Three-State-Involving Vibronic Resonance Is a Key to Enhancing Reverse Intersystem Crossing Dynamics of Organoboron-Based Ultrapure Blue Emitters

In organoboron OLED emitter DABNA, vibronic resonance strongly enhances reverse intersystem crossing rate even with a sizable T1-S1 energy gap. The resonance is peculiar in that the vibrational frequency has to match both (1) the T1-S1 energy gap and (2) the T1-T3 nonadiabatic coupling oscillation frequency. This three-state involving resonance is a result of combination of T1-T3-S1 superexchange and T1-T3 non-Condon coupling.