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

Abstract

The modeling of optical line shape of molecular ring aggregates with 9 and 18 molecular units of photosynthetic bacteria light-harvesting systems is investigated theoretically. The molecular units are described by two-level systems, with an average excitation energy ε, which interact with each other through nearest-neighbor interaction. A possible dimerization is taken into account by allowing for alternating strong ( J S) and weak ( J W) transfer integrals. 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 ( λ s) and large ( λ) decay constants, respectively. The optical line shape is discussed with respect to the model parameters.