Substituent Effects in BODIPY in Live Cell Imaging

Small‐molecule organoselenium‐based fluorescent probes possess great capacity in understanding biological processes through the detection of various analytes such as reactive oxygen/nitrogen species (ROS/RNS), biothiols (cysteine, homocysteine and glutathione), lipid droplets, etc. Herein, we present how substituents on the BODIPY system play a significant part in the detection of biologically important analytes for in vitro conditions and live cell imaging studies. The fluorescence of the probe was quenched by 2‐chloro and 6‐phenyl selenium groups; the probe shows high selectivity with NaOCl among other ROS/RNS, and gives a turn‐on response. The maximum fluorescence intensity is attained within ≈1–2 min with a low detection limit (19.6 nm ), and shows a ≈110‐fold fluorescence enhancement compared to signals generated for other ROS/RNS. Surprisingly, in live cell experiments, the probe specifically located and accumulated in lipid droplets, and showed a fluorescence turn‐on response. We believe this turn‐on response occurred because of aggregation‐induced emission (AIE), which surprisingly occurred only by introducing one lipophilic mesityl group at the meso position of the BODIPY.