Experimental investigation of exciton dynamics of thermally activated delayed fluorescence material exhibiting mono-exponential transient PL decay with sub-microsecond lifetime in solution

Abstract DMAc-sFL-PN is a reported emitter exhibiting an ultrashort emission lifetime via the triplet state with high oxygen sensitivity in toluene, explained by a direct singlet-harvesting mechanism. We comprehensively investigated the detailed emission mechanisms of DMAc-sFL-PN and its derivatives (D-sFL-PNs). Triplet exciton quenching experiments suggested a minor triplet contribution to the emissions of D-sFL-PNs. In addition, we successfully observed clear thermally activated delayed fluorescence (TADF) from DMAc-sFL-PN in low-temperature toluene. Moreover, DMAc-sFL-PN showed long-lived TADF in the solid state. These results reveal that D-sFL-PNs are a class of charge-transfer fluorophores characterized by slow emission dynamics and inefficient TADF.