Electronic excitations of polyalanine; test of the independent chromophore approximation

Abstract

Optical spectra of polyalanine in the W(nπ*) and NV₁(ππ*) bands are calculated using the time-dependent Hartree–Fock technique and the INDO/S Hamiltonian. Examination of the transition density matrices shows that excitations in the NV₁ band involve significant charge transfer between nearest and third-nearest neighbor amide groups. Our analysis suggests that the Frenkel exciton Hamiltonian cannot adequately describe the electronic excitations in the NV₁ band.