Simulation of excitonic optical line shapes of cyclic molecular aggregates with 9 and 18 units:: influence of quasi-static and dynamic disorder

For Frenkel excitons moving on molecular rings modeling in part bacteria photosynthetic antenna systems we investigate the influence of dynamic and static disorder on their optical line shape. The dynamic disorder, describing the influence of vibrational degrees of freedom, and static disorder are taken into account by fluctuations of the local excitation energies of the BChl molecules. The fluctuations are represented by dichotomic Markov processes with colored noise with different amplitudes and decay constants of the correlation functions. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape which is solved numerically. We display the optical line shapes of the circular aggregates with 9 and 18 BChls for different regimes of the exciton transfer under the influence of the disorders. The line shapes are discussed for various sets of the model parameters describing static and dynamic disorders. (C) 1999 Elsevier Science B.V. All rights reserved.