New chiral side chains for ferro- and antiferro-electric liquid crystals derived from the preen-gland wax of the domestic goose† Gerd Heppke,*a Detlef Lo�tzsch,a Michael Morrb and Ludger Ernstc aT echnische Universita� t Berlin, Sekr. ER11, Str. des 17. Juni 135, 10623 Berlin, Germany bGBF-Gesellschaft fu� r Biotechnologische Forschung mbH,Mascheroder Weg 1, 38124 Braunschweig, Germany cT echnische Universita� t Braunschweig, NMR-L aboratorium der Chemischen Institute, Hagenring 30, 38106 Braunschweig, Germany (2R,4R,6R,8R)-2,4,6,8-Tetramethyldecanoic acid and (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanol, as well as the (2R,4R,6R,8R) and the (2S,4R,6R,8R) diastereomers of 4,6,8-trimethyldecan-2-ol, have been obtained from the preen-gland wax of the domestic goose.Starting from these alkanols and alkanoic acid, novel ferro- and antiferro-electric liquid crystals bearing four methyl branchings in the chiral side chain have been synthesized and their mesomorphic and electro-optical properties have been investigated. The results obtained are compared with the properties of the respective chiral (S)-2-methyldecanoic acid, (S)-decan-2-ol and (S)-2- methyldecanol derivatives.The compounds with four methyl branchings in the chiral side chain are found to exhibit lower melting points, broader SmC* phase ranges, higher values of spontaneous polarization and larger tilt angles in comparison to the respective compound with only one methyl branching. Many physical properties which are used in modern appli- optical tilt angles and switching times) of the novel ferro- and antiferro-electric liquid crystals are discussed.cations of liquid crystals depend entirely on the presence of chiral molecules, e.g. the helical structure of cholesteric and some smectic phases, the ferroelectricity of uniformly tilted smectic phases and the antiferroelectricity of alternating tilted Experimental smectic phases.1 Moreover, in certain systems high chirality Synthesis causes the induction of novel phases (Blue phases, Twist Grain Boundary phases, Q phases etc.)1,2 Several chiral phases possess Methyl (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoate was frustrated structures displaying competition between chiral obtained by transesterification and Spaltrohr distillation of the forces and the tendency of the molecules to pack in a space- preen gland-wax of the domestic goose.According to the filling arrangement. For a better understanding of the chiral reaction scheme shown in Scheme 1, the methyl ester was forces as well as for electro-optical applications the develop- transformed into the free acid 1f as well as into (2R,4R,6R,8R)- ment of new chiral liquid crystals plays an important role. 2,4,6,8-tetramethyldecanol 1b, which was partially further However, the design of novel structures is restricted by the transformed into the (2R,4R,6R,8R) and the (2S,4R,6R,8R) available chiral moieties, which can be obtained either by diastereomers 1d and 1e of 4,6,8-trimethyldecan-2-ol. All these enantioselective reactions or by using the natural chiral pool. tetramethylalkanols, as well as (2R,4R,6R,8R)-2,4,6,8-tetra- A novel natural source of chiral mono-, di-, tri- or tetra- methyldecanoic acid, were obtained with a diastereomeric methyl branched alkanoic acids is the preen-gland wax of excess of more than 99%.6,7 Compounds 1b, 1d, 1e and 1f, as poultry.3 For example, the wax of the domestic goose consists well as the commercially available compounds (purchased of about 90% octadecyl (2R,4R,6R,8R)-2,4,6,8-tetramethyl- from the Japan Energy Corporation) (S)-2-methyldecanol 1a, decanoate,4,5 so that after