The present communication examines how the dynamics of the double helix affects the Frenkel excitons that
correspond to the low-energy absorption band of DNA. Two types of oligomers, (dA)
n
.(dT)
n
and
(dAdT)
n
/2.(dAdT)
n
/2, are studied theoretically, in the framework of the exciton theory in combination with
quantum chemical calculations. The properties of the exciton states (energy, oscillator strength, degree of
delocalization, “anisotropy”, etc.) found for canonical B-DNA geometries are compared to those obtained for
conformations extracted from molecular dynamics simulations. It is shown that, although structural fluctuations
reduce both the mixing between different monomer transitions and the spatial extent of the eigenstates,
excitations still remain delocalized over several bases. The presence of alternating base sequences makes the
eigenstates of the double-stranded oligomers more sensitive to disorder. All these effects result from a variation
of the coupling terms, with the diagonal energy being only slightly altered by the structural fluctuations. The
experimental absorption spectra presented here corroborate the theoretical results according to which the
absorption of (dA)
n
.(dT)
n
is centered at higher energies than that of (dAdT)
n
/2.(dAdT)
n
/2. Finally, it is shown
that, in contrast to what is commonly admitted, the formation of collective excited states in double-stranded
oligomers is not expected to induce large spectral shifts, with respect to a homogeneous mixture of monomers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.