Unraveling the photophysical characteristics and biological applications of vinyl sulfones as viscosity sensors.

For the first time, a series of vinyl sulfone-NH 2 -based push-pull fluorophores (4a-4d) were introduced for their potential use in biological applications. The fluorophores 4a-4d were readily synthesized upon reduction of the corresponding vinyl sulfones-NO 2 (3a-3d), which were prepared by sulfonylation of nitrostyrene. Both types of probes can be prepared in high yields through a few steps with minimal cost. In diverse solvents, probes 4a-4d exhibited fluorescence with strong emission peaking around 403-490 nm. Additionally, the fluorescence intensity of probe 4d rose approximately 85-fold with increasing viscosity. The probes 4a-4d demonstrated good stability and photostability in a broad pH range. Moreover, probes 4a-4d showed significantly improved biocompatibility compared to those derived from 3a-3d. For cell imaging applications, the developed probes 4a-4d exhibited much stronger blue fluorescence in cancer cells (HepG2) compared to 3a-3d. In addition, probes 4a-4d exhibited low cytotoxicity within 24 h toward both cancer and normal cells (HEK-293). Interestingly, probe 4d showed great sensitivity to viscosity in cancer cells. As a result, readily prepared vinyl sulfone-NH 2 -based push-pull fluorophores (4a-4d) offer a promising strategy for further development as cancer cell staining agents.