8), 78.3 (C-6), 74.0 (C-1), 69.5 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.2, 25.7, 22.6 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, (CH2), 14.1 (CH3). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-iodophenyl )-8-(4¾-octyl- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (17b) 4H, CH2), 0.90 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-iodobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 136.8 dimethyl acetal were followed. Yield 47.8 mg (73%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 134.5 °C; [a]D20+20.6 (c 0.89, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.71 (d, 2H, H-3, H-5), 7.25 (d, 4H, H-2, H-6, H-2¾, H-6¾), (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 6.86 (d, 2H, H-3¾, H-5¾), 5.54 (s, 1H, H-3), 4.47 (dd, 1H, H-8), (C-10), 31.6 (C-9), 29.2, 25.7, 22.6 (CH2), 14.1 (CH3). 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.76 (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.56 (ddd, 1H, H-6), 2.20 (mc, 1H, H- Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-octyl- 10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.75 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16b) (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc, 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq General reaction conditions using 4-bromobenzaldehyde 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.9, 3J1,6 8.9, dimethyl acetal were followed.Yield 32.0 mg (54%); colourless 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 137.4 (C-3, C-5), 133.4 crystals; mp 132.5°C; [a]D20+23.9 (c 0.82, CHCl3); dH (CDCl3) (C-1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 101.0 (C-3), 94.9 (C-4), 79.7 (C-8), 78.3 (C-6), 74.0 (C-1), 69.5 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, 26.04, 22.7 (CH2), 14.1 (CH3 ). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, Synthesis of 1S,3R,6R,8R)-3-(4-azidophenyl )-8-(4¾-octyl- 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (18b) 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-azidobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3 ) 158.8 (C-4¾), 136.8 dimethyl acetal were followed.Yield 37.5 mg (68%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 118.2 °C; [a]D20+20.1 (c 0.82, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.50 (d, 2H, H-2, H-6), 7.02 (d, 2H, H-3, H-5), 7.25 (d, 2H, (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, (C-10), 31.6 (C-9), 29.4, 29.3, 29.2, 26.0, 22.7 (CH2), 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, 14.1 (CH3). 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-decyl- (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16c ) H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.5, General reaction conditions using 4-bromobenzaldehyde 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, dimethyl acetal were followed.Yield 40.0 mg (69%); colourless 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3) 158.8 (C-4¾), 133.4 crystals; mp 128.0°C; [a]D20+22.2 (c 0.89, CHCl3); dH (CDCl3) (C-1¾), 127.8, 118.9 (C-2, C-3, C-5, C-6), 127.2 (C-2¾, C-6¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 114.5 (C-3¾, C-5¾), 101.2 (C-3), 79.7 (C-8), 78.4 (C-6), 74.0 (C- H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, 1), 69.6 (C-5), 68.1 (a-CH2 ), 33.1 (C-10), 31.8 (C-9), 29.4, 29.3, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, 26.0, 22.7 (CH2), 14.1 (CH3). