Conversion of tetraphenylethylene-substituted oxadiazolo[3,4-b]pyrazines into the corresponding imidazo[4,5-b]- and pyrazino[2,3-b]pyrazines, as chemosensors for the selective detection of nitroaromatics in aqueous media

Novel tetraphenylethylene-substituted [1,2,5]oxadiazolo[3,4-b]pyrazines have been synthesized, and their ability to be transformed into other annulated pyrazines in good yields has been demonstrated. The photophysical properties of all new fluorophores have been investigated, by using both absorption and emission spectral analyses in MeCN solutions and solid-state. All fluorophores proved to possess very low absolute quantum yields in solutions and absolute quantum yields up to 0.06 in solid-state, depending on their azine parts. The incorporation of tetraphenylethylene unit in the backbone endows the fluorophore a significant aggregation induced emission behavior. It has been demonstrated that novel tetraphenylethylene-substituted pyrazino[2,3-b]pyrazines can be used as aggregation induced emission active probes for the effective detection of nitroaromatics in solutions with a high selectivity, a high sensitivity and a fast response. On the basis of the experimental data and DFT calculations, it has been shown that a static mechanism of fluorescence quenching with a significant contribution of dynamic components takes place in case of new fluorophores. This research provides new insights into the rational design of aggregation induced emission fluorophores based on azaheterocyclic push-pull systems exploited for sensing applications.