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Long-range electron tunnelling in oligo-porphyrin molecular wires


Short chains of porphyrin molecules can mediate electron transport over distances as long as 5–10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction.

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Figure 1: Structure of the oligo-porphyrins.
Figure 2: Single-molecule conductance data for the dimer.
Figure 3: Dependence of conductance of oligo-porphyrins on length.
Figure 4: Dependence of electron transmission on dihedral angle.
Figure 5: Dependence of conductance on temperature.


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This work was supported by the Engineering and Physical Sciences Research Council (EPSRC; grant nos EP/D07665X/1, EP/D076552/1 and GR/S84064/01), QinetiQ, the Department of Trade and Industry, the Royal Society and the Northwest Regional Development Agency. The authors thank the EPSRC mass spectrometry service (Swansea) for mass spectra. V.G-S. acknowledges his Ramón y Cajal position and his previous Juan de la Cierva position from the Ministerio de Ciencia e Innovación, Spain. S.M. acknowledges his Juan de la Cierva position from the Ministerio de Ciencia e Innovación, Spain. The NWGrid is thanked for computing resources.

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G.S. performed experimental conductance measurements and analysed the data, in part with the assistance of S.M. V.G-S. performed DFT computations and analysed computational data. L.J.E. synthesized and chemically characterized the compounds. M.E. originated the analytical model and further developed it in consultation with C.J.L. N.B. performed supporting STM characterization measurements and contributed to numerical calculations of the Lorentzian model. G.S., V.G-S., H.L.A., C.J.L., S.J.H., M.E. and R.J.N. were involved in writing the manuscript and supporting information. H.L.A., C.J.L., D.B., S.J.H., M.E., E.M. and R.J.N. provided supervision at the different sites.

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Correspondence to Harry L. Anderson or Colin J. Lambert or Richard J. Nichols.

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Sedghi, G., García-Suárez, V., Esdaile, L. et al. Long-range electron tunnelling in oligo-porphyrin molecular wires. Nature Nanotech 6, 517–523 (2011).

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