Simplified Scheme for Deterministic Synthesis of Chiral-Nematic

Potentially useful for the fabrication of nonabsorbing polarizers, optical notch filters and reflectors, and polarized light sources, chiral-nematic g...
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Simplified Scheme for Deterministic Synthesis of Chiral-Nematic Glassy Liquid Crystals† Jason U. Wallace and Shaw H. Chen* Department of Chemical Engineering and Laboratory for Laser Energetics, Room COI-1210, 240 East RiVer Road, UniVersity of Rochester, Rochester, New York 14623-1212

Potentially useful for the fabrication of nonabsorbing polarizers, optical notch filters and reflectors, and polarized light sources, chiral-nematic glassy liquid crystals can be synthesized by a statistical or deterministic approach. A deterministic approach is characterized by the relative ease of product separation and purification and hence is more amenable to process scale-up. Prompted to minimize the effort involving protection and deprotection of functional groups, the present work has demonstrated the feasibility of reducing the number of synthesis steps from a previous synthesis scheme. The new methodology is widely applicable to the synthesis of a variety of right- and left-handed chiral-nematic glassy liquid crystals with desired phase transition temperatures. Introduction Liquid crystals are self-organizing fluids characterized by a uniaxial, lamellar, helical, or columnar arrangements in nematic, smectic, cholesteric, and discotic liquid crystals, respectively. Each type of liquid crystal has found its respective niche in optics, photonics, electronics, or optoelectronics. With these molecular arrangements frozen in the solid state, glassy liquid crystals (GLCs) represent a unique material class that combines properties intrinsic to liquid crystals with those common to polymers, such as glass transition and film- and fiber-forming abilities. In principle, all liquids should vitrify at a sufficiently rapid cooling rate. In practice, most organic materials, including liquid crystals, tend to crystallize upon cooling through the melting point, Tm. The preparation of a disclination-free (i.e., monodomain) GLC films requires slow cooling from mesomorphic melts without encountering crystallization, a challenge to thermal quenching as a traditional approach to vitrification. From a fundamental perspective, the glass transition of a liquid crystal to a mesomorphic solid adds a new dimension to the traditional view of glass transitions from isotropic liquid to isotropic solid.1,2 Conventional liquid crystals tend to crystallize upon cooling to below Tm, thus losing the desired molecular order characteristic of liquid crystals and resulting in polycrystalline films that scatter light or limit charge transport. The very first attempt to synthesize GLCs in 1971 yielded materials with a low glasstransition temperature, Tg, and poor morphological stability.3 Subsequent efforts in the last three decades have produced GLCs that can be categorized into (i) laterally or terminally branched, one-string compounds with a Tg mostly around room temperature;4-6 (ii) twin molecules with an above-ambient Tg but generally lacking morphological stability;7-10 (iii) cyclosiloxanes functionalized with mesogenic and chiral pendants;11-13 (iv) carbosilane dendrimers exhibiting a low Tg;14-16 and (v) macrocarbocycles with mesogenic segments as part of the ring structure.17 We have implemented a comprehensive molecular design strategy in which mesogenic and chiral pendants are chemically bonded to a volume-excluding core.18-31 While the * To whom correspondence should be addressed. E-mail: shch@ lle.rochester.edu. † The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.

