Tuning the electrical conductance of metalloporphyrin supramolecular wires.

Mohammed Noori,Giuseppe Di Palma,Nadim Darwish,David B Amabilino,Ismael Díez-Pérez,Iain Grace,Albert C Aragonès,Steven W D Bailey,Qusiy Al-Galiby,Colin J Lambert,Arántzazu González-Campo

doi:10.1038/srep37352

Abstract

In contrast with conventional single-molecule junctions, in which the current flows parallel to the long axis or plane of a molecule, we investigate the transport properties of M(II)-5,15-diphenylporphyrin (M-DPP) single-molecule junctions (M=Co, Ni, Cu, or Zn divalent metal ions), in which the current flows perpendicular to the plane of the porphyrin. Novel STM-based conductance measurements combined with quantum transport calculations demonstrate that current-perpendicular-to-the-plane (CPP) junctions have three-orders-of-magnitude higher electrical conductances than their current-in-plane (CIP) counterparts, ranging from 2.10−2 G0 for Ni-DPP up to 8.10−2 G0 for Zn-DPP. The metal ion in the center of the DPP skeletons is strongly coordinated with the nitrogens of the pyridyl coated electrodes, with a binding energy that is sensitive to the choice of metal ion. We find that the binding energies of Zn-DPP and Co-DPP are significantly higher than those of Ni-DPP and Cu-DPP. Therefore when combined with its higher conductance, we identify Zn-DPP as the favoured candidate for high-conductance CPP single-molecule devices.

Highlights

Porphyrins offer a variety of desirable features as building blocks for future molecular-scale devices including their highly-conjugated structure, rigid planar geometry, high chemical stability and their ability to form metalloporphyrins by coordinating metal ions in the center of their macrocyclic and aromatic skeleton[1,2,3,4,5]
For all four metallo-porphyrins, we find that the energetically-most-favorable configuration occurs when the PY nitrogen atoms are located above the metal atom of the porphyrin
We have investigated the electrical conductance with the current perpendicular to the plane (CPP) of supramolecular metalloporphyrin wires

Summary

EB eV

Extension of previous experimental measurement[21] which showed that the CPP conductance of the flat-laying sandwiches of a Co(II)-DPP shows a large conductance value of three orders of magnitude higher than the measured in-plane conductance[10]

Results and Discussion

Conclusion

Additional Information