Prediction of hydrazone colorimetric response for Novichok sensing: a combined experimental and TD-DFT study

Organophosphorus nerve agents, including Novichok agents, are highly toxic chemical warfare compounds regulated under the Chemical Weapons Convention (CWC). Detecting these agents is challenging due to their limited accessibility. This study presents a novel approach using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) to model and predict the colorimetric response of hydrazone-based chemosensors for Novichok detection. UV-visible spectroscopic data were collected for both neutral and anionic forms of hydrazone derivatives, revealing significant shifts in absorption maxima (λ max ) and molar absorption coefficients. A benchmark study comparing five hybrid functionals (B3LYP-D3, PBE0-D3, ωB97X-D, M06-2X, and CAM-B3LYP-D3) revealed that PBE0-D3 was most accurate for neutral species, while B3LYP-D3 performed best for anionic species. Theoretical UV-visible spectra and RGB triplets were generated to predict the visual color renderings. The predicted colors were compared with experimental observations, showing good agreement for neutral species and improved accuracy for anionic species after applying a spectral shift of +27 nm. This methodology enables the accurate prediction of colorimetric responses for hydrazone chemosensors, facilitating the design of new detection methods for Novichok agents without direct manipulation of these hazardous compounds. In conclusion, this study demonstrates the potential of DFT/TD-DFT modeling to enhance the development of colorimetric detection methods for chemical warfare agents, contributing to advancements in chemical safety and security.