Optical absorption of molecular aggregates under the influence of coloured noise

Abstract

Optical absorption lineshapes of electronic excitations are calculated for dimers and molecular chains. The interaction with phonons is described by dichotomic and Gaussian stochastic processes with exponentially decaying correlation functions (coloured noise) generalizing in this way the Haken-Strobl-Reineker treatment. A closed system of equations is obtained for dimers with dichotomic fluctuations of the excitation energy and the lineshape can be determined exactly. In the case of Gaussian fluctuations an approximate treatment is used, which, when applied to dichotomic fluctuations, can be compared with the exact solution. The lineshape for electronic excitations is calculated for a linear chain within this approximation scheme for Gaussian fluctuations. It is shown that the lineshapes are asymmetric for slow fluctuations and symmetric in the case of fast fluctuations. Finally, the question of whether the properties of exciton transport can be derived from the absorption lineshape is briefly considered.