Homologous series of liquid crystals with re-entrant nematic and two smectic A phases

Dielectric Studies of Monolayer Smectic A Phases of Strongly Polar Liquid Crystals

“…The discovery of reentrant nematic in compounds whose molecules possess a strongly polar end group led to considerable activity in the synthesis of terminally cyano-or nitro-substituted triaromatic compound^.^ Amongst the first such compounds to be synthesised were 4-octyloxybenzoyloxy-4'-cyanostilbene (T8) by the Bordeaux Group3 and 4-nonyloxybenzoyloxy-4'-cyanoazobenzene (90BCAB) by Heppke et al 5 In both these cases the interesting result was found that in addition to the nematic, smectic A and reentrant nematic phases, there was a second smectic A at the lowest temperature. Although initially referred to as the reentrant smectic A, it has since been shown to be a monolayer A (A,) phase with a layer spacing (d) > the molecular length (e) in contrast to the higher temperature partially bilayer (A,,) phase wherein C < d < 2 C. Thus it was clear that compounds whose molecules possess a strongly polar end group can exhibit both A, and A,, phases.…”

From the discovery of the partially bilayer smectic A phase to blue phases in polar liquid crystals

“…French scientists in the late 1970s and early 1980s [59][60][61][62][63][70][71][72][73][74][75][76][77][78][79][80][81][82] (and soon others [83][84][85][86]) synthesised many families of three-ring compounds terminated with polar CN or NO 2 groups and with different bridge groups (COO, N = N, CH = CH, CH = N, CH 2 -CH 2 ) between the aromatic rings. A very rich polymorphism of SmA phases as well as the presence of enantiotropic N re below SmA d phase is observed.…”

“…The SmA 1 layer spacings were insignificantly smaller than molecular length (d/l = 0.93-0.96). [38,39] Three-ring benzoyloxycyanostilbenes (members n = 1-12) were prepared by Heppke et al [83,86] The SmA 1 phase was observed for all members of the homologous series but its stability increased till n ≤ 6 and for n > 6 the stability decreased. The SmA d phase appeared for n = 9, and its temperature interval was enhanced at the side of lower as well as higher temperature range with increase of n.…”

Liquid Crystals Transition Temperature of 4-N-Alkoxy-2,3,5,6-Tetramethylphenyl-4 –Nitroazobenzene.

“…aromatic rings, broadening groups and substituted groups on the properties of liquid crystals in homologous series, especially phase-transition, had been studied extensively using different techniques [1][2][3][4][5] . It was found that liquid crystal phase is more sensitive to molecular geometry and that could be explained due to its more ordered structure on the surface.…”