Charge transmission through single molecules: Effects of nonequilibrium molecular vibrations and photoinduced transitions

A density matrix based description of charge transmission through a single molecule attached to two nano-electrodes is presented. By concentrating on a steady state situation the net current, electronic state populations and nonequilibrium vibrational distributions are computed. The dependence of these quantities on the applied voltage and on a cw-infrared as well as optical excitation is discussed. Effects are included of intra-molecular vibrational energy redistribution (IVR), of different charging states, and of an electron-hole pair generation in the leads. The considerations are valid for a sequential mechanism of charge transmission through the molecule. A possible current switch due to an infrared as well as an optical excitation is demonstrated and the crucial dependence of the switching mechanism on the strength of IVR is underlined. If the molecule attached to nano-electrodes is a part of an oligomer or supramolecular chromophore complex the current can be controlled by an external field induced Frenkel-exciton formation.