A single-molecule optoelectronic detection device with single-photon sensitivity and a method of making the same

Abstract

The application provides a single-molecule photoelectric detection device with single-photon sensitivity and a preparation method thereof, and belongs to the field of molecular electronics. The single-molecule photoelectric detection device is obtained by the following steps: 1) constructing a graphene device including a source electrode, a drain electrode and a conductive channel by mechanical exfoliation of graphene; 2) designing a gold electrode pattern in autoCAD, exposing the pattern by using an electron beam exposure technology, then hot evaporating a chromium gold electrode, and electron beam evaporating silicon dioxide; 3) constructing a nanoscale controllable triangular graphene point electrode pair in the graphene channel by hydrogen plasma etching; 4) designing and synthesizing a required A-D-A type molecule; 5) preparing a single-molecule photoelectric detection device by self-assembling a connection molecule through electrostatic interaction and π-π interaction; and 6) testing and evaluating the electrical property of the single-molecule photoelectric detection device for generating a photocurrent under light excitation. The single-molecule photoelectric detection device generates a photocurrent under light irradiation, and provides a prototype device model for preparing an efficient integrated single-molecule photoelectric detection device.

Description

Technical Field

[0001] This invention belongs to the field of molecular electronics, and in particular relates to the preparation of an atomically controllable single-molecule photodetector. Background Technology

[0002] Currently, our understanding of light is not as advanced as our understanding of electricity. Therefore, we cannot directly reconstruct the original signal from the light signal. Instead, we need to convert the light signal into an electrical signal, amplify it using electronic circuitry, and then reconstruct the original signal. This receiving and conversion element is called a photodetector. Photodetectors need to be highly sensitive, have a fast response speed, low noise, and be stable and reliable. An electrical signal should be output immediately after the light signal is incident, and should stop outputting the electrical signal as soon as the light signal stops, without any delay. As communication systems demand increasingly higher transmission rates, the requirements for the response speed of photodetectors are also increasing. The discovery of new technologies, materials, and mechanisms undoubtedly promotes the development of this field.

[0003] Remote hydrogen plasma etching technology can be used to construct monomolecular heterojunctions composed of individual molecules. Each molecule absorbs a single photon, causing a change in the conductivity of the monomolecular heterojunction. This change in conductivity can be used to fabricate single-molecule photodetectors. Designing molecules to construct monomolecular heterojunctions with photodetector functionality is essential, and this is inextricably linked to the mechanism of molecular conductivity changes. Several recognized photoconductivity mechanisms exist to date; three are listed here: the first is photoinduced structural change, where the molecular structure changes under light irradiation; the second is the opening of conduction channels during photoinduced single-electron transport, known as adiabatic photo-assisted tunneling or the Tien-Gordon mechanism; and the third is from exciton recombination within the molecule. Symmetrical monomolecular heterojunctions exhibit conductivity changes upon illumination. Photoconductivity arises from the Coulomb interaction between electrons and holes, i.e., exciton recombination. In other words, even without molecular asymmetry or configurational changes, photoconductivity can occur due to exciton generation. Assuming the Fermi level is closer to the HOMO, the transport process is dominated by hole tunneling into the HOMO and depends on the energy difference between the HOMO and the electrode Fermi level. Under illumination, when the illumination frequency resonates with the HOMO–LUMO bandgap, electrons are excited from the HOMO to the LUMO, and holes tunneling from the electrode to the HOMO attract electrons in the LUMO. As a result, the HOMO energy is pushed towards the Fermi level, leading to an increase in conductivity.

[0004] The A–D–A molecule designed in this invention possesses a broad absorption band, capable of absorbing light across a wide range of wavelengths, making it an ideal material for fabricating highly efficient and sensitive single-molecule detectors. A single-molecule detector is fabricated by connecting individual A–D–A molecular bridges to graphene point electrodes through atomically controllable bottom-up construction of graphene-based triangular point electrodes. Since a single molecule essentially absorbs a single photon, the fabricated single-molecule detector exhibits single-photon sensitivity. Compared to bulk batteries, for scientific research, focusing on individual molecules allows for a deeper exploration of the mechanisms of photoexcitation; for industrial production, integrating single molecules into photodetectors enables more precise and efficient photoelectric responses, maximizing efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating a single-molecule photodetector. This method not only solves the problems of insufficient efficiency and precision control in the current field of photodetector devices, but also makes full use of the good compatibility of graphene with molecules. By adopting a bottom-up construction method, graphene-based triangular point electrodes with controllable gaps and clear edge configurations are fabricated, achieving atomic-level precision of the single-molecule electronic device platform. By bridging A–D–A type molecules through π–π interactions, a single-molecule photodetector is fabricated. Its "photoelectric" response is tested and evaluated, and a prototype device of the single-molecule photodetector is developed, providing theoretical and technical guidance for the future industrial application of single-molecule photodetectors.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A single-molecule photoelectric detection device with single-photon sensitivity includes a graphene electrode, an atomically precise molecular heterojunction, and an A–D–A organic photoelectric functional molecule. The graphene electrode is configured as a triangular point electrode. The interaction between the A–D–A organic photoelectric functional molecule and graphene is a π–π interaction. A strong π–π interaction is formed between the strong electron-withdrawing groups at the ends of the A–D–A organic photoelectric functional molecule and the graphene, resulting in a stable connection. The A–D–A organic photoelectric functional molecule is one of the types shown in Formula A.

