Research ArticleCHEMICAL PHYSICS

Graphene catalyzes the reversible formation of a C–C bond between two molecules

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Science Advances  14 Dec 2018:
Vol. 4, no. 12, eaau9366
DOI: 10.1126/sciadv.aau9366
  • Fig. 1 CH2CN and TCNQ deposited on gr-Ru(0001) before and after the reaction.

    (A) STM image [20 nm by 20 nm, sample bias voltage (Vb) = +1.7 V, tunneling current (It) = 10 pA] showing the gr-Ru surface with all the HCP-top areas (blue triangle) functionalized with −CH2CN groups. White circle indicates a single −CH2CN. (B) STM image (12 nm by 12 nm, Vb = −0.8V, It = 25 pA) with TCNQ adsorbed on gr-Ru. Most of the TCNQ molecules are adsorbed in the so-called bridge positions. White circle indicates a single TCNQ. (C) STM image (27 nm by 15 nm, Vb = −1.5 V, It = 5 pA) showing the surface after the sequential deposition of −CH2CN groups followed by the TCNQ molecules at room temperature. All the TCNQ molecules present on the image have reacted with the −CH2CN groups. White circle indicates a reacted TCNQ. The inset shows an STM image (5.7 nm by 4.0 nm, Vb = −1.3V, It = 15 pA) with one pristine TCNQ molecule (top left) and a reacted one. The gr-Ru(0001) moiré pattern is visible in all the images. The blue (green) triangles highlight the HCP-top (FCC-top) parts of the moiré pattern. All images were measured at 4.8 K.

  • Fig. 2 DFT-calculated geometries.

    (A) Top view and (B) side view of the resulting molecule in the gas phase calculation: The cyanomethylene group is bonded to one of the exocyclic alkenes of the TCNQ. (C) Top view of the most stable adsorption configuration on the gr-Ru(0001). The molecule is adsorbed on the bridge position with the cyanomethylene end pointing toward the FCC-top areas (FT) of the moiré pattern. (D) Lateral view of the most stable configuration. The cyanomethylene group is located on top of the TCNQ and points toward the vacuum. In (C) and (D), the total corrugation of graphene is ~120 pm.

  • Fig. 3 STM images for positive and negative bias voltages.

    (A) STM image (6 nm by 8 nm) of two TCNQ-CH2CN molecules and one TCNQ on gr-Ru for negative bias voltage (Vb = −1.7 V, It = 5 pA). Total corrugation in the image is 240 pm. (B) STM image (6 nm by 8 nm) of the same area of the sample shown in (A) acquired at positive bias voltage (Vb = +1.1V, It = 5 pA). Total corrugation in the image is 186 pm. (C and D) Simulated STM image of a TCNQ-CH2CN on gr-Ru for (C) negative bias (Vb= −1.7 V, It = 5 pA) and (D) positive bias voltage (Vb = +1.1 V, It = 5 pA); the origin of the z scale is set on the z coordinate of the C atoms in the low region of the graphene moiré. The dashed black line rhombus in all the images indicates the moiré unit cell for gr-Ru.

  • Fig. 4 TCNQ and TCNQ-CH2CN molecular orbitals.

    STS spectra measured in the TCNQ molecule (blue circle and trace) and TCNQ-CH2CN (red circle and trace). Both spectra have been measured at 4.8 K with a lock-in technique using a peak-to-peak modulation of 90 mV. The inset shows an STM image (8 nm by 3 nm, Vb = −2.2 V, It = 20 pA) with the corresponding TCNQ and TCNQ-CH2CN on gr-Ru. arb. units, arbitrary units.

  • Fig. 5 Single molecule–induced dissociation.

    (A) STM image (8 nm by 8 nm) of four TCNQ-CH2CN molecules on gr-Ru. There are also four −CH2CN groups attached to the gr-Ru (Vb = +1.7 V, It = 10 pA). (B) STM image (8 nm by 8 nm) of the same area of the sample shown in (A), acquired with the same tunneling conditions after the single-molecule manipulation process discussed in the text. Four pristine TCNQ molecules can be observed in the image. The blue circles indicate the new −CH2CN groups on the surface that appear after the C–C bond breaking induced by the injection of electrons in the LUMO of TCNQ-CH2CN.

  • Fig. 6 Switching on the Kondo effect.

    LT (4.8 K) dI/dV spectra measured on the two molecules forming the dimer shown in the insets (STM images, 2.0 nm by 2.4 nm; Vb = −0.1V, It = 20 pA). (A) TCNQ and TCNQ-CH2CN. (B) Two TCNQ molecules (spectra were recorded at the positions marked by the corresponding colored dots).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/12/eaau9366/DC1

    Section S1. gr-Ru(0001) structure and growth

    Section S2. TCNQ on clean Ru(0001)

    Section S3. Reduced TCNQ structure

    Section S4. TCNQ-CH2CN in gas phase

    Section S5. TCNQ-CH2CN/gr-Ru(0001) adsorption configuration

    Section S6. Reaction pathway

    Section S7. Negative differential conductance

    Section S8. TCNQ and TCNQ-CH2CN molecular orbitals

    Section S9. Molecular orbitals occupancy and Kondo effect

    Section S10. Single-molecule manipulation and reaction reversibility

    Fig. S1. gr-Ru(0001) moiré pattern.

    Fig. S2. TCNQ on Ru(0001).

    Fig. S3. Gas phase calculations.

    Fig. S4. Transition states for the reaction.

    Fig. S5. Negative differential conductance and charge distribution.

    Fig. S6. Molecular orbitals in gas phase.

    Fig. S7. pDOS and molecular orbitals of TCNQ-CH2CN deposited on gr-Ru(0001).

    Fig. S8. Magnetic properties of the TCNQ-CH2CN molecule.

    Fig. S9. Magnetic properties of the TCNQ molecule.

    Fig. S10. Single-molecule manipulation and reaction reversibility.

    Table S1. TCNQ-CH2CN binding energies in the gas phase calculations.

    References (4158)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. gr-Ru(0001) structure and growth
    • Section S2. TCNQ on clean Ru(0001)
    • Section S3. Reduced TCNQ structure
    • Section S4. TCNQ-CH2CN in gas phase
    • Section S5. TCNQ-CH2CN/gr-Ru(0001) adsorption configuration
    • Section S6. Reaction pathway
    • Section S7. Negative differential conductance
    • Section S8. TCNQ and TCNQ-CH2CN molecular orbitals
    • Section S9. Molecular orbitals occupancy and Kondo effect
    • Section S10. Single-molecule manipulation and reaction reversibility
    • Fig. S1. gr-Ru(0001) moiré pattern.
    • Fig. S2. TCNQ on Ru(0001).
    • Fig. S3. Gas phase calculations.
    • Fig. S4. Transition states for the reaction.
    • Fig. S5. Negative differential conductance and charge distribution.
    • Fig. S6. Molecular orbitals in gas phase.
    • Fig. S7. pDOS and molecular orbitals of TCNQ-CH2CN deposited on gr-Ru(0001).
    • Fig. S8. Magnetic properties of the TCNQ-CH2CN molecule.
    • Fig. S9. Magnetic properties of the TCNQ molecule.
    • Fig. S10. Single-molecule manipulation and reaction reversibility.
    • Table S1. TCNQ-CH2CN binding energies in the gas phase calculations.
    • References (4158)

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