Electronic Coupling for Donor-Bridge-Acceptor Systems with a Bridge-Overlap Approach

Understanding the modulation of the electronic coupling in donor-acceptor systems connected through an aliphatic bridge is crucial from a fundamental point of view as well as for the development of organic electronics. In this work, we present a first-principles approach for the calculation of the electronic coupling (or transfer integrals) in such systems via a block-diagonalization of the Fock/Kohn-Sham matrix of the supersystem, followed by a projection on the basis of the fragment orbitals of the donor and acceptor groups. The strength of the approach is that the bridge is shared by the donor and acceptor blocks in the diagonalization step, so that through-space and through-bond couplings are obtained simultaneously. The method is applied to two test sets: a series of fused-ring bridged systems and G(T)_nG DNA oligomers. The results for the first set are compared to experiment and show an average error lower than 10%. For the DNA set, we show that the coupling may be significantly larger (and the decay with length slower) when the entire backbone is included.