Near-infrared aza-BODIPYs bearing tetraphenylethylene: Synthesis, photophysical studies, and cell imaging application.

• Two aza-BODIPY derivatives (AZB-TPE 1 and AZB-TPE 2) and their aggregation-induced emission features were reported. • Tetraphenylethylene (TPE) groups were added to para -positions of 3,5-phenyls of aza-BODIPY to improve the dye's aggregation emission. • Intramolecular energy transfer between the TPE donor and the aza-BODIPY acceptor was observed with energy transfer efficiencies of 84–97% and substantial pseudo-Stokes shifts of 395–406 nm. • Application of the dyes in NIR cancer cell imaging revealed intense fluorescence inside the cells with persistence signals. We provide a simple method to synthesize tetraphenylethylene-modified aza-BODIPY dyes (AZB-TPE 1 and AZB-TPE 2) with aggregation-enhanced emission. Single-crystal X-ray method, electrochemical experiments, and TD-DFT calculations were used to understand more about their electronic and photophysical properties. The intramolecular energy transfer between the TPE donor and the aza-BODIPY acceptor was observed from both dyes, with 84–97% energy transfer efficiencies and large pseudo-Stokes shifts of 395 – 406 nm. Aggregation studies in THF/water solution showed increased fluorescence in the aggregated form. X-ray crystal structure of AZB-TPE 2 suggested the reduction of intermolecular pi-pi interactions between the structures. Finally, these NIR-emitting particles with superior water dispersion and biocompatibility demonstrated amazing features in bioimaging applications. [ABSTRACT FROM AUTHOR]