Research ArticleMOLECULAR PHYSICS

Complex formation dynamics in a single-molecule electronic device

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Science Advances  25 Nov 2016:
Vol. 2, no. 11, e1601113
DOI: 10.1126/sciadv.1601113
  • Fig. 1 Fabrication and electrical characterization of SMJ devices.

    (A) Schematic representation of graphene point contacts. The carboxylic acid–terminated graphene point contact arrays were formed with ~2-nm gaps during the dash-line lithographic process. (B) Schematic representation of the BPP34C10-SMJ. After treatment with BPP34C10DAM solution in the presence of EDCI coupling reagent, the BPP34C10-SMJ was formed by bridging the conjugated molecular wire across graphene point contacts. (C) Schematic representation of the MV2+⊂BPP34C10-SMJ. The BPP34C10-SMJs were treated with MV to form MV2+⊂BPP34C10-SMJ by immersing BPP34C10-SMJ in an MV·2PF6 Me2SO solution for 12 hours (light brown, SiO2 substrate; blue, silicon substrate and electrode protection layers; gold, gold electrode). (D) Current-voltage (I-V) curves of graphene point contacts (black), BPP34C10-SMJ (red), and MV2+⊂BPP34C10-SMJ (blue) in the solid state. The black curve shows that no current occurs after etching; enhanced current (red curve) indicates a successful single-molecule connection; a further increase in current (blue curve) was observed after the addition of MV·2PF6.

  • Fig. 2 Schematic representation and electrical characterization of SMJs at the device-liquid interface.

    (A) Schematic illustration of the SMJ device-liquid interface characterization platform. The SMJ device was set onto a hot and cold chuck (silver) and further loaded with a PDMS reservoir (transparent). PID, proportion-integration-differentiation. (B) I-t curve of BPP34C10-SMJ immersed in a Me2SO solution of 1 mM MV·2PF6 at room temperature for 200 s with a sampling rate of 28.8 kSa/s. (C) Partial I-t curve of (B) (160 to 180 s). (D) Histogram of (B), showing a bimodal current distribution (Vbias = 100 mV).

  • Fig. 3 Computational analyses on BPP34C10 and MV2+⊂BPP34C10 between graphene electrodes.

    (A and B) Transmission spectra at the equilibrium of BPP34C10 (red) and MV2+⊂BPP34C10 (blue) around the Fermi level of graphene electrodes. (C and D) Diagrams of MPSH HOMO (below) and LUMO (above) of BPP34C10 macrocycle and MV2+⊂BPP34C10 pseudorotaxane connected to two graphene electrodes via amide bonds. (E and F) Schematic representations of charge carriers passing through BPP34C10-SMJ, which is less conductive, and MV2+⊂BPP34C10-SMJ, which is more conductive, according to the computational analyses.

  • Fig. 4 Real-time measurements of host-guest dynamics in SMJs at the device-liquid interface.

    (A) I-t curves and (B) the corresponding histograms of a BPP34C10-SMJ device immersed in a 1 mM MV·2PF6 Me2SO solution at six different temperatures (273 to 323 K) with a sampling rate of 28.8 kSa/s. (C) I-t curves and (D) the corresponding histograms of the same set of devices immersed in a 1 mM MV·2Cl aqueous solution at six different temperatures with a sampling rate of 28.8 kSa/s. In both Me2SO and aqueous environments, the electric currents passing through SMJs show bimodal distributions from 273 to 313 K. Binding constants (Ka), based on the Langmuir isotherm, can be derived from the current count distributions between two current levels, which change gradually at different temperatures. (E and F) Partial I-t curves (10 s) recorded in Me2SO and aqueous solutions at 293 K.

  • Fig. 5 Thermodynamic and kinetic analyses of the MV2+⊂BPP34C10 complex (de)formation in SMJs at the graphene-liquid interface.

