Theoretical investigation on the sensing mechanism of a fluorescent probe 3TBN for cyanide anion detection

In this study, we performed the theoretical simulations to investigate the sensing mechanism of a fluorescent probe 3TBN for cyanide anion (CN–) detection. This calculation details the interaction mechanism between 3TBN and CN– and the excited state properties for the probe 3TBN with addition of CN–. CN– attacks the CC bond of 3TBN, and induced the nucleophilic addition reaction. The Gibbs-free-energy profile demonstrates that the nucleophilic addition reaction is exothermic and has a low reaction barrier (19.0 kcal/mol), which are responsible for the rapid response speed of the probe 3TBN to the CN–. The larger binding energy and the strong interaction between 3TBN and CN– compared to other anions (F-, HCO3–, HSO3-, etc.) indicates that 3TBN has a high selectivity for CN–. The calculated spectrum of probe 3TBN and product 3TBN-CN are in reasonably good agreement with the experimental observations. The sensing mechanism of the probe 3TBN is attributed to the local excitation and the restraining of the intramolecular charge transfer (ICT) process.