Multi-channel Non-radiative Dynamics to Reveal ΔEST as the Key Efficiency Descriptor for Deep-Blue Pt(II) Phosphors

Tetradentate platinum(II) complexes are promising candidates for phosphorescent organic light-emitting diodes (OLEDs), combining deep-blue emission, high color purity, and potential for near-unity photoluminescence quantum yields (PLQYs). However, despite their rigid structures, which should suppress non-radiative decay, many of these complexes still show surprisingly low PLQYs, and the mechanism underlying this discrepancy has remained unclear. Here, through first-principle calculations of multi-channel transition rates for 25 tetradentate Pt(II) complexes, we show that this apparent paradox arises from a thermally activated S1 non-radiative channel (T1 → S1 → S0) that dominates the non-radiative decay. The rate of this channel depends exponentially on the singlet-triplet gap ΔEST, establishing ΔEST as a key descriptor for PLQY. Electronic structural analysis reveals that donors on the pyridine unit can delocalize LUMO, increase HOMO-LUMO overlap, and help enlarge ΔEST and PLQY. These results provide a unified mechanistic picture and a direct design rule for high-efficiency deep-blue Pt(II) emitters.