Abstract Dissipative excitation energy transfer in chromophore complexes (CC) is studied theoretically within the Frenkel-exciton model and in utilizing the density matrix theory. The obtained density matrix is used to compute the cw-absorption via a time-dependent formulation of optical spectra. Structural and energetic disorder is accounted for within a numerical Monte Carlo treatment. The approach is used to interpret recent measurements on Langmuir–Blodgett-layers (LB) formed of behenic acid molecules and doped by pheophorbide-a. Additionally, absorption spectra obtained for photosynthetic antenna systems are simulated.