Fluorescent probes based on quinoline and naphthidine derivatives with NIR and AIE properties for real-time monitoring mitochondrial viscosity during mitophagy

As a special form of autophagy, mitophagy is a pivotal mechanism governing cellular metabolism and physiology. Viscosity monitoring is an important aspect for real-time visualization of the mitophagy process. Hence, the development of high-performance viscosity probes is crucial for investigating dynamic pathological processes related to mitophagy. This study presents the discovery of mitochondria near-infrared and aggregation-induced emission probes with neutral structure. Probes 1a-1b were connected quinoline/naphthidine malononitrile and coumarin units with a double bond, the absorption maxima were at 433–471 nm; emission maxima were at 605–720 nm with large Stokes shifts of 170–279 nm in solvents of different polarity. As the environmental viscosity increases from 0.89 cP to 856 cP, the fluorescence intensity of probe 1a and probe 1b is enhanced by 418-fold and 769-fold, respectively, which due to the restricted rotation and inhibited twisted intramolecular charge transfer in high viscosity systems. In addition to excellent NIR, hypotoxicity, and mitochondrial targeting capabilities, probes 1a-1b were successfully applied to detect changes in mitochondrial viscosity during starvation or rapamycin-induced mitophagy. These remarkable features make probes 1a-1b as promising candidates for investigating dynamic pathological processes related to mitophagy with significant potential for biological applications.