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

ABSTRACT 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 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.