Metal-C covalent bond connected stable molecular device and preparation method and application thereof

Abstract

The invention discloses a stable molecular device with metal-C covalent bond connection, a preparation method of the stable molecular device and application of the stable molecular device in molecular electronic devices, logic and integrated circuits or rectifiers. The metal-C covalent bond connected stable molecular device comprises a first electrode, a second electrode and a connecting molecule anchored between the two electrodes, the connecting molecule has the following structure: # imgabs0 #, n is 1, 2 or 3, R is H or methyl, and R1, R2, R3 and R4 are respectively and independently selected from H, C1-C6 alkyl substituted or unsubstituted by one or more halogen atoms, C1-C6 alkoxy substituted or unsubstituted by one or more halogen atoms or halogen atoms; the carbon free radicals in the connecting molecules and the first electrode or the second electrode form metal-C covalent bond connection; the first electrode and the second electrode are both metal electrodes.

Description

Technical Field

[0001] The present invention relates to the field of micro-nanoelectronic devices, and in particular to a stable molecular device connected by metal-C covalent bonds, and a preparation method and application thereof. Background Art

[0002] With the continuous development and cross-integration of molecular electronics, organic chemistry, nanochemistry, information science, semiconductor science, and extreme device manufacturing, the application of electronic catalytic reactions in nanodevices and the construction of artificial molecular machines will have a profound impact on future information processing, anti-counterfeiting sensing, biological targeted therapy, and intelligent synthesis.

[0003] In recent years, with the gradual development of single-molecule electronics, many molecular switch devices, rectifier devices, and memory devices based on small molecule structures have been realized. However, the stability of these devices still needs to be significantly improved.

[0004] Modern microelectronics rely heavily on the properties of the interface between two different components to determine the efficiency of electron transfer, as well as the overall reproducibility and stability of the device. For example, in the past few years, there has been increasing interest in the formation of robust gold-carbon (Au-C) covalent bonds at the interface of single-molecule devices. The stability of Au-C covalent bonds in air and water, as well as their unique electronic properties, give them the advantage of having stronger coupling strength than commonly used anchor groups such as amino, thiol, thiomethyl, and pyridine. In addition, Au-C covalent bonds can effectively protect the interaction between heteroatoms and metal electrodes from changes caused by oxidation and thermal instability, thereby expanding their potential applications in the field of single-molecule devices.

[0005] Due to the chemical inertness of gold electrodes, the in situ formation of Au-C bonds relies on highly reactive reagents to facilitate the transfer of the desired carbon species to the gold surface and the construction of Au-C covalent bonds. A key issue involved in this approach is the selection of functional groups in the conductive molecular skeleton to achieve controllable regulation of the chemical reaction.

[0006] Although the methods reported so far have created Au-molecule covalent bonding at the interface, due to the chemical inertness of gold and the reactivity of carbon species, there are difficulties such as the inability to generate in situ, difficult synthesis, and high reagent toxicity (J.Am.Chem.Soc.2012,134(47),19425; Nature Nanotechnol.2011,6(6),353; J.Am.Chem.Soc.2016,138(27),8465). It is still challenging to utilize the rich chemistry associated with Au-C bond formation. Summary of the invention

[0007] The invention provides a metal-C covalently bonded stable molecular device and a preparation method and application thereof.

[0008] [1] A stable molecular device with metal-C covalent bonding, comprising a first electrode, a second electrode and a connecting molecule anchored between the two electrodes;

[0009] The connecting molecule has the following structure:

[0010]

[0011] Wherein, n is 1, 2 or 3, R is H or methyl, R1, R2, R3, R4 are independently selected from H, C1-C6 alkyl substituted or unsubstituted by one or more halogen atoms (such as F, etc.), C1-C6 alkoxy substituted or unsubstituted by one or more halogen atoms, or halogen atoms (such as F, etc.);

[0012] The carbon free radical in the connecting molecule forms a metal-C covalent bond with the first electrode or the second electrode;

[0013] The first electrode and the second electrode are both metal electrodes.

[0014] Furthermore, the first electrode and the second electrode can be independently selected from Au, Ag, Pt or gallium-indium alloy.

