Molecules with tunable conductivity due to aromaticity differences, preparation methods and single-molecule devices

Abstract

The present invention discloses a conductance - tunable molecule with aromaticity differences, a preparation method thereof, and a single - molecule electronic device. The molecule has a structure of Formula I. By changing the substituent R1 on the central ring, the electronic structure of the central ring of the molecule can be regulated, making it exhibit aromaticity, anti - aromaticity or non - aromaticity respectively. The present invention, by combining theoretical calculations with STM - BJ single - molecule conductance measurements, clearly reveals that the aromaticity difference of the central ring of the molecule is the key internal factor determining its single - molecule conductance size, and among them, the molecule with an anti - aromatic center exhibits the highest conductance. The present invention reveals the influence rules of aromaticity, anti - aromaticity and non - aromaticity on single - molecule electron transport behavior, providing a reliable basis for subsequent structural design of regulating molecule conductance based on aromaticity.

Description

Technical Field

[0001] This invention belongs to the field of organic materials technology, specifically relating to electrically tunable molecules with aromaticity differences, preparation methods, and single-molecule devices. Background Technology

[0002] As microelectronic devices continue to evolve towards miniaturization and high integration, traditional silicon-based devices are gradually approaching their physical size limits. Single-molecule electronics, which utilizes a single or a small number of molecules to construct electronic functional units, has become an important research direction. Single-molecule devices typically refer to devices that bridge a single organic molecule between two metal electrodes, forming a stable molecular junction, and whose electron transport behavior within the molecule is measured by applying an external voltage. These devices possess characteristics such as extremely small size, high structural designability, and highly tunable electronic structure, and are considered important candidate systems for next-generation nanoelectronic devices.

[0003] In single-molecule devices, electrons are injected into a molecule from one electrode and then transported from the molecule to another electrode. This transport behavior primarily depends on the molecule's electronic energy level structure, especially the positional relationship between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) relative to the electrode Fermi level. When the molecular orbital energy levels are close to the electrode Fermi level, electrons can be transported within the molecule via resonance, exhibiting high conductivity. When the molecular orbitals are far from the Fermi level, electrons are mainly transported through quantum tunneling, and the conductivity decreases rapidly with molecule length. Therefore, the HOMO-LUMO energy level distribution is considered one of the core factors determining the conductivity characteristics of a single molecule.

[0004] In the field of single-molecule electronics, existing technologies are usually based on cutting-edge molecular orbital theory. They adjust molecular conductivity by controlling factors such as the position of HOMO and LUMO energy levels, molecular-electrode coupling mode, conjugation length, or molecular configuration rigidity. However, these technologies mainly focus on the resulting control brought about by changes in energy level position, and fail to deeply reveal the intrinsic electronic structure factors of molecules that determine energy level distribution and electron transport behavior.

[0005] Based on the above understanding, existing technologies for regulating single-molecule conductivity mainly focus on the following aspects: First, by changing the conjugation length of the molecular backbone or introducing electron-donating / electron-withdrawing substituents to adjust the HOMO or LUMO energy level positions; second, by selecting different anchoring groups (such as thiols, pyridines, etc.) to change the coupling strength between the molecule and the metal electrode; and third, by enhancing the rigidity of the molecular skeleton or changing the molecular configuration to reduce the adverse effects of conformational fluctuations on electron transport. These technical solutions have achieved a certain degree of regulation of molecular conductivity and have been verified in various single-molecule device systems, such as single-molecule junction structures based on linear conjugated molecules, aromatic ring-linked molecules, or oligomeric conjugated systems.

[0006] However, the aforementioned existing technical solutions mainly focus on adjusting the relative positions of HOMO-LUMO energy levels from the perspective of energy level regulation or structural modification, failing to deeply reveal the decisive role of intrinsic characteristics of the molecular electronic structure in the electronic transport mechanism. In existing research, aromaticity and antiaromaticity are mostly used to explain molecular stability, reactivity, or magnetic properties, but their role in single-molecule electronic devices has not been systematically elucidated. Some studies have reported single-molecule junction structures based on aromatic rings, but aromatic rings are usually treated as ordinary conjugated units, and aromaticity is not designed as an independent regulatory parameter. For antiaromatic or non-aromatic structures, there is a lack of systematic comparison and clear regulatory schemes for their electronic transport behavior in single-molecule junctions. In addition, existing technologies have not fully considered the coupling effect of molecular geometry (such as straight-chain or bent-chain structures) on aromaticity characteristics and their electronic transport behavior, thus limiting the predictability and design freedom of conductance regulation in single-molecule devices.

