A wide-range fluorescent pH-indicator based on 3-hydroxyflavone structure

With the aim to develop wide-range pH-indicators, we synthesized a new water-soluble compound, 3,4′-dihydroxy-3′,5′-bis-(dimethylaminomethyl)flavone (FAM345), which displays a spectral sensitivity to pH in the range from 2 to 12 in absorption spectra as well as in fluorescence excitation or emission spectra. In all three cases, the estimation of pH is possible, either from the position of the maxima or from the absorbance or fluorescence intensity at one or several separated wavelengths, or also from absorbance or fluorescence intensity ratios. This last feature allows determining pH value of the medium independently from the probe concentration, from its possible photobleaching, as well as from any variation of light source intensity (at least in fluorescence methods).