The Electrical Properties of Porphyrin Single Molecule Wires

Abstract

Measurement of the electrical properties of porphyrin single molecular wires sandwiched between metal contacts is now an experimental reality and such methods have contributed to understanding charge flow through and the current-voltage response of porphyrin wires. We have exploited scanning-tunneling-microscopy-based methods such as the STM break junction method and the non-contact I(s) technique (I=current and s=distance between STM tip and substrate) for achieving this feat. In both these techniques single molecule junctions are formed by bringing a gold STM tip into contact or very close to the gold substrate surface. As the tip is rapidly retracted the conductance of the porphyrin molecule junction or the complete current-voltage response can be recorded. When combined with statistical analysis this provides a strong platform for investigating the electrical properties of porphyrin junctions. This presentation will review some of our findings on the electrical properties of porphyrin single molecule wires as well as presenting our latest data recorded using the STM break junction method, with a focus on the mechanochemical properties of 5,15-diaryl porphyrins with thiol end groups. Topics to be discussed include:(1) The mechanochemical properties of 5,15-diaryl porphyrins with thiol end groups. (2) Single molecule junction formation mechanisms and evolution during junction stretching.(3) The influence of contacting groups on porphyrin electrical junctions.(4) Long range electron transport in porphyrin oligomers, their current-voltage response and unusual voltage dependent length decay of conductance.(5) Mechanisms of charge transport in porphyrin single molecule wires.REFERENCES to our work on porphyrin single molecule electronics(1) G. Sedghi, K. Sawada, L. J. Esdaile, M. Hoffmann, H. L. Anderson, D. Bethell, W. Haiss, S. J. Higgins, and R. J. Nichols, Single Molecule Conductance of Porphyrin Wires with Ultralow Attenuation, Journal of the American Chemical Society 130, 8582 (2008).(2) G. Sedghi, V.M. Garcia-Suarez, L.J. Esdaile, H.L. Anderson, C.J. Lambert, S. Martin, D. Bethell, S.J. Higgins, M. Elliott, N. Bennett, J.E. Macdonald and R.J. Nichols, Long-range electron tunnelling in oligo-porphyrin molecular wires, Nature Nanotechnology, 6, 517-523, (2011).(3) G. Sedghi, L.J. Esdaile, H.L. Anderson, S. Martin, D. Bethell, S.J. Higgins and R.J. Nichols, Comparison of the Conductance of Three Types of Porphyrin-Based Molecular Wires: beta,meso,beta-Fused Tapes, meso-Butadiyne-Linked and Twisted meso-meso Linked Oligomers, Advanced Materials, 24, 653-, (2012).(4) Edmund Leary, Cécile Roche, Hua-Wei Jiang, Iain Grace, M. Teresa González, Gabino Rubio-Bollinger, Yaoyao Xiong, Qusiy Al-Galiby, Maria A. Lebedeva, Kyriakos Porfyrakis, Nicolás Agrait, Andrew Hodgson, Simon J. Higgins, Colin J. Lambert, Harry L. Anderson, and Richard J. Nichols, JACS submitted 2017. Figure 1