Binding of coumarin 334 with β-cyclodextrin and with C-hexylpyrogallol[4]arene: Opposite fluorescence behavior

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 p k a values for the protonation equilibrium of c334 in water and the difficulty of protonation in the presence of the host molecules are discussed. © 2013 chandrasekaran sowrirajan and enoch israel vijayaraj muthu vijayan.