Unveiling the mechanisms of organic room temperature phospho-rescence in various surrounding environments: a computational study

Room-temperature phosphorescence (RTP) from pure organic materials has been prom-ising in the next-generation OLEDs. Understanding of the photophysical properties of RTP molecules is attractive but challenging. In this study, through a combined quantum mechanics and molecular mechanics (QM/MM) method taking 2-(3,4-dimethoxybenzyl)isoindoline-1,3-dione (complex b) as example, we compara-tively investigated the photophysical properties of complex b in diverse environments (solution, crystal, and amorphous). From solution to amorphous to crystal phase, the excited-state decay rates for the molecule indicate that the AIE phenomenon of complex b is mainly induced by the increased phosphorescence rates. However, the increased nonradiative decay rate knr of T1→S0 from the solution to the crystal phase could be at-tributed to be the different electron coupling in the crystal phase. Meantime, the theoret-ical results also show that the small energy gap between the lowest singlet excited state (S1) and triplet excited state (T1) and low reorganization energy can help enhance inter-system crossing to facilitate to a more competitive radiative process from T1 state to ground state (S0). Additionally, the stronger intermolecular π-π interaction can cause high phosphorescence quantum efficiency in the crystalline phase. Our study presents a rational explanation for the aggregation induced RTP, which is beneficial for the design of new organic RTP materials in the future.