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

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.