Comparative study of the dicyanovinyl-functionalized 1,1-dimethyl-2,3,4,5-tetraphenylsilole derivatives on their structures, properties, and applications in thiol detection

Abstract

Integrating electron-accepting dicyanovinyl (DCV) moieties with aggregation-induced emission (AIE)-active 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS) skeleton on the meta-positions of the 2,5-phenyl groups via simple Knoevenagel condensation derived the novel polar silole derivative, i.e. DMTPS-m-DCV. Systematic and comparative studies on the structures, properties and application in the thiol detection of DMTPS-m-DCV and its para-isomer DMTPS-p-DCV shed light on their structure-property relationships. The multiple rotors and non-planar 3D configurations bestow aggregation-enhanced emission (AEE) or AIE feature on them and the A-D-A type electronic structures impart intramolecular charge transfer (ICT) effect to them. The reactive DCV units endow these two isomers with the capability of specifically recognizing thiol species. The subtle variation in the substitution position of DCV units leads to a number of differences in the crystal and electronic structures, thermal stability, fluorescence properties, solvatochromism, ICT effect, thiol-reactivity, and thus detection performances. Benefiting from their AIE/AEE plus ICT attributes, both DMTPS-p-DCV and DMTPS-m-DCV perform well as ratiometric probes for thiols with minimal background noise, remarkable blue shift in fluorescence maxima, large enhancement in fluorescence intensity as well as high contrast in the biocompatible aqueous solutions or on the solid matrices. Intriguingly, DMTPS-p-DCV could differentiate cysteine (Cys) and homocysteine (Hcy) from glutathione (GSH) relying on the distinctive differences in kinetics. The fluorescence turn-on ratiometric probe DMTPS-m-DCV holds a superb sensitivity to Cys with a detection limit lower than 0.5 μM. Fast and sensitive responses of TLC plates with DMTPS-m-DCV spots to Cys in water demonstrated the practicability of these simple and handy test strips.