Sensing behaviours to Fe³⁺, Co²⁺ ions and cyanide detection performance of 4,5-diazafluorene-based colorimetric chemosensors

Three novel colorimetric chemosensors were synthesized by Schiff base condensation of 4,5-diazafluoren-9-one with different hydrazine derivatives, which included benzothiazole (DAF-BT), quinoline (DAF-QU) and phthalazine groups (DAF-PHT). Structural characterization was supported by Fourier transform infrared spectroscopy, and nuclear magnetic spectroscopy (¹H-NMR and ¹³C-NMR) analyses. Photophysical properties of colorimetric chemosensors synthesized in the study were investigated systematically in different solvents of polarities such as chloroform, dichloromethane, acetonitrile, and then their sensing probe activities mainly with Fe⁺³ and Co⁺² ions were evaluated using UV-vis absorption and fluorescence emission spectroscopy. DAF-PHT, DAF-QU and DAF-BT chemosensors absorption maxima between 424 and 492 nm were associated with the intramolecular charge transfer transitions, and metal sensing abilities were also supported by the formation of metal-to-ligand charge transfer transitions. One of the studied complex, sensor DAF-PHT/Co²⁺, showed highly selective to CN^- anion in acetonitrile solution and colour changes could be detected with the naked eye. (author)