THEORETICAL-STUDIES OF OPTICAL-ABSORPTION SPECTRA OF SOLITON CONTAINING POLYENES

Optical absorption spectra of polyenes with one, two and three charged solitons are calculated using the INDO method combined with configuration interaction. The calculations are performed both with and without counterions. The effect of screening of the Coulomb potential is studied and observed to increase the electron-hole interaction which is of vital importance for a qualitatively correct description of the excitation energies. In contrast to the results of single particle theories, the soliton-induced transition appears below midgap when no counterions are present. This excitation energy increases in the presence of counterions by about 0.2 eV, in excellent agreement with experimental data.