Asymmetric dimeric liquid crystals with charge transfer groups

Attard, George S.; Garnett, Sarah P.; Hickman, Christopher G.; Imrie, Corrie T.; Taylor, L.

doi:10.1080/02678299008033826

Cited by 69 publications

(24 citation statements)

References 13 publications

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“…The reason for this is quite simple ± the description of the phase behaviour did not refer to the type of mesogenic units in the non-symmetric dimer nor did it consider the nature of the mixed interaction. Similar behaviour was indeed found for the NABOnO.4 series [70], 14 for which DT SC is initially relatively large and negative, becoming more positive as n is increased. If the non-symmetric dimer does not contain a terminal chain then DT SC would be predicted to be small and positive for all spacer lengths and such behaviour is seen for the a-(4-cyanobiphenyl-4¢-yloxy)-x-(1-pyreniminebenzylidene-4¢-oxy)alkanes [71], 15 whose clearing temperatures can be compared with those of the BCBOn series [18] and the a,x-bis(1-pyreniminebenzylidene-4¢-oxy)alkanes [104].…”

Section: Non-symmetric Calamitic Liquid Crystal Dimerssupporting

confidence: 79%

Liquid Crystal Dimers

Imrie

1999

Structure and Bonding

230

104

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A liquid crystal dimer is composed of molecules containing two conventional mesogenic groups linked via a¯exible spacer. These materials show quite different behaviour to conventional low molar mass liquid crystals and in particular their transitional behaviour exhibits a dramatic dependence on the length and parity of the¯exible spacer. In this review a comprehensive overview of the relationships between molecular structure and liquid crystallinity in dimers is provided. This includes a description of the novel modulated and intercalated smectic phases exhibited by dimers.

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Section: Non-symmetric Calamitic Liquid Crystal Dimerssupporting

confidence: 79%

Liquid Crystal Dimers

Imrie

1999

Structure and Bonding

230

104

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“…The smectic A-chiral nematic transition temperatures for n = 10, 11 and 12 for the Chol-n-SS-n-Chol series show the same odd−even trend as the melting point and T NI . For conventional liquid crystal dimers, both symmetric [48] and non-symmetric [50,51], the alternation in T SmAN tends to attenuate on increasing the length of the spacer.…”

Section: Resultsmentioning

confidence: 95%

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

Lee¹,

Lü²,

Henderson³

et al. 2012

Liquid Crystals

129

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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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“…4-Methoxy-4'-hydroxyazobenzene, 1, was synthesized according to the method described by Stewart and Imrie [34], and the a-bromov-(4-methoxyazobenzene-4'-oxy)alkanes, 2, were synthesized using the method described by Attard et al [35].…”

Section: Methodsmentioning

confidence: 99%

Oligomeric liquid crystals: From monomers to trimers

2004

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A homologous series of linear liquid crystal trimers, the 4,4'-bis[v-(4-methoxyazobenzene-4'-yloxy)alkoxy]azobenzenes, has been synthesized and characterized. The transitional properties of the trimers are compared with those of the corresponding series of dimers, the a,v-bis(4-methoxyazobenzene-4'-oxy)alkanes, and monomers, the 4-methoxy-4'-alkoxyazobenzenes. Characteristically pronounced odd-even effects were seen for the transitional properties of both dimers and trimers on varying the spacer lengths. The clearing temperatures of the trimers were higher than those of the corresponding dimers, but as the length of the flexible spacers was increased this difference became rather small. The ratios of T NI , and DS NI /R for monomer:dimer and dimer:trimer are discussed. These are very similar to reported values for similar materials, suggesting that there may be a rather general relationship between the transitional properties of liquid crystal oligomers as the number of mesogenic units is increased.

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Asymmetric dimeric liquid crystals with charge transfer groups

Cited by 69 publications

References 13 publications

Liquid Crystal Dimers

Liquid Crystal Dimers

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

Oligomeric liquid crystals: From monomers to trimers

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