Influence of a Coordinated Metal Center on Charge Transport through a Series of Porphyrin Molecular Junctions

Porphyrin-based molecular wires as promising candidates for nanoelectronic devices have attracted much attention. Therefore, it is fundamentally important to investigate structure-electrical properties involving such molecules. Herein, a series of 5-ethynyl-2,3-dihydrobenzo[b]thiophene-substituted free-metal porphyrins and metalloporphyrins have been synthesized. Rigid, structurally well-defined, and highly conjugated porphyrin-based molecular wires offer a good platform to explore the impact of coordinated metal ions (Cu, Fe, and Zn) on charge transport at a single-molecule scale. Using the scanning tunneling microscope break-junction (STM-BJ) technique, it is found that single-molecule conductance can change by nearly 500% when the central coordinated metal ions are changed. The theoretically simulated energy-dependent transmission spectra reveal that the spin state of FeTPP can tune charge transport at E = E-F, and transmission coefficient T(E) is well correlated with the experimental observation. Our work proves a pronounced metal ion effect on charge transport through a porphyrin plane, providing guidance to design high-performance porphyrin-based nanodevices.