Plcosecond Laser Studies on Photochemical Reactions in Restricted Environments: The Photoisomerization of trans-Stfibene Complexed to Cyciodextrins

The effect on picosecond reaction dynamics due to complexation of a reactive molecule with cyclodextrins was examined, with the trans-cis photoisomerization of stilbene as an example. In the presence of a-cyclodextrin, a single, slow exponential decay of trans-stilbene fluorescence is observed, consistent with the formation of a single complex. In contrast, in the presence of 8-cyclodextrin, the fluorescence of trans-stilbene showed a clear double-exponential decay, consistent with the formation of two complexes. In the latter case, a dynamic equilibrium between a loose and a more tightly bound conformation of the complex is proposed, resulting in different photoisomerization reaction rates of trans-stilbene.