Push-pull luminescent imidazole derivatives: ICT enables efficient picric acid sensing.

Abstract

Two push-pull fluorophores (3a-b) based on a tri-substituted imidazole core appended with donor-acceptor groups were successfully synthesized by the catalysis of Amberlite IR 120H+ and were fully characterized by NMR and mass spectral analyses. The synthesized compounds exhibit strong luminescent properties due to their donor-acceptor (push-pull) electronic structures and possess pronounced excited-state charge transfer characteristics, as evidenced by steady-state and time-resolved spectroscopic experiments. Imidazole incorporated with donor groups in the phenyl rings at the 4- and 5-positions (3b) shows a greater extent of charge transfer and emits yellow color in polar solvents like DMSO and acetonitrile. Both the fluorophores were found to act as sensors of picric acid in the solution phase with a very low detection level (nM) by static quenching of the fluorescence emission mechanism. The sensitivity of the detection of picric acid by 3b was found to be almost 1000 fold higher than that by 3a, and the response time of 3b towards picric acid was ∼3 times faster than that of 3a.

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