Precision engineering of cholesteryl azobenzene dimers: investigating the impact of spacer lengths and terminal groups on photo-responsiveness

Abstract

The rational molecular engineering of cholesteryl azobenzene dimers provides an effective strategy for designing precisely tunable photo-switchable materials with controllable chiral optical responses. This study systematically explores how spacer length parity and terminal group polarity dictate phase transitions, helical twisting power (HTP) and photoisomerization kinetics of cholesteryl azobenzene dimers, enabling predictive control over their functional performance. A key finding is an odd–even effect of the spacer length, which determines the sign of the helical twisting power change in liquid crystals (LC) upon UV irradiation. Dimers with odd-parity spacers exhibit lower LC compatibility in their cis-conformation, resulting in reduced HTP values. In contrast, even-parity dimers, with their larger molecular aspect ratios, tend to promote the formation of smectic clusters that reversibly assemble and disassemble during photoisomerization, which leads to a higher effective HTP in the cis-conformation. By integrating molecular design with dynamic self-assembly, this study advances the engineering of chiral dopants for cholesteric liquid crystals tailored to adaptive photonic materials and reconfigurable optical systems, underscoring the role of precise molecular modifications in achieving controllable functionality of cholesteryl azobenzene dimers. This is expected to promote the development of photo-responsive LCs with tunable optical properties and practical applications in adaptive photonic technologies.