Journal of the American Chemical Society
COMMUNICATION
For the longer derivatives, the effective through-π-system
coupling between the AuꢀC MOs is reduced. The correspond-
ing energy splitting between the even and odd combinations of
these MOs also gets smaller, and the two distinct resonances seen
for P1 merge into a single, broad feature at ∼ꢀ0.5 eV, with
decreased transmission at the peak (Figure 4b). However, the
distinct even and odd combinations of the AuꢀC MOs can still
be clearly seen in the transmitted scattering states (SI Figures
5ꢀ7). The charge transfer from the molecule to the electrodes is
similar to that for P1, and the Fermi level is pinned at an energy
just above the highest resonance. The computed decay constant
β for P2ꢀP4 is 1.2/phenyl group.
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There are inherent errors in the use of the DFT MOs and
energies for transport calculations in nanoscale junctions.18 While
the impact is minor for cases where the junction conductance is
close to G0, e.g., for metal point contacts,19 the calculated conduc-
tance values in the tunneling regime for single-molecule junctions
are typically larger than those measured in experiment.18d,f,20 In
the present case, we expect that corrections to the DFT-based
theory will only change the P1 transmission modestly, leaving a
resonance with near-unit transmission close to the Fermi energy.
However, the DFT-calculated π backbone MO energy is likely
too close to the Fermi energy in general, an effect that will be
larger for longer oligomers, where screening by the electrodes
becomes less effective. In this case, the conductance will be
smaller than indicated by the DFT calculations, with an increase
in the effective β value for P2ꢀP4.
In conclusion, we have demonstrated a clear method to create
circuits with strong electronic coupling between gold electrodes
and conjugated molecules. We achieve a single-molecule junction
conductance close to one quantum across a length of ∼0.8 nm. This
remarkable result opens up new methods to create long and
highly conducting molecular junctions.
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’ ASSOCIATED CONTENT
(12) Hybertsen, M. S.; Venkataraman, L.; Klare, J. E.; Whalley, A. C.;
Steigerwald, M. L.; Nuckolls, C. J. Phys.: Cond. Mat. 2008, 20, 374115.
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M. L.; Hybertsen, M. S.; Nuckolls, C.; Venkataraman, L. J. Am. Chem.
Soc. 2009, 131, 10820.
S
Supporting Information. Synthetic procedures, measure-
b
ment details, additional data, and computational details. This material
(14) Soler, J. M.; Artacho, E.; Gale, J. D.; Garcia, A.; Junquera, J.;
Ordejon, P.; Sanchez-Portal, D. J. Phys.: Cond. Mat. 2002, 14, 2745.
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’ AUTHOR INFORMATION
Corresponding Author
rb33@columbia.edu; mhyberts@bnl.gov; lv2117@columbia.edu
(17) Paulsson, M.; Brandbyge, M. Phys. Rev. B 2007, 76.
’ ACKNOWLEDGMENT
(18) (a) Toher, C.; Filippetti, A.; Sanvito, S.; Burke, K. Phys. Rev.
Lett. 2005, 95, 4. (b) Evers, F.; Weigend, F.; Koentopp, M. Phys. Rev. B
2004, 69. (c) Neaton, J. B.; Hybertsen, M. S.; Louie, S. G. Phys. Rev. Lett.
2006, 97, 216405. (d) Ke, S. H.; Baranger, H. U.; Yang, W. T. J. Chem.
Phys. 2007, 126, 201102. (e) Sai, N.; Zwolak, M.; Vignale, G.; Di Ventra,
M. Phys. Rev. Lett. 2005, 94. (f) Thygesen, K. S.; Rubio, A. Phys. Rev. B
2008, 77. (g) Thygesen, K. S.; Rubio, A. Phys. Rev. Lett. 2009, 102.
(19) (a) Darancet, P.; Ferretti, A.; Mayou, D.; Olevano, V. Phys. Rev.
B 2007, 75, 075102. (b) Calzolari, A.; Di Felice, R.; Manghi, F. Phys. Rev.
B 2005, 72.
This work was supported in part by the Nanoscale Science and
Engineering Initiative of the NSF (award CHE-0641523), the
New York State Office of Science, Technology, and Academic
Research (NYSTAR), and NSF Career Award CHE-07-44185
(L.V.). J.R.W. was supported by the EFRC program of the U.S.
Department of Energy (DOE) under Award No. DE-SC0001085.
S.T.S. was the recipient of a Guthikonda Graduate Chemistry
Fellowship. Part of this work was carried out at the Center for
Functional Nanomaterials, Brookhaven National Laboratory,
which is supported by the DOE Office of Basic Energy Sciences,
under contract no. DE-AC02-98CH10886.
(20) (a) Quek, S. Y.; Choi, H. J.; Louie, S. G.; Neaton, J. B. Nano Lett.
2009, 9, 3949. (b) Quek, S. Y.; Venkataraman, L.; Choi, H. J.; Loule, S. G.;
Hybertsen, M. S.; Neaton, J. B. Nano Lett. 2007, 7, 3477. (c) Strange, M.;
Rostgaard, C.; Hakkinen, H.; Thygesen, K. S. Phys. Rev. B 2011, 83.
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