[0007] Therefore, there is an urgent need for a new technical solution that can systematically introduce the intrinsic electronic structure features of aromaticity and antiaromaticity into single-molecule devices, and combine them with molecular configuration design to effectively regulate the electronic transport mechanism and electrical conductivity, so as to overcome the limitations of existing technologies that rely solely on HOMO-LUMO energy level regulation. Summary of the Invention

[0008] To address the aforementioned problems, this invention proposes molecules with tunable conductivity exhibiting aromaticity differences, their preparation methods, and single-molecule devices. By introducing aromatic, anti-aromatic, and non-aromatic structural units into linear molecules, this invention achieves effective control over the single-molecule electronic transport mechanism and conductivity properties. This clarifies the differences in molecular conductivity at different aromaticity levels and their formation mechanisms, improves the predictability of molecular conductivity design, and provides a novel method for conductivity regulation in single-molecule electronic devices, distinct from relying solely on HOMO-LUMO energy level position control.

[0009] Aromaticity, as a core concept describing the degree of delocalization of π-electron systems, directly determines the delocalization range of π electrons in a molecule, its orbital degeneracy, and the continuity of charge transport channels in the molecular skeleton. This, in turn, affects the HOMO-LUMO energy level distribution, band gap size, and the stability of tunneling and resonance mechanisms during electron transport. It is a more fundamental and intrinsic structural factor influencing molecular conductivity. However, current research on aromaticity is largely limited to molecular stability or reactivity. In the field of single-molecule electron transport, there is a lack of systematic research and engineering applications that treat aromaticity as an independent control parameter. In particular, there is a lack of systematic comparisons of electron transport behavior in aromatic, antiaromatic, and non-aromatic structures within single-molecule structures, and the coupling effect of molecular geometry changes on the relationship between aromaticity and conductivity has not been clearly defined. This limits the predictability and designability of molecular conductivity regulation.

[0010] Aromaticity, a fundamental concept in organic chemistry describing the degree of delocalization of π-electron systems, reflects the extent and stability of electron delocalization within the molecular skeleton. Aromatic molecules typically satisfy Hückel's rule, possessing 4n+2 π electrons, exhibiting high π-electron delocalization and stable electronic structure. In contrast, antiaromatic molecules possess 4n π electrons, exhibiting unstable delocalization and significantly different energy level distribution and orbital degeneracy compared to aromatic systems. Molecules that do not strictly meet the requirements of 4n+2 or 4n π electrons are considered non-aromatic molecules. Since the degree of π-electron delocalization directly affects the orbital distribution, band gap, and electron transport paths within molecules, aromaticity, antiaromaticity, and non-aromaticity have a significant impact on unimolecular electron transport behavior.

[0011] A first aspect of the present invention provides an electrically tunable molecule with aromaticity differences, characterized in that the molecule is a compound having the structure of Formula I, wherein R1 is a group that imparts aromaticity, anti-aromaticity, or non-aromaticity to Formula I; and R2 is an anchoring group.

[0012] Formula I:

[0013] In some embodiments, R1 is selected from O, C=O, and R3; R2 is selected from mercapto, methylthio, and ethylthio; R3 is selected from C1-C8 alkyl groups, preferably one of methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and 2-ethylhexyl. In some embodiments, R2 is methylthio. In some embodiments, R3 is isopropyl.

[0014] In some embodiments, the molecule has a Linear-1 structure.

[0015] The structure of Linear-1 is as follows: .

[0016] In some embodiments, the molecule has a Linear-2 structure.

[0017] The structure of Linear-2 is as follows: .

[0018] In some embodiments, the molecule has a Linear-3 structure.

[0019] The structure of Linear-3 is as follows: .

[0020] In a second aspect of the invention, a method for preparing compound of formula I is provided, characterized in that its reaction formula is: .

[0021] R1 is a group that gives Formula I aromaticity, anti-aromaticity, or non-aromaticity; R2 is an anchoring group.

[0022] In some embodiments, R1 is selected from O, C=O, and R3; R2 is selected from mercapto, methylthio, and ethylthio; R3 is selected from C1-C8 alkyl groups, preferably one of methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and 2-ethylhexyl. In some embodiments, R2 is methylthio. In some embodiments, R3 is isopropyl.