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-thiocyanatophenyl )-8-(4¾- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, octyloxyphenyl )-2,4,7-trioxabicyclo[ 4.4.0]decane (19b) 12H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-thiocyanatobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3 ) 158.8 (C-4¾), 136.8 dimethyl acetal were followed.Yield 26.9 mg (47%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 80.7 °C; [a]D20+21.6 (c 0.21, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.60, 7.53 (d, 2H, H-2, H-3) and (d, 2H, H-5, H-6), 7.26 (d, (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C- 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.60 (s, 1H, H-3), 4.48 10), 31.6 (C-9), 29.6, 29.5, 29.4, 29.3, 29.3, 29.2, 26.0 22.7, (CH2), (dd, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.78 14.1 (CH3).(dd, 1H, H-5ax), 3.67 (ddd, 1H, H-1), 3.57 (ddd, 1H,, H-6), 2.21 (mc, 1H, H-10eq), 2.04 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-iodophenyl )-8-(4¾-hexyl- H-10ax), 1.75 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (17a) 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.3, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-iodobenzaldehyde dimethyl acetal were followed.Yield 37.2 mg (55%); colourless 3J1,10ax 10.9, 3J1,6 8.9, 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 139.4, 131.0 (C-4, C-1), 133.3 (C-1¾), 129.7, 128.2 (C-2, C-3, crystals; mp 148.8°C; [a]D20+22.6 (c 0.92, CHCl3); dH (CDCl3) 7.71 (d, 2H, H-3, H-5), 7.25 (d, 4H, H-2, H-6, H-2¾, H-6¾), C-5, C-6), 125.0 (SCN), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 100.4 (C-3), 79.7 (C-8), 78.4 (C-6), 73.9 (C-1), 69.6 (C-5), 68.1 6.86 (d, 2H, H-3¾, H-5¾), 5.54 (s, 1H, H-3), 4.47 (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.76 (dd, 1H, H-5ax), (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.36, 29.25, 29.18, 26.04, 22.66 (CH2), 14.1 (CH3). 3.65 (ddd, 1H, H-1), 3.56 (ddd, 1H, H-6), 2.20 (mc , 1H, HJ. Mater. Chem., 1997, 7(6), 893–899 895Synthesis of (1S,3R,6R,8R)-3-(4-methylphenyl )-8-(4¾-octyl- H-6), 2.20 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.86 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (20b) 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3), 0.25 (s, 9H, SiMe3 ); General reaction conditions using 4-methylbenzaldehyde 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax dimethyl acetal were followed.Yield 31.8 mg (61%); colourless 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; crystals; mp 118.0°C; [a]D20+24.2 (c 0.92, CHCl3); dH (CDCl3) dC (CDCl3) 158.8 (C-4¾), 137.8 (C-1), 133.5 (C-1¾), 131.9 (C- 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H-6¾), 7.17 (d, 2H, 3, C-5), 127.2 (C-2¾, C-6¾), 126.1 (C-2, C-6), 123.8 (C-4), H-3, H-5), 6.86 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 114.5 (C-3¾, C-5¾), 104.9, 94.6 (C-alkyne), 101.2 (C-3), 79.7 (C- (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C-10), (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-5eq), 31.8 (C-9), 29.4, 29.3, 29.2, 26.1, 22.7 (CH2), 14.1 2.34 (s, 3H, CH3 Aryl), 2.20 (mc, 1H, H-10eq), 2.02 (mc, 1H, (CH3), 0.032 (SiMe3).H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 8H, CH2), 0.89 (t, 3H, CH3); Synthesis of 4-ethynylbenzaldehyde dimethyl acetal (11) 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax Bu4NF (1.0 M solution in THF, 3.22 ml) was added to a 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.4; solution of 10 (0.4 g, 1.61 mmol) in 10 ml of abs.THF at room dC (CDCl3) 158.8 (C-4¾), 138.8 (C-4), 135.0 (C-1), 133.6 (Ctemp. under nitrogen. The reaction mixture was stirred at 1¾), 129.0 (C-3, C-5), 127.2 (C-2¾, C-6¾), 126.1 (C-2, C-6), room temp.over night, and then water (80 ml) was added. 