A Highly Selective and Sensitive 8-Hydroxyquinoline-Based Chemodosimeter for Turn-on Fluorescent Detection of Cyanide: Spectral and TD-DFT Studies.

A simple 8-hydroxyquinoline-based chemodosimeter R was developed to detect CN^- with high selectivity and sensitivity. The receptor R distinguished CN^- over other competing anions via a unique greenish-yellow fluorescence turn-on response resulting from the deprotonation, followed by a nucleophilic addition mechanism as evidenced by NMR and LC-MS analysis. The addition of CN^- to the olefinic bond interrupts the π-conjugation of the R and disturbs the ICT process, which instantly triggers the fluorescence turn-on response in R. The Job's plot analysis revealed a 1:1 binding stoichiometry between R and CN^-, with a strong binding affinity of 4.365 × 10⁴ M^-1. Theoretical studies reiterated the proposed sensing mechanism and uncovered the correlation between conformational constraints and fluorescence response. The remarkably low detection limit of R (0.3 µM), high specificity, anti-interference ability, and rapid optical responses of R towards CN^- motivated us to develop portable test strips and test buds coated with R for facile and on-site detection of CN^- ions.