Synthesis of a new fluorescent cyanide chemosensor based on phenothiazine derivative

Abstract

A new phenothiazine derivative containing two dicyano-vinyl groups as the cyanide receptor on both sides was synthesized and fully characterized. The chemosensor showed an intramolecular charge transfer (ICT) absorption band at 494 nm and emission band at 633 nm in acetonitrile solution. Upon titration with different concentrations of cyanide anion both absorption and emission bands decreases in a ratiometric manner. This optical response for cyanide anion is due to the nucleophilic Michael addition of CN− on the α-position of the dicyano-vinyl groups present in the chemosensor in both sides and thus converting these electron acceptors to anionic electron donors and consequently breaking the conjugation, which ultimately affect the ICT and the fluorescence of the chemosensor. The result indicated that the chemosensor showed high sensitivity with a fast response of less than 50 s and selectivity toward cyanide anion with a detection limit as low as 3.2 × 10−9 M, which is the lowest ever reported. The chemosensor reaction mechanism with CN− was studied by 1H NMR and 13C NMR, FTIR and mass spectroscopies.