114.5 (C-3¾, C-5¾), 101.9 (C-3), 79.7 (C-8), 78.3 (C-6), 74.1 (CThe mixture was extracted with diethyl ether (3×50 ml), the 1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C-10), 31.8 (C-9), 29.4, 29.3, combined organic extracts dried with sodium carbonate, and 29.3, 29.2, 25.1, 22.7 (CH2), 21.3 (CH3 Aryl), 14.1 (CH3).concentrated. The crude residue was purified by column chrom- Synthesis of (1S,3R,6R,8R)-3-(4-isopropylphenyl )-8-(4¾-octyl- atography [light petroleum (bp 60–70 °C)–ethyl acetate 551]. oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (21b) Yield 0.24 g (85%); dH (CDCl3 ) 7.50 (d, 2H, H-3¾, H-5¾), 7.41 (d, 2H, H-2¾, H-6¾), 5.38 (s, 1H, CH), 3.30 (s, 6H, OCH3), 3.08 General reaction conditions using 4-isopropylbenzaldehyde (s, 1H, H alkyne); 3JAryl 8.2.dimethyl acetal were followed. Yield 28.1 mg (51%); colourless crystals; mp 88.3°C; [a]D20+18.3 (c 1.19, CHCl3 ); dH (CDCl3) Synthesis of (1S,3R,6R,8R)-3-(4-ethynylphenyl )-8-(4¾-octyl- 7.43 (d, 2H, H-2 H-6), 7.26 (d, 2H, H-2¾, H-6¾), 7.23 (d, 2H, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (23b) H-3, H-5), 6.86 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.47 General reaction conditions using 4-ethynylbenzaldehyde (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 dimethyl acetal were followed.Yield 29.5 mg (55%); colourless (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.58 (ddd, 1H, H-6), 2.90 crystals; mp 114.1 °C; [a]D20+23.9 (c 0.91, CHCl3); dH (CDCl3) (sep, 2H, CH Pri), 2.20 (mc, 1H, H-10eq ), 2.02 (mc, 1H, H-9eq), 7.50 (d, 2H, H-2, H-6), 7.47 (d, 2H, H-3, H-5), 7.26 (d, 2H, 1.85 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.59 (s, 1H, H-3), 4.48 (dd, c-CH2), 1.30 (mc , 8H, CH2 ), 1.22 (d, 6H, CH3 Pri), 0.89 (t, 3H, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, CH3); 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.2, 3J8,9ax 10.9, 3J8,9eq 2.4, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 3.07 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, (s, 1H, H alkyne), 2.20 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 149.8 (C-4), 135.3 (C-1), 1.86 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, 133.6 (C-1¾), 127.2 (C-2¾, C-6¾), 126.4 (C-3, C-5), 126.1 (C-2, c-CH2), 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ c-6), 114.5 (C-3¾, C-5¾), 101.9 (C-3), 79.7 (C-8), 78.3 (C-6), 74.1 8.6, 3J2¾,3¾;5¾,6¾ 8.9, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 (C-1), 69.6 (C-5), 68.1 (a-CH2), 34.0 (CH Pri), 33.1 (C-10), 31.8 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3) (C-9), 29.4, 29.3, 29.3, 29.2, 26.1, 22.7 (CH2), 23.9 (CH3 Pri), 158.8 (C-4¾), 138.2 (C-1), 133.5 (C-1¾), 132.1 (C-3, C-5), 127.2 14.1 (CH3).(C-2¾, C-6¾), 126.2 (C-2, C-6), 122.7 (C-4), 114.5 (C-3¾, C-5¾), Synthesis of 4-(trimethylsilylethynyl )benzaldehyde dimethyl 101.1 (C-3), 83.4 (C alkyne), 79.7 (C-8), 78.4 (C-6), 77.5 (C acetal (10) alkyne), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 26.1, 22.7 (CH2), 14.1 (CH3).Trimethylsilylacetylene (0.6 ml, 4.31 mmol) was added to a solution of 4-iodobenzaldehyde dimethyl acetal 5 (1.0 g, Synthesis of 4-octyloxybiphenyl-4¾-carbaldehyde dimethyl acetal 4.31 mmol), tetrakis(triphenylphosphine)-palladium(O) (258 (12) mg, 0.22 mmol), CuI (172 mg, 0.86 mmol) and butylamine A solution of 4-octyloxyphenylboronic acid (2.75 g, 11 mmol) (0.65 ml, 6.46 mmol) in 53 ml abs.toluene at room temp. in 20 ml ethanol was added to a stirred mixture of 4-bromobenz- under nitrogen. The reaction mixture was stirred at room aldehyde (1.96 g, 8.5 mmol) and tetrakis(triphenylphosphine)- temp. for 28 h and then quenched with