Phenothiazine-based oligomers as novel fluorescence probes for detecting vapor-phase nitro compounds

To meet the need for rapid and low-cost chemical sensing of explosive, new fluorescence chemosensors based on oligophenothiazines for probing vapor-phase nitro compounds have been developed. The phenothiazine-based trimer P3 and pentamer P5 have been synthesized via Heck and Wittig reactions by convergent approach. It was found that they can detect the vapors of nitro compounds, including p-nitrotoluene (p-NT), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) with good sensitivity and reversibility. And the sensor of P3 film gave a linear fluorescence quenching response to 7-800 ppb TNT with the detection limit of 4 ppb. For DNT vapor, a linear working range of the sensor was 2-24 ppm with the detection limit of 40 ppb. Meanwhile, the interferents, including common organic solvents, p-nitrophenol and 2,4-dinitrophenylhydrazine cannot lead to obvious fluorescence quenching, meaning that the film based on oligophenothiazines exhibited good specificity of fluorescence response to explosive. Based on the fluorescence lifetime and UV-vis absorption measurements, we suggested that the fluorescence quenching of oligophenothiazine-based films exposed to the vapors of nitro compounds was due to the formation of non-fluorescent charge-transfer complex between oligophenothiazine and nitro compounds.