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.

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