Hydrophilic, Red‐Emitting, and Thermally Activated Delayed Fluorescence Emitter for Time‐Resolved Luminescence Imaging by Mitochondrion‐Induced Aggregation in Living Cells

Thermally activated delayed fluorescence (TADF) materials have provided new strategies for time‐resolved luminescence imaging (TRLI); however, the development of hydrophilic TADF luminophores for specific imaging in cells remains a substantial challenge. In this study, a mitochondria‐induced aggregation strategy for TRLI is proposed with the design and utilization of the hydrophilic TADF luminophore ((10‐(1,3‐dioxo‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[de]isoquinolin‐6‐yl)‐9,9‐dimethyl‐9,10‐dihydroacridin‐2‐yl)methyl)triphenylphosphonium bromide (NID‐TPP). Using a nonconjugated linker to introduce a triphenylphosphonium (TPP+) group into the 6‐(9,9‐dimethylacridin‐10(9H)‐yl)‐2‐phenyl‐1H‐benzo[de]isoquinoline‐1,3(2H)‐dione (NID) TADF luminophore preserves the TADF emission of NID‐TPP. NID‐TPP shows clear aggregation‐induced delayed fluorescence enhancement behavior, which provides a practical strategy for long‐lived delayed fluorescence emission in an oxygen‐containing environment. Finally, the designed mitochondrion‐targeting TPP+ group in NID‐TPP induces the adequate accumulation of NID‐TPP and results in the first reported TADF‐based time‐resolved luminescence imaging and two‐photon imaging of mitochondria in living cells. A hydrophilic, red‐emitting emitter NID‐TPP is constructed by using a nonconjugated linker to introduce a triphenylphosphonium group into the hydrophobic thermally activated delayed fluorescence emitter 6‐(9,9‐dimethylacridin‐10(9H)‐yl)‐2‐phenyl‐1H‐benzo[de]isoquinoline‐1,3(2H)‐dione (NID). ((10‐(1,3‐dioxo‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[de]isoquinolin‐6‐yl)‐9,9‐dimethyl‐9,10‐dihydroacridin‐2‐yl)methyl)triphenylphosphonium bromide (NID‐TPP) demonstrates obvious aggregation‐induced delayed fluorescence enhancement behavior, and its application for specific time‐resolved luminescence imaging by mitochondria‐induced aggregation in living cells is conducted.