Asymmetric electronic structures within a single molecule have been investigated by scanning tunneling microscopy and spectroscopy. Inside of a phenyl-linked porphyrin dimer, the asymmetric electronic structures are achieved by the incorporation of a cobalt ion in one porphyrin moiety. We find that a p-n junction between two π-conjugated segments is formed within the porphyrin dimer. The understanding of the local electronic structures of the intramolecular p-n junction should represent a fundamental step to realizing single molecular devices.
Keywords: Kondo effect; porphyrin; scanning tunneling microscopy; single-molecule electronics.