Exciton dynamics in light harvesting systems

The optical line shape of molecular ring aggregates with 18 molecular units, modeling bacteria photo-synthetic light harvesting systems, is investigated theoretically, The molecular units are described by two-level systems with an average excitation energy epsilon and interacting with each other through nearest-neighbor interaction. Furthermore, quasi-static and dynamic fluctuations of the local excitation energies are taken into account simulating slow motions of the protein backbone and fast molecular vibrations, respectively. The fluctuations are described by colored dichotomic Markov processes with exponentially decaying correlation functions with small (lambda(s)) and large (lambda) decay constants, respectively. The optical line shape is discussed in dependence of the model parameters including a possible elliptical deformation. Furthermore we investigate the coupled coherent and incoherent energy transport in chlorosomes. (C) 2002 Elsevier Science B.V. All rights reserved.