Local solvent acidities in β-cyclodextrin complexes with PRODAN derivatives.

The local solvent acidities (SA scale) of six 6-carbonyl-2-aminonaphthalene derivatives as β-cyclodextrin complexes in water are determined through fluorescence quenching. The local polarities (E(T)(N) scale) are determined through the shift of the emission center-of-mass. The apparent SA values reflect the solvent structure surrounding the guest’s carbonyl group, whereas the apparent E(T)(N) values reveal the net polarity of the entire guest molecule. Comparison of these values affords greater insight into the structures of the host–guest complexes. Derivatives 1 and 5 show unusually large acidities, indicative of highly exposed carbonyl groups. The remaining compounds give emission intensities pointing to shielded carbonyl groups. In this study, PRODAN and its derivatives are functioning as dual channel sensors of their local environment.