Low-temperature three-terminal transport measurements through a thiol end-capped pi-conjugated molecule have been carried out. Electronic excitations, including zero and finite-bias Kondo-effects, have been observed and studied as a function of magnetic field. Using a simplified two-orbital model, we have accounted for the spin and the electronic configuration of the first four charge states of the molecule. The charge-dependent couplings to gate, source, and drain electrodes suggest a scenario in which charges and spins are localized at the ends of the molecule, close to the electrodes.

We have studied the gate and temperature dependence of molecular junctions containing sulfur end-functionalized tercyclohexylidenes. At low temperatures we find temperature-independent transport; at temperatures above 150 K the current increases exponentially with increasing temperature. Over the entire temperature range (10−300 K), and for different gate voltages, a simple toy model of transport through a single level describes the experimental results. In the model, the temperature dependence arises from the Fermi distribution in the leads and in a three-parameter fit we extract the level position and the tunnel rates at the left and right contact. We find that these parameters increase as the bias voltage increases.