A Novel Optical Sensor for Metal Ions Based on Ground-State Intermolecular Charge-Transfer Complexation

A derivative of dipyridylethylene 2 was synthesized in order to study intermolecular coordination between the 18-crown-6 ether units of bis-crown stilbene 1 and the NH3+ groups of 2. In acetonitrile solution, the formation of a supramolecular complex is evidenced by a considerable upfield shift of the 1H NMR signals from the aromatic and olefinic protons. Emission quenching and the appearance of a new absorption band in the visible spectral region indicate the formation of a charge-transfer complex. The addition of Ba2+ to a solution of the complex leads to significant fluorescence enhancement and to the disappearance of the charge-transfer absorption band.