[0015] The first electrode may be a base electrode, and the second electrode may be a needle-shaped electrode. Further, the tip size of the needle-shaped electrode is micrometer level.

[0016] In the metal-C covalently bonded stable molecular device, one end of the carbon free radical in the connecting molecule forms a metal-C covalent bond connection with one of the electrodes, and one end of the -SR forms a covalent bond or non-covalent bond anchor connection with the other electrode.

[0017] [2] The method for preparing a stable molecular device connected by metal-C covalent bonds according to [1] comprises:

[0018] The pyridinium salt model molecule solution is transferred to the surface of the first electrode, and after the solvent is evaporated, a thin film molecular layer of the pyridinium salt model molecule is formed on the surface of the first electrode, and the second electrode is placed close to the surface of the first electrode assembled with the thin film molecular layer, so that the pyridinium salt model molecule is anchored between the first electrode and the second electrode, and electrons are injected to make the cations in the pyridinium salt model molecule remove the 2,4,6-trimethylpyridine molecule to form the connecting molecule anchored between the first electrode and the second electrode, and the carbon free radicals in the connecting molecule form a metal-C covalent bond connection with the first electrode or the second electrode, so as to obtain the metal-C covalently bonded stable molecular device;

[0019] The pyridinium salt model molecule comprises a cation having the structure shown below:

[0020]

[0021] Wherein, n is 1, 2 or 3, R is H or methyl, and R1, R2, R3, and R4 are independently selected from H, C1-C6 alkyl substituted or unsubstituted by one or more halogen atoms (such as F, etc.), C1-C6 alkoxy substituted or unsubstituted by one or more halogen atoms, or halogen atoms (such as F, etc.).

[0022] An exemplary method for preparing a stable molecular device with metal-C covalent bond connection includes: installing a first electrode and a second electrode on a scanning tunnel fracture junction device, controlling the motion trajectory of the second electrode by the expansion and contraction motion of a piezoelectric ceramic built into the scanning tunnel fracture junction device, so that the second electrode is close to or away from the first electrode; dropping a pyridinium salt model molecule solution on the surface of the first electrode, when the first electrode material is in the pyridinium salt model molecule solution environment, the pyridinium salt model molecule is anchored to the second electrode and the first electrode by covalent or non-covalent bonds to form a loop; the pyridinium salt model molecule has an active skeleton for redox, and through a single electron transfer mechanism (SET), electrons in the electrode connected to the pyridine structure end are injected into the molecule as a reducing agent, and the pyridinium salt model molecule is rapidly decomposed to form a carbon free radical intermediate, and forms a stable covalent bond connection with the electrode, thereby forming a stable molecular device with metal-C covalent bond connection.

[0023] The present invention forms a stable molecular device mechanism of metal-C covalent bond connection in a scanning tunneling break junction device as follows: a series of pyridinium salt molecules (with -SR group at one end and pyridine unit at the other end) are selected as model compounds, and the method involves the use of a scanning tunneling microscope (STM) based break junction (STM-BJ), in which the electrons from the STM tip are used as a reducing agent in a SET method to (i) initiate the homolysis of the pyridinium salt, then (ii) lead to the release of carbon radicals, and finally (iii) lead to the in situ formation of metal-C covalent bonds in a single molecule junction. This strategy is demonstrated using STM-BJ measurements combined with integrated electrochemical experiments in solution.

[0024] The present invention can change the bias voltage between the first electrode and the second electrode to affect the electron injection into the pyridinium salt model molecule, so that the pyridinium salt model molecule undergoes a SET process, thereby forming a stable molecular device with a stable metal-C covalent bond connection, thereby constructing a stable metal-C covalent bond.

[0025] During the experiment, a bias voltage may be applied to a certain electrode so that the bias voltage between the electrode and another electrode is gradually increased to adjust the probability of electron injection between the two electrodes. For example, the bias voltage may be -0.6V to 0.6V.

[0026] When the bias voltage between the two electrodes is small, the transmission probability of electrons in the pyridinium model molecule is low, and a stable molecular device connected by metal-C covalent bonds fails to form; when the bias voltage between the two electrodes increases, the transmission probability of electrons in the pyridinium model molecule increases, and a stable molecular device connected by metal-C covalent bonds is formed in situ.