water (200 ml).The palladium(O) (0.326 g, 0.28 mmol) in 15 ml benzene and aqueous layer was extracted with diethyl ether (3×70 ml), the aqueous sodium carbonate (2 M, 15 ml) at room temp. under combined organic extracts were dried with sodium carbonate nitrogen. The stirred mixture was heated at the temperature and concentrated. The crude residue was purified by column of reflux for 23 h.Then water was added, the product was chromatography [light petroleum (bp 60–70 °C)–ethyl acetate extracted with light petroleum (bp 60–70°C), the combined 2051+1% triethylamine]. Yield 0.81 g (91%); dH (CDCl3) 7.47 organic extracts dried with sodium carbonate and the solvent (d, 2H, H-3¾, H-5¾), 7.37 (d, 2H, H-2¾, H-6¾), 5.38 (s, 1H, CH), removed in vacuo. The crude residue was purified by repeated 3.30 (s, 6H, OCH3), 0.25 (s, 9H, SiMe3); 3JAryl 8.2.recrystallization from methanol. Yield 2.43 g (80%); colourless Synthesis of (1S,3R,6R,8R)-3-[4-(trimethylsilyethynyl )- crystals; mp 49.4 °C; dH (CDCl3 ) 7.55 (d, 2H, H-2, H-6), 7.52 phenyl]-8-(4¾-octyloxyphenyl )-2,4,7-trioxabicyclo[4.4.0]- (d, 2H, H-3, H-5), 7.48 (d, 2H, H-2¾, H-6¾), 6.96 (d, 2H, H-3¾, decane (22b) H-5¾), 5.42 (s, 1H, CH), 3.99 (t, 2H, a-CH2), 3.36 (s, 6H, OCH3), 1.80 (q, 2H, b-CH2 ), 1.47 (q, 2H, c-CH2), 1.31 (mc, General reaction conditions using 4-(trimethylsilyethynyl)ben- 8H, -CH2), 0.89 (t, 3H, -CH3); 3JAryl 8.8, 3JAryl¾ 8.5.zaldehyde dimethyl acetal were followed. Yield 36.0 mg (58%); colourless crystals; mp 146.1°C; [a]D20+21.5 (c 0.88, CHCl3); Synthesis of (1S,3R,6R)-2-(4-octyloxybiphenyl )-2,4,7- dH (CDCl3) 7.47 (d, 2H, H-2, H-6), 7.44 (d, 2H, H-3, H-5), trioxabicyclo[4.4.0]decane (33) 7.26 (d, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a- General reaction conditions using 4-octyloxybiphenyl-4¾-carbaldehyde diemthyl acetal were followed. The product was CH2), 3.77 (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, 896 J.Mater. Chem., 1997, 7(6), 893–899purified by column chromatography [light petroleum (bp (CDCl3 ) 8.18 (d, 2H, H-3¾, H-5¾), 7.63 (d, 2H, H-2¾, H-6¾), 7.11 (d, 2H, H-2, H-6), 6.92 (d, 2H, H-3, H-5), 5.63 (s, 1H, H- 60–70°C)–ethyl acetate 1051].Yield 75.4 mg (49%); colourless crystals; mp 122.9°C; [a]D20-4.8 (c 1.01, CHCl3 ); dH (CDCl3) 3), 4.28 (dd, 1H, H-5eq ), 3.96 (m, 3H, a-CH2, H-8eq), 3.71 (dd, 1H, H-5ax), 3.59 (ddd, 1H, H-1), 3.51 (ddd, 1H, H-8ax), 3.36 7.53 (s, 4H, H-2¾, H-3¾, H-5¾, H-6¾), 7.49 (d, 2H, H-2, H-6), 6.95 (d, 2H, H-3, H-5), 5.60 (s, 1H, H-3), 4.26 (dd, 1H, H- (ddd, 1H, H-6), 2.15 (mc, 1H, H-10eq), 1.74–1.93 (m, 4H, H- 9ax, H-9eq, b-CH2), 1.69 (dddd, 1H, H-10ax), 1.46 (q, 2H, c- 5eq), 3.92–4.02 (m, 3H, a-CH2, H-8eq), 3.70 (dd, 1H, H-5ax), 3.58 (ddd, 1H, H-1), 3.51 (ddd, 1H, H-8ax), 3.36 (ddd, 1H, H- CH2), 1.31 (mc, 8H, CH2), 0.89 (t, 3H, CH3 ); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.5, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 11.5, 6), 2.13 (mc, 1H, H-10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b- CH2), 1.68 (dddd, 1H, H-10ax), 1.47 (q, 2H, c-CH2), 1.35 (mc, 3J1,6 8.9, 3J1,10eq 4.8, 2J8ax,8eq 11.6, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 3J10ax,9eq 4.4; dC (CDCl3) 165.3 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 11.5, 3J1,6 8.9, 3J1,10eq 4.4, 2J8ax,8eq (C=O), 156.9 (C-4), 144.2 (C-1), 142.8 (C-1¾), 130.2 (C-3¾, C- 5¾), 130.1 (C-4¾), 126.4 (C-2¾, C-6¾), 122.4 (C-2, C-6), 115.1 11.6, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 3J10ax,9eq 4.4; dC (CDCl3) 158.9 (C-4), 141.6 (C-4¾), 136.1 (C- (C-3, C-5), 100.9 (C-3), 78.7 (C-1), 74.0 (C-6), 69.5 (C-5), 68.5 (C-8), 68.1 (a-CH2 ), 31.8 (CH2 ), 29.3 (C-9), 28.8 (C-10), 1¾), 133.2 C-1), 128.2 (C-2, 6), 126.7, 126.5 (C-2¾, C-3¾, C-5¾, C-6¾), 114.8 (C-3, C-5), 101.7 (C-3), 78.6 (C-1), 74.2 (C-6), 29.4, 29.3, 26.1, 25.6, 22.7 (CH2), 14.1 (CH3). 