1,8-Naphthalimide Derivative Dyes with Large Stokes Shifts for Targeting Live-Cell Mitochondria

An ideal fluorescent dye for staining cell organelles should have multiple properties including specificity, stability, biocompatibility, and a large Stokes shift. Tunable photophysical properties enable 1,8-naphthalimide to serve as an excellent fluorophore in biomedical applications. Many naphthalimide derivatives have been developed into drugs, sensors, and other dyes. In this study, a series of 1,8-naphthalimide derivatives targeting live cell mitochondria were synthesized. Among these probes, Mt-4 was characterized as the best one, with highly specific mitochondrial localization, low cytotoxicity, and a large Stokes shift. More importantly, Mt-4 stood out as a potential mitochondrial dye for living-cell experiments involving induced mitochondrial stress arising from the treatments because Mt-4 shows enhanced fluorescence in mitochondrial stress situations.