Abstract We present a systematic density matrix theory of excitons interacting with charge transfer states in molecular systems subject to influence of a semiclassical bath. An excitonic dimer interacting non-linearly with an overdamped Brownian oscillator bath is studied, and the effect of eigenstate renormalization by interaction with the bath is shown to be essential in a correct description of the unusual temperature dependence of the absorption spectrum of the exciton-charge transfer state system. Ó 2006 Published by Elsevier B.V. Intermolecular charge transfer (CT) states, which occur in molecular aggregates with close packing of their building blocks, can strongly influence their exciton spectral properties [4] and references therein). Considerable effort has been invested into developing suitable theoretical models based on exciton-CT (EX-CT) state mixing that would allow for correct descriptions of absorption, Stark, hole burning and transient spectra of these systems Consider a dimer composed of two molecules, A and B. The electronic states of such an aggregate include excited states jEX A ae and jEX B ae representing excitation localized on the molecules A and B, respectively, while the other molecule is in its electronic ground state. Linear combinations of the states jEX A ae and jEX B ae form the usual excitonic states of the aggregate. Further, such a complex may display CT states jCT A ae and jCT B ae denoting transitions of an electron from the local excitation on molecule A to the molecule B and from B to A, respectively. W
