EXCIMER FLUORESCENCE OF TRANS-STILBENE IN TERNARY AQUEOUS-SOLUTIONS OF GAMMA-CYCLODEXTRIN

A dual fluorescence of trans-stilbene (TS) is reported which involves an apparent ternary complex of TS/gamma-cyclodextrin/cyclohexane. This dual fluorescence is not observed to an appreciable extent in the absence of cyclohexane. Only monomer fluorescence of TS is observed in the latter samples. These observations are interpreted in terms of spatial and screening restrictions on the TS photoisomerization and cycloaddition. The cyclohexane in the ternary complex is believed to induce restrictions by co-inclusion into the cyclodextrin cavity. As a result, formation of the cis-isomer upon irradiation is reduced. Consequently, the excimer yield of TS is increased. The inclusion of cyclohexane as a partition between two included stilbene molecules in the cyclodextrin cavity is also proposed. This is the first reported excimer of TS in fluid or aqueous cyclodextrin solutions which does not involve covalently linked or severely constrained TS molecules. Alcohols and other hydrophobic compounds such as toluene, xylene, and hexane are also examined as ternary components.