[0027] The molecular device of the present invention does not require external chemical or optical stimulation and the participation of other auxiliary molecules. It only needs to repeatedly mechanically stretch and compress the needle-shaped electrode connected to the model molecule and change the bias voltage applied between the needle-shaped electrode and the substrate electrode to make the pyridinium salt model molecule undergo SET process, thereby forming a stable molecular device with stable metal-C covalent bond connection.

[0028] [2] In the preparation method described above, the solvent may be a polar organic solvent, specifically at least one of acetonitrile, water, ethylene glycol diethyl ether, etc., preferably acetonitrile. On the one hand, acetonitrile can better dissolve the pyridinium salt model molecule; on the other hand, acetonitrile has a very low boiling point and can evaporate rapidly during the membrane assembly process, thereby quickly forming a molecular membrane containing the pyridinium salt model molecule; at the same time, the solvent does not cause signal interference to the electrical test.

[0029] [2] In the preparation method described above, the concentration of the pyridinium salt model molecule in the pyridinium salt model molecule solution can be 0.1-1.0 mM, preferably 0.1 mM. The above concentration limit ensures that the molecular film layer can be effectively formed at a relatively low concentration, and increases the signal of the needle-shaped electrode capturing a single molecule, thereby improving the success rate of the molecule being connected to the electrode gap, avoiding the problem of difficulty in capturing molecular signals due to too low concentration; on the other hand, it prevents the concentration from being too high, resulting in the formation of a too thick molecular film layer, which makes it difficult for the needle-shaped electrode to contact the base electrode and difficult to achieve the construction of a sandwich molecular junction.

[0030] In the preparation method described in [2], the cation in the pyridinium salt model molecule may be BF4 - .

[0031] In the present invention, the method for preparing the pyridinium salt model molecule may include: reacting 2,4,6-trimethylpyrylium salt with a benzylamine derivative to obtain the pyridinium salt model molecule;

[0032] The benzylamine derivative has the structure shown below:

[0033]

[0034] Wherein, n is 1, 2 or 3, R is H or methyl, and R1, R2, R3, and R4 are independently selected from H, C1-C6 alkyl substituted or unsubstituted by one or more halogen atoms (such as F, etc.), C1-C6 alkoxy substituted or unsubstituted by one or more halogen atoms, or halogen atoms (such as F, etc.).

[0035] In the method for preparing the pyridinium salt model molecule, 2,4,6-trimethylpyrylium salt and a benzylamine derivative may be reacted in the presence of isopropanol.

[0036] In the method for preparing the pyridinium salt model molecule, the temperature for the reaction of 2,4,6-trimethylpyrylium salt with the benzylamine derivative can be 85-95° C., such as 90° C., and the time can be 10-14 hours, such as 12 hours.

[0037] In the preparation method of the pyridinium salt model molecule, after the reaction of 2,4,6-trimethylpyrylium salt and benzylamine derivative is completed, the pyridinium salt model molecule can be obtained by post-treatment. Further, the post-treatment may include: extracting the reaction product with dichloromethane, collecting the organic phase, drying, removing the solvent, and purifying by silica gel column flash chromatography, using methanol and dichloromethane as the mobile phase. Furthermore, in the mobile phase, the volume ratio of methanol to dichloromethane can be 1:9.

[0038] [3] Application of the metal-C covalently bonded stable molecular device according to [1] in molecular electronic devices, logic and integrated circuits or rectifiers. For example, the metal-C covalently bonded stable molecular device itself can be regarded as a single molecule rectifier device.

[0039] One end of the pyridinium salt model molecule is -SR, and the other end is a 2,4,6-trimethylpyridine molecule (TMP), to ensure that the molecular system can be oriented on the surface of electrodes such as Au, Ag, Pt or gallium-indium alloy (such as substrate electrode), and complete the construction of the metal electrode-molecule-metal electrode sandwich molecular junction. By using EGaIn electrodes to test the sandwich molecular junction by IV, the difference in coupling strength between the two electrodes and the molecules is reflected as a rectification ratio of up to one order of magnitude.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention constructs a stable molecular device connected by metal-C covalent bonds, which has a sandwich structure of electrode / molecule / electrode and can be constructed under mild experimental conditions. It has the advantages of stable performance and easy integration. It can realize device functions with stable properties and excellent performance at room temperature and pressure. It is easy to synthesize, non-toxic, environmentally friendly and efficient.

