Tunable phenothiazine hydrazones as colour displaying, ratiometric and reversible pH sensors

Abstract Design, synthesis and characterization of pH responsive, ratiometric and colorimetric phenothiazine hydrazone sensors have been described. Structural modifications in probes 1 – 3 lead to fine tuning of colour, absorption and pH in both acidic and basic pH ranges. Probe 1 acts as a pH sensor in 11–14 pH range with a tetracolour change from yellow to orange to red to magenta-purple whereas 3 acts as a pH sensor in 2–9 pH range accompanied by a colour change from pale-yellow to yellow. Probe 3 also displays fluorescence quenching through d-PET mechanism. NMR studies were performed to get an insight into the interaction of the probes ( 1 – 3 ) with H + /OH − . UV absorption, fluorescence emission and colour switching of the synthesized molecules were found to be reversible upon a change in the pH.