ELECTRON-TRANSFER PROPERTIES OF QUANTUM MOLECULAR WIRES

It is shown that interelectrode tunnel current through a quantum molec ular wire (QMW) depends essentially on the relation between the dynami c properties of QMW and the relaxation processes within electrodes and donor (acceptor) units. Within the framework of the adiabatic approxi mation, it is found that image forces from the electrodes change the t unnel current by several orders of magnitude. It depends on: (1) the p osition of the donor-bridge chain-acceptor (DBA) system with respect t o the electrode surfaces; (2) the ratios between the static and high-f requency permittivities of the interelectrode medium; (3) the effectiv e radii of donor (acceptor) and QMW units. The orientation effects con nected both with the orientation of DBA units and with mutual spin ori entations 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 tunne l current. In the case of an antiferromagnetically ordered QMW, the in terelectrode 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 th e magnetic field to influence changes in the spin orientations.