Phosphine Oxides Manipulate Aggregation‐Induced Delayed Fluorescence for Time‐Resolved Bioimaging

Abstract

Delayed fluorescence (DF) materials have shown great potential in time‐resolved luminescence imaging (TRLI), due to the relatively elongated emission lifetimes. However, the sensitivity of DF to environmental quenching leads to a challenge to realize TRLI directly using pure thermally‐activated DF (TADF) molecules. Herein, two TADF molecules, namely CzPOTCF and tBCzPOTCF, are designed and synthesized, featuring a diphenylphosphine oxide (DPPO) group substituted at the ortho‐position of the carbazole group. Compared with DPPO‐free CzTCF, the steric hindrance of DPPO groups enlarges dihedral angles between TCF and the carbazole groups in CzPOTCF and tBCzPOTCF; meanwhile, PO provides other channels for forming intermolecular hydrogen bonds. The optimized intermolecular interactions facilitate the dimer formation of CzPOTCF and tBCzPOTCF, which simultaneously enhance aggregation‐induced DF and mitigate disordered packing‐induced quenching. As a consequence, CzPOTCF and tBCzPOTCF show the enhanced aggregation‐induced DF with largely increased lifetimes. Without any additional assistance, the long‐lived fluorescence of CzPOTCF and tBCzPOTCF is successfully observed for cell TRLI, with 1–1.7 μs elongated average lifetimes of 6.69 and 7.41 μs, respectively.