Interplay of Aggregation-Induced Enhanced Emission and Thermally Activated Delayed Fluorescence in Asymmetric Fluorenyl-Benzothiadiazole Derivatives.

Combining thermally activated delayed fluorescence (TADF) with aggregation-induced enhanced emission (AIEE) provides an effective strategy to improve solid-state emission in organic materials. Here, we design four fluorenyl-benzothiadiazole (FL-BTD) derivatives bearing additional donor groups, aryloxy (-OAr), aryl (-Ar), iminodibenzyl (-IDB), and phenoxazine (-PXZ), to investigate how molecular structure influences their photophysical properties. FL-BTD-OAr and FL-BTD-IDB display AIEE, with quantum yields that are significantly higher in the solid state (0.70 and 0.30, respectively) than in solution. FL-BTD-IDB also exhibits delayed emission = 1.03 μs and enhanced luminescence under vacuum compared to an O atmosphere, consistent with TADF. Organic light-emitting diodes (OLEDs) fabricated with these materials show green emission (FL-BTD-Ar and FL-BTD-OAr) or orange emission (FL-BTD-IDB). Device performance trends closely follow the solid-state photophysics. FL-BTD-Ar, subject to partial aggregation quenching, delivers the weakest performance, whereas FL-BTD-OAr benefits from AIEE, resulting in improved brightness and efficiency. The best-performing device is based on FL-BTD-IDB, which combines AIEE and TADF to achieve high brightness (15,000 cd m) and higher external quantum efficiency (EQE) compared to the analogs.