Key Role of Electronic and Structural Properties in Regulating Intersystem Crossing: An In-Depth Investigation on Naphthalene-Diimide Triads for Thermally Activated Delayed Fluorescence Applications

We report an extensive theoretical investigation of the photophysical properties of new carbazole core-substituted naphthalene-diimide dyes to elucidate the effects of different donor-acceptor arrangements on the direct and reverse intersystem crossing rates. These dyes were recently experimentally characterized using steady-state and time-resolved spectroscopy ( J. Phys. Chem. B 2021, 125, 10813 ). We analyzed the molecular structures of ground states, singlet and triplet excited states, excitation energies, orbital characteristics, and spin-orbit couplings using density functional theory (DFT)/time-dependent DFT calculations to determine the rates of the electronic spin-flip processes. Our findings reveal how different donor-acceptor configurations, by modulating ground and excited state conformational dynamics, may significantly influence the energetic landscape of singlet and triplet electronic states, their nature, and thus the extent of spin-orbit couplings, finally impacting the intersystem crossing rate constants and the reverse ones for thermally activated delayed fluorescence applications.