MO calculations on the absorption spectra of organic dimers. The interaction energy between dipole moments of electronic transitions in monomers and the shape of absorption bands

The interaction energy between dipole moments of electronic transitions in the monomers and the shape of absorption bands of organic dimers are calculated by the CNDO/S-CI method. It is found that the through-space resonance interaction between π orbitals of the monomers has a strong effect on the shifts and widths of absorption bands of dimers with the structure of H-aggregates. A large intermediate region of structures is found between structures corresponding to H- and J-aggregates. In the intermediate region, the interaction energy between the dipole moments of electronic transition in the monomers is small, and the dimer has a broad unshifted spectral band similar to that of the monomers. The large size of the intermediate region is due to a violation of the point-dipole approximation.