Spectroscopic and TD-DFT Studies on Colourimetric Detection of Cyanide by a Triphenylphosphine-based Chemodosimeter Via ICT Modulation.

Cyanide, a silent pillar of modern industry, and its extreme effect on public health and the environment, even at trace levels, necessitate the development of sensors for CN− ions. Optical sensors are a better choice for cyanide detection due to their distinct benefits over conventional techniques. Concerning this, a triphenylphosphine-based chemodosimeter, SS1, was designed as a D-π-A system to make it effective to detect CN−. The unique, instantaneous and observable colour change of SS1 (yellow to lilac) and spectral modifications on contact with CN− attesting its selectivity towards CN−. The nucleophilic addition is a fact behind the colour and spectral responses of SS1 as uncovered from the UV-Vis, 1H NMR, 13C NMR, 31P NMR, and mass spectral analysis. Binding studies reveal a 1:1 stoichiometric ratio between SS1 and CN−, with a binding constant of 3.31 × 104 M− 1, indicating strong interaction and efficient cyanide recognition. The far below detection limit (55 nM) of SS1 to CN− authenticated its sensitivity in real matrices. The Density Functional Theory (DFT)/Time-Dependent Density Functional Theory (TD-DFT) calculations reveal that the added CN− triggered the spatial intramolecular charge transfer (ICT) in SS1 by conformational alterations through nucleophilic addition, offering a visual colour change, enabling naked eye CN− detection. The SS1 can be utilized for fingerprint visualization due to its excellent solid-state fluorescence. In addition to that, test buds and real-water analysis were also conducted to assess its real-world applicability, which substantiated the excellent sensing performance of SS1 in real-world matrices.