Diminishable solvatochromic emission of a phenothiazine-derived triad for high-performance detection of ClO2

Phenothiazine (PTZ) chromophores have gained extensive attention due to easy modification and unique fluorescence property tuned by oxygen functionalization. Herein, a PTZ-derived triad HDPP-PTZ with strong intramolecular charge transfer (ICT) property is designed. Upon oxidizing the sulfur atom in the PTZ unit into sulfoxide, the polarity sensitive ICT emission of the synthesized fluorophore totally disappears. Inspired by the discovery, a highly selective, sensitive and rapid detection method for a widely used disinfectant chlorine dioxide (ClO2) is established. The detection limit (DL) in THF/water is < 0.052 mg/L, satisfying the setting limit by WHO (1.0 mg/L), and the response time is less than 20 s. Moreover, no significant interference is found. Take advantage of the remarkable fluorescence changes, real samples are visualized and evaluated by RGB analysis. Testing strips are further fabricated for in-situ and at real-time detection of ClO2 both in aqueous solution and gas states. Present study provides significant understanding of the oxidation states of the PTZ derivatives and guides development of fluorescent probes for specific analyte.