Transmission properties of molecular switches in semiconducting polymers

The control of the transmission of electrons along a polyene chain by an impurity is studied. A semiconducting chain of atoms is modeled by a tight-binding Hamiltonian with alternating bonds into which the impurity is inserted. The energy-dependent transmission coefficient t and the change in the chain’s electronic density of states are extracted from the transfer matrix across the impurity. The switching ability of the impurity is considered by altering either its site energy or one of its bonds with the conducting chain. Invoking the Joyce-Dixon approximation enables us to write the Azbel’s energy-dependent effective-transmission coefficient ${\mathit{t}}_{\mathit{e}\mathit{f}\mathit{f}}$, in a for m where its Fermi level is temperature dependent, so that thermal effects can be investigated. The effects of site energy, impurity coupling, and bond ratio of both the impurity and chain are investigated by comparing their ability to alter the energy-averaged effective transmission coefficient as a function of either switching parameter to the ideal switch—a step function.