Fig 1

(a) Schematic of mechanically controlled break junction (MCBJ) 5; (b) Schematic of scanning tunneling microscope break junction (STM-BJ)5; (c) Working principle of "electrochemical gating" based on the break junction technique 40. Adapted from Springer Nature and Royal Society of Chemistry."

Fig 2

(a) 1D conductance histograms of oligophenylenediamines at different potentials and schematic illustrating the formation of the novel Au-N contact upon oxidation of a dative Au←N bond 43; (b) In Situ Formation of N-Heterocyclic Carbene-Bound Single-Molecule Junctions 44; (c) Schematic of the electrochemical cleavage of the terminal groups of probe molecules 49; (d) Schematic of gold-carbon contacts from oxidative addition of aryl Iodides 51. Adapted with permission from Refs. 43, 49, 51. Copyright 2017, 2013, 2020 American Chemical Society, and adapted from American Chemical Society."

Fig 3

(a) Molecular model for the two states; (b) Model of a double-well potential for ON and OFF states of the molecular head group and Statistical switching as a function of applied bias voltage 52; (c) The two possible junction configurations formed by direct interaction of the Au electrodes to either the aromatic ring or the carboxylic acid groups of single TMA molecules; (d) The transmission spectra for TMA single-molecule junctions between the Au(111) surface and the STM tip for both the planar and the upright TMA orientations 38. Adapted with permission from Refs. 52, 38. Copyright 2017, Springer Nature and copyright 2019 John Willey and Sons."

Fig 4

(a) The structure of 4, 4'-vinylenedipyridine (44VDP), and schematic representation of the electrochemically controlled STM-BJ technique 55. (b) Schematics of single-molecule switch modulated by connectivity switching. (c) (left) The strength and direction of dipole moments for M1 and M1–H were shown by the red and blue arrows nearby; (middle) Plots of total energy difference ∆E(EFz - EFz = 0) versus the applied electric field when θ = 0; (right) Plots of total energy difference ∆E(Eθ - Eθ = 0) versus θ, with electric field Fz = + 0.002 a.u. applied 56. Adapted with permission from Refs. 55, 56. Copyright 2018, American Chemical Society and copyright 2020, Elsevier."

Fig 5

(a) (Top) The single-molecule junctions with DFT-optimized structures of cis[3] and trans[3], (bottom) resonance structure cis-trans isomers under an applied electric field 58; (b)Schematic of the molecular device with a modulating bias, and the processes for controlling the NB-QC switching within a molecular junction 62. Adapted with permission from Refs. 58, 62. Copyright 2019, Springer Nature and copyright 2020 John Willey and Sons."

Fig 6

(a) voltage-driven Raman switching in a molecular junction spectroscopy setup; (b) Single-molecule current histogram curves; (c) characteristic I–V curves (dark blue) and corresponding derivatives dI/dV (cyan); (d) Raman signature of the pertinent junctions at biases of 1.0 and 0.1 V, respectively 66. Adapted with permission from Ref. 66. Copyright 2018 American Chemical Society."

Fig 7

(a) Schematic illustration of the stages encountered during a blinking event (left), and a real-time data capture of blinking events (right). (b) (left) Possible resonance structures of the transition state. When an electric field is present, minor contributors I or III may be stabilized enough to undergo resonance with II, lowering the reaction barrier; (right) Frequency of blinks (junctions) as a function of the applied bias 73. Adapted from Springer Nature publisher."

Fig 8

(a) Schematic of the MCBJ technique for in situ single-molecule conductance measurement. (b) The reaction rate for the transformation from compound b to c varies under different bias voltages; (c) A) Reaction barriers (1 kcal·mol-1 = 4.1868 kJ·mol-1) of a→TS and b→TS1 under various OEEF strength along the z direction 74. Adapted from The American Association for the Advancement of Science publisher."

Fig 9

(a) Schematic depiction of the STM–BJ setup for investigating the effect of an external electric field on the breaking of a C－O bond (left), and breaking probability of single molecules (right) 76; (b)Schematic depiction of Si－Si Bond Rupture in Single Molecule Junctions 78. Adapted with permission from Ref. 76, 78. Copyright 2017, 2016 American Chemical Society."

Fig 10

Idealized sketch of the voltage-triggered spin crossover switch in a single-molecule junction. (a) Low-spin FeII complex bridging the two electrodes at a small applied voltage; (b) High-spin FeII complex with distorted coordination sphere due to the alignment of the push–pull system in the applied electric field 83. Adapted with permission from Ref. 83. Copyright 2015 John Willey and Sons."

Fig 11

(a) Cyclic voltammetry at 50 mV·s-1 vs Ag of an Au(111) surface modified with a SAM of 5AQ5 in 0.5 mol·L-1 phosphate buffer, pH 3 (black line) and pH 8 (grey line); (b) Evolution of the conductance of 5AQ5 with a gate potential at pH 3 (black line) and pH 8 (grey line) 96; (c) Structures of ferrocene compounds (left), Scheme of charge transport through a ferrocene molecule that switches between oxidized and reduced states (right); (d) Measured and simulated conductance vs. potential sweeps for single molecules. (top) Conductance vs. potential of single 3C-Fc molecules: (top right) discrete two-level, (top middle) intermediate, and (top left) continuous variations of conductance with potential. The red, blue, and black colors represent different sweeps of potential. (bottom) Simulations of conductance vs potentials with standard rate constant 99. Adapted with permission from Ref. 96. Copyright 2015 John Willey and Sons. And adapted from National Academy of Sciences."

Fig 12

(a) (top right) Schematic illustration of the measurement system for side-gating Raman scattering, (top left) Dependence of HOMO and LUMO energy shift on the applied gate voltage, (bottom left) SERS spectra recorded when the bias voltage between the source and drain electrodes is fixed at 100 mV, (bottom right) I–V curves of 1, 4-benzenedithiol molecular junction upon different gate voltages 105; (b) (left) Schematic view of the electrochemically gated MCBJ technique and molecular structures of thiophene derivatives, (right) Tendency of the molecular conductance of 2, 5-TP-SAc (purple) and 2, 4-TP-SAc (orange) vs electrode potentials from -0.6 to 1.3 V 106. Adapted with permission from Ref. 105. Copyright 2018 American Chemical Society. And adapted from Springer Nature."