core and pendant are crystalline as separate entities, the chemical hybrid with a proper flexible spacer connecting the two readily vitrifies into a GLC on cooling. A definitive set of GLCs has been synthesized and characterized to furnish insight into structure-property relationships and to demonstrate device concepts. In the limit of a vanishing volume of the core, pentalerythritol has been reported to yield glassy liquid crystals with widely varying Tg and morphological stability.32-34 Chiral-nematic GLCs are of particular interest because of the potential for use as large area nonabsorbing polarizers, optical notch filters and reflectors, and polarizing fluorescent films. This class of materials had been synthesized by a statistical approach, which requires intensive workup procedures to arrive at pure components.35 The first deterministic synthesis was accomplished using 2,4-dioxo-3-oxabicyclo[3.3.1]nonane-7-carboxylic acid chloride as an unstable intermediate prepared under demanding conditions.36 Three distinct methodologies, which are more amenable to process scale-up, have been successfully implemented recently:37 monohydrolysis of the trimethyl 1,3,5cyclohexanetricarboxylate and that of 1,3,5-benzenetricarboxylate as well as using 5-hydroxyisophthalic acid as the central core. The present study aims to develop a simplified deterministic synthesis scheme illustrated with glassy chiral-nematic liquid crystals containing cyanobiphenyl in both the chiral and the nematic pendants. The goal of this study is two-fold: to establish a facile material synthesis strategy with general applicability and to identify structurally similar pendants for the construction of a glassy chiral-nematic liquid crystal. Experimental Procedures Reagents and Chemicals. All chemicals, reagents, and solvents were used as received from Sigma-Aldrich Chemical Co. or VWR Scientific, except tetrahydrofuran, which was freshly distilled over sodium in the presence of benzophenone before use. Silica gel 60 (EM Science; 230-400 mesh) was used for liquid chromatography. Material Synthesis. The GLC depicted as I in Chart 1 was synthesized by the reactions in Schemes 1-3. The nematic pendant, 4-(3-hydroxypropoxy)-4′-cyanobiphenyl (Nm-OH), was synthesized following a published procedure.38 An intermediate used in Scheme 1, 4-bromo-4′-cyanobiphenyl, was synthesized according to a literature procedure.39 Scheme 2 and

10.1021/ie060015r CCC: $33.50 © 2006 American Chemical Society Published on Web 05/17/2006

Ind. Eng. Chem. Res., Vol. 45, No. 13, 2006 4495 Chart 1. Molecular Structures of Nematic and Chiral Precursors, Nm-OH and Ch-OH, as well as that of a Model Chiral-Nematic Glassy Liquid Crystal Illustrating a New Deterministic Synthesis Strategy

Scheme 1. Synthesis of the Chiral Precursor, Ch-OH

the procedures for the synthesis of intermediates 3-5 have been reported elsewhere.37 The synthesis and purification procedures as well as structural elucidation of all other intermediates and the final product are described in what follows. (S)-3-Bromo-2-methyl-1-[(tert-butyldimethylsilyl)oxy]propane (1). To a solution of (S)-(+)-3-bromo-2-methylpropanol (1.17 g, 7.64 mmol) and tert-butyldimethylsilyl chloride (1.73 g, 11.5 mmol) in anhydrous N,N-dimethylformamide (6 mL), imidazole (1.04 g, 15.3 mmol) was quickly added. The reaction was carried out under argon at room temperature overnight before quenching with water for extraction with diethyl ether (2 × 75 mL). The combined organic extracts were washed with saturated NaHCO3(aq) and brine and then dried over anhydrous MgSO4. The oil resulting from evaporation of the solvent was purified by flash column chromatography with petroleum ether to yield 1 (1.85 g, 91%). 1H NMR (400 Mz, CDCl3): δ 0.07 (s, 6H, -OSi(CH3)2), δ 0.92 (s, 9H, -OSiC(CH3)3), δ 1.01 (d, 3H, -CH3), δ 2.01 (m, 1H, -CHCH3-), δ 3.46-3.59 (dd+qd, 4H, -SiOCH2CH(CH3)CH2Br). (S)-4-(3-Hydroxy-2-methylpropyl)-4′-cyanobiphenyl (ChOH). A solution of 1 (0.410 g, 1.50 mmol) in anhydrous tetrahydrofuran (7.5 mL) was cooled to -78 °C before dropwise addition of tert-butyllithium (1.7 M in pentane, 3.29 mmol). The reaction was allowed to stir for 5 min before dropwise addition of 9-methoxy-9-BBN (1 M in hexanes, 3.59 mmol). The reaction vessel was allowed to warm to room temperature while stirring for 1 h. Then, a solution of 4-bromo-4′cyanobiphenyl (0.23 g, 0.89 mmol) in anhydrous N,N-dimethylformamide (15 mL) was slowly added, and volatile solvents were removed by evaporation under vacuum. Under inert atmosphere, Pd(PPh3)4 (0.086 g, 0.075 mmol) and K2CO3 (0.62 g, 4.5 mmol) were added to the reaction mixture. The reaction was continued at 75 °C for 24 h and then quenched with water and extracted with ethyl acetate (3 × 75 mL). The combined organic extracts were washed with brine and dried over anhydrous MgSO4. The solvent was removed under reduced pressure, and the resultant solid was purified by flash column chromatography with 4:1 petroleum ethe/methylene chloride to yield the protected product. This solid was dissolved in tetrahydrofuran (10 mL), to which 0.5 M HCl(aq) (10 mL) was added to accomplish hydrolysis. The reaction was allowed to stir at room temperature for 2 h before evaporating off 50% of the solvent under reduced pressure; the white precipitate was collected by filtration. The resultant solid was purified by flash column chromatography with a solvent gradient from 0 to 4%

