Ab initio Hartree-Fock study of electron transfer in organic molecules

Electron transfer (ET) in sigma -bonded organic cage structures (bicyclo[1. 1.1]pentane, cubane, and bicyclo[2.2.2]octane) has been studied with the he lp of ab initio Hartree-Fock calculations in the framework of a two-state m odel. The calculated values of the ET coupling matrix element V-AB exhibit strong dependence on the basis set employed. A minimal basis set underestim ates the value of V-AB with respect to an extended (double-zeta and polariz ation) basis set. The ET shows correlation with the electronic and geometri cal structure of the molecules studied. It is found that the more strained the chemical bonds in the cage structure are, the stronger is the coupling between the two states participating in ET. Furthermore, the ET matrix elem ent V-AB is calculated to have its maximum value when the two end groups at tached to the cage structures are coplanar, and its minimum value when two end pi groups are perpendicular to each other. However, for coplanar end-gr oups, minimal changes are noted in the value of V-AB with respect to the ro tation of the sigma -bonded cage. The dependence of ET on the relative orie ntation of the planes of the end groups offers a mechanism for designing mo lecular switches. (C) 2001 American Institute of Physics.