Tuning dual-channel fluorescence-enhanced chemosensor for imaging of living cells in extreme acidity

A class of high-resolution ratiometric fluorescent probes, which possess N, N-dimethylaniline and triphenylamine as electron donors and imidazopyridine rings via the different number of ethylene bridging, are rationally designed and synthesized. These ICT-based ratiometric probes, namely Me, TPH and CIN, possess excellent photostability, conductive to longtime detecting of persistent pH changes without disturbance of other biological active species and reversibility as well as low cytotoxicity in the lysosomes of live cells. Moreover, these probes have excellent cell membrane permeability and biological applications. Among these probes, the probe CIN displayed emission maxima in the NIR region in acidic media by improvement of π-conjugated system with ideal pKa 3.1 and linear response to extreme-acidity range of 2.5–4.1. Moreover, CIN exhibits the largest emission shift about 90 nm from 560 to 650 nm with the pH environment changes, which could be considered as a good candidate for high resolution imaging of pH fluctuations in live cells and extreme acidity in Escherichia coli cells.