A model describing photochemical processes in molecular dimers (bichromophores) is developed, incorporating electronic interactions between the dimer components that lead to intramolecular energy and charge transfer. The energy structure of the low-lying excited states is analyzed, and the dipole moments of the optical transitions are calculated. The effects of electron transfer matrix elements and medium interaction parameters on the absorption spectrum of the bichromophore are examined. The model is shown to reproduce some features of the absorption spectra of perylenediimide derivatives (tpPDI) in polar solvents.