Bright Long-Wavelength Multi-State TADF Emitters

To achieve multi-state, visible-light-excited, long-wavelength thermally activated delayed fluorescence (TADF) with high emission efficiency within a single molecular dye system remains a significant challenge. Herein, we developed a series of V-shaped emitters comprising electron-deficient benzothiadiazole and electron-rich triphenylamine (TPA) or carbazole (Cz) units, featuring small singlet-triplet energy gaps. These molecules exhibit long-wavelength TADF emission and bright luminescence in both single-molecule and aggregate states. The V-shaped structure prompts multiple intramolecular hydrogen bonds, while the intramolecular charge transfer effect significantly relaxes the molecular conformation in the excited state. These synergistic effects result in a rigid excited-state molecular conformation, facilitating strong single-molecule state emission with a high luminescence efficiency up to 75.90% (delayed: 26.57%). Meanwhile, the unique V-shaped structure and long alkyl chains enable these luminophores to maintain a twisted conformation and staggered stacking in the aggregate state, effectively preventing aggregation-caused quenching effects. Furthermore, the regular crystal environment ensures that these molecules possess a bright aggregate-state TADF luminescence with a high quantum yield up to 53.50% (delayed: 11.23%). Benefiting from their excellent photophysical properties, these molecules were successfully applied as functional dyes for concentration-independent cell imaging and antibacterial treatment. This work paves the way for designing long-wavelength TADF materials with efficient multi-state emission.