MULTICHROMOPHORIC CYCLODEXTRINS .4. LIGHT CONVERSION BY ANTENNA EFFECT

A water soluble beta`-cyclodextrin (CD-NA) bearing seven naphthoyl chr omophores forms ver stable 1:1 complexes with a merocyanine laser dye DCM-OH -(bis(hydroxyethyl)amino)-styryyethyll)-4H-pyran): The antenna effect, i.e. energy transfer from the naphthoyl antenna chromophores t o the encased dye,is shown to occur with 100% efficiency. The stabilit y of the complexes is very high (K-s approximate to 10(5)) owing to th e contribution of the naphthoate residues. The structural features of the complexes have been examined in detail: circular dichroism experim ents confirm the expected axial orientation of DCM-OH in the cavity of CD-NA, and fluorescence anisotropy measurements together with C-13-NM R longitudinal relaxation time measurements show that the complex form ed between CD-NA and DCM-OH is tight. The mechanisms of homotransfer ( i.e., between naphthoate chromophores) and heterotransfer (i.e., from naphthoate chromophores to DCM-OH included in the cavity) are discusse d in light of existing theories. In both cases, the major contribution arises more likely from Coulombic interaction than from short-range i nteractions. Such multichromophoric cyclodextrins are good model for m imicry of the antenna function in photosynthesis and show great promis e as photochemical microreactors.