    (A) Plots of the thermodynamic parameters (ln Ka versus 1000/T and ΔGo versus 1000/T) deduced from single-molecule measurements at the SMJ device-Me2SO interfaces at 293 K. Error bars were calculated from the data obtained from five different devices. ΔHo and ΔSo were obtained by using the van’t Hoff equation. (B) I-t curve (black) of a BPP34C10-SMJ device in a Me2SO solution of 1 mM MV·2PF6 at 293 K, and the idealized fit (orange) obtained from segmental k-means method based on hidden Markov model analysis using a QUB software (Vbias = 100 mV). (C) Plots of time intervals of the high (Thigh, blue) and low (Tlow, red) current states in the idealized fit in (B), and their exponential fits in which the lifetimes of two states (τhigh and τlow) can be derived. (D) Arrhenius plots of association (ka = 1/τlow) and dissociation (kd = 1/τhigh) rate constants deduced (Ea = −38.7 kJ mol−1 and Ed = 31.5 kJ mol−1).

  • Table 1 Thermodynamic parameters for the complex of MV2+ with BPP34C10.

    Thermodynamic data of MV2+⊂BPP34C10 for SMJ device-liquid interface measurements and 1H NMR titrations. N/A, not available.

    SolventMethodKa (M−1)ΔGo
    (kJ mol−1)
    ΔHo
    (kJ mol−1)
    ΔSo
    (J K−1 mol−1)
    Ea
    (kJ mol−1)
    Ed
    (kJ mol−1)
    323 K313 K303 K293 K283 K273 K
    Me2SOSMJN/A35271785416663501−15.7−39−80−38.731.5
    1H NMR1.73.16.214.4N/AN/A−3.9−56−169N/AN/A
    H2OSMJN/A370858157225154786−17.3−44−90−46.138.5
    1H NMR34.137.144.546.1N/AN/A−9.4−8.5−3N/AN/A

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/11/e1601113/DC1

    Supplementary Materials and Methods

    scheme S1. Synthesis of BPP34C10DAM from BPP34C10DA.

    fig. S1. Schematic representation of the fabrication procedure to form graphene field-effect transistor arrays.

    fig. S2. Optical microscopic images of graphene devices with different magnification.

    fig. S3. Characterization of an indented nanogap array.

    fig. S4. Solid-state electrical characterization.

    fig. S5. Reproducibility and differential conductance spectra.

    fig. S6. Schematic processes used to fabricate molecular devices.

    fig. S7. Control experiments using a partially cleaved graphene ribbon device.

    fig. S8. Control experiments using an OPEDAM-connected device.

    figs. S9 to S12. Real-time measurements of host-guest dynamics in SMJs at the device-liquid interface.

    fig. S13. Thermodynamic analyses of SMJ devices.

    fig. S14. 1H NMR titration.

    fig. S15. Thermodynamic analyses of SMJ devices.

    figs. S16 to S19. Host-guest kinetics analysis.

    fig. S20. Host-guest kinetics analysis.

    fig. S21. Geometric optimizations of BPP34C10 and MV2+⊂BPP34C10 complexes.

    tables S1 to S6. Binding constants.

    table S7. Chemical shifts for 1H NMR titrations in CD3SOCD3.

    table S8. Chemical shifts for 1H NMR titrations in D2O.

    tables S9 to S14. Dissociation (kd) and association (ka) rate constants.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • scheme S1. Synthesis of BPP34C10DAM from BPP34C10DA.
    • fig. S1. Schematic representation of the fabrication procedure to form graphene field-effect transistor arrays.
    • fig. S2. Optical microscopic images of graphene devices with different magnification.
    • fig. S3. Characterization of an indented nanogap array.
    • fig. S4. Solid-state electrical characterization.
    • fig. S5. Reproducibility and differential conductance spectra.
    • fig. S6. Schematic processes used to fabricate molecular devices.
    • fig. S7. Control experiments using a partially cleaved graphene ribbon device.
    • fig. S8. Control experiments using an OPEDAM-connected device.
    • figs. S9 to S12. Real-time measurements of host-guest dynamics in SMJs at the device-liquid interface.
    • fig. S13. Thermodynamic analyses of SMJ devices.
    • fig. S14. 1H NMR titration.
    • fig. S15. Thermodynamic analyses of SMJ devices.
    • figs. S16 to S19. Host-guest kinetics analysis.
    • fig. S20. Host-guest kinetics analysis.
    • fig. S21. Geometric optimizations of BPP34C10 and MV2+⊂BPP34C10 complexes.
    • tables S1 to S6. Binding constants.
    • table S7. Chemical shifts for 1H NMR titrations in CD3SOCD3.
    • table S8. Chemical shifts for 1H NMR titrations in D2O.
    • tables S9 to S14. Dissociation (kd) and association (ka) rate constants.

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