A pH-sensitive excited state intramolecular proton transfer fluorescent probe for imaging mitochondria and Helicobacter pylori

An hydroxythiophene-conjugated benzothiazole (T-2(OH)B) was synthesized as a pH sensitive fluorescent probe. T-2(OH)B displayed dual emission behavior due to the excited state intramolecular proton transfer (ESIPT) process, while the methoxy analogs, T-2(OMe)B, did not. T-2(OH)B showed strong fluorescence enhancement above physiological pHs. The applicability of T-2(OH)B as a biological pH indicator was demonstrated by its use for staining mitochondrial compartment and H. pylori. Owing to its strong fluorescence emission with a large stokes shift and its effective response to pH, T-2(OH)B serves as a platform for the design of new types of fluorescent probes.