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

Abstract

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.