[0023] The method for preparing compound I includes the following steps: adding appropriate amounts of compound III, compound II, catalyst, and inorganic base to a mixed solution of organic solvent and water under a nitrogen atmosphere, stirring, heating to 80-100°C, and reacting for 10-30 hours. The reaction product is then extracted, washed, dried, and purified to obtain a white solid, which is compound I.

[0024] In some embodiments, the organic solvent is tetrahydrofuran or N,N-dimethylformamide. In some embodiments, the catalyst is a palladium catalyst, preferably tetra(triphenylphosphine)palladium. In some embodiments, the inorganic base is sodium carbonate. In some embodiments, the reaction progress is monitored using silica gel thin-layer chromatography. In some embodiments, the reaction product is extracted using ethyl acetate and purified water to obtain the organic layer. In some embodiments, the reaction product is purified by silica gel column chromatography.

[0025] The compound of Formula 1 can be used to prepare single-molecule electronic devices.

[0026] In a third aspect of the invention, a single-molecule electronic device is provided, comprising the compound having the structure of Formula I described above. Specifically, STM-BJ technology was used to perform single-molecule conductivity tests on the three molecules. All three linear molecules exhibited relatively obvious conductivity plateaus. This indicates that all three molecules can form single-molecule bridges when connected between electrodes, and exhibit relatively consistent configurational stability and connection characteristics, suggesting that there is no significant difference among the three molecules in the probability of molecular bridge formation and the stability of the connection configuration.

[0027] This invention has at least one of the following beneficial effects: The present invention provides an electrically tunable molecule with aromatic differences, which has a simple synthesis method, low raw material cost, and is easy to industrialize.

[0028] This invention systematically reveals the influence of aromaticity, anti-aromaticity, and non-aromaticity on the electron transport behavior of single molecules in linear molecular systems with comparable structures, providing a reliable basis for subsequent structural design based on aromaticity-regulated molecular conductivity.

[0029] The electrically tunable molecules with aromatic differences of the present invention can all form monomolecular bridges when connected between electrodes, exhibiting relatively consistent configurational stability and connection characteristics. They can be directly anchored to metal electrodes through molecular self-assembly, simplifying device fabrication and playing an important role in the practical application of single-molecule electronic devices. Attached Figure Description

[0030] Figure 1 The HOMO isosurface distribution and LUMO isosurface distribution, molecular configuration and length for linear-1, linear-2, and linear-3.

[0031] Figure 2 The image shows the test results for STM-BJ.

[0032] Figure 3 This is the 1H NMR spectrum of the linear-1 of this invention.

[0033] Figure 4 This is the carbon NMR spectrum of the linear-1 of this invention.

[0034] Figure 5 The above is the 1H NMR spectrum of the linear-2 of this invention.

[0035] Figure 6 This is the carbon NMR spectrum of the linear-2 of the present invention.

[0036] Figure 7 The above is the 1H NMR spectrum of the linear-3 of this invention.

[0037] Figure 8 This is the carbon NMR spectrum of the linear-3 of the present invention. Detailed Implementation

[0038] The invention will be described in more detail below with reference to the embodiments and the accompanying drawings, which will enable those skilled in the art to have a more complete understanding of the invention, but does not limit the invention in any way.

[0039] Example 1: Preparation of Linear-1 .

[0040] The reaction formula for preparing Linear-1 is shown in formula (a). The preparation steps are as follows: 2,7-dibromodibenzofuran (326 mg, 0.1 mmol, 1 eq), molecule 1 (472 mg, 0.2 mmol, 2 eq), tetra(triphenylphosphine)palladium (112.4 mg, 0.1 mmol, 0.1 eq), anhydrous sodium carbonate (424 mg, 0.4 mmol, 4 eq), and a magnetic stir bar are added to a 100 mL double-necked flask, connected to a reflux condenser, and sealed. Nitrogen gas is repeatedly injected into the flask and then removed three times to remove any oxygen from the air. Subsequently, 25 mL of tetrahydrofuran and 10 mL of purified water are injected into the flask after similar treatment. The magnetic stir bar is turned on, and the entire flask is heated in an oil bath to a constant temperature of 90 degrees Celsius to initiate the reaction. The reaction time is 18 hours, and the reaction progress is monitored using silica gel thin-layer chromatography. After the reaction system stopped without the formation of any new compounds, the mixture was removed and extracted multiple times with ethyl acetate and purified water. The organic layer was collected, washed with water, dried with anhydrous magnesium sulfate to remove the organic solvent, and a solid crude product was obtained. Finally, it was purified by silica gel column chromatography using a 2:1 (v / v) hexane / dichloromethane eluent. The eluted product was recrystallized from dichloromethane / hexane to give a white solid, Linear-1, with a yield of 65%. The NMR data for Linear-1 are shown below. The 1H and 1C NMR results are shown in [link to NMR spectrum]. Figure 3 and Figure 4 .

