Exploring the Triplet Excited State Potential Energy Surfaces of a Cyclometalated Pt(II) Complex: Is There Non-Kasha Emissive Behavior?

In this Article, we address the complexity of the emissive processes of a square-planar heteroleptic Pt(II) complex bearing 2-phenylpyridine (ppy) as cyclometalated ligand and an acetylacetonate derivative (dbm) as ancillary ligand. The origins of emission were identified with the help of density functional theory (DFT) and quadratic response (QR) time-dependent (TD)-DFT calculations including spin-orbit coupling (SOC). To unveil the photodeactivation mechanisms, we explored the triplet potential energy surfaces and computed the SOCs and the radiative decay rates (k(r)) from possible emissive states. We find that emission likely originates from a higher-lying (MLCT)-M-3/(LLCT)-L-3 state and not from the Kasha-like (MLCT)-M-3/(LCdbm)-L-3 state. The temperature-dependent nonradiative deactivation mechanisms were also elucidated. The active role of metal-centered ((MC)-M-3) triplet excited states is confirmed for these deactivation pathways.