Preparation of chiral luminescent liquid crystals and manipulation effect of phase structures on the circularly polarized luminescence property

Realizing a larger luminescence asymmetry factor (glum) and a higher solid-state luminescence quantum yield are vital for promoting the application of circularly polarized luminescence (CPL) materials; however, they are challenging to achieve. This study utilizes the chirality amplification effect from chiral liquid crystals and the intense solid-state emission feature from aggregation-induced emission enhancement (AIEE) fluorophores to generate a high efficiency CPL-active chiral luminescent liquid crystal (NO2-CS-C6-Chol). During annealing, cholesteric phase, chiral smectic C (SmC*) phase and crystalline phase were observed successively. To suppress the strong thermo-activated nonradiative decay, we froze the assembly structure of the cholesteric phase and SmC* phase with liquid nitrogen. As a result, the cholesteric film (State C), SmC* film (State B) and crystalline film (State A) stable at room temperature were obtained. The study focuses on the photophysical properties in different phase state films, particularly the impact of phase structures on the properties of CPL. The results show that NO2-CS-C6-Chol presented a large glum value and excellent fluorescence efficiencies in State C and B, while no CPL signal was detected in State A. Based on the thermo-driven phase transition feature of NO2-CS-C6-Chol, CPL can switch from one state to the other two states at our will, indicating the significant manipulation effect of phase structures on the CPL properties. This work is conducive to deeply understand the generation and amplification mechanisms of chirality.