MULTICHROMOPHORIC CYCLODEXTRINS .2. INHOMOGENEOUS SPECTRAL BROADENINGAND DIRECTED ENERGY HOPPING

A beta-cyclodextrin bearing seven 2-naphthoyloxy chromophores is a goo d model for the study of the effect of the excitation wavelength on en ergy hopping among chromophores in well-defined positions, as in photo synthetic antennae. Absorption spectra, emission spectra, and excitati on polarization spectra were recorded in a propylene glycol-dioxane gl ass at 200 K. Comparison is made with a bis(naphthoate) bichromophoric molecule. The parallelism between the increase of emission spectrum d isplacement and fluorescence anisotropy observed for the red edge of m ost vibronic bands, and especially for the 0-0 one, is established for the first time. It can be interpreted in terms of inhomogeneous spect ral broadening due to solvation heterogeneity. The decrease of energy transfer that is observed upon red-edge excitation is evidence that en ergy hopping is not chaotic but directed toward lower-energy chromopho res.