Solvent dependent photophysical properties and near-infrared solid-state excited state intramolecular proton transfer (ESIPT) fluorescence of 2,4,6-trisbenzothiazolylphenol

A new excited-state intramolecular proton transfer (ESIPT) fluorophore, 2,4,6-trisbenzothiazolylphenol (4), was synthesized and its photophysical properties were studied with steady state absorption and emission spectroscopy as well as time-dependent density functional theory calculation. It was found that 4 showed solvent dependent absorption and fluorescence emission. In the nonpolar solvents, ESIPT occurred and only keto tautomer emission at 570 nm was observed, whereas an emission at 510 nm from the deprotonated anion species was observed in polar solvents. With addition of fluoride, the keto emission was quenched, whereas the anion emission was drastically enhanced, making a ratiometric fluorescence sensing of fluoride achievable. In solid state, 4 showed a fluorescence emission at 605 nm, which is longer than those of 2,4-dibenzothiazolylphenol (575 nm) and 4-methyl-2,6-dibenzothiazolylphenol (592 nm) respectively. Thus, the color tuning of solid state ESIPT emission were achieved from green to yellow and near-infrared by extending of the pi-conjugation. (C) 2015 Elsevier Ltd. All rights reserved.