69.4 (C-5), 68.1 (C-8), 31.8 (CH2), 29.4, 29.3, 29.3 (C-9, CH2), 28.9 (C-10), 26.1, 25.6, 22.7 (CH2), 14.1 (CH3). Synthesis of (1S,3R,6R)-3-[4¾-(4-hexyloxyphenyloxycarbonyl) phenyl]-2,4,7-trioxabicyclo[4.4.0] decane (37) Synthesis of (1S,3R,6R)-3-[ 4¾-(4-octyloxybenzoyloxy)- General reaction conditions using 4-(4-hexyloxyphenyloxycar- phenyl]-2,4,7-trioxabicyclo[4.4.0]decane (34) bonyl)benzaldehayde dimethyl acetal were followed.Yield General reaction conditions using 4-(4-octyloxybenzoyloxy) 25.2 mg (15%); colourless crystals; mp 122.5°C; [a]D20-10.3 benzaldehyde dimethyl acetal were followed. Yield 136.0 mg (c 1.01, CHCl3); dH (CDCl3 ) 8.18 (d, 2H, H-3¾, H-5¾), 7.63 (d, (65%); colourless crystals; mp 126.9 °C; [a]D20-4.3 (c 1.08, 2H, H-2¾, H-6¾), 7.11 (d, 2H, H-2, H-6), 6.92 (d, 2H, H-3, HCHCl 3); dH (CDCl3) 8.12 (d, 2H, H-2, H-6), 7.54 (d, 2H, H- 5), 5.63 (s, 1H, H-3), 4.28 (dd, 1H, H-5eq), 3.96 (m, 3H, a- 2¾, H-6¾), 7.20 (d, 2H, H-3¾, H-5¾), 6.96 (d, 2H, H-3, H-5), 5.59 CH2, H-8eq), 3.71 (dd, 1H, H-5ax), 3.59 (ddd, 1H, H-1), 3.51 (s, 1H, H-3), 4.26 (dd, 1H, H-5eq), 4.04 (t, 2H, a-CH2 ), 3.95 (ddd, 1H, H-8ax), 3.36 (ddd, 1H, H-6), 2.15 (mc, 1H, H-10eq), (ddd, 1H, H-8eq), 3.70 (dd, 1H, H-5ax), 3.57 (ddd, 1H, H-1), 1.74–1.93 (m, 4H, H-9ax, H-9eq, b-CH2), 1.69 (dddd, 1H, H- 3.51 (ddd, 1H, H-8ax), 3.35 (ddd, 1H, H-6), 2.13 (mc, 1H, H- 10ax), 1.47 (q, 2H, c-CH2), 1.35 (mc, 4H, CH2), 0.91 (t, 3H, 10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b-CH2), 1.67 (dddd, 1H, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.5, 2J5eq,5ax 10.2, 3J5eq,6 4.8, H-10ax), 1.47 (q, 2H, c-CH2), 1.32 (mc, 8H, CH2), 0.89 (t, 3H, 3J5ax,6 10.2, 3J1,10ax 11.5, 3J1,6 8.9, 3J1,10eq 4.8, 2J8ax,8eq 11.6, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 2J8ax,8eq 11.5, 3J8eq,9ax 4.8, 3J8eq,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 3J10ax,9eq 4.4 Hz; dC (CDCl3) 165.3 (C=O), 156.9 (C-4), 144.2 11.6, 3J10ax,9eq 4.2; dC (CDCl3) 164.7 (C-4), 163.6 (C=O), 151.5 (C-1), 142.8 (C-1¾), 130.2 (C-3¾, C-5¾), 130.1 (C-4¾), 126.4 (C- (C-4¾), 135.2 (C-1¾), 132.3 (C-2, C-6), 127.4 (C-2¾, C-6¾), 121.6, 2¾, C-6¾), 122.4 (C-2, C-6), 115.1 (C-3, C-5), 100.9 (C-3), 121.5 (C-3¾, C-5¾, C-1), 114.3 (C-3, C-5), 101.2 (C-3), 78.6 78.7 (C-1), 74.0 (C-6), 69.5 (C-5), 68.5 (C-8), 68.1 (a-CH2), 31.6 (C-1), 74.1 (C-6), 69.4 (C-5), 68.3, 68.1 (C-8, a-CH2), 29.1 (C- (CH2), 29.3 (C-9), 28.8 (C-10), 25.7, 25.6, 22.6 (CH2), 14.1 9), 28.8 (C-10), 31.8, 29.3, 29.2, 26.0, 25.6, 22.7 (CH2), 14.0 (CH3).(CH3 ). Results and Discussion Synthesis of (1S,3R,6R)-3-[ 4¾-(4-hexyloxybenzoyloxy]- phenyl )-2,4,7-trioxabicyclo[4.4.0]decane (35) We first synthesized a series of compounds with a halogen or pseudo halogen head group, while the length of the terminal General reaction conditions using 4-(4-hexyloxybenzoyloxy) alkoxy chain was kept constant (Table 1).In the case of the benzaldehyde dimethyl acetal were followed. Yield 73.9 mg fluorine compound 14b we could observe a change of the (49%); colourless crystals; mp 146.6 °C; [a]D20-4.8 (c 1.01 helical pitch with increasing temperature, but the clearing CHCl3); dH (CDCl3) 8.12 (d, 2H, H-2, H-6), 7.54 (d, 2H, H- point of 125.0°C is too low to observe the complete inversion. 