Side-chain chiral fluorescent liquid crystal polymers with highly efficient circularly polarized luminescence emission in a glassy-state SmC* film

How to improve the performance of circularly polarized luminescence (CPL) materials in the film state is a significant subject to realize their further application. Herein, we synthesized side-chain chiral fluorescent liquid crystalline polymers (namely PMCmCSChol, where m represents the length of the rgw spacer between the rgw backbone and side-chain, m = 6, 8, or 10) by taking cyanostilbene with aggregation-induced emission enhancement (AIEE) properties as a mesogen and cholesteryl as a chirality unit. The aim is to unite the chirality amplification effect of chiral liquid crystals and the high solid-state emission efficiency of AIEE fluorophores to realize highly efficient CPL emission. The studies show that all polymers not only inherit the AIEE properties from cyanostilbene, but can also self-assemble into helical-stacking chiral smectic C (SmC*) phase under chirality induction. As a result, they present excellent solid-state fluorescence efficiency, and strong CPL signals are detected in the polymeric glassy-state SmC* film. Notably, the emission efficiency and CPL behavior strongly depend on the spacer length. The longer the spacer length, the higher the solid luminous efficiency, and the larger the g(lum) value. The maximum of the solid luminous efficiency and g(lum) can reach 15.3% and -0.037 for PMC10CSChol. This study unfolds a practical avenue for fabricating high-efficiency non-doped CPL polymer materials in the film state with modulated optical properties.