Zincke’s Salt-Substituted Tetraphenylethylenes for Fluorometric Turn-On Detection of Glutathione and Fluorescence Imaging of Cancer Cells

In this paper, we report Zincke's salt-substituted tetraphenylethylenes 1a and 1b with Cl^- and PF₆^- as counteranions, respectively. The crystal structure of 1b was determined. Both 1a and 1b are almost nonemissive even in the aggregated states. This is attributed to the photoinduced electron transfer from 2,2-bis(4-methoxyphenyl)-1-phenylvinyl-phenyl unit to 1-(2,4-dinitrophenyl) pyridinium unit within 1a and 1b. The results demonstrate that the emissions of 1a and 1b in aqueous solution can be switched on upon either reaction with GSH or light irradiation. On the basis of the reaction between 1a and GSH, 1a can be utilized for the fluorescence turn-on detection of GSH selectively, and GSH with concentration as low as 36.9 nM can be detected. The transformation of 1b into 2 under light irradiation results in the fluorescence imaging of Hela and U2OS cells and phototoxicity toward Hela and U2OS cells after the protonation of pyridine unit in 2 because of the acidic environment of tumor cells. Aggregates of 1b can be up-taken by Hela and U2OS cells and fluorescence imaging has been successfully recorded with CLSM. Moreover, the protonated form of 2 can function as photosensitizer and 1b shows phototoxicity toward tumor cells such as Hela and U2OS cells.