2¾, H-6¾), 7.20 (d, 2H, H-3¾, H-5¾), 6.96 (d, 2H, H-3, H-5), 5.59 The same holds true for the iodo compound 17b and the (s, 1H, H-3), 4.26 (dd, 1H, H-5eq), 4.04 (t, 2H, a-CH2 ), 3.95 thiocyanato compound 19b, but in these cases, a strong (ddd, 1H, H-8eq), 3.70 (dd, 1H, H-5ax), 3.57 (ddd, 1H, H-1), concentration-dependent inversion of the helical pitch in con- 3.51 (ddd, 1H, H-8ax), 3.35 (ddd, 1H, H-6), 2.13 (mc, 1H, H- tact with N4 was observed [sequence of textures in the contact 10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b-CH2), 1.67 (dddd, 1H, area: cholesteric (Grandjean texture), nematic (schlieren tex- H-10ax), 1.48 (q, 2H, c-CH2), 1.35 (mc, 4H, CH2), 0.92 (t, 3H, ture), cholesteric (fan texture), nematic (schlieren texture). Since CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, the unwinding of the helix was mainly a function of the 2J8ax,8eq 11.5, 3J8eq,9ax 4.8, 3J8eq,9eq 1.7, 3J5ax,6 10.2, 3J1,10ax 11.5, concentration and a smectic A phase could not be observed, 3J1,6 8.9, 3J1,10eq 4.8, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, an unwinding of the helix as a pretransitional eect of a 3J10ax,9ax 11.6, 3J10ax,9eq 4.2; dC (CDCl3) 164.7 (C-4), 163.6 transition to a smectic A phase can be excluded as reason for (C=O), 151.5 (C-4¾), 135.2 (C-1¾), 132.3 (C-2, C-6), 127.4 (C- this inversion eect.].In addition compound 19b shows a 2¾, C-6¾), 121.6, 121.5 (C-3¾, C-5¾, C-1), 114.3 (C-3, C-5), crystal–crystal interconversion to a crystalline phase resem- 101.2 (C-3), 78.6 (C-1), 74.1 (C-6), 69.4 (C-5), 68.3, 68.1 (C-8, bling a soft crystal.a-CH2), 29.1 (C-9), 28.8 (C-10), 31.6, 25.7, 25.6, 22.6 (CH2), The compounds with chloro 15b, bromo 16b and azido 18b 14.0 (CH3). terminal groups exhibited a helix inversion in the pure form, with inversion temperatures lying close togther at ca. 130 °C. Synthesis of (1S,3R,6R)-3-[ 4¾-(4-octyloxyphenyloxy- To elucidate the influence of volume eects, we synthesized carbonyl )phenyl]-2,4,7-trioxabicyclo[4.4.0]decane (36) 20b and 21b with a terminal methyl and isopropyl group.Neither compound 20b nor 21b showed an inversion of the General reaction conditions using 4-(4-octyloxyphenyloxycarbonyl) benzaldehyde dimethyl acetal were followed. The prod- helical pitch, and while the methyl compound still displayed a cholesteric phase besides a monotropic smectic A phase, we uct was purified by column chromatography [light petroleum (bp 60–70°C)–ethyl acetate 551].Yield 75.5 mg (62%); colour- could only observe a smectic A phase in the case of a broad terminal isopropyl group. less crystals; mp 106.7 °C; [a]D20-10.9 (c=1.04, CHCl3); dH J. Mater. Chem., 1997, 7(6), 893–899 897Table 1 Data for compounds 13b–23b recryst.a no.X /°C Cr/°C SA/°C Ch/°C Ti/°C C 13b H 105.8 — 61.4 14b F 48.0 113.8 — 125.0 >130.0 b 15b Cl 89.0 128.8 — 143.0 127.0 16b Br 132.5 — 140.1 132.0 Tm2 119.0°C 17b I 91.0 134.5 — 132.2 c 18b N3 83.0 118.2 — 145.2 123.0 19b NCS 80.7 — 97.0 c,d 20b Me 118.0 95.9 136.1 — 21b Pri 20.0 88.3 121.1 — — Tm2 85.0°C Tm3 79.0°C 22b Me3SiCOC 106.0 146.1 157.2 — — 23b HCOC 62.0 114.1 — 153.1 96.5 Tm2 104.0°C aAbbreviations: recryst.=recrystallization; Cr=crystallization; Ch=cholesteric; SA=smectic A; Ti=inversion temperature; Tmx=melting points of additional crystalline modifications.bThe inversion temperature is an extrapolated value. cConcentration-dependent helix inversion in contact with N4. dCr2 65.0 Cr1 80.7 Ch 97.0 decomp., Cr1=soft crystals.Table 2 Data for compounds 14a,b, 16a–c and 17a,b recryst. no. X OR /°C Cr/°C Ch/°C Ti/°C C 16a Br OC6H13 144.9 151.7 110.0 16b Br OC8H17 132.5 140.1 132.0 Tm2 119.0°C 16c Br OC10H21 70.0 128.0 136.5 >137.0 a 14a F OC6H13 119.3 135.2 124.0 14b F OC8H17 48.0 113.8 125.0 >130.0 a 17a I OC6H13 99.0 148.8 137.5 b 17b I OC8H17 91.0 