Synthesis and spectral properties of novel chlorinated pH fluorescent probes

► Eight chlorinated fluoresceins have been synthesized in the presence of methanesulfonic acid. ► Emission spectra of these compounds shifted towards long wavelength with increase in chlorine. ► Eight chlorinated fluoresceins showed a strongly pH-sensitive range of 3.0-7.0. ► They have emission maxima at long wavelengths and high fluorescence quantum yields.