transesterification and Spaltrohr (S)-decan-2-ol 1c and (S)-2-methyldecanoic acid 1g, were then distillation large quantities of methyl (2R,4R,6R,8R)-2,4,6,8- used as chiral starting materials for the synthesis of three series tetramethyldecanoate are obtained,6 which can be transformed of liquid crystalline products.These series diVer by the linking into the free acid by standard methods. As recently shown, group between mesogenic core and chiral side chain. Within methyl (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoate can also each series, the number and the position of the chiral methyl be transformed into (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanol branchings are varied.As outlined in Scheme 2, compounds and further into (4R,6R,8R)-4,6,8-trimethyldecan-2-ol, from 2a–d were synthesized by esterification of 4-benzyloxybenzoic which both the (2R,4R,6R,8R) and the (2S,4R,6R,8R) diastereo- acid with the chiral alkanols 1a–d, followed by hydrogenation mers can be isolated by column chromatography.7 These to remove the benzyloxy protecting group and finally esterifi- tetramethylalkanols, as well as (2R,4R,6R,8R)-2,4,6,8-tetra- cation of the obtained phenols with 4¾-octyloxybiphenyl-4- methyldecanoic acid, are promising chiral side chains for the carboxylic acid.The respective liquid crystalline ethers 3a–d design of novel liquid crystals. were obtained by a reaction between 4-hydroxyphenyl 4¾- Here we present the first ferro- and antiferro-electric liquid octyloxybiphenyl-4-carboxylate and the chiral alkanols 1a–c crystals having tetramethylalkyl groups in the chiral side chain.and 1e in the presence of diethylazodicarboxylate (DEAD) In order to study the influence of the additional optically and triphenylphosphine8 (see Scheme 3).Compound 4c active methyl branchings, the respective chiral 2-methylde- was synthesized by esterification of the acid chloride of 1g canoic acid, decan-2-ol and 2-methyldecanol derivatives have with 4-hydroxyphenyl 4¾-octyloxybiphenyl-4-carboxylate (see also been synthesized. Polymorphy, phase transition tempera- Scheme 3), whereas compound 4d could not been obtained tures and electro-optical properties (spontaneous polarization, optical pure in a similar way.Compound 4d was synthesized by esterification of 1f with 4-hydroxyphenyl 4¾- octyloxybiphenyl-4-carboxylate in the presence of dicyclo- † Presented in part at the 5th International Conference on Liquid Crystals, Cambridge, 1995. hexylcarbodiimide (DCC). All products were purified by J. Mater. Chem., 1997, 7(10), 1993–1999 1993Scheme 1 Reagents and conditions: i, LiAlH4; ii, PCC, CH2Cl2; iii, 2,2¾- bipyridyl–Cu complex, DABCO, ButOH, air; iv, methyloxazaborolidine, BH3–THF, THF; v, column chromatography [silica gel, Scheme 3 Reagents and conditions: i, MeOH, H2SO4; ii, K2CO3, CH2Cl2–Pri2O (951)]; vi, NaOH, dioxane C8H17Br, DMF; iii, KOH, EtOH; iv, HCl; v, SOCl2; vi, 4- BnOC6H4OH, pyridine; vii, H2, Pd; viii, ROH (1a–c,e), DEAD, PPh3, THF; ix, 1f, DCC; x, RCOCl (from 1g and SOCl2) were then transferred to the remaining compounds while considering the usual substituent eVects on chemical shifts11 and attempting maximum internal consistency.The purity of the products was checked by TLC and HPLC (pump: Knauer HPLC pump 64, column: Nucleosil 120-5 C18, solvent: methanol, detector: Severn Analytical SA 6503 at 303 nm) and their optical purity was characterized by measuring the optical rotation (Perkin-Elmer polarimeter 241).All compounds were found to be of high purity (HPLC purity above 99%). The synthesis of compound 2c has already been described;12 however no detailed information