A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene-porphyrin pair

A fullerene molecular tip was used to detect electron tunneling from a single porphyrin molecule. Electron tunneling was found to occur locally from an electron-donating moiety of the porphyrin to the fullerene through charge-transfer interaction between them. In addition, electron tunneling within the single fullerene-porphyrin pair exhibited rectifying behavior in which electrons can be driven only at the direction from the porphyrin to the fullerene. It is demonstrated that localized electron tunneling enables us to spatially visualize the frontier orbital of the porphyrin involved in electron tunneling. In addition, rectification demonstrates that the fullerene-porphyrin pair constitutes a molecular rectifier. We believe that molecular tips bring insight into intermolecular electron transmission toward realization of molecular electronics as shown here.