[0042] The present invention is the first to utilize the single electron transfer mechanism (SET) to generate carbon free radical intermediates to in situ construct metal-C covalent bonds. The SET process does not require external chemical, optical or other auxiliary molecular stimulation, and there is no need to consider the impact of the introduction of other substances on device performance. Moreover, a molecular-scale electrical device that can be directed self-assembled can be successfully constructed simply by controlling the bias voltage between the two electrodes.

[0043] The metal-C covalently bonded stable molecular device of the present invention has a high rectification ratio and can be used in molecular electronic devices, logic and integrated circuits or rectifiers. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the H NMR spectrum of the pyridinium salt model molecule PhTMP-1.

[0045] Figure 2 This is the H NMR spectrum of the pyridinium salt model molecule PhTMP-2.

[0046] Figure 3 This is the H NMR spectrum of the pyridinium salt model molecule PhTMP-3.

[0047] Figure 4 This is a microscope imaging photograph of a needle-shaped electrode of a molecular device in a specific implementation manner.

[0048] Figure 5 Schematic diagram of the SET mechanism for constructing a stable molecular device with Au-C covalent bonds in a specific implementation method.

[0049] Figure 6 It is a schematic diagram of the SET structure for constructing a stable molecular device with Au-C covalent bonds in a specific implementation method.

[0050] Figure 7 It is a molecular electrical information diagram corresponding to a molecular device under different needle electrode-substrate electrode biases in a specific implementation method.

[0051] Figure 8 It is a schematic diagram of the structure of a single molecule film measured under a eutectic gallium-indium alloy (EGaIn) electrode of a molecular device in a specific implementation manner.

[0052] Fig. 9 It is a characteristic diagram of IV signal of a single molecule film measured under EGaIn electrode of a molecular device in a specific implementation manner. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0054] Preparation of pyridinium salt model molecule PhTMP-n (n is 1, 2 or 3, indicating the number of benzene rings):

[0055] Under nitrogen atmosphere, benzylamine derivative (5.0mmol) and 2,4,6-trimethylpyrylium tetrafluoroborate (5.5mmol) were added to a dry flask, followed by isopropanol, and the mixture was reacted at 90°C for 12 hours. After the reaction, the solvent was removed by vacuum distillation, and the remaining mixture was extracted with dichloromethane (3×15mL). The organic phase was collected and dried over MgSO4. After the solvent was removed by vacuum distillation, the corresponding pyridinium salt model molecule was purified by flash chromatography (silica gel, methanol / dichloromethane volume ratio 1:9).

[0056] Benzylamine derivatives have the following structure:

[0057]

[0058] Wherein, n is 1, 2 or 3;

[0059] The corresponding pyridinium salt model molecules are PhTMP-1, PhTMP-2, and PhTMP-3:

[0060]

[0061] For the corresponding H NMR results, see Figures 1 to 3 .

[0062] Example 1

[0063] The pyridinium salt model molecule PhTMP-n (n is 1, 2 or 3, indicating the number of benzene rings) is dissolved in acetonitrile solvent to prepare a pyridinium salt model molecule solution with a concentration of 0.1mM. A commercial gold wire with a diameter of 0.25mm is used for electrochemical etching to prepare a needle-shaped electrode with a tip size of micrometers. The electrolyte used in the electrochemical etching process is ethanol: hydrochloric acid volume ratio = 1:1; the etching material used is Au wire with a diameter of 0.25mm and a purity of 99.99%. The gold wire with a diameter of 0.25mm is placed in the center of the gold ring and placed in a mixed solution of hydrochloric acid / ethanol (volume ratio 1:1), and a needle-shaped electrode with a tip size of micrometers is prepared by electrochemical etching, such as Figure 4 A vacuum thermal evaporation method is used, that is, a 5nm thick Cr layer is deposited on the surface of the silicon wafer to improve adhesion, and then a gold wire of about 15cm is deposited on the surface of the silicon wafer containing the Cr layer to prepare a base electrode with a thickness of 100nm.

