Binding of Coumarin 334 with β-Cyclodextrin and with C-Hexylpyrogallol[4]arene : Opposite Fluorescence Behavior

Abstract EN

We report here the structure of the host-guest complexes of Coumarin 334 (C334) with β-cyclodextrin (β-CD) and with C-hexylpyrogallol[4]arene (C-HPA) and the effect of acidity on the neutral-cation equilibrium of C334 in water and in the presence of the host molecules.

The structures of the host-guest complexes are proposed on the basis of the change of fluorescence on the addition of β-CD or C-HPA to C334 and by 2D ROESY spectroscopy.

Opposite fluorescence behaviors, that is, quenching of fluorescence in β-CD and enhancement of fluorescence in C-HPA are observed.

Time-resolved fluorescence analysis is done for the complexation, and biexponential decay pattern is observed.

The possible strong inclusion complexation with C-HPA is explained.

The ground and the excited state pKa values for the protonation equilibrium of C334 in water and the difficulty of protonation in the presence of the host molecules are discussed.