acetone in methylene chloride to yield Ch-OH (0.097 g, 43% for the two consecutive steps). 1H NMR (400 Mz, CDCl3): δ 0.96 (d, 3H, -CH3), δ 2.02 (m, 1H, -CHCH3-), δ 2.48-2.88 (qd, 2H, -CH2Ar), δ 3.56 (m, 2H, HOCH2-), δ 7.31 (d, 2H, Ar), δ 7.54 (d, 2H, Ar), δ 7.70 (d, 2H, Ar), δ 7.74 (d, 2H, Ar). 1,3,5-Benzenetricarboxylic Acid, 1,3-bis(3-[4′-Cyanobiphenyl-4-yloxy]propyl) Ester, 5-tert-Butyl Ester (6). To a solution of 5 (0.359 g, 1.35 mmol), 4-(3-hydroxypropoxy)-4′cyanobiphenyl (Nm-OH) (0.703 g, 2.76 mmol), and triphenylphosphine (0.785 g, 2.96 mmol) in anhydrous tetrahydrofuran (11 mL) was slowly added diethyl azodicarboxylate (0.564 g, 3.24 mmol). The reaction was continued under argon at room temperature overnight. The solvent was then evaporated off under reduced pressure, and the solid residue was purified by flash column chromatography with a solvent gradient from 0 to 2% acetone in methylene chloride to yield 6 (0.789 g, 79%). 1H NMR (400 MHz, CDCl ) δ 1.63 (s, 9H, -C(CH ) ), δ 2.34 3 3 3 (quin, 4H, -CH2-), δ 4.21 (t, 4H, -CH2OAr), δ 4.62 (t, 4H, COOCH2-), δ 7.02 (d, 4H, Ar), δ 7.54 (d, 4H, Ar), δ 7.65 (d, 4H, Ar), δ 7.71 (d, 4H, Ar), δ 8.81 (d, 2H, Bz core), δ 8.85 (t, 1H, benzene core). 1,3,5-Benzenetricarboxylic Acid, 1,3-bis(3-[4′-Cyanobiphenyl-4-yloxy]propyl) Ester (7). To a solution of 6 (0.784 g, 1.06 mmol) in anhydrous methylene chloride (22 mL) were added triethylsilane (0.50 mL, 3.2 mmol) and trifluoroacetic acid (11 mL). It is noted that triethylsilane was introduced as a cation scavenger40 to improve the yield and ease of purification over a previous method37 for the hydrolysis of the tert-butyl ester in 6. The reaction was continued at room temperature for 3 h. The solvent was then evaporated off under reduced pressure to yield a white solid, which was triturated with diethyl ether and washed with methylene chloride to yield 7 (0.69 g, 95%). 1H NMR (400 MHz, DMSO-d ): δ 2.24 (m, 4H, -CH -), δ 6 2 4.20 (t, 4H, -CH2OAr), δ 4.53 (t, 4H, COOCH2-), δ 7.04 (d, 4H, Ar), δ 7.68 (d, 4H, Ar), δ 7.82 (d, 4H, Ar), δ 7.86 (d, 4H, Ar), δ 8.66 (t, 1H, Ar), δ 8.68 (d, 2H, Ar), δ 13.8 (broad s, 1H, -COOH). 1,3,5-Benzenetricarboxylic Acid, Monomethyl Ester (8). Trimethyl 1,3,5-benzene-carboxylate (2.50 g, 9.91 mmol) was dissolved in methanol (200 mL) and 0.95 N NaOH(aq) (10.4 mL, 9.91 mmol) by stirring at room temperature for 1 h. Stirring was continued for an additional 15 h before 0.9 N NaOH(aq) (11.5 mL, 10.4 mmol) was added in 10 equal portions every 45 min. The reaction was continued at room temperature for 2 days before being neutralized to pH 7 with 0.5 M HCl(aq). The solvent was evaporated off, and 1 M HCl(aq) was added for extraction with ethyl acetate. The combined organic extracts were washed with 1 M HCl(aq) and then dried over anhydrous MgSO4. The crude product resulting from evaporating off the solvent was triturated with methylene chloride. The resultant powder was purified by flash column chromatography with 1% acetic acid in 3:1 (v/ v) CH2Cl2/THF to yield 8 (1.56 g, 70%). 1H NMR (400 Mz, DMSO-d ): δ 3.93 (s, 3H, -COOCH ), δ 6 3 8.64 (d, 2H, Ar), δ 8.66 (t, 1H, Ar), δ 13.61 (s, 2H, -COOH). 1,3,5-Benzenetricarboxylic Acid, 1,3-bis(3-[4′-Cyanobiphenyl-4-yloxy]propyl) Ester, 5-Methyl Ester (9). To a solution of 8 (0.863 g, 3.85 mmol), Nm-OH (2.01 g, 7.90 mmol), and triphenylphosphine (2.22 g, 8.47 mmol) in anhydrous tetrahydrofuran (24 mL) was slowly added diethyl azodicarboxylate (1.61 g, 9.24 mmol) at 0 °C. The reaction was continued under argon at room temperature overnight. The solvent was then evaporated off under reduced pressure, and the solid residue was purified by flash column chromatography with 0.5% acetone in chloroform to yield 9 (2.23 g, 83%). 1H