[0064] Before performing the conductivity characterization of the model molecule, the pyridinium salt model molecule solution is first dropped on the surface of the prepared Au substrate electrode. After the solution evaporates, a thin film molecular layer containing the model molecule is formed on the surface of the Au substrate electrode. The substrate electrode assembled with the thin film molecular layer will be used for the subsequent construction of molecular devices, forming Figure 5 The Au-C covalently bonded stable molecular device shown. By changing the bias voltage between the tip and the substrate, as Figure 6 As shown, electrons are injected from the needle tip into the pyridine skeleton, and carbon radicals and the same amount of 2,4,6-trimethylpyridine TMP are quickly formed to obtain a stable molecular device with gold-C covalent bond connection. When the distance between the needle tip and the substrate increases from 0.5nm to 2.5nm, the statistical length is about 0.2nm (this distance is the step length statistically shown in the figure plus the retraction distance of the gold-gold atoms. The sum of the two represents the length of the molecule in the electrode gap. Therefore, when the statistical result is 0.2nm, the actual length of the molecule is 0.7nm).

[0065] Example 2

[0066] The electrical characterization results of the Au-C covalent bond formation process and the stable molecular device connected by Au-C covalent bonds at room temperature are shown in this example. Figure 7 As shown in the figure, by changing the bias voltage between the tip and the substrate, electrons are injected and the SET process is carried out. Taking PhTMP-1 as a model compound, when the positive bias voltage increases, a Gaussian-fitted conductive peak gradually appears in the 1D conductive histogram, with a peak value of 10 –2.9 log(G / G0). In the 2D conductivity histogram, a clear conductive platform with a length of 0.2nm was observed at a bias of 0.6V. According to the SET-induced CN bond dissociation mechanism, we successfully constructed a single-molecule structure with a covalent Au-C bond at one end and a coordinated Au-S bond at the other end. Due to the difference in coupling strength between the gold electrode and the two anchor points, the charge transfer direction may have a profound effect on the charge transfer characteristics. Therefore, we conducted additional conductive signal exploration at negative bias voltages ranging from -0.1 to -0.6V. Our observations in the 2D histogram showed a conductive platform of similar length (0.2nm), but the conductivity was reduced tenfold. The rectification ratio between the two reached 1 order of magnitude, and the device had excellent rectification performance.

[0067] Example 3

[0068] The electrical characterization results of the stable molecular device with metal-C covalent bonding at room temperature in this example are as follows: Figure 8 , Fig. 9As shown. We immersed the gold substrate obtained by the template stripping method in a solution. Considering the low binding energy between the positively charged steric hindrance TMP group and the Au surface, the PhTMP-n (n is 1, 2 or 3) molecules can only self-assemble on the Au surface through the ordered and directional arrangement of the -SMe group. Using the eutectic gallium-indium alloy as the top electrode, electron injection is achieved by changing the bias between the top electrode and the gold substrate to form carbon radicals and the same amount of 2,4,6-trimethylpyridine TMP, and then a stable molecular device with metal (eutectic gallium-indium alloy)-C covalently bonded is obtained. The monomolecular film of the stable molecular device is tested by IV under the EGaIn electrode, in which a large-area stable EGaIn / GaO x / / SAM (self assemebly membrane)-Au structure, obtains the rectification ratio of a single molecule film, which can reach up to an order of magnitude.

[0069] It can be seen that the molecular device provided by the present invention has a simple construction and stable performance, and does not require external stimulation and the participation of other auxiliary molecules. By applying a bias voltage between the needle electrode and the substrate electrode, the SET process can be realized through electron injection, and carbon free radicals can be quickly split to form metal-C covalent bonds in situ; and a molecular-scale electrical device with directional self-assembly and a rectification ratio of 10 is successfully constructed.

