Symmetric and non-symmetric liquid crystal dimers with branched terminal alkyl chains: racemic and chiral

Blatch, A. E.; Fletcher, I. D.; Luckhurst, G. R.

doi:10.1039/a602980i

Cited by 92 publications

(57 citation statements)

References 15 publications

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“…This may be accounted for in terms of the increased biaxiality of the cholesteryl-based unit compared to conventional rod-like mesogenic units such as, for example, cyanobiphenyl. Reduced values of S NI /R have also been observed for liquid crystal dimers containing branched terminal chains [26,54] or dimers in which the biaxiality of the mesogenic groups has been increased [55][56][57].…”

Section: Resultsmentioning

confidence: 82%

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Lee¹,

Lü²,

Henderson³

et al. 2012

Liquid Crystals

130

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Seven members of the homologous series of the liquid crystal dimers, the bis(ω-(cholesteryloxycarbonyl)alkyl) disulfides, which contain a sulfur−sulfur link in the flexible spacer have been synthesised and their liquid crystal properties characterised. The dimers are referred to using the acronym Chol-n-SS-n-Chol in which n denotes the number of carbon atoms linking the cholesteryl-based groups and the sulfur atoms, and was varied between 3, 5, 6, 8, 10, 11 and 12. All seven homologues exhibit a chiral nematic phase and for the longest three members a smectic A phase was also observed. An odd−even effect is apparent in both the transition temperatures and the values of the entropy change associated with the chiral nematic−isotropic transition, S N * I /R, in which dimers with even values of n show the higher values. This is interpreted in terms of the average molecular shapes in which the C−S−S−C dihedral angle is around 90 • . The values of S N * I /R shown by these dimers are very small for liquid crystal dimers and this is attributed to the increased molecular biaxiality arising from the C−S−S−C dihedral angle. The smectic A phase exhibited by the homologues with n = 10, 11 and 12 is proposed to consist of an intercalated arrangement of the dimers which is driven by the mismatch in cross-sectional areas of the cholesteryl-based groups and alkyl chains.

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Section: Resultsmentioning

confidence: 82%

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Lee¹,

Lü²,

Henderson³

et al. 2012

Liquid Crystals

130

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show abstract

“…For example, recent investigations by Marcelis et al [11,12,14] and Tamaoki and coworkers [22] on such dimers have shown that the selective reflection wavelength of the N* phase displays an oddeven effect as a function of the parity of the interlinking spacer. In fact, Luckhurst and co-workers have also reported analogous results for chiral dimers without cholesterol entity [31]. Remarkably, photolysis of the supercooled N* phase formed by dimers comprising cholesterol-azobenzene leads to a hypsochromic shift (decrease) in the reflected wavelength indicating that the pitch of the helical structure can be photo controlled.…”

Section: Optical Properties Of the Chiral Nematic Phasementioning

confidence: 67%

Mesomorphic chiral non‐symmetrical dimers: synthesis and characterization

Yelamaggad

Shanker

2007

Liquid Crystals

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The preparation and phase transitional properties of several optically active non-symmetrical dimers are reported. Two types of dimeric mesogens formed by covalently combining promesogenic cholesterol with either phenyl 4-cyanobenzoate (polar) or phenyl trans-4-pentylcyclohexanecarboxylate (apolar) cores in an end-to-end fashion through an voxyalkanoyl spacer were investigated. The phase behaviour of these two types of dimers differs, indicating that the nature and extent of mesomorphism are sensitive to the structure of the mesogen attached to the cholesterol. However, within the series, the spacer parity greatly influences the clearing temperatures of the materials, as expected. In general, all the compounds display an enantiotropic chiral nematic (N*) phase; several of them also stabilize smectic and/or twist grain boundary phases. The optical properties of the N* phase of all the compounds were investigated with the aid of both UV-visible and chiroptical spectroscopic techniques. These complementary studies revealed that the dimers exhibit an odd-even effect in the wavelength of selective reflection, with even-parity members having higher values, similar to previous reports. The chiroptical spectroscopy indicated that the N* pitch is righthanded for all the investigated dimers, which is in accordance with the fact that most steroidal esters are right-handed.

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“…For low molar mass mesogens, reductions in the entropy change associated with the liquid crystal-isotropic transition are most often interpreted in terms of an increase in the molecular biaxiality arising from, for example, chain branching (Yeap et al, 2009;Imrie, 1989) or changes to the mesogenic core structure Donaldson et al, 2010;Blatch et al, 1997). Such an interpretation, however, cannot account for the entropy changes seen here.…”

Section: Resultsmentioning

confidence: 83%

Carbohydrate liquid crystals: Synthesis and characterisation of the methyl-6-O-(n-acyl)-α-d-glucopyranosides

Cook

Wardell

Imrie

2011

Chemistry and Physics of Lipids

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Symmetric and non-symmetric liquid crystal dimers with branched terminal alkyl chains: racemic and chiral

Cited by 92 publications

References 15 publications

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Cholesteryl-based liquid crystal dimers containing a sulfur–sulfur link in the flexible spacer

Mesomorphic chiral non‐symmetrical dimers: synthesis and characterization

Carbohydrate liquid crystals: Synthesis and characterisation of the methyl-6-O-(n-acyl)-α-d-glucopyranosides

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