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Scheme 2. Previously Reported Deterministic Synthesis Methodology for Chiral-Nematic Glassy Liquid Crystals37

Scheme 3. New Deterministic Synthesis Methodology for Chiral-Nematic Glassy Liquid Crystals

NMR (400 MHz, CDCl3): δ 2.35 (m, 4H, -CH2-), δ 4.22 (t, 4H, -CH2OAr), δ 4.63 (t, 4H, COOCH2-), δ 7.02 (d, 4H, Ar), δ 7.53 (d, 4H, Ar), δ 7.64 (d, 4H, Ar), δ 7.71 (d, 4H, Ar), δ 8.88 (s, 3H, Ar). 1,3,5-Benzenetricarboxylic Acid, 1,3-bis(3-[4′-Cyanobiphenyl-4-yloxy]propyl) Ester (7′). This procedure is distinct from that for the conversion of 6 to 7 as described previously. A solution of 9 (0.306 g, 0.432 mmol) and lithium iodide (0.137 g, 1.03 mmol) in anhydrous pyridine (2.7 mL) was refluxed under argon for 22 h with a precaution to avoid exposure to room light. The reaction mixture was allowed to cool to room temperature before evaporating off pyridine under vacuum. The resultant solid was dissolved in tetrahydrofuran for treatment with trifluoroacetic acid (2 mL) to liberate the carboxylic acid. This solution was then filtered to remove inorganic salts. After evaporating off the solvent under reduced pressure, the residue was triturated with ethanol. The resultant solid was dissolved in ethyl acetate and washed with saturated copper(II) sulfate and 2 M HCl(aq) to remove residual pyridine. Upon evaporating off the solvent under reduced pressure, the white solid was triturated with diethyl ether to yield 7′ (0.215 g, 73%). 1H NMR (400 MHz, DMSO-d6): δ 2.24 (m, 4H, -CH2-), δ 4.20 (t, 4H, -CH2OAr), δ 4.53 (t, 4H, COOCH2-), δ 7.04 (d, 4H, Ar), δ 7.68 (d, 4H, Ar), δ 7.82 (d, 4H, Ar), δ 7.86 (d, 4H, Ar), δ 8.66 (t, 1H, Ar), δ 8.68 (d, 2H, Ar), δ 13.8 (broad s, 1H, -COOH). 1,3,5-Benzenetricarboxylic Acid, 1,3-bis(3-[4′-Cyanobiphenyl-4-yloxy]propyl) Ester, 5-((S)-3-[4′-Cyanobiphenyl-4yl]-2-methylpropyl) Ester (I). To a solution of triphenylphosphine (0.070 g, 0.27 mmol) in anhydrous tetrahydrofuran (0.80 mL), diethyl azodicarboxylate (0.045 mL, 0.26 mmol) was added dropwise at -78 °C and stirred for 20 min; the betaine complex was preformed at low temperature to avoid formation of radicals41 in the presence of the benzylic hydrogens on the chiral pendant, Ch-OH. Then, 7 (0.13 g, 0.20 mmol) and ChOH (0.045 g, 0.18 mmol) in tetrahydrofuran (0.80 mL) were added. The reaction was allowed to warm to room temperature with stirring overnight under argon. The solvent was removed under reduced pressure, and the resultant solid was purified by flash column chromatography with a solvent gradient from 0 to 1% acetone in methylene chloride. The product was collected by precipitation from methylene chloride into methanol to yield I (0.076 g, 46%). Anal. Calcd. for C58H47N3O8: C 76.22%, H 5.18%, N 4.60%. Found: C 76.05%, H 5.22%, N 4.48%. 1H NMR (400 Mz, CDCl3) δ 1.08 (d, 2H, -CH3), δ 2.35 (m, 5H, -CH2- and -CHCH3-), δ 2.64-2.88 (qd, 2H, -CH2Ar), δ 4.21 (t, 4H, -CH2OAr), δ 4.28 (qd, 2H, -COOCH2CH(CH3)), δ 4.62 (t, 4H, -COOCH2CH2-), δ 7.01 (d, 4H, -OAr), δ