[0041] 1 H NMR (400 MHz, Chloroform- d ) δ 8.10-8.05 (m, 2H), 7.60 (dd, J =8.6, 1.9 Hz, 2H), 7.58-7.50 (m, 6H), 7.34-7.26 (m, 4H), 2.48 (s, 6H). 13 C NMR (101 MHz, Chloroform- d ) δ 156.22, 138.12, 137.41, 135.87,127.76, 127.11, 118.90, 111.96, 16.00. Example 2 Preparation of Linear-2 .

[0042] The reaction formula for preparing Linear-2 is shown in formula (b). The preparation steps are as follows: 2,7-dibromo-9H-fluorene-9-one (337 mg, 0.1 mmol, 1 eq), molecule 1 (472 mg, 0.2 mmol, 2 eq), tetrakis(triphenylphosphine)palladium (112.4 mg, 0.1 mmol, 0.1 eq), anhydrous sodium carbonate (424 mg, 0.4 mmol, 4 eq), and a magnetic stir bar are added to a 100 mL double-necked flask, connected to a reflux condenser, and sealed. Nitrogen gas is repeatedly injected into the flask and then drawn off to remove any oxygen from the air. Subsequently, 25 mL of tetrahydrofuran and 10 mL of purified water are injected into the flask after similar treatment. The magnetic stir bar is turned on, and the entire flask is heated in an oil bath to a constant temperature of 90 degrees Celsius to initiate the reaction. The reaction time is 18 hours, and the reaction progress is monitored using silica gel thin-layer chromatography. After the reaction system stopped without the formation of any new compounds, the mixture was removed and extracted multiple times with ethyl acetate and purified water. The organic layer was collected, washed with water, dried with anhydrous magnesium sulfate to remove the organic solvent, and a solid crude product was obtained. Finally, it was purified by silica gel column chromatography with a 2:1 (v / v) hexane / dichloromethane eluent. The eluted product was recrystallized from dichloromethane / hexane to give a yellow solid, Linear-2, in 50% yield. The NMR data for Linear-2 are shown below. The 1H and 1C NMR spectra are shown in [link to NMR data]. Figure 5 and Figure 6 .

[0043] 1 H NMR (400 MHz, Chloroform- d ) δ 7.75-7.59 (m, 4H), 7.58-7.47 (m,4H), 7.47-7.38 (m, 2H), 7.33-7.25 (m, 4H), 2.47 (d, J = 2.0 Hz, 6H). 13 C NMR (101 MHz, Chloroform- d ) δ 192.96, 147.07, 144.89, 139.49,136.70, 133.47, 127.58, 126.69, 118.72, 15.62. Example 3 Preparation of Linear-3 .

[0044] The reaction formula for preparing Linear-3 is shown in formula (c). The preparation steps are as follows: 2,7-dibromo-9,9-dimethyl-9H-fluorene (352 mg, 0.1 mmol, 1 eq), molecule 1 (472 mg, 0.2 mmol, 2 eq), tetrakis(triphenylphosphine)palladium (112.4 mg, 0.1 mmol, 0.1 eq), anhydrous sodium carbonate (424 mg, 0.4 mmol, 4 eq), and a magnetic stir bar are added to a 100 ml double-necked flask, connected to a reflux condenser, and sealed. Nitrogen gas is repeatedly injected into and then drawn out of the flask to remove any oxygen from the air. Then, 25 mL of tetrahydrofuran and 10 mL of purified water are injected into the flask after similar treatment. The magnetic stir bar is turned on, and the entire flask is heated in an oil bath to a constant temperature of 90 degrees Celsius to start the reaction. The reaction time is 18 hours, and the reaction progress is monitored using silica gel thin-layer chromatography. After the reaction system stopped without the formation of any new compounds, the mixture was removed and extracted multiple times with ethyl acetate and purified water. The organic layer was collected, washed with water, dried over anhydrous magnesium sulfate to remove the organic solvent, and a solid crude product was obtained. Finally, it was purified by silica gel column chromatography with a 3:1 (v / v) hexane / dichloromethane eluent. After elution, the eluent was evaporated to dryness to obtain a white solid, which was Linear-3, with a yield of 60%. The NMR data for Linear-3 are shown below. The results of the 1H and 1C NMR spectra are shown in [link to NMR spectrum]. Figure 7 and Figure 8 .