134.5 132.2 b aThe inversion temperature is an extrapolated value.bConcentration-dependent helix inversion in contact with N4. Examining the synthesized trioxadecalin molecules discussed compounds, the following series is obtained: H<SCN<F< I<Me<Br<Cl<N3<NO2<OMe<ethynyl<CN. so far, it seemed that a polar terminal group might be necessary for the occurrence of a helix inversion.To verify this idea, we To examine the eect of the length of the alkoxy chains we synthesized the bromo compounds 16a and 16c with a hexyloxy synthesized 23b with an ethynyl head group, which we expected not to exhibit an inversion, in contrast to the same compound and a dexyloxy chain instead of the octyloxy chain of 16b. The shortening of the alkoxy chain by two CH2 groups led to a with a terminal cyano group.Contrary to our assumption, compound 23b exhibited a pitch inversion at a temperature of decrease of the inversion temperature by 22.0°C and to an increase of the clearing temperature by 11.6 °C (Table 2). In 96.5 °C, indicating that the reasons for the occurrence of the cholesteric helix inversions have to be more complex than our the case of 16c, with the extended chain, only a change of the helical pitch with increasing temperature could still be simple supposition.Moreover, we observed a second crystal modification of observed, since 16c cleared at 136.5 °C before reaching the inversion point. compound 23b. The frequently observed polymorphism of crystal forms of the compounds synthesized in this work Since the shortening of the alkoxy chain led to a distinct decrease of the inversion temperature, it seemed to be interes- reflects the dierent stacking possibilities and may be the polymorphism of orientation possibilities.Unfortunately, we ting to synthesize the compounds analogous to 14b and 17b, but with a hexyloxy instead of an octyloxy chain, since in the could not obtain crystals suitable for X-ray diraction to elucidate the stacking possibilities.Compound 22b with a trimethylsilylethynyl head group Table 3 Data for compound 33 showed, as well as compound 21b, only a smectic A phase indicating that this phase might be stabilized by a broad terminal group. A broad terminal group changes the molecular shape towards a cylinder; if the width of the terminal group is comparable to the width of the core, and favours therefore smectic phases.no. Cr/°C Ch/°C C If the terminal groups are arranged in order of increasing clearing temperature of the cholesteric phase and in consider- 33 122.9 96.0 N at TC, Tm2 100.6°C ation of the already described nitro, cyano and methoxy 898 J. Mater. Chem., 1997, 7(6), 893–899Table 4 Data for compounds 34–37 recryst.no. m Y /°C Cr/°C Ch/°C C 34 8 C(O)-O 126.9 90.1 a 35 6 C(O)-O 146.6 96.6 a 36 8 O-C(O) 72.0 106.7 87.5 a, Tm2 99.8°C, Tm3 91.7°C 37 6 O-C(O) 57.0 122.5 90.9 a, Tm2 ?, Tm3? aConcentration dependent helix inversion in contact with N4. case of the latter only a change of the helical pitch could be 15b and 16a,b exhibited an inversion whereas the methyl observed because of the low clearing temperatures.The short- compound 20b did not. ening of the alkoxy chain, in case of 14b, indeed led to a The polarity of the terminal group can be excluded as the sucient drop of the inversion temperature, so that the pitch cyano compound as well as compound 23b with its ethynyl inversion was observed, while 17b still showed only an inver- head group show an inversion of the helical pitch at a sion in contact with N4. comparable temperature.With the results obtained so far, it seems that the chiral The chiral trioxadecalin structure does not need to