Lysosomal tracking with a cationic naphthalimide using multiphoton fluorescence lifetime imaging microscopy.

A naphthalimide-based chemosensing motif turns ON the fluorescence emission in solution in the presence of aqueous iron(iii) chloride, and maintains this property in living cancer cells. The emission response to Fe(iii) ions occurs simultaneously with a change in pH. The protonation of methyl piperazine-conjugated naphthalimide promotes its lysosomal localisation as assessed by co-localisation tests and fluorescence lifetime imaging microscopy (FLIM) in vitro.