Structure-property relationships in azobenzene-based twist-bend nematogens

The synthesis and characterisation of a new set of azobenzene-based non-symmetric liquid crystal dimers, the 1-(4-substitutedazobenzene-4MODIFIER LETTER PRIME-yloxy)-6-(4-methoxybiphenyl-4MODIFIER LETTER PRIME-yl)hexanes (MeOB6OABX), that exhibit the twist-bend nematic phase, N-TB, is described. The terminal substituents are methyl, methoxy, ethyl, butyl, butoxy, and nitrile. All six dimers exhibit both the N-TB and conventional nematic, N, phases. The identification of the N-TB phase was performed using polarised light microscopy and confirmed for binary mixtures with a standard twist-bend nematogen 1,7-bis-4-(4MODIFIER LETTER PRIME-cyanobiphenyl) heptane (CB7CB). The transitional behaviour of the MeOB6OABX dimers is compared with that of the corresponding ether-linked 1-(4-substitutedazobenzene-4MODIFIER LETTER PRIME-yloxy)-6-(4-methoxybiphenyl-4MODIFIER LETTER PRIME-yloxy)pentanes, MeOBO5OABX, all of which exhibit a conventional nematic phase. In addition, the nitrile-substituted MeOBO5OABCN shows the N-TB phase. The behaviour of these non-symmetric dimers is also compared to that of the corresponding symmetric dimers. Differences in the transitional properties between these sets of new materials are accounted for in terms of not only molecular shape but also other factors including the strength of the mixed mesogen interaction.