[0008]

[0009] The thickness of the atomically precise and controllable molecular heterostructure is 1 nm.

[0010] Furthermore, it also includes a substrate; the substrate is a silicon wafer coated with silicon dioxide, silicon nitride, or mica.

[0011] The present invention provides a method for fabricating a single-molecule photoelectric detection device with single-photon sensitivity, comprising the following steps:

[0012] 1) Constructing a graphene device, wherein the graphene device includes a source, a drain, and a conductive channel, wherein the conductive channel is graphene;

[0013] 2) Metal electrodes were fabricated on graphene using electron beam lithography and vapor deposition techniques;

[0014] 3) Electron beam exposure is performed in the region outside the graphene channel to prepare a pre-etched pattern, and the lattice orientation of the graphene is prepared and confirmed by remote hydrogen plasma etching technology.

[0015] 4) Electron beam exposure is performed in the channel of graphene to prepare a positive etching pattern, and nanoscale controllable graphene point electrodes are prepared along the direction determined by the pre-etching by remote hydrogen plasma etching technology.

[0016] 5) The graphene point electrodes described in step 4) are self-assembled into monomolecular bridges through π–π interactions.

[0017] 6) Evaluate the electrical properties of the single-molecule device;

[0018] Step 5) involves assembling A–D–A type molecules to the ends of graphene point electrodes via electrostatic and π–π interactions assisted by an electric field. The A–D–A type molecule is one of the A–D–A organic optoelectronic functional molecules shown in Formula A, and is obtained through the following synthetic routes:

[0019]

[0020] Further, step 2) includes: drawing electrode patterns on the graphene layer using AutoCAD software, preparing electrode patterns using electron beam exposure, and depositing protective films of chromium, gold and silicon dioxide using thermal evaporation.

[0021] The thickness of the chromium is 6–10 nm; the thickness of the gold is 60–100 nm; and the thickness of the silicon dioxide is 20–60 nm.

[0022] The pre-etching described in step 3) involves constructing hexagonal holes along the graphene lattice orientation by electron beam exposure and remote hydrogen plasma etching of the graphene electrode layer.

[0023] Step 4) includes: constructing an electrode gap of less than 5 nm by positive etching of the graphene electrode layer to obtain a graphene electrode pair with controllable gap and well-defined configuration.

[0024] Step 5) includes: immersing the graphene device in a solution of a compound having structural formula A. The solvent can be any one of tetrahydrofuran, pyridine, dimethyl sulfoxide, or dichloromethane. The solvent concentration is 0.001–1 mmol. The solution is allowed to stand at room temperature in the dark for 48 hours. After the reaction is complete, the device is rinsed repeatedly with a large amount of dichloroethane, acetone, and water, and then dried.

[0025] Furthermore, during the self-assembly of molecules, an electrostatically assisted method is used to apply a positive bias voltage to both ends of the graphene to improve the assembly efficiency of the negatively charged groups; the graphene electrode layer is obtained by mechanical exfoliation.

[0026] The present invention provides a single-molecule heterojunction, which is composed of a graphene point electrode, an electrode, and a molecular heterojunction; wherein, the gate is a dielectric material located at the bottom of the graphene point electrode and has no conductive contact with the graphene point electrode; the graphene point electrode is prepared by a hydrogen plasma etching method; the molecular heterojunction and the graphene point electrode are self-assembled and connected through π–π interaction.

[0027] This application realizes the construction of a prototype device of a graphene-based single-molecule photodetector. The entire device, from the graphene electrode to the A–D–A type molecule, is atomically precise and controllable. This single-molecule photodetector has high testing stability and reproducibility, providing an experimental basis for studying the mechanism of single-molecule photodetectors, exploring prototype devices of single-molecule photodetectors, broadening the research field of single-molecule photodetectors, and establishing new models and new mechanisms. Attached Figure Description

[0028] Figure 1 This is a flowchart of the fabrication process for atomically precise single-molecule electronic devices.

