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Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes


To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials.

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Figure 1: Characterization of the nature of the charge carriers using the STM-BJ technique.
Figure 2: Energy-level characterization of the TDOn family.
Figure 3: Single-molecule conductance data.
Figure 4: Single-molecule thermopower data.


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This work was supported primarily by the National Science Foundation under award DMR-1206202. E.J.D. thanks the Howard Hughes Medical Institute, American Australian Association and Dow Chemical Company for International Research Fellowships.

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B.C., E.J.D., L.V. and L.M.C. conceived and designed the experiments. B.C. performed the conductance and thermopower measurements. E.J.D. and J.X. synthesized and characterized the molecules. All authors discussed the results. E.J.D. and B.C. contributed equally to this work. E.J.D., B.C., L.V. and L.M.C. wrote the paper with contributions from all authors.

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Correspondence to Latha Venkataraman or Luis M. Campos.

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The authors declare no competing financial interests.

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Dell, E., Capozzi, B., Xia, J. et al. Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes. Nature Chem 7, 209–214 (2015).

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