[0045] 1 H NMR (400 MHz, Chloroform- d ) δ 7.69 (d, J = 7.9 Hz, 2H), 7.57-7.44(m, 8H), 7.31-7.24 (m, 4H), 2.45 (s, 6H), 1.49 (s, 6H). 13 C NMR (101 MHz, Chloroform- d ) δ 154.59, 139.73, 138.43, 138.08,137.48, 127.55, 127.06, 126.00, 121.09, 120.42, 47.07, 27.34, 16.01. Example 4: Theoretical calculations of the leading-edge orbitals of Linear-n molecules Theoretical calculations were performed on the leading molecular orbitals of Linear-1(a), Linear-2(b), and Linear-3(c), and the results are as follows: Figure 1As shown. The top shows the HOMO isosurface distribution of the corresponding molecule, the middle shows the LUMO isosurface distribution of the corresponding molecule, and the bottom shows the corresponding molecular configuration and length. Different colored (red / blue) regions represent the phase difference of the orbital wavefunction.

[0046] exist Figure 1 In the frontier orbital distribution shown, the visualized isosurfaces of HOMO and LUMO correspond to the spatial electron cloud distribution of the highest occupied orbital and the lowest unoccupied orbital in the molecular system, respectively. Generally speaking, the closer the HOMO is to the π system of the molecular backbone, the stronger the electron-donating ability of that region, while the more concentrated the LUMO distribution, the more pronounced the electron acceptor characteristics of the molecule in this region. For a complete conjugated system, the spatial position and overlap of HOMO and LUMO not only affect the photoelectric properties of the molecule itself, but also determine the alignment efficiency with the Fermi level of the electrode. In this invention, the HOMO / LUMO distributions of the three linear molecules all revolve around their five-membered ring cores, but due to the differences in aromaticity, antiaromaticity, and non-aromaticity, the coverage and energy levels of their respective orbitals in the ring backbone are different.

[0047] Specifically, the HOMO and LUMO of Linear-1 are concentrated on the relatively stable aromatic ring, with a relatively uniform and compact electron cloud within the ring, exhibiting typical aromatic characteristics of a six-π electron system. Because such aromatic molecules often have relatively low electronic instability, their leading orbitals are not strongly coupled with the Fermi level of the external electrode, thus typically not exhibiting the highest conductivity in single-molecule junction measurements. In contrast, Linear-2, as an antiaromatic molecule, shows a more significant orbital distribution at the central ring, with both HOMO and LUMO exhibiting strong electronic participation, suggesting that the molecule is in a higher-energy state where electrons are more readily mobile. It is precisely because of this instability caused by antiaromaticity that the leading orbitals are more likely to resonate and tunnel with the electrode energy level, making Linear-2 potentially capable of achieving the highest conductivity in experiments. As for Linear-3, according to the Hückel criterion, its electrons do not meet the strict conditions for aromatic or antiaromatic properties. Therefore, in the HOMO / LUMO distribution, it exhibits a delocalization characteristic between the two. It is neither as stable as Linear-1 nor as easy to couple as Linear-2, resulting in its single-molecule conductivity often being at a moderate level.

[0048] The HOMO-LUMO gap is of significant indicative importance in molecular electronics and optoelectronic materials: it determines the ease of electron exchange between molecules and electrodes. For molecules with antiaromatic properties, the gap is often small, indicating that their electronic structure is in an unstable state, making them more susceptible to resonant coupling with external electrodes, thus significantly increasing conductivity. Conversely, aromatic or non-aromatic molecules have larger gaps, resulting in more stable system energies and making electron injection or extraction less likely, thus limiting their conductivity.

