Coumarin-based fluorescent probes for colorimetric and ratiometric fluorescent detection of sulfite: Structure-activity relationship

Six coumarin-based fluorescent probes were designed and synthesized for the detection of sulfite. The probes were constructed based on "fluorophore-receptor/linker-steric group" mode with N,N-diethyl-7-aminocoumarin (DEA) or 2,3,5,6-1H,4H-tetrahydro-quinolazino-(9,9a,1-gh)coumarin (THQ) as the fluorophore, 2-naphthyl ketone (N) or phenyl ketone (B) as the steric group and vinyl (1) or 1,3-butadienyl (2) as the receptor/linker. The effects of the fluorophore, the linker and the steric group on the photophysical properties and sensing performance were systematically studied. Among all the probes, DEA-N2 exhibited the most excellent spectral responses toward sulfite: upon addition of sulfite, the absorption and emission maxima shifted from 488 nm and 684 nm to 405 nm and 484 nm, respectively. I484/I688 displayed good linear relationship with sulfite concentration in the range of 3-50 μM, with a detection limit of 0.31 μM. The experimental results demonstrate that DEA-N2 has potential in ratiometric fluorescent imaging of mitochondrial sulfite in living cells.