Localized and delocalized electronic excitations in biological and artificial antenna complexes

The Collective Electronic Oscillators (CEO) approach based on the Time-Dependent Hartree-Fock approximation is applied to analyze localization and delocalization of electronic excitations, charge and energy transfer in LH2 aggregates (biological antenna complexes) and in phenylacetylene dendrimers (artificial antenna macromolecules). Two-dimensional analysis of transition density matrices indicates that electron-hole pairs created upon optical excitation in LH2 aggregate are localized within separate chromophores. In addition LH2 has a band of low-lying charge-transfer states unaccessible with linear absorption spectroscopy. In phenylacetylene dendrimers, electronic excitation are shown to be localized within linear segments connected by benzene rings substituted at the meta-position. These results are used to construct effective Frenkel exciton hamiltonians in these biological and artificial light-harvesting antenna complexes.