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 help of ab initio Hartree-Fock calculations in the framework of a two-state model. The calculated values of the ET coupling matrix element V-AB exhibit strong dependence on the basis set employed. A minimal basis set underestimates the value of V-AB with respect to an extended (double-zeta and polarization) basis set. The ET shows correlation with the electronic and geometrical 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 element V-AB is calculated to have its maximum value when the two end groups attached to the cage structures are coplanar, and its minimum value when two end pi groups are perpendicular to each other. However, for coplanar end-groups, minimal changes are noted in the value of V-AB with respect to the rotation of the sigma -bonded cage. The dependence of ET on the relative orientation of the planes of the end groups offers a mechanism for designing molecular switches. (C) 2001 American Institute of Physics.