On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants

Abstract

A series of achiral hockey stick-shaped mesogens forming tilted smectic liquid crystal phases of synclinic SmC-as well as anticlinic SmC a -type was prepared and characterized. While all homologues exhibit both phases, the balance shifts from anticlinic to synclinic order upon 10 elongation of the terminal chain at the meta (m) position, defining the hockey stick shape. The elongation also leads to an increased kinetic hindrance of the transition between syn-and anticlinic phases and a decreased transition enthalpy. These observations indicate that a well-defined kink (short m-substituted chain) promotes the anticlinic structure while a higher flexibility between kinked and rod-shape (long m-substituted chain) promotes synclinic order. An intermediate chain-15 length homologue was selected as host material for doping with syn-and anticlinic rod-shaped chiral dopants, respectively, at varying concentrations. Opposite of what might be expected the balance between syn-and anticlinic order was not simply dictated by the choice of dopant. Instead both types of tilting order prevailed with roughly the same strength as in the achiral host regardless of which chiral material was added, up to concentrations well beyond normal doping conditions. 20Thus, at least with hockey stick-shaped achiral hosts, syn-as well as anticlinic chiral compounds can be used effectively as chiral dopants without necessarily having an important impact on the clinicity of the resulting mixture. The hockey stick design concept should be useful in producing achiral anticlinic-forming mesogens for low-polarization, long-pitch antiferroelectric liquid crystal mixtures. Finally, we point out that a mixture study like the one carried out here yields a 25 conclusive means of establishing the clinicity of achiral tilted smectics, an endeavour that can sometimes be far from trivial.

Photochromic azobenzene functionalised banana–calamitic dimers and trimers: mesophase behaviour and photo-orientational phenomena

“…This dimorphism is only rarely observed for non-chiral compounds. It has been reported for hockey stick-shaped mesogens [96][97][98][99][100][101][102][103] and terminally branched mesogens [104][105][106]. For these compounds the sequence SmC s -SmC a was reported on cooling that is, surprisingly, opposite to the sequence of the dimers 1b and 1c which is SmC a -SmC s with decreasing temperature.…”

“…The dimers 1b and 1c and several hockey stick-shaped compounds exhibit the rare synclinicanticlinic SmC phase transition [96][97][98][99][100][101][102][103]. For both types of materials, this phase transition is characterised by strong turbulences in the textures and by low transition enthalpies.…”

Preparation and Study of the Electro-optical Properties of Binary Mixtures of Orthoconic Anti-ferroelectric Esters and Achiral Phenyl Pyrimidine Liquid Crystal

“…Potential applications of these mixtures for light shutter, photonics, telecommunication and high speed micro-display are foreseeable where a broad temperature range, low polarization and long pitch are desired [43,44]. Potential applications of these mixtures for light shutter, photonics, telecommunication and high speed micro-display are foreseeable where a broad temperature range, low polarization and long pitch are desired [43,44].…”

Chemical Structures, Mesogenic Properties, and Synthesis of Liquid Crystals with Bent‐Core Structures

“…Yu et al [119c] were able to stabilize the SmCa phase both by modulating the length of the chain (n: 4-10) in the meta-position and by increasing the number of aromatic rings from 3 to 4 while fixing an n-dodecyloxy chain in the para-position. These authors -along with Enz et al [120] -proved that short terminal chains in the meta-position favor anticlinic arrangements whereas terminal chains that are too long, promote synclinic organizations when the chain in the para-position is fixed at 10 or 12 carbon atoms. However, this trend can be changed when a methyl group is introduced orthoto the meta-located chain, [121] resulting in suppression of the SmCs phase for the shorter chains and wide ranges of N-SmCa mesomorphism for the longer ones.…”