Development of meso -Five-Membered Heterocycle BODIPY-Based AIE Fluorescent Probes for Dual-Organelle Viscosity Imaging.

Fluorescent rotors with aggregation-induced emission (AIE) and organelle-targeting properties have attracted great attention for sensing subcellular viscosity changes, which could help understand the relationships of abnormal fluctuations with many associated diseases. Despite the numerous efforts spent, it remains rare and urgent to explore the dual-organelle targeting probes and their structural relationships with viscosity-responsive and AIE properties. Therefore, in this work, we reported four -five-membered heterocycle-substituted BODIPY-based fluorescent probes, explored their viscosity-responsive and AIE properties, and further investigated their subcellular localization and viscosity-sensing applications in living cells. Interestingly, the -thiazole probe showed both good viscosity-responsive and AIE (in pure water) properties and could successfully target both mitochondria and lysosomes, further imaging cellular viscosity changes by treating lipopolysaccharide and nystatin, attributing to the free rotation and potential dual-organelle targeting ability of the -thiazole group. The -benzothiophene probe with a saturated sulfur only showed good viscosity-responsive properties in living cells with the aggregation-caused quenching effect and no subcellular localization. The -imidazole probe showed the AIE phenomenon without an obvious viscosity-responsive property with a C═N bond, while the -benzopyrrole probe displayed fluorescence quenching in polar solvents. Therefore, for the first time, we investigated the structure-property relationships of four -five-membered heterocycle-substituted BODIPY-based fluorescent rotors with viscosity-responsive and AIE properties, and among these, with a C═N bond and a saturated sulfur on the -thiazole, potentially contributing to their corresponding AIE and viscosity-responsive properties, served as a sensitive AIE fluorescent rotor for imaging dual-organelle viscosity in both mitochondria and lysosomes.