[0049] Example 5: Aromaticity Study of Linear-n Molecules To further quantify the aromaticity differences among Linear-1, Linear-2, and Linear-3, this invention employs nuclear independent chemical shift (NICS(1)zz) and ACID methods for analysis. Specifically, the geometric structure of the target molecule is first optimized using quantum chemical calculation software (such as Gaussian series or equivalent quantum chemical programs) on a conventional workstation or server environment. The computing platform can be a computer device with a multi-core CPU and at least 16 GB of memory. The electronic structure method used can be density functional theory (DFT) with appropriate basis sets (such as 6-31G(d), 6-311+G(d,p), or equivalent basis sets commonly used in the field). The convergence criterion adopts the software default or a more stringent criterion. After structural optimization, a "virtual probe point" (ghost atom / Bq point) is set 1 Å above the geometric center of each ring to be analyzed to calculate the magnetic shielding tensor component at that point, and extract the zz component perpendicular to the ring plane, denoted as NICS(1)zz; where the numbers "Ring 1" to "Ring 5" correspond to the key rings in the molecular skeleton from left to right, and the probe point position is obtained by shifting 1 Å outward along the normal direction based on the geometric center of each ring. Subsequently, based on the same optimized structure and the same electronic structure method, the π electron circulation distribution is calculated under an applied magnetic field using an ACID calculation program or a software module that can perform equivalent current density analysis (e.g., by generating a wavefunction file and importing it into ACID-related tools). The direction of the applied magnetic field is usually perpendicular to the ring plane, and the ACID isosurface parameters (such as isosurface threshold and grid density) can be set using commonly used settings in this field or software recommended settings to ensure the comparability of results between different molecules. By comparing the quantitative indices of NICS(1)zz with the qualitative analysis of the ACID circulation image, the aromatic / anti-aromatic / non-aromatic characteristics of different ring segments of the molecule can be determined, and the NICS(1)zz calculation results and corresponding circulation direction and intensity differences can be obtained as shown in Table 1. The results are shown in Table 1.

[0050] Table 1. Calculated values ​​of NICS(1)zz at 1 Å above the geometric center of each ring for the three linear molecules.

[0051] The numbers “Ring 1” to “Ring 5” in the table correspond to the five key rings in the molecular skeleton from left to right. As can be seen from the table, in Linear-1, the NICS(1)zz values ​​of rings 1 to 5 are all negative, with most values ​​concentrated in the range of -15 to -19. Under traditional criteria, this often corresponds to a significant paramagnetic current, which is consistent with aromatic molecules. Since the furan core ring contains 6π electrons, which satisfies Hückel’s 4n+2 rule, the electron delocalization is relatively stable, and a significant paramagnetic current is usually generated under an external magnetic field. According to the calculated data (Table 1), these negative values ​​still indicate that the molecular skeleton is generally biased towards an aromatic stable state. Since the π electron energy of aromatic molecules is relatively stable, the HOMO-LUMO gap usually does not shrink drastically, and electrons are not easy to form a strong coupling with the Fermi level of the electrode. Therefore, this molecule often does not reach the highest value in single-molecule conductivity experiments.

[0052] Example 6: Single-molecule conductivity test of Linear-n molecules This invention employs STM-BJ technology to test the single-molecule conductivity of three molecules. Specifically, it uses STM-BJ (Scanning Tunneling Microscope – Break Junction) technology to test the single-molecule conductivity of Linear-1, Linear-2, and Linear-3. The testing apparatus includes a piezoelectrically driven scanning tunneling microscope mainframe (or a functionally equivalent broken junction conductivity measurement platform), a metallic conductive probe and a gold substrate electrode, a displacement control and data acquisition module, a current-to-voltage conversion amplifier, and a computer control system. Both the upper and lower electrodes are preferably made of gold (Au), where the substrate electrode can be a vapor-deposited gold film or a polished gold sheet, and the probe can be prepared by electrochemical etching of gold wire or using commercially available gold probes. The test is conducted in an air environment at room temperature, without the need for vacuum or inert atmosphere protection. The analyte molecule is dissolved in 1,2,4-trichlorobenzene (TCB) to prepare a low-concentration solution (typically on the micromolar to millimole range). This solution is then dropped onto or immersed in a gold substrate, allowing the molecules to adsorb onto the electrode surface and participate in the formation of molecular bridges during the measurement process. During the test, the gold probe is periodically brought into contact with and withdrawn from the gold substrate via piezoelectric drive, repeatedly forming and breaking gold-gold atom contacts. A constant bias voltage (e.g., within the commonly used range of 0.05–0.3 V) is applied in each contact-break cycle, and current signals are simultaneously acquired, recording current-displacement data. Each molecule is subjected to at least several thousand cycles to obtain sufficient statistical samples. The withdrawal process uses a constant withdrawal speed (e.g., within the commonly used range of nanometers per second to micrometers per second), and piezoelectric displacement is used as the relative displacement coordinate. The acquired current signals are converted to obtain the corresponding conductance values, and statistical analysis is performed using the conductance quantum number G0 (2e² / h) as the normalized unit, resulting in the following data: Figure 2 The one-dimensional conductance histogram shown ( Figure 2 (a) Two-dimensional conductivity-displacement distribution diagram ( Figure 2 (b) and the relative displacement distribution diagram of molecular junctions ( Figure 2 (c) was used to characterize the electrical conductivity and configurational stability of the single-molecule junction. A large amount of current-displacement data was obtained through thousands of electrode contact-break cycles, and the statistical results are as follows: Figure 2 . Figure 2 (a) is a 1D conductance histogram. Figure 2 (b) is a 2D conductance-displacement diagram. Figure 2 (c) is a diagram showing the relative displacement distribution.

