New thermotropic chiral nematic copolymers. 2. A study of helical sense and twisting power based on copolymers containing (S)-(-)-1-phenylethanol and (R)-(-)-methyl mandelate

Krishnamurthy, Sushil; Chen, Shaw H.

doi:10.1021/ma00012a003

Cited by 13 publications

(5 citation statements)

References 2 publications

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“…Specifically, it is difficult to relate physical parameters invoked in theories to real chemical systems. As an alternative approach, chirahematic molecular interaction models of a steric origin have been constructed to elucidate handedness in low molar mass 128,291 as well as side chain polymeric systems [30]. In what follows, an attempt will be made to furnish new insights into the chiral nematic mesomorphism via the synthesis and characterization of novel GLMLCs that also hold promise for practical applications.…”

Section: Introductionmentioning

confidence: 99%

Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

Shi¹,

Chen²

1995

Liquid Crystals

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Based on nematic and chiral precursors comprising of acetylenic, phenyl, naphthyl and terminal cyan0 groups in conjugation and cyclohexane as the central core, a series of novel nematic and chiral nematic glass-forming liquid crystals with a T . 3 6 0°C were synthesized for an investigation of handedness and helical twisting power, HTP, as functions of chemical structure.Three chiral building blocks with a single asymmetric carbon Centre were employed: (S)-( -)-1-phenylethanol, (9-( -)-u-methyl-2-naphthalenemethanol, and (S)-( -)-1-phenylethylamine, were all found to yield a left-handed cholesteric mesophase. With reference to (5')-( -)-1-phenylethanol, the HTP value was found to be nearly doubled in the presence of a strong anchoring plane furnished by a naphthyl group surrounding the asymmetric carbon centre, but reduced by one third in the presence of intermolecular hydrogen bonding through the amide group. All these observations were properly accounted for by a molecular interaction model of a steric nature while allowing for hydrogen bonding. Consistent with previous observations on naturally occurring ( -)-cholesterol, ( + )-estrone was found to give a left-handed cholesteric mesophase and an HTP value a quarter of that of (8-( -)-1-phenylethanol under otherwise identical structural settings, both remaining unaccounted for from a molecular point of view. The cyclohexane ring to which chiral as well as nematic precursors are attached was found to improve miscibility with cyclohexane-based nematic hosts and to elevate the T . of the blends with an improved morphological stability but a very modest increase in HTP, all in comparison to c h i d precursors as the dopant. The optical elements prepared on a single glass substrate and between a pair of substrates using the presently reported materials showed broad selective wavelength reflection bands with a monodomain feature characterized by pronounced side band oscillations.

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Section: Introductionmentioning

confidence: 99%

Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

Shi¹,

Chen²

1995

Liquid Crystals

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“…It is evident that the chemical structures of the low molar mass analogues closely resemble the repeat units of the nematogenic and chiral components in the copolymers synthesized for this work and those reported earlier. 27 Although LMMAl showed an endotherm at 323 47.51 J/g 447 K 2.02 J/g 325 375 425…”

Section: Resultsmentioning

confidence: 96%

A comparative study of helical sense and twisting power in low-molar-mass and polymeric chiral nematics

Krishnamurthy¹,

Chen²

1992

Macromolecules

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The issues of helical sense and helical twisting power (HTP) have been addressed using low molar mass analogues of chiral nematic copolymers containing (S)-(+)-2-methoxy-2-phenylethanol, (S)-(-)-1-phenylethanol, and (R)-(-)-methyl mandelate. As reported by other workers, it is found that the empirical rules proposed by Gray et al. for interpreting helical sense are limited in scope. However, the handedness observed in the new copolymeric system and that of the copolymers reported earlier are consistent with the low molar mass counterparts. The HTP's of chiral nematic mixtures based on (S)-(-)-1 -phenylethanol and (/Z)-(-)-methyl mandelate are much lower than those of the corresponding copolymeric structures reported earlier, which is attributed to hindered rotation imposed by polymerization. In contrast, chiral nematic mixtures containing (S)-(+)-2-methoxy-2-phenylethanol show an HTP value only slightly lower than that of the copolymer. In addition, for all three systems, the selective reflection wavelength is observed to increase with decreasing temperature, consistent with Keating's model and with the molecular statistical theory of Kimura et al.

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“…22 Whereas handedness of a chiral-nematic film is related to the absolute configuration of the chiral pendant, no correlation between the two has been established. 23 To determine the handedness presented by films of III-x containing (S)-(-)-1-phenylethanol, the transmittances of both left-and right-handed circularly polarized light at normal incidence were measured, as illustrated with a film of III-0.12 in Figure 3c. Since left-handed circularly polarized light is selectively reflected, it is concluded that the film prepared with III-x presents a left-handed, helical stack of quasinematic layers.…”

Section: Resultsmentioning

confidence: 99%

Thermotropic Chiral−Nematic Poly(p-phenylene)s as a Paradigm of Helically Stacked π-Conjugated Systems

et al. 2000

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As an emerging class of multifunctional optical materials, chiral-nematic poly(pphenylene)s with cyanobiphenyl and (S)-1-phenylethyl pendants were synthesized and characterized. Nematic homopolymer was also synthesized for preparation into a uniaxially aligned film. Linearly polarized photoluminescence (LPPL) and FTIR dichroism revealed that both the conjugated backbone and the nematic pendant are oriented along the director with an orientational order parameter, S ) 0.62 and 0.73, respectively. Films prepared with chiral-nematic copolymers were found to selectively reflect left-handed circularly polarized light in the ultraviolet, visible, and infrared region at a decreasing chiral content. The helically stacked poly(p-phenylene)s were further characterized in terms of circularly polarized photoluminescence (CPPL). On the basis of a recent theory, S ) 0.67 was found for the orientational order of conjugated backbones within quasinematic layers comprising the chiral-nematic film. Within experimental uncertainty, the S values determined with the LPPL and CPPL techniques are in good agreement, thereby validating the proposed supramolecular structure on the basis of which theories governing light absorption, emission, and propagation in structured media were constructed.

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New thermotropic chiral nematic copolymers. 2. A study of helical sense and twisting power based on copolymers containing (S)-(-)-1-phenylethanol and (R)-(-)-methyl mandelate

Cited by 13 publications

References 2 publications

Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

Novel glass-forming liquid crystals. III Helical sense and twisting power in chiral nematic systems

A comparative study of helical sense and twisting power in low-molar-mass and polymeric chiral nematics

Thermotropic Chiral−Nematic Poly(p-phenylene)s as a Paradigm of Helically Stacked π-Conjugated Systems

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