Excitons in Chains of Dimers

Abstract

Excitons in circular aggregates of dimers are discussed with the aim to understand the possible spectral and energy transfer properties of the ringlike peripheral complexes of photosynthetic bacteria. The system is explicitly heterogeneous (i.e., the difference in transition energies of the molecules within the dimer as, well as the difference in the intra- and interdimer resonance interactions, is accounted for). It is demonstrated that the energy spectrum of such a system exhibits many of the features as observed in spectrally inhomogeneous circular aggregates. The model is used to illustrate the changes in absorption and circular dichroism spectra that take place upon incorporating a dimer into a circular chain. The exciton dynamics in the aggregate is considered in the Haken−Strobl−Reineker approach. When terms are neglected describing the phase relaxation between nonnearest neighbors, the equations for the diagonal density matrix elements are obtained containing both coherent exciton motion within th...