SUPEREXCHANGE-PATHWAY MODEL FOR LONG-DISTANCE ELECTRONIC COUPLINGS

Long-distance electronic couplings for electron-transfer reactions are calculated in a method which makes use of McConnell's superexchange model. The necessary matrix elements come from ab initio molecular orbital calculations by transforming the UHF wave function to localized bond orbitals using Weinhold's natural bond orbital method. The result is a series of visualizable pathways between the donor (D) and acceptor (A) groups. When the material between the donor and acceptor is a saturated hydrocarbon, it is found that (1) the bulk of the interaction comes from pathways which "skip" over some bonds in contrast to the more usual "tight binding" picture, (2) C-C bonds provide most of the interaction, and (3) pathways containing C-H bonds give smaller contributions but cannot be neglected because they give rise to a large number of pathways. The method appears to have excellent potential for developing an understanding of how electronic coupling is transmitted through molecular material between donor and acceptor groups.