Comprehensive kinetic analysis of inverted <i>S</i> ₁ – <i>T</i> ₁ materials with a dynamic exciton model

Abstract Thermally activated delayed fluorescence materials have attracted attention for organic light-emitting diodes owing to their high efficiency and stability. Accurate evaluation of the singlet–triplet energy gap (Δ E ST ), particularly in near-zero-gap systems, remains a key challenge. Here, we investigate the photophysical properties of HzTFEX 2 , a proposed inverted singlet–triplet (InvE ST ) emitter, using temperature- and solvent-dependent analyses based on a dynamic exciton model. The results show that InvE ST explains the emission decay profiles of HzTFEX 2 in the Marcus normal region. We demonstrate that conventional kinetic analyses are insufficient in the near-zero Δ E ST regime, highlighting the necessity of the dynamic exciton model.