Frenkel Excitons (FEs) as collectivized electronic excitations are treated using two models of helical
two-strand regular polymers with B-DNA geometry. As basis excitations we consider two excitations of
a pair of complementary bases, not the excitations of separate bases (due to the permanent pairing, e.g.
A-T, of complementary bases and small inter-bases distance). The studied regular structures contain
combination of one pair only ordered as follows: A. Complementary homopolymers, i.e. pairing of
two strands each with one type of base (A or T) B. Self-complementary copolymers in which each
strand is supposed to contain alternatively ordered A-T-A:… (and each step of double helix contains the
pair A-T). The linear absorption and circular dichroism (CD), correspondingly the tensor of dielectric
permittivity and of gyration are calculated near the frequencies of FEs, using method of Green functions
at T=0 (T-temperature). Two types of FEs appear in the helices: a) two branches of FEs with transition
dipole moment perpendicular to the helical axis (like strong π→π* transitions) do not couple each
other; b) two branches with parallel to the axis n→π* transitions dipoles are mixed and this modulates
linear absorption spectra but for antiparallel DNA strands phenomenon CD in model B does not appear
near n→π* maxima. Exciton spectra and their splitting (like Davydov splitting) are exposed, as well as
the approximate connection between FEs of the pair and FEs of separate bases which compose the pair.
10.33425/2690-8077.1246
Published: 02 Sep, 2026