Regioisomeric carbazole–dicyano–dioxin AIDF emitters for efficient triplet harvesting, two-photon absorption and bioimaging

Abstract

Integrating aggregation-induced emission (AIE) with thermally activated delayed fluorescence (TADF) offers a useful strategy to achieve efficient triplet harvesting in the condensed phase. Here, we report three carbazole–dicyano–dioxin donor–acceptor regioisomers (oCN1, oCN2, and pCN) that exhibit pronounced aggregation-induced delayed fluorescence (AIDF) from solution to aggregates, neat films and crystals. Oxygen incorporation and peripheral tert-butyl groups make the molecular framework more rigid and help suppress aggregation caused quenching. These substitutions also promote twisted donor–acceptor geometries. In addition, subtle ortho/para changes in connectivity tune the charge-transfer character, the singlet–triplet energy gaps, and the reverse intersystem crossing dynamics. In THF-water mixtures, all isomers display clear AIDF signatures, with PLQYs up to 63% and microsecond delayed lifetimes, enabled by up to ∼20-fold suppression of internal conversion (IC) upon aggregation. In neat films, all these isomers exhibit bright green to yellow-orange emission with PLQYs of 78%, 31% and 54% for oCN1, oCN2, and pCN, respectively. Moreover, all three regioisomers exhibit an RISC rate of ∼105 s−1 in neat films. This fast RISC rate is attributed to the small singlet–triplet energy gap and appreciable spin–orbit coupling. The strong charge-transfer character and robust AIDF further enable efficient two-photon bioimaging and the fabrication of converted LEDs.