Bright Long‐Wavelength Multi‐State TADF Emitters

Abstract

Abstract 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.