  Experimental measurements of electron transport properties of molecular
junctions are often performed in solvents. Solvent-molecule coupling and
physical properties of the solvent can be used as the external stimulus to
control electric current through a molecule. In this paper, we propose a model,
which includes dynamical effects of solvent-molecule interaction in the
non-equilibrium Green's function calculations of electric current. The solvent
is considered as a macroscopic dipole moment that reorients stochastically and
interacts with the electrons tunnelling through the molecular junction. The
Keldysh-Kadanoff-Baym equations for electronic Green's functions are solved in
time-domain with subsequent averaging over random realisations of rotational
variables using Furutsu-Novikov method for exact closure of infinite hierarchy
of stochastic correlation functions. The developed theory requires the use of
wide-band approximation as well as classical treatment of solvent degrees of
freedom. The theory is applied to a model molecular junction. It is
demonstrated that not only electrostatic interaction between molecular junction
and solvent but also solvent viscosity can be used to control electrical
properties of the junction. Aligning of the rotating dipole moment breaks
particle-hole symmetry of the transmission favouring either hole or electron
transport channels depending upon the aligning potential.
