Novel pH-sensitive probes with a ratiometric detection for intracellular pH

The development of new pH-sensitive fluorescent probes based on a push-pull architecture is presented with a 2- dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofurane as strong electron acceptor group. With a small structural change, it is possible to obtain a large range of phenolic pKa from 4.8 to 8.6 with some close to neutrality, underlining the role of the electron density modulation on the acidic properties. Remarkable changes in the optical properties (both absorption and fluorescence) were observed as a function of the pH. Ratiometric imaging of intracellular pH was carried out with the most promising probes and highlighted the possibility to distinguish near-neutral minor pH fluctuations in cells.