Highly Sensitive and Fast Responsive Fluorescence Turn‐On Chemodosimeter for Cu 2+ and Its Application in Live Cell Imaging

A rhodamine B derivative 4 containing a highly electron‐rich S atom has been synthesized as a fluorescence turn‐on chemodosimeter for Cu 2+ . Following Cu 2+ ‐promoted ring‐opening, redox and hydrolysis reactions, comparable amplifications of absorption and fluorescence signals were observed upon addition of Cu 2+ ; this suggests that chemodosimeter 4 effectively avoided the fluorescence quenching caused by the paramagnetic nature of Cu 2+ . Importantly, 4 can selectively recognize Cu 2+ in aqueous media in the presence of other trace metal ions in organisms (such as Fe 3+ , Fe 2+ , Cu + , Zn 2+ , Cr 3+ , Mn 2+ , Co 2+ , and Ni 2+ ), abundant cellular cations (such as Na + , K + , Mg 2+ , and Ca 2+ ), and the prevalent toxic metal ions in the environment (such as Pb 2+ and Cd 2+ ) with high sensitivity (detection limit ≤10 ppb) and a rapid response time (≤1 min). Moreover, by virtue of the chemodosimeter as fluorescent probe for Cu 2+ , confocal and two‐photon microscopy experiments revealed a significant increase of intracellular Cu 2+ concentration and the subcellular distribution of Cu 2+ , which was internalized into the living HeLa cells upon incubation in growth medium supplemented with 50 μ M CuCl 2 for 20 h.