Rosamine with pyronine-pyridinium skeleton: unique mitochondrial targetable structure for fluorescent probes.

Two rosamine-based probes (1a-b) with pyronine-pyridinium skeleton were designed and prepared. Probe 1a bearing boron ester unit was oxidized and eliminated upon addition of hydrogen peroxide (H2O2), and the emission spectrum exhibited OFF-ON response accompanied by 33-fold fluorescent enhancement. In contrast, the fluorescence intensity of probe 1b enhanced 58 times after the dinitrophenyl ether part within the probe was removed by nucleophilic substitution with hydrosulfide (H2S). The design concept was based on the d-PET process in pyronine-pyridinium structures, and free 4-pyridinyl-substituted pyronine dye showing strong fluorescence was released followed by elimination. Furthermore, as biocompatible molecules, probes 1a-b have been successfully applied for imaging in live HeLa and Ges-1 cells, and all of them can serve as mitochondrial targetable probes in red channel for detecting independent species.