Confinement effect on the photophysics of ESIPT fluorophores

Abstract

The photophysics of three benzothiazole derivatives that exhibit excited state intramolecular proton transfer (ESIPT) were investigated in a confined medium afforded by the water soluble supramolecular host octaacid (OA). The dye@(OA)₂ inclusion complexes were probed by UV-Vis absorption, steady-state and time resolved fluorescence emission techniques. Comparison studies of the free dyes in solution were also conducted. All three benzothiazole derivatives free in solution and as OA complexes in water absorb in the UV region. The fluorescence maxima of the OA complexes in water are similar to those in an apolar environment. This is different from the emission behavior of the dyes dissolved alone in water. The observed Stokes shift when confined within OA is related to the intramolecular proton transfer mechanism. Within OA only neutral species are present, indicating that these compounds are shielded from the bulk water. The excited state behavior of the benzothiazole derivatives in a confined medium indicates that supramolecular effects significantly alter the nature of the fluorescence emission.