7.30 (d, 2H, -CH2Ar), δ 7.54 (m, 6H, Ar), δ 7.64 (m, 6H, Ar), δ 7.71 (m, 6H, Ar), δ 8.86 (m, 3H, Ar). Molecular Structures and Thermotropic Properties. Molecular structures were elucidated with 1H NMR spectroscopy in CDCl3 or DMSO-d6 (Avance-400, 400 MHz) and elemental analysis (Quantitative Technologies, Inc.). Thermal transition temperatures were determined by differential scanning calorimetry (DSC; Perkin-Elmer DSC-7) with a continuous N2 purge at 20 mL/min. Samples were preheated to the isotropic state followed by cooling at -20 °C/min to -30 °C before heating at 20 °C/min, furnishing the reported first cooling and second heating scans. Liquid crystal mesomorphism was characterized with hot-stage polarizing optical microscopy (DMLM, Leica, FP90 central processor and FP82 hot stage, Mettler, Toledo). Preparation and Characterization of Glassy ChiralNematic Films. Optically flat fused-silica substrates (25.4 mm diameter × 3 mm thickness, Escoproducts; n ) 1.458 at 589.6 nm) were coated with a polyimide alignment layer (Nissan SUNEVER) and uniaxially rubbed. Glassy chiral-nematic films were prepared between two surface-treated substrates with the film thickness defined by glass sphere spacers as 4 µm (Bangs Laboratories). Upon melting of a powdered sample, the fluid film underwent annealing below Tc before quenching to room temperature. Transmittance at normal incidence and reflectance at 6° off normal were measured with polarized and unpolarized incident light, respectively, using a UV-vis-NIR spectrophotometer (Lambda-900, Perkin-Elmer). Fresnel reflections from the air-glass interfaces were accounted for with a reference cell containing an index matching fluid (n ) 1.500 at 589.6 nm) between two surface-treated substrates. Results and Discussion Our prior research has resulted in a plethora of chiral-nematic glassy liquid crystals comprising chiral and nematic pendants chemically bonded to a central core through a flexible spacer24,30-32 To illustrate the development of a new synthesis methodology, a model system depicted as I in Chart 1 was designed with the following considerations: (i) a nematic pendant consisting of cyanophenyl, (ii) a structurally similar mesogenic pendant with a chiral spacer, (iii) a strong helical twisting power to yield selective reflection in the blue region, and (iv) trimethyl 1,3,5-benzenetricarboxylate that can be selectively hydrolyzed to a desired extent. Also included in Chart 1 are the nematic and chiral precursors, Nm-OH and Ch-OH. While Nm-OH was synthesized following a literature procedure,38 Scheme 1 was followed to prepare Ch-OH. Consisting of six steps, Scheme 2 represents a previously reported

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Figure 1. DSC heating and cooling scans at (20 °C/min of Nm-OH and Ch-OH preheated to beyond the clearing point. Symbols: K, crystal; Nm, nematic; and I, isotropic. Polarizing optical microscopy images for Nm-OH and Ch-OH exhibiting schlieren textures and oily streaks, respectively.

