Two highly sensitive fluorescent probes based on cinnamaldehyde with large Stokes shift for sensing of HSO3- in pure water and living cells.

Two simple and novel fluorescent probes (CDC1 and CDC2) have been designed and prepared here for sensing HSO3- with large Stokes shifts (about 250 nm). The synthesized probes can react with HSO3- just in 2 min, followed by the obvious color change from blue to colorless. The colorimetric and ratiometric absorbance response of the probes to HSO3- is due to the addition of HSO3- to the electron-deficient C=C double bond group, which prevents significant intramolecular charge transfer (ICT). Besides, CDC1 and CDC2 can detect HSO3- in pure water and detection limits of CDC1 and CDC2 reached 4.59 nM and 8.19 nM, respectively. Considering the delicate difference in the two prepared probes' molecular structures, CDC1 containing the carboxyl group has a more significant fluorescence intensity change response to HSO3- in pure water than CDC2 (with sulfinyl group). Beyond better response characteristics, CDC1 also has lower cytotoxicity and better biocompatibility compared with CDC2, which could be chosen to detect HSO3- in living cells. With these superior properties, probe CDC1 could have a potential application in the fields of environmental and biological detection.