Synergistic effect of ESIPT and hRISC properties for 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol: A theoretical...

Materials that simultaneously enable excited-state intramolecular proton transfer (ESIPT) and high-lying reverse intersystem crossing (hRISC) can effectively circumvent the energy transfer challenges in white organic light-emitting diodes (WOLEDs) while offering high exciton utilization, making them ideal candidates for multi-emissive layers in WOLEDs. This study systematically investigates the ESIPT and hRISC properties of 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol (PyHBT) and their solvent effects using density functional theory/time-dependent DFT (DFT/TD-DFT). Solvents exert a minor influence on this process, but fluorescence intensity is positively correlated with polarity. Hole-electron analysis indicates that the charge transfer characteristics of Enol*-form emission result in lower fluorescence intensity compared to Keto*-form emission, and the Enol* forms are more conducive to reverse intersystem crossing (RISC). The pronounced separation of HOMO-LUMO further confirms its hRISC potential. The smaller Enol*-form singlet-triplet energy gap indicates that hRISC occurs between S₁ and T₃ states, with its rate decreasing as solvent polarity increases. Collectively, this study deepens the comprehension of synergistic ESIPT-hRISC mechanism and offers valuable guidelines for designing next-generation WOLED materials.