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 transition s 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-s pace resonance interaction between rr orbitals of the monomers has a s trong effect on the shifts and widths of absorption bands of diners wi th the structure of H-aggregates. A large intermediate region of struc tures is found between structures corresponding to H- and J-aggregates . In the intermediate region, the interaction energy between the dipol e moments of electronic transition in the monomers is small, and the d imer has a broad unshifted spectral band similar to that of the monome rs. The large size of the intermediate region is due to a violation of the point-dipole approximation.