Viscosity sensitive fluorescent dyes with excellent photostability based on hemicyanine dyes for targeting cell membrane

In this paper, three viscosity sensitive cell membrane fluorescent dyes (1a-c) were obtained. Dyes 1a-c were linked by benzaldehyde (5) and benzoindole (2a), benzoxazole (2b) and benzothiazole (2c), with double bond, respectively. The optical properties showed that dyes 1a-c had larger molar extinction coefficients (3.34 × 104-2.64 × 105 M−1 cm−1) and excellent photostability (89–93 %). In particular, dyes 1a-c had obvious specific response to viscosity. More specifically, they indicated significant OFF-ON fluorescent response at 563 nm, 599 nm and 601 nm to the increase of viscosity (0.89–865 cp), respectively, and displayed an excellent linear relationship with viscosity. Further, the excited-state lifetime of dye 1b was evaluated as long as 828 ps in high viscosity environment by transient absorption spectra. The low cytotoxicity of dyes 1a-c, provided the possibility to be used in living cells. Accordingly, laser confocal experiments clearly exhibited that dyes 1a-c could be well located in the cell membrane. The results can assist in our understanding of the functions of cell membrane as well as application in biosensor and diagnostics.