A mitochondria-targeted NIR ratiometric and colorimetric fluorescent probe with large Stokes shift for Hg2+ based on deselenation-hydrolysis-induced self-immolative reaction.

A mitochondria-targeted NIR ratiometric and colorimetric fluorescent probe with large Stokes shift for Hg2+ sensing was rationally designed and synthesized. The fluorescence probe exhibited the maximum fluorescence emission peak at 721 nm (NIR region) and absorption peak at 558 nm. Upon addition of Hg2+, the maximum fluorescence emission and absorption peaks underwent significant blue shifts to 578 nm and 448 nm respectively. Concurrently, distinct color changes were observed: from purple to orange under 365 nm UV light and from pale purple to pale yellow under daylight. These changes arise from Hg2+-triggered deselenation-hydrolysis of the diphenylphosphinoselenoate moiety in the fluorescence probe, which involves cleavage of the P-O bond and formation of intermediate A containing phenolic hydroxyl group, subsequently self-immolative reaction of p-hydroxybenzyl moiety in the intermediate A by 1,6-elimination to release a fluorophore. The fluorescence probe demonstrated excellent sensing performance for Hg2+, characterized by a large Stokes shift (163 nm), rapid response (6 min), high sensitivity (LOD of 37.3 nM), and outstanding selectivity over other metal ions. Furthermore, the fluorescence probe was successfully applied to both time-dependent and concentration-dependent ratiometric fluorescence imaging of intracellular Hg2+ and demonstrated specific mitochondrial targeting. Notably, this work proposes for the first time a novel design strategy involving the modification of diphenylphosphinoselenoate onto the N atom of quinoline to construct Hg2+-responsive probes.