Synthesis and liquid crystal behaviour of tetrathiafulvalenes/1,3-dithiol-2-thione and p-cyanoazobenzene

Abstract

ABSTRACT The synthesis and characterisation of tetrasubstituted tetrathiafulvalenes (TTFs) 1a–1c, which bear photoresponsive 4ʹ-cyanoazobenzenyl units, are described. These units were linked to the TTF core through spacers of different lengths. All synthesised compounds displayed mesogenic phases over a wide temperature range and no crystallisation, but vitrified to form glassy mesogens during cooling from the isotropic melt. Compound 1a with a short spacer (n = 6) exhibited enantiotropic nematic and smectic A mesophases. In contrast, compound 1b showed monotropic smectic A and oblique columnar phases. However, compound 1c with the longest spacer (n = 10) only possessed an oblique columnar phase. The results for this compound series showed that the molecular packing pattern depended on the spacer length and that cool-crystallisation was observed upon further heating. Furthermore, cyclic voltammetry and impedance tests confirmed that compound 1a has potential applications in organic semiconductor materials. A new series of compounds derived from heterocycle TTF was successfully designed and synthesised using simple synthetic methods. All compounds formed glassy mesogens with an above-ambient glass transition temperature during cooling from the isotropic melt. With increasing spacer length, the self-assembled structures changed from Lam to Colo. These TTF‐based LCs, in combination with good electron-donating properties and the inherent optoelectronic properties of azobenzene, might be attractive new candidates for organic optoelectronic devices.