Photoswitchable carbosilane-based polycatenars forming nematic, tilted smectic, hexatic, and cubic liquid crystalline phases

Abstract

This study introduces a novel class of non-symmetric photoswitchable polycatenar liquid crystals (LCs) designed to investigate the influence of terminal chain architecture on mesophase behaviour and photo switching properties. These molecules feature a photoresponsive azobenzene core with distinct end groups: a linear alkoxy chain at one end and a branched carbosilane moiety, connected via an aliphatic spacer of varying length, at the other end. This non-symmetry promotes the formation of diverse LC phases, including nematic (N), smectic C (SmC), hexatic I (HexI), and a bicontinuous cubic phase with Ia[3 with combining macron]d space group (Cubbi/Ia[3 with combining macron]d). Small- and wide-angle X-ray scattering confirmed the presence of all observed LC phases. Comparison with the previously reported compounds having the flat taper-shaped 3,4,6-trialkoxyaryl substitution pattern instead of the tetrahedral carbosilane branching highlights the critical role of chain topology in controlling molecular self-assembly. UV-vis spectroscopy and polarized optical microscopy confirm efficient and reversible photoisomerization in solution and the bulk LC state, with light-triggered phase transitions (N ↔ Iso, SmC ↔ N). These results offer a promising pathway for designing advanced functional soft materials with integrated photoswitchable and structural complexity.