about the physical properties of this compound were reported.Synthesis of 2a–d A synthetic procedure for 2d is given as an example. Dicyclohexylcarbodiimide (DCC) (1.24 g, 6 mmol) was added Scheme 2 Reagents and conditions: i, MeOH, H2SO4; ii, K2CO3, C8H17Br, DMF; iii, KOH, EtOH; iv, HCl; v, SOCl2; vi, ROH (1a–d); at room temperature to a solution of 4¾-octyloxybiphenylvii, H2, Pd; viii, DCC, CH2Cl2 4-carboxylic acid (0.98 g, 3 mmol), (1R,3R,5R,7R)-1,3,5,7- tetramethylnonyl 4-hydroxybenzoate (0.95 g, 3 mmol) and 4-dimethylaminopyridine (DMAP) (0.06 g, 0.5 mmol) in dry chromatography, followed by recrystallization until the transdichloromethane (50 ml ), and the mixture was stirred for 24 h.ition temperatures remained constant. The structure of the After filtration the solvent was evaporated and the resulting products irmed by 1H and 13C NMR experiments product was purified by chromatography over silica gel using (Bruker ARX-400, AM-400 and DPX-300; 9.4 and 7.0 T, dichloromethane as the eluent (Rf 0.70), followed by re- respectively) and, in case of compounds 2d, 3d and 4d, additioncrystallization from ethanol until the transition temperature ally by IR (Perkin-Elmer PE 257) and mass (Varian MAT remained constant.Yield: 1.34 g (71%); n (CCl4)/cm-1 2955, 44F) spectroscopy. Signal assignments in the 13C NMR spectra 2925, 2871, 2854, 1735, 1715, 1604, 1504; m/z 628.5 (M+); 1H were achieved by DEPT-135 experiments,9 by two-dimensional and 13C NMR data are given in Tables 1 and 2; [a]20D -0.30 13C, 1H COSY10 and COLOC10 experiments for 2a, 3b and 4d and by comparison with literature data.6,7 These assignments (c 5, CHCl3) (2b, -2.36; 2c, +18.29; 2d, -18.68). 1994 J. Mater. Chem., 1997, 7(10), 1993–1999Table 1 1H NMR data for compounds 2a–d, 3a–d and 4c–d (400 or 300 MHz; CDCl3; Me4Si) chemical shift (multiplicity, coupling constant)a,b proton 2a 2b 2c 2d 3a 3b 3c 3d 4c 4d O1 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 (t,6.6) (t,6.6) (t,6.6) (t,6.6) (t,6.6) (t,6.6) (t,6.5) (t,6.6) (t,6.6) (t,6.6) O2 1.81 1.82 1.81 1.81 1.88 1.81 1.80 (qi,7.0) (qi,7.0) (qi,7.0) (qi,7.0) (qi,7.0) (qi,7.0) (qi,7.0) O8 0.89† 0.89† 0.89† 0.89 0.89† 0.89† 0.89 (t,6.9) (t,6.9) (t,6.9) (t,ca. 7) (t,6.9) (t,6.9) (t,6.9) B2 7.69 7.70 7.69 7.69 7.67 7.67 7.67 7.68 7.68 7.68 (8.4) (8.3) (8.4) (8.4) (8.3) (8.4) (8.3) (8.5) (8.4) (8.4) B3 8.23 8.23 8.23 8.22 8.22 8.22 8.21 8.22 8.22 8.22 B2¾ 7.59 7.59 7.59 7.59 7.59 7.58 7.58 7.58 7.59 7.58 (8.7) (8.7) (8.7) (8.7) (8.7) (8.7) (8.6) (8.8) (8.7) (8.7) B3¾ 7.00 7.00 7.00 7.00 7.00 6.99 6.99 7.00 7.00 7.00 P2 7.31 7.32 7.30 7.31 7.12 7.12 7.11 7.12 7.24‡ 7.24† (8.6) (8.6) (8.6) (8.7) (9.0) (9.0) (8.9) (9.0) (9.0) (9.0) P3 8.13 8.13 8.12 8.12 6.93 6.93 6.91 6.92 7.13‡ 7.13† D1 4.22 4.25 1.34 1.35 3.82 3.84 1.30 1.30 (dd,10.7,5.8) (dd,10.7,5.0) (d,6.3) (d,6.1) (dd,8.9,5.8) (dd,8.9,5.0) (d,ca. 6) (d,ca. 6) 4.12 4.09 3.72 3.70 (dd,10.7,6.7) (dd,10.7,6.8) (dd,8.9,6.8) (dd,8.9,6.8) D2 1.93 2.06 5.16 5.28 1.93 2.04 4.32 4.43 2.69 2.82 (oct,6.4) (oct,6.5) (sext,6.3) (m) (oct,6.4) (oct,6.5) (sext,6.0) (m) (sext,7.0) (dqd,9.8,6.9,4.9) D10 0.88† 0.88† 0.88† 0.85 0.88† 0.88† 0.85 (t,6.9) (t,6.9) (t,6.9) (t,7.3) (t,6.9) (t,6.9) (t,ca. 7) D2-Me 1.02 1.04 1.02 1.04 1.30 1.31 (d,6.7) (d,6.6) (d,6.7) (d,6.8) (d,6.9) (d,6.9) aCoupling constants (J) are given in Hz; qi=quintet, sext=sextet, oct=octet. Footnote symbols (†,‡) indicate interchangeable assignments. For the B and P protons, which are parts of AA¾XX¾ spin systems, the N values (JAX+JAX¾ ) are given in parentheses.bFurther signals: 2a: d 1.52–1.27 (m); 2b: d 1.71–0.81 (m); 2c: d 1.73–1.26 (m); 2d: d 1.90–0.80 (m); 3a: d 1.54–1.21 (m); 3b: d 1.68–0.82 (m); shifts assigned by 2D experiments: d 1.64 (m, D4), 1.60 (m, D6), 1.47 (m, D3), 1.46 (m, O3), 1.43 (m, D8), 1.38 (m, D9), 1.36, 1.32 (m, O4, O5), 1.30 (m, O7), 1.28 (m, O6), 1.22 (m, D5, D7), 1.05 (m, D9), 0.98 (m, D3), 0.90, 0.86 (m, D5, D7), 0.90 (d, 6.6, D4-Me), 0.85 (d, 6.6, D8-Me), 0.83 (d, 6.5, D6-Me); 3c: d 1.73–1.28 (m); 3d: d 1.87–0.83 (m); 4c: d 1.86–1.28 (m); 4d: d 1.96–0.83 (m); shifts assigned by 2D experiments: d 1.90 (ddd, 13.9, 9.7, 4.3, D3), 1.66 (m, D4), 1.63 (m, D6), 1.46 (m, O3)1.43 (m, D8), 1.36 (m, D9), 1.36, 1.32 (m, O4, O5), 1.30 (m, O7), 1.28 (m, O6), 1.23 (m, D5), 1.20 (m, D7), 1.16 (m, D3), 1.08 (m, D9), 0.97 (m, D5), 0.96 9d, 6.5, D4-Me), 0.90 (m, D7), 0.85 (d, ca. 7, D6-Me, D8-Me). Synthesis of 3a–d 13C NMR data are given in Tables 1 and 2; [a]20D+3.05 (c 5, CHCl3) (3b, -2.02; 3c, -2.11; 3d, -3.44). A synthetic procedure for 3d is given as an example. 4- Hydroxyphenyl 4¾-octyloxybiphenyl-4-carboxylate (1.26 g, Synthesis of 4c 3 mmol), triphenylphosphine (0.79 g, 3 mmol) and (2S,4R,6R,8R)-4,6,8-trimethyldecan-2-ol 1e (0.4 g, 2 mmol) 4-Hydroxyphenyl 4¾-octyloxybiphenyl-4-carboxylate (1.26 g, 3 mmol) was dissolved in dry pyridine (50 ml ) and (S)-2- were dissolved in dry tetrahydrofuran (50 ml ).While the temperature was kept at 0 °C, diethyl azodicarboxylate methyldecanoyl chloride (0.71 g, 3 mmol) was added while the temperature was kept at 0 °C.Stirring was continued for (DEAD) (0.52 g, 3 mmol) was added dropwise under a nitrogen atmosphere and stirring was continued for 36 h at room 16 h at room temperature. After hydrolysis in an excess of diluted HCl, the product was extracted into dichloromethane temperature. Afterwards the solvent was removed and the resulting product was purified by chromatography over silica (3×150 ml).The combined dichloromethane solutions were washed with water (200 ml) and dried (MgSO4). The solvent gel using dichloromethane as the eluent (Rf 0.90), followed by recrystallization from ethanol until the transition temperature was removed and the resulting product purified by chromatography over silica gel using dichloromethane as the eluent remained constant.Yield: 0.64 g (53%); n(CCl4)/cm-1 2954, 2926, 2870, 2854, 1733, 1606, 1504; m/z 600.5 (M+); 1H and (Rf 0.71), followed by recrystallization from ethanol until the J. Mater. Chem., 1997, 7(10), 1993–1999 1995Table 2 13C NMR data for compounds 2a–d, 3a–d and 4c–d (101 or 75 MHz; CDCl3) chemical shifta carbon 2a 2b 2c 2d 3a 3b 3c 3d 4c 4d O1 68.2 68.2 68.3 68.2 68.2 68.2 68.2 68.2 68.2 68.2 O2 29.3 29.3 29.3 29.3 29.3 29.3 29.3 29.3 29.3 29.3 O3 26.1 26.1 26.1 26.1 26.1 26.1 26.1 26.1 26.1 26.1 O4 29.3† 29.3† 29.3† 29.3† 29.3† 29.3† 29.3† 29.3† 29.3† 29.3† O5 29.4† 29.4† 29.4† 29.4† 29.4† 29.4† 29.4† 29.4† 29.4† 29.4† O6 31.9‡ 31.8 31.9 31.9 31.9‡ 31.9 31.9 31.9 31.9‡ 31.9 O7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 O8 14.1 14.1 14.1 14.1 14.1 14.1 14.1 14.1 14.1 14.1 B1 146.3 146.3 146.3 146.3 145.9 145.9 145.9 145.9 146.1 146.1 B2 126.7 126.6 126.7 126.7 126.6 126.6 126.6 126.6 126.6 126.6 B3 130.8 130.8 130.8 130.8 130.7 130.7 130.7 130.7 130.7 130.8 B4 127.1 127.0 127.1 127.1 127.7 127.7 127.7 127.7 127.3 127.4 B4-CO 164.6 164.6 164.7 164.7 165.5 165.5 165.5 165.5 165.0 165.0 B1¾ 131.9 131.8 131.9 131.9 132.1 132.0 132.1 132.0 131.9 132.0 B2¾ 128.4 128.4 128.4 128.4 128.4 128.4 128.4 128.4 128.4 128.4 B3¾ 115.1 115.0 115.1 115.1 115.0§ 115.0 115.0 115.0 115.0 115.1 B4¾ 159.7 159.7 159.7 159.7 159.6 159.6 159.6 159.6 159.6 159.7 P1 154.7 154.7 154.6 154.6 144.4 144.3 144.3 144.3 148.3 148.4 P2 121.8 121.8 121.7 121.8 122.4 122.4 122.5 122.5 