A reaction-based carbazole-dicyanovinyl conjugated colorimetric and ratiometric fluorescent probe for selective detection of cyanide ions.

In the present work, 4-(9'-hexylcarbazol-3'-yl)benzylidenemalononitrile 5 (probe L) was tested as a colorimetric and ratiometric fluorescent probe in dimethyl sulfoxide (DMSO) medium towards anions, cations and neutral molecules. The sensing properties of probe L were investigated by using UV-Vis absorption and fluorescence spectroscopy techniques. Probe L showed selectivity and sensitivity towards cyanide ions (CN) in the presence of analytes used. Upon the addition of CN, intramolecular charge transfer (ICT) band at 425 nm in UV spectrum disappeared. In addition, ICT emission intensity at 593 nm decreased and ligand-centred (LC) emission intensity at 480 nm increased. These findings indicate that nucleophilic conjugate addition of CN to the dicyanovinyl group of probe L successfully occurs, hence forming a new adduct between probe L and CN. In this adduct, π-conjugation was partially blocked, and the ICT transfer was hindered. Adduct formation was proved by Job's plot, H NMR and FT-IR analysis. Probe L showed very low limit of detection (LOD) value of 1.467 nM towards CN. Probe L was also applied to the CN detection in real-world water samples by the spike and recovery method. The maximum relative standard deviation (RSD) value was 4.24, indicating this method works successfully. Therefore, probe L could find a potential use in detection of CN in liquid media.