AIE-active bis-cyanostilbene-based organogels for quantitative fluorescence sensing of CO2 based on molecular recognition principles

Abstract

Carbon dioxide is a major greenhouse gas, probably responsible for climate change, and a safety concern for workers under specific conditions. Simple and effective means for its detection are thus highly desirable. Herein, the aggregation-induced emissive bis-cyanostilbene derivative 1 was used to develop two sensor systems based on (i) dispersed gel aggregates and (ii) solid supported xerogels for the optical detection of CO₂ gas. In the presence of diethylamine, CO₂ is transformed into a carbamate ionic liquid (CIL), which binds to 1 acting as an anion receptor. The formation of such a host–guest adduct alters the aggregation state of the system and consequently its fluorescence, which thus responds to CO₂ concentration. While the gel aggregate sensing system responds to CO₂via fluorescence quenching, the xerogel sensor system works in a dual mode, i.e., by both fluorescence quenching and modulation, reaching very high sensitivity and a low detection limit (4.5 ppm). The sensing behavior of 1 (gel aggregate and xerogel systems) towards CO₂ gas was studied in detail by solid state fluorescence and solution ¹H-NMR spectroscopies.