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.