deterministic synthesis approach beginning with the monohydrolysis of trimethyl 1,3,5-benzenetricarboxylate.37 The resulting dimethyl ester of 1,3,5-benzenetricarboxylic acid was protected as a tert-butyl ester before dihydrolysis of the two methyl ester groups for esterification with Nm-OH. The tert-butyl ester group was then deprotected for reaction with Ch-OH to yield I. Presented in Scheme 3 is a new deterministic synthesis methodology beginning with the dihydrolysis of trimethyl 1,3,5benzenetricarboxylate. After the esterification of the dicarboxylic acid with Nm-OH, the methyl ester was deprotected with LiI to form 7′, a key step in the new scheme inspired by the ability of LiI to differentiate between methyl and ethyl phenyl acetate in dealkylation.42 The overall yields of I amount to 17 and 20% following Schemes 2 and 3, respectively. Although the gain in the overall product yield is insignificant, the number of synthesis steps is reduced from six to four as Scheme 3 is compared to Scheme 2, representing a substantial saving in the manufacturing cost. The thermotropic properties of Nm-OH and Ch-OH were characterized by differential scanning calorimetry, DSC, and polarizing optical microscopy, POM. The DSC thermograms and the POM image, as shown in Figure 1a, indicate that NmOH is nematic liquid crystal with a crystalline melting point, Tm, at 91.1 °C and a clearing point, Tc, at 118.4 °C on heating. In contrast, the DSC heating and cooling scans of Ch-OH shown in Figure 1b revealed no mesomorphic transition. The heating scan shows a Tm at 80.0 °C with thermally activated crystallization at 35.7 °C presumably because of incomplete crystallization on cooling from isotropic melt. While no liquid crystalline mesomorphism was observed under hot-stage POM, the POM image (see the inset in Figure 1b) of a melt of ChOH quenched in liquid nitrogen revealed cholesteric mesomorphism in terms of oily streaks. It is concluded that both NmOH and Ch-OH are thermotropic liquid crystals with a strong tendency to crystallize. Model compound I is a chiral-nematic glassy liquid crystal containing two Nm and one Ch pendants, as demonstrated by the DSC thermograms and the POM image shown in Figure 2.

The absence of crystallization on cooling and that of crystalline melting on heating is an indication of its short-term morphological stability. To determine the selective reflection property, a 4 µm thick film was sandwiched between alignment coated fused-silica substrates by thermal processing of I. Left at room temperature for months, the film did not undergo crystallization, evidence of long-term morphological stability. The transmission and reflection spectra, as shown in Figure 3, reveal a selective reflection band centered at 420 nm, the consequence of a high helical twisting power presumably due to the structural similarity between the chiral and the nematic pendants by analogy to the generation of cholesteric mesomorphism through doping nematic liquid crystals with chiral compounds.43 With unpolarized incident light, the observed reflectance of 48% is close to the theoretical limit of 50% for a perfectly ordered chiral-nematic film, which is a manifestation of the highly ordered, disclination-free film that I is capable of forming. The well-aligned film comprises a right-handed helical stack based on the facts that the right-handed circularly polarized incident is reflected and that the left-handed counterpart is transmitted. As (S)-(+)-3-bromo-2-methylpropanol as the chiral building block yields a right-handed chiral-nematic glassy liquid crystal, its enantiomer, (R)-(-)-3-bromo-2-methylpropanol, is expected to result in the left-handed counterpart. Single-handed chiralnematic glassy liquid crystalline films are useful as large-area nonabsorbing circular polarizers, a stack of two films with opposite handedness constitutes notch filters and reflectors, as we have demonstrated previously.31,37 The new synthesis methodology reported here is generally applicable, and both the glass-transition temperature and the clearing point can be elevated using nematic and/or chiral pendants with a greater aspect ratio.29 Conclusion Chiral-nematic glassy liquid crystals with selective wavelength reflection in the visible to infrared spectral region are

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Figure 2. DSC heating and cooling scans at (20 °C/min of I preheated to beyond the clearing point. Symbols: G, glassy; Ch, cholesteric; and I, isotropic. Polarizing optical microscopy image exhibiting oily streaks.

