Modulation of Intersystem Crossing Rate Induced by Singlet-triplet Energy Level Alignment in 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene Single Crystals

In this study, we investigated the photophysical properties in a single crystal (SC) state. We found that the forward intersystem crossing (ISC) and reverse ISC rate constants (kISC and kRISC) of a 4CzIPN-SC are one order magnitude higher than that of the amorphous film. Further, an unusual long-lived emission component was observed in 4CzIPN-SC, indicating that the excitons generated by optical excitation spontaneously dissociate into free carriers in 4CzIPN-SC.