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 of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) 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. Comprehensive photoluminescence properties of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) in a single-crystal state are reported. We found that a 4CzIPN single-crystal has forward and reverse intersystem crossing rate constants that are one order of magnitude greater than those of the amorphous film. Further, an unusual longlived emission was observed in the single-crystal, indicating that the 4CzIPN excitons spontaneously dissociate into free carriers.