Multichromophoric Cyclodextrins. 6. Investigation of Excitation Energy Hopping by Monte-Carlo Simulations and Time-Resolved Fluorescence Anisotropy

• Published in: Journal of the American Chemical Society Vol. 121; no. 11; pp. 2526 - 2533
• Main Authors: Berberan-Santos, Mário N, Choppinet, Patricia, Fedorov, Aleksandre, Jullien, Ludovic, Valeur, Bernard
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.03.1999
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja983601n

Excitation energy transport in several β-cyclodextrins containing seven appended chromophores was studied theoretically and experimentally by steady-state and time-resolved fluorescence anisotropy. The absorption spectra compared to those of reference chromophores did not reveal significant interactions between the chromophores in the ground state, thus allowing us to assume a very weak coupling regime for energy transfer. The measured long time anisotropies were found to be in all cases close to one-seventh of the fundamental anisotropy, showing that the chromophores are randomly oriented. A realistic model in which the chromophores are in fixed positions but randomly oriented was developed to interpret the steady-state and time-resolved emission anisotropy data. A Monte-Carlo simulation based on the appropriate master equation allowed the calculation of the theoretical anisotropy decay in terms of reduced variables and parameters. The decay contains a wide spectrum of rate constants. A good fit to the experimental decays was obtained. Moreover, the nearest-neighbor distance recovered from the anisotropy and the steady-state anisotropy for all cyclodextrins (5−7 Å in all cases) are compatible with the nearest-neighbor distances expected from molecular modeling, which confirms the validity of the theoretical model.