TADF Mechanism in a Carbene-Copper Emitter: Insights from the Nuclear Ensemble Simulations

We use the nuclear ensemble approach to study the mechanism of thermally activated delayed fluorescence (TADF) in a carbene-copper-amide (CMA1) emitter. The results obtained for the emitter in the gas phase are consistent with previously published surface hopping nonadiabatic dynamics simulations for the same system. CMA1 has two excited state conformations with distinct excited state dynamics. For both conformations, the intersystem crossing (ISC) from the S1 state occurs via higher-lying triplets, but the reverse ISC (rISC) can occur exclusively in the perpendicular orientation of the ligands, directly between the T1 and S1 states. Nonadiabatic mixing with higher triplet states is not required for efficient rISC, but T1 changes diabatic character significantly along the vibrational modes. Furthermore, we find that the inclusion of the solvent effects has a significant impact on the TADF mechanism, enabling rISC in both conformations. The calculated rate constants and lifetimes are within an order of magnitude of the experimental values.