Effect of beta-cyclodextrin on the excited state proton transfer in 1-naphthol-2-sulfonate

The photophysical properties of 1-naphthol-2-sulfonate (1-NOH-2-S) in vario us solvents and in aqueous B-cy clodextrin (CD) solution have been investig ated. The fluorescence quantum yields in non-aqueous solvents are approxima tely 0.5, while in water the fluorescence quantum yield is 0.1. The fluores cence quantum yield doubled on the addition of beta -CD. In aqueous solutio n, proton transfer to water takes place efficiently leading to the formatio n of the anion form with its longer wavelength emission broad band at about 460 nm. Any environmental changes have been found to affect the rate of de protonation and subsequently the band intensity at 460 nm. In non-aqueous s olution the anion emission band disappears completely. Upon the addition of beta -CD to the aqueous solution of 1-NOH-2-S, the anion emission decrease s with an increase in the intensity of the neutral form at 362 nm. Fluoresc ence measurements show 1:1 inclusion of 1-NOH-2-S in the beta -CD cavity wi th an association constant of 1915 M-1 using Benesi-Heldbrand treatment. H- 1 NMR studies are used to confirm the inclusion and to provide information on the orientation of 1-NOH-2-S inside the cavity of beta -CD (C) 2001 Else vier Science B.V. All rights reserved.