Near-Degenerate T2-State Assisted Thermally Activated Delayed Fluorescence in Carbene-Metal-Amide Complexes: A Mechanistic Study.

Two-coordinated carbene-metal-amide (CMA) complexes represent an important class of thermally activated delayed fluorescence (TADF) emitters, yet the underlying mechanisms governing their high efficiency remain to be fully elucidated. Here, we report a systematic theoretical study of two CMA complexes (M = Cu(I), Ag(I)) supported by a cyclic alkyl(amino)carbene (CAAC) ligand and a carbazolyl amide donor. We find that delayed fluorescence arises from ligand-centered intermolecular charge transfer with minimal involvement of the metal in frontier orbitals or spin-orbit coupling. Remarkably, efficient reverse intersystem crossing is facilitated by the presence of near-degenerate T1 and T2 states, enabled by a mirrored hole-electron distribution reminiscent of the multiple-resonance effect observed in B/N systems. This unique electronic characteristic promotes intramolecular short-range charge transfer and enhances triplet-to-singlet spin-flip processes, ultimately leading to a high photoluminescence quantum yield. Our results uncover a previously overlooked TADF mechanism in CMA emitters and offer a design strategy for efficient metal-assisted TADF materials through tailored electronic degeneracy and spatial overlap.