Synthesis of bisbenzimidazo quinoline fluorescent receptor for Fe2+ ion in the aqueous medium – An experimental and theoretical approach

• Bisbenzimidazo quinoline receptor was synthesized and characterized.
• Metal binding properties were analyzed by optical and electrochemical studies.
• DFT calculations were performed and correlated to the experimental binding results.

Bisbenzimidazo quinoline receptor 1 bearing diethylene oxide spacer linkage was synthesized and characterized by spectral and analytical techniques. Metal binding properties of the receptor 1 in aqueous ethanol medium were studied through absorption, emission and electrochemical studies. Emission analyses were performed at higher excitation wavelength (λex 750 nm). Binding studies exhibited specific “turn-on-type” fluorescent enhancement character of the receptor 1 for the Fe2+ ion (Ka = 6.67 × 105 M–1). The appreciable metal binding property of the receptor 1 was theoretically studied by the quantum mechanical calculation. In the illustration of metal binding mechanism three binding modes A, B and C for the receptor 1 with Fe2+/Fe3+ ions were proposed and the active molecular sites were analyzed using DFT descriptors, fukui functions and molecular electron density map (MEP). Theoretically results were correlated to the experimentally observed results.

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