Polymerization-Induced Liquid Crystallinity With Broadened Mesophase Temperature Range in Side-Chain Polymers Incorporating Photoresponsive 4-Cyanoazobenzene Units.

A series of 4-cyanoazobenzene containing monomers and their corresponding side-chain polymers with different polymer backbones and alkoxy spacer lengths were analyzed to investigate the influence of polymer backbones on the thermotropic liquid crystalline behavior. The solid-state features of the monomers were elucidated by single crystal X-ray diffraction, revealing the presence of C─H···X (X = O/N/F), C─X···π (X = H/O) and π···π interactions. Hirshfeld surface and energy framework analysis further demonstrated that dispersion interactions are the dominant contributor to the overall crystal packing. Thermal analysis of the acrylate and 2-fluoroacrylate based monomer indicated the presence of nematic mesophase over a narrow temperature window (1°C-2°C), whereas the methacrylate-terminated monomers did not display liquid crystalline behavior. In contrast, polymerization resulted in a significantly broadened nematic mesophase range exceeding 70°C, highlighting the critical role of the polymer backbone in mesophase stabilization. Further, the monomers displayed photoinduced nematic-isotropic phase transition upon irradiation with 365 nm UV light. Additionally, the monomers and polymers exhibited reversible trans ↔ $ \leftrightarrow $ cis isomerization in solution under 365 nm UV and 510 nm visible light irradiation, achieving up to 90% conversion efficiency. These findings underscore the role of the polymer backbone in promoting liquid crystallinity and photoresponse toward the development of stimuli-responsive materials.