A novel pH probe based on ratiometric fluorescent properties of dicyanomethylene-4H-chromene platform

We report here a ratiometric pH probe (Z)-2-(2-(2-(4-hydroxyphenyl)-2-(pyrrolidin-1-yl)vinyl) -4H-chromen-4-ylidene)-malononitrile over the pH range of 2.44-6.00. It was synthesized by Knoevenagel Reaction from dicyanomethylene-4H-chromene and pyrrolidine. This is the first example of pyrrolidine as a part of the product structure in Knoevenagel condensation. High selectivity and sensitivity for pH variation were observed with significant fluorescent ratiometric responses and a remarkable Stokes shift (about 138nm). The probe was stable in the studied solvent and no obvious fluorescence changes were detected in acidic media within one month at room temperature.