Exciton Band Structures in Polypeptides

Abstract

The singlet and triplet states of π-electrons in peptide group are first determined such that the ASMO–SCF–CI calculation including all the possible configurations can reproduce the observed wavelength of optical absorption maximum. It is shown that the doubly-excited configurations make a non-negligible contribution to the electronic states. Next, in terms of the Frenkel-Peierls method, the singlet and triplet exciton bands for both the H-bonded and the main polypeptide-chains in the two β-structures and in the α-helix are calculated to the second-order perturbation. It is shown that the exciton band structures are dependent only on the sorts of peptide-chains but non on the conformations, and that the interaction between bands does not exert any important effect on the structures.