  We study the model of a molecular switch comprised of a molecule with a soft
vibrational degree of freedom coupled to metallic leads. In the presence of
strong electron-ion interaction, different charge states of the molecule
correspond to substantially different ionic configurations, which can lead to
very slow switching between energetically close configurations (Franck-Condon
blockade). Application of transport voltage, however, can drive the molecule
far out of thermal equilibrium and thus dramatically accelerate the switching.
The tunneling electrons play the role of a heat bath with an effective
temperature dependent on the applied transport voltage. Including the
transport-induced "heating" selfconsistently, we determine the stationary
current-voltage characteristics of the device, and the switching dynamics for
symmetric and asymmetric devices. We also study the effects of an extra
dissipative environment and demonstrate that it can lead to enhanced
non-linearities in the transport properties of the device and dramatically
suppress the switching dynamics.
