1-(2-Methyl-5H-chromeno[2,3-b]pyridin-5-ylidene) hydrazone as fluorescent probes for selective zinc sensing in DMSO

Two methyl-chromeno-pyridinylidene hydrazone derivatives L1, a cyclen derivative, and L2 were studied as potential fluorescent OFF–ON sensors towards Zn2+ in DMSO. Upon addition of one equivalent of Zn2+, L1 fluorescence was quenched, but addition of a second equivalent of Zn2+ restored partially the signal. Therefore ZnL1 behaved as a OFF–ON sensor for zinc. By comparison, L2 behaved as a very sensitive probe for zinc. ZnL1 and L2 sensor efficiencies were correlated to Zn2+ coordination via the hydrazone moiety of the fluorophore, which prevented a photoinduced electron transfer (PET), and allowed an efficient CHelation-Enhanced Fluorescence (CHEF) effect.