[0070] In summary, the present invention synthesizes suitable carbon radical transfer reagents based on redox active skeletons. These reagents are used as precursors to generate free radical species, and the reaction is triggered by the SET method to release free radicals. In this process, the electron transfers electrons to the pyridine unit as a suitable reducing agent, and then undergoes rapid homolysis of the CN bond, thereby controlling the release of synthetic important free radicals and producing a considerable amount of pyridine. The metal-C covalent bond formed in situ by the single electron transfer mechanism is used to achieve the construction of a stable metal-C covalent bond molecular device. When the pyridinium salt model molecule undergoes a SET reaction, the neutral 2,4,6-trimethylpyridine molecule (TMP) leaves and forms an asymmetric molecular junction with -SR at one end and a benzyl radical at the other end. The benzyl radical interacts with the electrode, and a covalent metal-C bond is established in situ in the nanogap. The difference in coupling strength between the two electrodes and the two ends of the molecule, the constructed directional self-assembled monolayer, is embodied in the present invention as a rectification ratio of up to one order of magnitude.

[0071] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A stable molecular device connected by metal-C covalent bonds, characterized in that: comprising a first electrode, a second electrode and a connecting molecule anchored between the two electrodes; The connecting molecule has the following structure: wherein n is 1, 2 or 3, R is H or methyl, and R1, R2, R3, and R4 are independently selected from H, C1-C6 alkyl substituted or unsubstituted by one or more halogen atoms, C1-C6 alkoxy substituted or unsubstituted by one or more halogen atoms, or halogen atoms; The carbon free radical in the connecting molecule forms a metal-C covalent bond with the first electrode or the second electrode; The first electrode and the second electrode are both metal electrodes.

2. The metal-C covalently bonded stable molecular device according to claim 1, characterized in that: The first electrode and the second electrode are independently selected from Au, Ag, Pt or gallium-indium alloy.

3. The metal-C covalently bonded stable molecular device according to claim 1, characterized in that: The first electrode is a base electrode, and the second electrode is a needle electrode; The tip size of the needle-shaped electrode is in micron order.

4. The method for preparing a stable molecular device connected by metal-C covalent bonds according to any one of claims 1 to 3, characterized in that: include: The pyridinium salt model molecule solution is transferred to the surface of the first electrode, and after the solvent is evaporated, a thin film molecular layer of the pyridinium salt model molecule is formed on the surface of the first electrode, and the second electrode is placed close to the surface of the first electrode assembled with the thin film molecular layer, so that the pyridinium salt model molecule is anchored between the first electrode and the second electrode, and electrons are injected to make the cations in the pyridinium salt model molecule remove the 2,4,6-trimethylpyridine molecule to form the connecting molecule anchored between the first electrode and the second electrode, and the carbon free radicals in the connecting molecule form a metal-C covalent bond connection with the first electrode or the second electrode, so as to obtain the metal-C covalently bonded stable molecular device; The pyridinium salt model molecule comprises a cation having the structure shown below:

5. The preparation method according to claim 4, characterized in that: The solvent is a polar organic solvent, including at least one of acetonitrile, water, and ethylene glycol diethyl ether.

6. The preparation method according to claim 4, characterized in that: The concentration of the pyridinium salt model molecule in the pyridinium salt model molecule solution is 0.1-1.0 mM.

7. The preparation method according to claim 4, characterized in that: The cation in the pyridinium salt model molecule is BF4 - .

8. The preparation method according to claim 4, characterized in that: The preparation method of the pyridinium salt model molecule comprises: reacting 2,4,6-trimethylpyrylium salt with a benzylamine derivative to obtain the pyridinium salt model molecule; The benzylamine derivative has the structure shown below:

9. The preparation method according to claim 8, characterized in that: Reacting 2,4,6-trimethylpyrylium salt with a benzylamine derivative in the presence of isopropanol; The temperature of the reaction of 2,4,6-trimethylpyrylium salt and benzylamine derivative is 85-95° C. and the time is 10-14 hours; After the reaction of 2,4,6-trimethylpyrylium salt and benzylamine derivative is completed, the pyridinium salt model molecule is obtained by post-treatment; the post-treatment includes: extracting the reaction product with dichloromethane, collecting the organic phase, drying, removing the solvent, and purifying by silica gel column rapid chromatography, and using methanol and dichloromethane as the mobile phase.

10. Use of the stable molecular device connected by metal-C covalent bonds according to any one of claims 1 to 3 in molecular electronic devices, logic and integrated circuits or rectifiers.

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