Origin of Dual-Peak Phosphorescence and Ultralong Lifetime of 4,6-Diethoxy-2-carbazolyl-1,3,5-triazine

Abstract

Recently, ultralong phosphorescence lifetime has been observed in 4,6-diethoxy-2-carbazolyl-1,3,5-triazine, and H-aggregation induced stabilization of the T1 state was suggested as its source. The response theory calculations demonstrate that the Davydov stabilization of the T1 state of the dimer is marginal with respect to the monomer and the corresponding transition moments are virtually the same. Moreover, the calculated radiative rate constant is far from the experimental value, indicating that the ultralong lifetime is not likely to be of electronic origin only. Our calculations reveal that the dual-peak emission from the T1 state is due to strong vibronic coupling between the T1 and S0 states along selected normal modes. Interestingly, the calculated vibronic radiative rate constant of the dimer (2.33 × 10–3 s–1) is comparable to the experimental value (4.7 × 10–3 s–1), supporting the notion that vibronic contributions to the transition moment are responsible for the ultralong lifetime observed in the bulk system.