An Organic Laser Based on Thermally Activated Delayed Fluorescence with Aggregation‐Induced Emission and Local Excited State Characteristics

The spatial separation between the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) in thermally activated delayed fluorescent (TADF) molecules leads to charge transfer (CT) states, which degrade the oscillator strength of emission transition and sacrifices high solid‐state photoluminescence quantum yield (PLQY), together limiting its application in organic solid‐state lasers (OSSLs). Here, we demonstrated organic microwire lasers from TADF emitters that combine aggregation induced emission (AIE) and local excited (LE) state characteristics. The unique AIE and LE feature lead to a PLQY approaching 50 % and a high optical gain of 870 cm−1 for TADF microwires. The regenerated singlet excitons by reverse intersystem crossing (RISC) process are conducive to population inversion. As a result, we demonstrated microwire lasers around 465 nm with a low threshold of 3.74 μJ cm−2. Therefore, our work provides insight to design TADF materials for OSSLs. A material that achieves thermally activated delayed fluorescence (TADF) properties from the local excited (LE) state is confirmed. The emission dominated by LE states leads to aggregation induced emission (AIE) in single crystal organic microwires. This result expands the way to realize electric driving laser by using aggregation induced TADF (AI‐TADF) material as gain medium.