be trioxadecalin structure in the centre of the molecule is respon- located directly in the centre of the molecule, since compounds sible for the occurrence of the cholesteric helix inversion, but 33–37 with a terminal decalin system also display helix at the same time an unsymmetrical substitution pattern is inversions in contact with N4.necessary: that is X must not be an alkoxy or alkyl chain and The concentration dependence of the helical pitch is stronger further X must not have a broad structure, since otherwise a in most cases than the temperature dependence [the cholesteric smectic A phase will be stabilized, preventing the observation phase in the contact preparation (fan texture) shows selective of the helix inversion.reflection and has a short helical pitch. The absolute change In all the compounds discussed so far which show cholesteric of the helical pitch going from the area in the contact prep- helix inversion, the trioxadecalin structure was located in the aration with a cholesteric phase to the area with a nematic centre of the molecule.The molecules 33–37 were synthesized phase is large, while the helical pitch is great and hence the to elucidate whether this is a necessary requirement. absolute change quite low in the case of the compounds with Compound 33 exhibited a monotropic cholesteric phase e.g. a terminal nitro group5 which show a helix inversion in (fan texture at low temperatures) with a strong temperature- the pure form on heating].dependent helical pitch being just nematic (schlieren texture) Orientation eects of the molecular axis being defined by at the clearing temperature of 96.0 °C (Table 3). the chiral molecular core7 seem to be the reason for these The introduction of a carboxy linkage between the two inversion eects. Because of the dierent flexibility of the phenyl rings in 33 eects, almost independently from the molecular core and the wing groups the direction of the mean orientation of the linkage, a small decrease in the clearing molecular axis changes slightly with temperature, leading to a temperature (Table 4). All these compounds display cholesteric change of the eective chirality, which is a function of the phases with a fan texture without visible changes of the texture mean molecular axis. with temperature. However, all of them show a concentration dependent helix inversion in contact with N4. It is noteworthy that some of our dimethyl acetals used for We thank the DAAD/ARC for financial support and the the synthesis of the decalin system also showed mesogenic ‘Studieustiftung des deutschen Volkes’ for a grant for properties. The separation of the biphenyl system through a H. M. v. M. carboxy linkage eected in this case a decrease of the clearing point of the monotropic smectic A phase by 20°C. References 1 J. W. Goodby, J.Mater. Chem., 1991, 1, 307. 2 A. J. Slaney, I. NIshiyama, P. Styring and J. W. Goodby, J. Mater. Chem., 1992, 2, 805. 3 V. Vill, H.-W. Tunger and H. M. von Minden, J. Mater. Chem., 1996, 6, 739. 4 V. Vill, H.-W. Tunger, H. Stegemeyer and K. Diekmann, T etrahedron: Asymmetry, 1994, 5, 2443. 5 V. Vill and H.-W. Tunger, L iq. Cryst., 1996, 20, 449. 6 Z. Benko and B. Fraser-Reid, J. Org. Chem., 1988, 82, 2066. 7 H.-G. Kuball, H. Bru�ning, T. Mu�ller, O. Tu� rk and A. Scho�nhofer, J. Mater. Chem., 1995, 5, 2167. Conclusions The space filling of the terminal groups is not the reason for the helix inversion since chloro and bromo compounds Paper 7/00234C; Received 10th January, 1997 J. Mater. Chem., 1997, 7(6), 893&ndash

ISSN:0959-9428    

DOI:10.1039/a700234c

出版商:RSC    

年代:1997

数据来源: RSC