ESIPT-inspired benzothiazole fluorescein: Photophysics of microenvironment pH and viscosity

A series of novel substituted ESIPT benzothiazole fluorescein derivatives were synthesized from the intermediate, (1H-benzo[d]thiazole-2-yl) benzene-1,3-diol and different anhydrides. The photophysical properties of these fluorescein derivatives were studied as a function of pH and viscosity. Enhancement in fluorescence emission was observed with increasing percentage of glycerin in water. The relative fluorescence quantum yields of these derivatives were determined by using anthracene and fluorescein as a reference standards. Density Functional Theory computations were performed to optimize the geometry at the ground state. The excited state geometry was optimized using the time dependent-DFT. The synthesized fluorescein derivatives were characterized by using elemental analysis, FT-IR and H-1 NMR spectroscopy. (C) 2013 Elsevier Ltd. All rights reserved.