Contribution of Radiative Rate Constants to Crystallization-Induced Emission Enhancement in Boron-Fused Azobenzene Complexes

Analysis of emission enhancement in an aggregated state has been developed by focusing on suppression of nonradiative processes by intermolecular interactions. On the other hand, it is difficult to evaluate contribution of radiative processes despite its significant role in improving emission. Herein, the contribution of radiative processes to crystallization-induced emission enhancement (CIEE) is evaluated. By comparing optical properties between isolated and crystalline states at 77 K to minimize structural relaxation, acceleration phenomena of the radiative process originating from the intermolecular interactions in crystal are clarified. Consequently, it is experimentally proved that a large refractive index in an organic crystal mainly promotes the radiative processes in CIEE even without significant intermolecular electronic interactions.