122.6§ 122.6‡ P3 131.2 131.2 131.2 131.1 115.2§ 115.1 116.6 116.5 122.5§ 122.5‡ P4 128.2 128.1 128.6 128.5 157.1 157.1 156.0 156.2 148.3 148.4 P4-CO 166.0 165.9 165.5 165.5 D1 70.1 69.8 20.1 20.6‡ 73.7 73.5 19.8 20.4‡ 175.3 175.3 D2 32.8 30.2 72.0 70.0 33.2 30.7 74.6 72.4 39.7 37.7 D3 33.5 41.4 36.1 43.1 33.6 41.3 36.6 44.1 33.8 41.3 D4 26.9 27.6‡ 25.5 26.7 27.0 27.7 25.6 26.6 27.3 28.5 D5 29.9† 44.7 29.5† 45.0 30.0† 44.7‡ 29.7† 44.9 29.6† 45.6 D6 29.6† 27.5‡ 29.5† 27.4 29.6† 27.5 29.6† 27.4 29.5† 27.4 D7 29.3† 45.7 29.5† 45.5 29.4† 45.6‡ 29.3† 45.7 29.3† 45.0 D8 31.8‡ 31.5 31.9 31.6 32.0‡ 31.6 31.9 31.6 31.8‡ 31.6 D9 22.7 28.8 22.7 29.1 22.7 28.9 22.7 29.0 22.7 29.1 D10 14.1 11.2 14.1 11.2 14.1 11.2 14.1 11.2 14.1 11.2 Me-D2 17.1 18.3 17.1 18.3 17.0 18.3 Me-D4 20.9 20.6‡ 21.1 20.7‡ 20.5 Me-D6 20.9 21.0‡ 21.0 20.7‡ 20.8 Me-D8 20.0 19.9 20.0 20.0 20.0 aFootnote symbols (†,‡,§) indicate interchangeable assignments.transition temperature remained constant. Yield: 1.18 g (67%); heptyloxycarbonyl)phenyl 4¾-octyloxybiphenyl-4-carboxylate (MHPOBC)13 have been used as reference compounds. 1H and 13C NMRdata are given in Tables 1 and 2; [a]20D+8.60 (c 5, CHCl3). Commercially available test cells (E.H.C.) with a layer spacing of 10 mm were used for the electro-optical investigations.The spontaneous polarization was measured by the triangular wave Synthesis of 4d method. Optical tilt angles were obtained by an extrapolation Dicyclohexylcarbodiimide (DCC) (0.70 g, 3.4 mmol) was of the switching angles to zero field. Switching times, defined added at room temperature to a solution of 4-hydroxyphenyl as the rise time from 10 to 90% transmission, were determined 4¾-octyloxybiphenyl-4-carboxylate (0.71 g, 1.7 mmol), by measuring the optical response to an applied electric field (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid 1f (0.82 g, (rectangular wave) at a field strength of ±10 V mm-1 (com- 3.4 mmol) and 4-dimethylaminopyridine (DMAP) (0.27 g, pounds 2a–d, 3a–d and 4c) or ±20 V mm-1 (compound 4d). 2.2 mmol) in dry dichloromethane (50 ml ), and the mixture was stirred for 24 h. After filtration, the reaction mixture was washed twice with a solution of 5% citric acid in water (50 ml ) Results and once with water (50 ml ). The organic phase was dried (Na2SO4), the solvent removed and the resulting product Liquid crystalline properties purified by chromatography over silica gel using dichloro- Textural observations and miscibility studies have been carried methane as the eluent (Rf 0.81), followed by recrystallization out in order to determine the liquid crystalline properties of from ethanol until the transition temperature remained conthe compounds of series 2–4.On cooling from the isotropic stant. Yield: 0.42 g (39%); n(CCl4)/cm-1 2954, 2925, 2870, phase for all compounds the SmA phase appears showing 2854, 1756, 1732, 1604, 1504; m/z 628.5 (M+); 1H and 13C NMR characteristic textures (planar oriented region: focal-conic fan data are given in Tables 1 and 2; [a]20D-10.53 (c 5, CHCl3).texture, homeotropic oriented regions: no texture). On further cooling a phase transition into the SmC phase occurs: in the Equipment and methods planar oriented region the focal-conic fan texture of the SmA phase transforms into a broken focal-conic fan texture and in Phase transition temperatures were determined optically by observing the textural changes with a polarizing microscope.the homeotropic regions a schlieren texture appears. Below the SmC phase, most of the compounds show a direct transition Transition enthalpies were measured by diVerential scanning calorimetry (DSC) using a Perkin-Elmer DSC 