Dissecting non-radiative decay in donor-functionalized radicals with a mode-resolved model

Donor-functionalized radicals based on the poly-chlorinated trityl moiety are an emerging class of efficient emitters for next-generation optoelectronics. Their performance is governed by the non-radiative decay of a charge-transfer (CT) state, making its understanding crucial for molecular design. We present a mode-resolved model that links the decay to structural motifs through molecular vibrations. The decisive role of exact exchange in density functional modeling is highlighted, alongside solvation and anharmonic effects. Using representative radical emitters, we show that suppression of non-radiative decay in systems with a perpendicular donor-acceptor arrangement arises from reduced coupling of the promoting mode to the CT exciton and a diminished anharmonic contribution. To elucidate this mechanism, we perform a sensitivity analysis of the contributions of individual modes to the Franck-Condon weighted density of states, including anharmonic effects.