Thiophene anchored coumarin derivative as a turn-on fluorescent probe for Cr3+: Cell imaging and speciation studies

A thiophene–coumarin hybrid molecule, (6E)-6-((thiophen-2-yl)methyleneamino)-2H-chromen-2-one (TMC) has been prepared and its single crystal X-ray structure is reported. TMC can selectively detect Cr3+ in presence of other common cations. Both TMC and its Cr3+ complex are well characterized by different spectroscopic techniques like 1H NMR, QTOF-MS ES+, FTIR and elemental analysis as well. TMC exhibits fluorescence enhancement upon binding Cr3+ in CH3CN–HEPES buffer (0.02 M, pH 7.4) (4:6, v/v) medium. Detection limit of the method is 1 × 10−6 M. Binding constant is estimated with the Benesi–Hildebrand method and the value 8 × 104 indicates a fairly strong interaction between TMC and Cr3+. Speciation studies have been performed in a fast and environment friendly way using least sample volume, less hazardous chemicals and solvents. Cr3+ assisted restricted rotation around the imine bond and inhibited photo-induced electron transfer from the N,S-donor sites to the coumarin unit are responsible for fluorescence enhancement. TMC is capable to detect intracellular Cr3+ in living cells.