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

Abstract

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.