[0053] Depend on Figure 2 As can be seen, all three molecules exhibited significant conductivity signals. Specifically, the main conductivity peak of Linear-1 is centered around 10. -4.25 G0, Linear-2 at 10-4.24 G0, Linear-3 at 10 -4.28 G0. The values ​​of the three are very close. Figure 2 (b) As can be seen, all three linear molecules exhibit relatively obvious conductivity plateaus. This indicates that all three molecules can form monomolecular bridges when connected between electrodes, exhibiting relatively consistent configurational stability and connection characteristics, suggesting that there is no significant difference among the three molecules in the probability of molecular bridge formation and the stability of the connection configuration. Figure 2 (c) shows that the length of the molecular junction is about 0.7~0.8 nm. These length values ​​are obtained by adding about 0.5 nm of gold-gold rebound distance, resulting in a relative displacement distribution peak of about 1.3 nm.

[0054] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A molecule with tunable electrical conductivity exhibiting aromatic differences, characterized in that, The molecule is a compound having the structure of Formula I, where R1 is a group that imparts aromaticity, anti-aromaticity, or non-aromaticity to Formula I; and R2 is an anchoring group. Formula I: 。 2. The electrically tunable molecule with aromatic differences according to claim 1, characterized in that, R1 is selected from O, C=O and R3; R2 is selected from mercapto, methylthio and ethylthio; R3 is selected from C1-C8 alkyl groups, preferably one of methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl.

3. The electrically tunable molecule with aromatic differences according to claim 2, characterized in that, R2 is a methylthio group.

4. The electrically tunable molecule with aromatic differences according to claim 3, characterized in that, R3 is isopropyl.

5. The electrically tunable molecule with aromatic differences according to claim 1, characterized in that, The molecule has a structure of one of Linear-1, Linear-2, and Linear-3; 、 、 。 6. The method for preparing an electrically tunable molecule with aromatic differences according to claim 1, characterized in that, Its reaction formula is: R1 is a group that imparts aromaticity, anti-aromaticity, or non-aromaticity to Formula I; R2 is an anchoring group. The method for preparing compound I includes the following steps: adding compound III, compound II, catalyst, and inorganic base to a mixed solution of organic solvent and water in a nitrogen atmosphere, stirring, heating to 80-100°C, and reacting for 10-30 hours; and extracting, washing, drying, and purifying the reaction product.

7. The method for preparing an electrically tunable molecule with aromatic differences according to claim 6, characterized in that, R1 is selected from O, C=O and R3; R2 is selected from mercapto, methylthio and ethylthio, preferably methylthio; R3 is selected from C1-C8 alkyl groups, preferably one of methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl, more preferably isopropyl.

8. The method for preparing an electrically tunable molecule with aromatic differences according to claim 6, characterized in that, The organic solvent is tetrahydrofuran or N,N-dimethylformamide.

9. The method for preparing an electrically tunable molecule with aromatic differences according to claim 6, characterized in that, The catalyst is a palladium catalyst, preferably tetra(triphenylphosphine)palladium.

10. A single-molecule electronic device comprising a conductivity-tunable molecule having aromatic differences as described in any one of claims 1-5.

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