Modeling excitonic line shapes of photosynthetic light harvesting systems:influence of quasi-static and dynamic disorder

The modeling of optical line shape of molecular ring aggregates with 9 and 18 molecular units of photosynthetic bacteria light-harvesting systems is i nvestigated theoretically. The molecular units are described by two-level s ystems, with an average excitation energy epsilon, which interact with each other through nearest-neighbor interaction. A possible dimerization is tak en into account by allowing for alternating strong (J(S)) and weak (J(W)) t ransfer integrals. Furthermore, quasi-static and dynamic fluctuations of th e local excitation energies an taken into account simulating slow motions o f the protein backbone and fast molecular vibrations, respectively. The flu ctuations are described by colored dichotomic Markov processes with exponen tially decaying correlation functions with small (lambda(s)) and large (lam bda) decay constants, respectively. The optical line shape is discussed wit h respect to the model parameters. (C) 2000 Elsevier Science B.V. All right s reserved.