beta-Cyclodextrin-Promoted Colorimetric and Fluorescence Turn-on Probe for Discriminating Highly Toxic Thiophenol from Biothiols

A complex that was composed of beta-cyclodextrin (beta-CD) and a flavone derivative (compound 5) was designed as a colorimetric and fluorescence turn-on probe to discriminate thiophenol (PhSH) from biothiols in environmental water samples. The probe worked via a combination of photoinduced electron transfer (PET) and excited-state intramolecular proton transfer (ESIPT) mechanisms. In this complex (beta-CD-5), the 2,4-dinitrobenzenesulfonyl group efficiently quenched the fluorescence of compound 5 through a PET mechanism, and sulfonate was cleaved by PhSH to produce a compound that has strong fluorescence. Meanwhile, ESIPT fluorescence that originated from the flavone was observed. Significantly, beta-CD improved the response time and sensitivity of compound 5 with respect to PhSH. Under optimized conditions, the response time was 5 min, and the limit of detection of beta-CD-5 for PhSH was similar to 2.8 nM. The outstanding sensing performance of beta-CD-5 was demonstrated to be originated from the geometric match between compound 5 and beta-CD and enrichment of PhSH in the beta-CD cavity.