Novel Fluorescein-Based Fluorophores: Synthesis, Photophysics and Micro-Environmental Study.

Carboxylic acid substituted fluorescein derivatives were synthesized from 2,4-dihydroxy carboxylic acid and phthalic anhydride or trimellitic anhydride. The photophysical properties like absorption, emission and fluorescence quantum yields of these fluorophores were studied. The conjugation studies of these fluorophores with different proteins at different concentrations were carried out. The effect of pH on photophysical properties was studied at different pH ranges from 5 to 12. The change in the absorption and emission with respect to viscosity of medium was also studied. The changes in the electronic transition, energy levels, and orbital diagram of the fluorescein derivatives were computed using the TD-DFT computations and co-related with experimental photophysical data.