7.Miscibility into a higher ordered smectic phase (denoted as SmIII phase in the following text, probably SmI) which exhibits either a studies were carried out by the contact method and, in one case, in addition, by choosing specific concentrations.broken focal-conic fan texture with thin round coloured bands or a schlieren texture. In the other two compounds, a SmCA For these investigations both enantiomers of 4-(1-methyl- 1996 J. Mater. Chem., 1997, 7(10), 1993–1999antiferroelectric phases. For both antiferroelectric phases (SmCA and SmIA) of compounds 2c and 4d, a ‘tristate’ switching has been observed, confirming the antiferroelectric nature of these phases.In order to allow a comparison to the electrooptical properties of the SmC phases of the other compounds, in the temperature range of the antiferroelectric SmCA phases polarization and optical tilt angle of the field induced ferroelectric states, as well as the rise time from 10 to 90% transmission for the direct switching between the two ferroelectric switching states, have been determined.Since no switching was observed for the SmCA phase of compound 4d at E±10 V mm-1, the switching times of this compound were measured at E±20 V mm-1. For the compounds of series 2 the results of the electrooptical investigations are shown in Figs. 2–4. Both tetramethyl derivatives (2b, 2d) are found to exhibit two to three times higher values of spontaneous polarization in comparison to their respective reference compound (2a, 2c) with only one chiral methyl branching.Additionally, an increase of the optical Fig. 1 Phase diagram between (R)-MHPOBC and 4d tilt angle by about a factor of 1.5 is observed; e.g. 50 K below phase occurs between the SmC and the higher ordered smectic phase SmIA. At the transition from the SmC to the SmCA phase the number of chirality lines in the broken focal-conic fan texture strongly decreases and the number of chevron defects strongly increases.The SmC–SmCA phase transition is also indicated by an inversion of the helical twist sense which can be observed in the schlieren texture. Moreover, in the supercooled region of three compounds a transition into a high ordered smectic phase SmIV can clearly be observed by the formation of a mosaic texture.The classification of the SmA, SmC, SmCA and SmIA phases was confirmed by miscibility studies. As an example, the phase diagram between the compounds 4d and (R)-MHPOBC, which has been investigated in more detail, is shown in Fig. 1. The Fig. 2 Temperature dependence of spontaneous polarization of compounds 2; (#) 2a, ($) 2b, (%) 2c and (&) 2d SmA, SmC, SmCA and SmIA phases of (R)-MHPOBC are uninterruptedly miscible, with the respective smectic modifications of 4d confirming thereby the phase sequence SmIA–SmCA–SmC–SmA for compound 4d.Polymorphy, phase transition temperatures and transition enthalpies of the liquid crystalline products are shown in Table 3 [NB: compounds with diVerent linking groups X are distinguished by diVerent numbers (2–4), whereas the letters (a–d) label the kind of the chiral side chain].As can be seen, the introduction of three additional methyl branchings leads to a decrease of the melting points of about 10 K for series 2 and 4 and 25 K for series 3, as well as to about 30 K lower clearing temperatures, resulting in a smaller liquid crystalline phase range for the tetramethyl derivatives.However, the SmC temperature range increases slightly in the case of series 2 and 4 and by more than a factor of three in case of series 3. The Fig. 3 Temperature dependence of the tilt angle of compounds 2; largest SmC phase ranges are observed in series 2, ranging (#) 2a, ($) 2b, (%) 2c and (&) 2d from 47 to 62 K.In the two compounds 2c and 4d, an alternating tilted SmCA phase occurs in a broad temperature range. With respect to the appearance of this SmCA phase the influence of the three additional methyl branchings is puzzling. Whereas in series 2 the SmCA phase of the 2-methyldecanol derivative 2c is replaced by a SmC phase in the respective tetramethyl derivative 2d, the opposite eVect is observed in series 4.Electro-optical properties All compounds of series 2–4 (see Table 3) show ferroelectric switching in the SmC and SmIII phases. To characterize the ferroelectric properties the temperature dependence of spontaneous polarization, optical tilt angle and switching time (t10–90 at E±10 V mm-1) of the SmC phases have been measured.In two of the compounds (2c, 4d) the ferroelectric Fig. 4 Temperature dependence of the switching time of compounds 2; (#) 2a, ($) 2b, (%) 2c and (&) 2d smectic modifications (SmC, SmIII) are almost replaced by J. Mater. Chem., 1997, 7(10), 1993–1999 1997Table 3 Polymorphy, phase transition temperatures and transition enthalpies of the liquid crystalline products compound X R transition temperatures/°C [enthalpies/kJ mol-1] 2a CO2 Cr 66.4 (SmIII 54.5) SmC 108.0 SmA 164.1 I [30.6] [1.02] [0.00] [6.24] 2b CO2 Cr 53.9 SmIII 54.0 SmC 115.7 SmA 134.3 I [22.9] [0.80] [0.00] [7.08] 2c CO2 Cr 62.8 (SmIA 62.5) SmCA 109.3 SmC 113.4 SmA 140.4 I [29.4] [1.50] [0.021] [0.00] [5.83] 2d CO2 Cr 53.5 (SmIII 38.0) SmC 94.8 SmA 102.1 I [19.9] [0.43] [0.50] [1.98] 3a O Cr 84.4 (SmIV 56.6) SmIII 101.6 SmC 107.9 SmA 164.4 I [31.2] [1.96] [2.96] [0.00] [7.04] 3b O Cr 55.1 (SmIV 44.7) SmIII 80.6 SmC 104.6 SmA 133.6 I [18.8] [1.84] [2.40] [0.00] [4.80] 3c O Cr 65.2 SmIII 81.3 SmC 94.5 SmA 144.2 I [23.5] [2.16] [0.00] [6.07] 3d O Cr 41.6 SmIII 49.5 SmC 90.4 SmA 116.3 I [22.7] [1.04] [0.00] [4.22] 4c O2C Cr 62.6 (SmIV 58.5) SmIII 91.7 SmC 136.1 SmA 157.5 I [26.1] [1.66] [2.72] [0.00] [5.48] 4d O2C Cr 56.3 SmIA 59.5 SmCA 108.5 SmC 109.4 SmA 119.2 I [23.2] [1.32] [0.12] [0.28] [2.68] Table 4 Spontaneous polarization, optical tilt angles and switching Table 5 Spontaneous polarization, optical tilt angles and switching times of the compounds of series 4 at 5, 10, 20, 30 and 40 K below times of the compounds of series 3 at 5, 10, 20, 30 and 40 K below the SmA–SmC transition temperature the SmA–SmC transition temperature compound T-Tc/K Ps/nC cm-2 h(°) t/ms compound T-Tc/K Ps/nC cm-2 h(°) t/ms 3a -5 1.8 9.1 22.3 4c -5 8.0 18.0 17.6 4c -10 10.7 21.5 19.1 3b -5 5.1 17.7 48.6 3b -10 6.8 20.4 70.0 4c -20 13.9 24.5 21.3 4c -30 16.2 25.9 22.9 3b -20 8.8 22.5 90.0 3c -5 24.4 11.1 9.6 4c -40 18.0 26.5 26.4 4d -5 25.6 27.1 12.4a 3c -10 32.6 13.5 9.9 3d -5 49.2 19.0 12.3 4d -10 29.6 29.6 14.4a 4d -20 35.7 32.2 20.2a 3d -10 63.6 23.0 13.8 3d -20 82.8 26.3 18.4 4d -30 41.0 33.5 32.9a 4d -40 44.3 33.8 62.1a 3d -30 93.3 27.5 25.5 3d -40 97.9 27.2 45.8 aMeasured at a field strength of ±20 V mm-1.the SmCA phase of compound 2c remains almost constant the SmA–SmC transition temperatures, optical tilt angles of about 30° for the tetramethyl derivatives are measured, com- close above the transition to the SmIA phase.For the electro-optical properties of the compounds of series pared to about 20° for the reference compounds. Thus the strong increase of the spontaneous polarization can not only 3, similar results are obtained (see Table 4). Again, the tetramethyl derivatives are found to exhibit nearly two times larger be attributed to an increase of the polarization–tilt angle coupling constant (as expected for the introduction of three optical tilt angles and two to