Low-temperature nematic phase in azo functionalised reactive hockey stick mesogens possessing lateral methyl group

Abstract

We report, the design, synthesis and mesomorphic behaviour of new hockey stick mesogens containing photochromic azo group and a reactive double bond. The structure of the compounds resemble the hockey stick due to unequal distribution of the phenyl rings in the two arms of the molecule and possess a reactive 4-n-undecenyloxy chain attached at short arm of the bent-core molecule, while the elongated arm consists of a small methoxy group and photochromic azo linkage between two phenyl rings. All the compounds exhibit a wide-range of enantiotropic nematic phase at low temperature. The photo-responsive behaviour of nematic phase was characterized by polarising optical microscopy with in situ white light irradiation. Upon irradiation, the nematic phase almost completely disappeared in about 20s. We have also investigated the effect of the position of methyl group substitution at the outer phenyl ring of the elongated arm of the molecule on the nematic phase of azo functionalised compounds. Our theoretical calculations predict that different position of methyl group does not bring any significant change in reactivity profile, electronic properties and spectroscopic properties. Irrespective of the position of a methyl group, trans conformation has slightly greater stability as well as less reactivity than cis conformation.