Phase-Transition-Induced Fluorescence Changes in a Calamitic Liquid Crystal With an AIEgen Mesogen

Aggregation-induced emission (AIE) luminogens have attracted considerable attention because of their environmental responsiveness. In particular, combining AIE with liquid crystals holds promise for multifunctional materials, but this area remains underexplored. Here, we investigate the photophysical properties of 3,8-bis(4-hexylphenyl)-6,7-dihydro-5H-benzo[7]annulene (DPB[7]-C6), which exhibits smectic A (SmA) and nematic (N) phases as well as AIE behavior. Temperature-dependent fluorescence spectroscopy revealed that the fluorescence intensity shows a distinct change at the SmA-N transition. To elucidate the origin of this distinct change, the temperature dependences of the absorbance, fluorescence quantum yield, and orientational order were examined, showing that the observed change originates from variation in the quantum yield. These results suggest that the accessibility of the conical intersection (CI) is enhanced in the N phase. This study reveals a clear correlation between liquid-crystalline phase morphology and the photophysical processes of AIE luminogens and highlights their potential as single-component, stimuli-responsive materials.