Reversal of Solvatochromism: A New Strategy to Construct Activatable Two-photon Fluorescent Probes for Sensing.

Two-photon (TP) imaging with a donor-acceptor (D-A) type fluorophore is an emerging tool for bioimaging and sensing. However, current TP probes suffer from serious solvatochromic quenching in aqueous solution due to their strong intramolecular charge transfer (ICT) in excited states. In this work, based on solvatochromism reversal, we report a novel strategy to develop TP probes for bioimaging. Specifically, compared with the normal two-photon probes that showed a fluorescence off with ICT suppressed, the novel probes exhibited strong fluorescence in the aqueous solution when their ICT was inhibited. This strategy not only provides a new way for the design of high-performance TP probes, but also expands the biological analysis toolbox for use in living systems.