Fluorescence enhancement of 1-napthol-5-sulfonate by forming inclusion complex with β-cyclodextrin in aqueous solution

Abstract

Fluorescence enhancement of 1-naphthol-5-sulfonate (1N5S) upon inclusion in β-cyclodextrin is studied by spectrophotometry and spectrofluorimetery techniques. The spectral shifts were only observed in the emission spectra in different solvents and were found to be directly correlated to the solvent's hydrogen-bond donor strength (α). Spectral changes in the absorption spectra upon the addition of β-cyclodextrin to 1N5S in aqueous medium were too small to allow for the determination of the binding constant. On the other hand; fluorescence measurements show that the emission of both the anionic and neutral forms of 1N5S increase upon the addition of β-cyclodextrin with an increase in the quantum yield by about 60%. Fluorescence measurements show 1:1 inclusion of 1N5S in the β-cyclodextrin cavity with an association constant of 88 ± 10 M −1. 1H NMR studies are used to confirm the inclusion and to provide information on the geometry of 1N5S inside the cavity of β-cyclodextrin.