A Novel Ferrocenyl Naphthoquinone Fused Crown Ether as a Multisensor for Water Determination in Acetonitrile and Selective Cation Binding

A multisensor which is based on a novel multifunctional triad molecule, ferrocenyl naphthoquinone fused crown ether (Fc-cnq) bearing ferrocene, quinone, and crown ether functional groups together, was synthesized and characterized in this study. Sensing performance of a trace amount of water and the selective cation binding capabilities of this multisensor were carried out by the electrochemical, spectroelectrochemical, and spectrophotometric titration techniques in acetonitrile (CH₃CN). It was shown that the potential separation (E^(Fc)_1/2 - E⁽²⁾_1/2) between the second reduction of naphthoquinone and the oxidation processes of ferrocene in the triad molecule Fc-cnq was proportional to the amount of water due to the hydrogen-bonding interactions between water and the doubly reduced species (Fc-cnq^2-). This property enabled Fc-cnq to detect the trace amount of water in CH₃CN. The half-wave potential (E^(Fc)_1/2) of the ferrocene in Fc-cnq was used as an internal reference potential, and it defined the accuracy of the detection. In addition, by using the UV-vis spectrophotometric titration technique in CH₃CN, it was also shown that the Fc-cnq multisensor could bind Ba²⁺ and Ca²⁺ cations selectively. We proposed that the intramolecular charge-transfer (CT) transition which occurred between the donor ferrocene and the acceptor naphthoquinone was the principle mechanism for the selective binding property of this multisensor. Quantum chemical calculations were also performed to investigate optical and electronic properties of the Fc-cnq molecule.