Energy transfer and spectroscopic characterization of multichromophoric assemblies

The description and interpretation of electronic spectra of aggregates and the relationship of these quantities to the electronic transfer matrix element for energy transfer between its components are examined. An analysis of higher multipole interactions in the Coulombic integral as well as an introduction to the consequence of the ''through-configuration'' interaction (involving interchromophore charge transfer states) on spectral shifts, band intensities, and radiative rates is presented. It is found that as higher multipole contributions become significant in comparison with the dipole-dipole interaction, short-range, interchromophore orbital overlap (IOO) dependent interactions often become much greater than the higher multipole corrections to the dipole-dipole interaction. It is shown that IOO effects due to the through-configuration interaction may be evident in the absorption spectra of molecular aggregates as hypochromism or hyperchromism. It is postulated that fluorescence lifetime data for a single chromophore as compared to a dimer should convey information regarding the strength of the electronic coupling in the lowest excited state. The analysis of interactions that lead to interchromophore energy transfer or delocalization in photosynthetic light harvesting complexes, monolayer assemblies, and bichromophores is discussed.