A novel alkaline pH-responsive ratiometric probe based on hybrid fluorophores and its applications

The current study describes a novel development in the field of chromogenic and ratiometric fluorescence probes designed for pH sensing purposes. Of particular interest is the incorporation of coumarin as the recognition component in this probe, which was synthesized utilizing hybrid fluorophores containing fluorescein and coumarin. This probe exhibited two distinct fluorescence response modes toward changes in pH: a ratiometric fluorescence response at 328 nm excitation and a fluorescence switch-on response at 514 nm excitation. These responses are attributed to the structure changes induced by coumarin hydrolysis in alkaline conditions above a pH of 9, as confirmed through MS and DFT analysis. Furthermore, the practical utility of the probe was effectively evaluated through visual detection on silica gel plates and bio-imaging with Bacillus subtilis, illustrating its potential for the advancement of alkaline pH-responsive fluorescence probes.