ELECTRON-TRANSFER PROPERTIES OF QUANTUM MOLECULAR WIRES

It is shown that interelectrode tunnel current through a quantum molecular wire (QMW) depends essentially on the relation between the dynamic properties of QMW and the relaxation processes within electrodes and donor (acceptor) units. Within the framework of the adiabatic approximation, it is found that image forces from the electrodes change the tunnel current by several orders of magnitude. It depends on: (1) the position of the donor-bridge chain-acceptor (DBA) system with respect to the electrode surfaces; (2) the ratios between the static and high-frequency permittivities of the interelectrode medium; (3) the effective radii of donor (acceptor) and QMW units. The orientation effects connected both with the orientation of DBA units and with mutual spin orientations of neighbouring magnetic QMW units are studied. It is shown that even small changes of the orientation of porphyrin molecules may cause changes of several orders of magnitude of the QMW-mediated tunnel current. In the case of an antiferromagnetically ordered QMW, the interelectrode tunnel current can be regulated by a magnetic field in a wide region up to 7-8 orders of magnitude because of the ability of the magnetic field to influence changes in the spin orientations.