three times higher values of spontaneous polarization in comparison to their respective additional chiral centres), but is also caused by the remarkable increase of the tilt angle.Although the spontaneous polariz- reference compounds.In series 4 only two compounds with the (first) chiral centre ation of the tetramethyl derivatives are much higher, their switching times are of the same order. In the vicinity of the in the a-position have been synthesized. The electro-optical properties of compounds 4c and 4d are summarized in Table 5. higher ordered smectic phase (probably SmI), an exponential increase of the switching times is observed for the SmC phases As in series 2 and 3, the introduction of the additional methyl branchings leads to a remarkable increase of the optical tilt of compounds 2a, 2b and 2d, whereas the switching time of 1998 J.Mater. Chem., 1997, 7(10), 1993–1999angle and of the spontaneous polarization. In comparison to References the respective compounds of series 2, whose molecular struc- 1 J.W. Goodby, A. J. Slaney, C. J. Booth, I. Nishiyama, J. D. Vuijk, tures diVer only by the direction of the ester group between P. Styring and K. J. Toyne, Mol. Cryst. L iq. Cryst., 1994, 243, 231. the mesogenic core and the chiral side chain, the spontaneous 2 A.-M. Levelut, D. Bennemann, G.Heppke and D. Lo� tzsch, Mol. polarization of compounds 4c and 4d is reduced by about a Cryst. L iq. Cryst., in the press. 3 J. Jacob, Fortschr. Chem. Org. Naturst., 1976, 34, 373. factor of five. 4 K. E. Murray, Aust. J. Chem., 1962, 15, 510. 5 G. Odham, Ark. Kemi, 1963, 21, 379. Conclusion 6 M. Morr, V. Wray, J. Fortkamp and R. D. Schmid, L iebigs Ann. Chem., 1992, 433. Starting from the natural source of the preen-gland wax of 7 M.Morr, C. Proppe and V.Wray, L iebigs Ann., 1995, 2001. poultry, novel ferro- and antiferro-electric liquid crystals bear- 8 O. Mitsonubu, Synthesis, 1981, 1. 9 D. M. Doddrell, D. T. Pegg and M. R. Bendall, J. Magn. Reson., ing tetramethylalkyl chains have been synthesized. In compari- 1982, 48, 323. son to the respective compounds with only one methyl 10 W. R. Croasmun and R. M. K. Carlson, T wo-Dimensional NMR branching, lower melting points and broader SmC phase Spectroscopy. Applications for Chemists and Biochemists, VCH, ranges are exhibited which favour the tetramethyl derivatives Weinheim, 2nd edn., 1994. for use in broad range SmC room temperature mixtures. 11 H.-O. Kalinowski, S. Berger and S. Braun, 13C-NMRAccording to the electro-optical investigations, the introduc- Spektroskopie, Thieme, Stuttgart 1984. tion of the additional methyl branchings leads to an increase 12 A. Fukuda, Y. Takanishi, T. Isozaki, K. Ishikawa and H. Takazoe, J.Mater. Chem., 1994, 4, 997. of the spontaneous polarization and the optical tilt angle. The 13 A. D. L. Chandani, T. Hagiwara, Y. Suzuki, Y. Ouchi, H. Takezoe use of new chiral tetramethylalkyl side chains seems to be and A. Fukuda, Jpn. J. Appl. Phys., 1988, 27, L729. promising, especially for the development of new materials for 14 J. Fu� nfschilling and M. Schadt, J. Appl. Phys., 1989, 66, 3877. device applications where switching angles of 45° are required 15 A. G. H. Verhulst and G. Cnossen, Ferroelectrics, 1996, 179, 141. (e.g. for deformed helix ferroelectric liquid crystal displays14,15 16 K. Nakamura, A. Takeuchi, N. Yamamoto, Y. Yamada, Y.-I. or for antiferroelectric liquid crystal displays).16 Suzuki and I. Kawamura, Ferroelectrics, 1996, 179, 131. The authors thank the Deutsche Forschungsgemeinschaft (Sfb 335) for financial support. Paper 7/04503D; Received 26th June, 1997 J. Mater. Chem., 1997, 7(10), 1993–1999