of right- and left-handed chiral-nematic glassy liquid crystals containing a benzene core with desired phase transition temperatures. Acknowledgment

Figure 3. Transmission spectra with right- and left-handed circularly polarized (RCP and LCP) incident, and reflection spectrum with unpolarized incident on a 4 µm thick glassy-nematic film of I.

potentially useful for the fabrication of nonabsorbing polarizers, optical notch filters and reflectors, and polarized light sources. Chiral-nematic liquid crystals have been synthesized by a statistical or a deterministic approach. A deterministic approach is characterized by relative ease of product separation and purification and hence is more amenable to process scale-up in comparison to a statistical approach. With an objective of reducing the effort involving protection and selective deprotection of benzoic acid groups, the present work has demonstrated the feasibility of dihydrolysis of trimethyl 1,3,5benzenetricarboxylate and the selective dealkylation of methyl benzoate by lithium iodide. In consequence, the number of synthesis steps is reduced from six to four with an improved overall product yield as compared to a previously reported synthesis scheme. As an illustration of the new scheme, a chiralnematic glassy liquid crystal comprising a benzene core with two nematic and one chiral pendants, both consisting of a cyanobiphenyl group, was synthesized and characterized to possess a glass-transition temperature at 63 °C, a clearing point at 130 °C, and a selective reflection wavelength at 420 nm. The new methodology is applicable to the synthesis of a variety

The authors thank Prof. Robert Boeckman in the Chemistry Department at the University of Rochester for helpful suggestions regarding organic synthesis, Dr. Philip Chen and Mr. Chunki Kim for assistance in the synthesis of some intermediates, and Mr. Kenneth L. Marshall and Prof. Stephen D. Jacobs of the Laboratory for Laser Energetics for assistance in material characterization. The authors are grateful for the financial support provided by the National Science Foundation under CTS-0204827 and the Office of Naval Research under N0001403-C-0418, an STTR program with Cornerstone Research Group, Inc. in Dayton, OH. Additional funding was provided by the Department of Energy, Office of Inertial Confinement Fusion, under Cooperative Agreement DE-FC03-92SF19460 with the Laboratory for Laser Energetics, and the New York State Energy Research and Development Authority. Literature Cited (1) Angell, C. A. Science 1995, 267, 1924. (2) Debenedetti, P. G.; Stillinger, F. H. Nature 2001, 410, 259. (3) (a) Tsuji, K.; Sorai, M.; Seki, S. Bull. Chem. Soc. Jpn. 1971, 44, 1452. (b) Sorai, M.; Seki, S. Bull. Chem. Soc. Jpn. 1971, 44, 2887. (4) Wedler, W.; Demus, D.; Zaschke, H.; Mohr, K.; Schafer, W.; Weissflog, W. J. Mater. Chem. 1991, 1, 347. (5) Loddoch, M.; Marowsky, G.; Schmid, H.; Heppke, G. Appl. Phys. B 1994, 59, 591. (6) Rauch, S.; Selbmann, C.; Bault, P.; Sawade, H.; Heppke, G.; MoralesSaavedra, O.; Huang, M. Y.; Ja´kli, A. Phys. ReV. E 2004, 69, 021707. (7) Attard, G. S.; Imrie, C. T. Liq. Cryst. 1992, 11, 785. (8) Dehne, H.; Roger, A.; Demus, D.; Diele, S.; Kresse, H.; Pelzl, G.; Wedler, W.; Weissflog, W. Liq. Cryst. 1989, 6, 47. (9) Attard, G. S.; Imrie, C. T.; Karasz, F. E. Chem. Mater. 1992, 4, 1246. (10) Tamaoki, N.; Kruk, G.; Matsuda, H. J. Mater. Chem. 1999, 9, 2381. (11) (a) Kreuzer, F. H.; Andrejewski, D.; Haas, W.; Haberle, N.; Riepl, G.; Spes, P. Mol. Cryst. Liq. Cryst. 1991, 199, 345. (b) Kreuzer, F. H.; Maurer, R.; Spes, P. Macromol. Chem., Macromol. Symp. 1991, 50, 215.

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ReceiVed for reView January 4, 2006 ReVised manuscript receiVed April 8, 2006 Accepted April 19, 2006 IE060015R