Optical Sensing and Supramolecular Cyanide Recognition Sites of Salophenes as Molecular Tweezers: The First Example of Recognition via Intramolecular Aldimine Condensation Cyclization

Abstract The optical sensing and supramolecular cyanide recognition sites of two dipodal Schiff bases having conjugated to catecols (1) and phenols (2) (namely, salophenes 1 and 2) have been studied. In the case of optical sensing, both probes recognized only cyanide (CN¯) ions in 30% PBS buffer CH3CN (pH 7.4) as confirmed from the changes of absorption and emission bands, resulting in color changes. From the supramolecular recognition point of view, probes 1 and 2 show the different recognition bahaviour toward CN¯, as evidenced by the fluoroscence and NMR data, as well the OH¯ and reversibility experiments. While 1 recognizes CN¯ via deprotonation, that of 2 is the first example of Schiff base which senses CN¯ through an intramolecular aldimine condensation cyclization, leading to formation of dihydroxyquinoxaline 4. In general, probes 1, 2 and 4 are promising on-site optical sensors in terms of easy prepared, selectivity, sensitivity (1–10 nM), ease of use, rapid response (< 5 s) and test kits.