[0029] Figure 2 This is a diagram of a metal electrode structure; in the diagram: 1 is the metal electrode, 2 is graphene, and 3 is the bottom gate and substrate.

[0030] Figure 3 These are scanning electron micrographs of the pre-etched image.

[0031] Figure 4 This is a scanning electron microscope image of the groove after positive etching.

[0032] Figure 5 These are the current-bias characteristic curves of a single-molecule electronic device assembled by π–π interactions.

[0033] Figure 6 The current-time characteristic curve is the optical response characteristic tested and evaluated using this prototype device. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the protection scope of this application. Unless otherwise specified, the raw materials can be obtained from publicly available commercial sources.

[0035] The electrical tests involved in this invention are performed under vacuum conditions (<1×10⁻⁴ Pa). The main testing instruments involved are the Agilent B1500A semiconductor parameter analyzer and the TTPX cryogenic probe platform (Lakeshore). The testing temperature is precisely controlled using a combination of liquid nitrogen and a heating platform.

[0036] Example 1: Construction of a single-molecule detector based on molecule 1. See Appendix for detailed experimental procedures. Figure 1 Taking carbon-based single-molecule devices as an example, the molecular device with a graphene electrode is first constructed. This includes the following steps:

[0037] (1) Preparation of graphene

[0038] First, the silicon wafers are pretreated. A 300nm layer of silicon dioxide is applied to the surface of the wafer, which is then cut into 1cm squares. The wafers are immersed in a solution of concentrated sulfuric acid and 30% hydrogen peroxide (volume ratio 7:3) at 100–120°C for 2–5 hours to remove surface contaminants. After heating, the wafers are sonicated in a piranha solution for 10 minutes, followed by ultrasonic cleaning twice with ultrapure water for 10 minutes each time. The wafers are then rinsed with ultrapure water, dried with high-purity nitrogen, and sealed. Since graphene is subsequently prepared using a mechanical exfoliation method, the graphene dispersion on the silicon wafer is random; therefore, markers are needed to position the graphene. In a cleanroom, the cleaned silicon wafer was heated on a 110°C hot table for 3 minutes to remove surface moisture. After cooling, the wafer was placed in the center of the spin coater's suction cup, and 1-2 drops of photoresist (AR-P 5350 ALLRESIST) were added. The spin coater was pre-rotated at 600 rpm for 6 seconds, then at 4000 rpm for 45 seconds. The photoresist was cured by heating on the 110°C hot table for 3 minutes. The mask pattern was then exposed on the silicon wafer surface using a 365nm UV exposure machine (BG-401A) (exposure time 25 seconds). Development was performed for approximately 20 seconds, with the developer-to-water ratio being 1:7 (developer was All Resist 300-26). Fixing was then performed in deionized water for approximately 10 seconds. Afterward, the surface was rinsed with deionized water to remove residual impurities and dried with nitrogen. Evaporation was then performed using a thermal evaporation system (Beijing Taikeno Technology Co., Ltd., ZHD-300). Cr and After Au deposition, the silicon wafer is immersed in acetone for at least 10 hours to dissolve the photoresist. Residual photoresist is then cleaned with acetone and dried with nitrogen to obtain a silicon wafer with a mark consisting of a cross and numbers, with a distance of 200 μm between adjacent marks. The pretreated silicon wafer is then ultrasonically treated in the following order: isopropanol, acetone, water, and ethanol, for 10 minutes each, to remove surface organic and inorganic adsorbates. It is then dried with high-purity nitrogen. Finally, it is etched with oxygen plasma in a reactive etching system for 6 minutes.

[0039] Take a piece of Scotch tape (3M), select a Kish graphite sheet from Covalent Materials, and stick it to the middle of the tape. Fold it repeatedly; the adhesive between the tape and the graphite overcomes the van der Waals forces between the graphite layers, causing the graphene to peel off. Continue folding until the graphene is evenly distributed. Adhere a silicon wafer to the area where the graphene is evenly distributed, fix it on a glass slide, and let it stand for 3-4 hours. Then, very slowly remove the silicon wafer; the peeled graphene is dispersed on the silicon wafer. Take a picture of the graphene under a 20x objective lens for in-situ mapping and EBL template fabrication. Because the range of the optical microscope image may have errors, resulting in skewed images that are imperceptible to the naked eye, it is necessary to correct the size and angle of the optical microscope image. The image shown is the corrected image using MATLAB. Using the corrected photograph as a reference, a design was created using AutoCAD. The square had a side length of 150 μm, the distance between the small crosses was 40 μm, and the electrode spacing was 4 μm. The electrodes needed to avoid graphene and gold labels to prevent poor adhesion between the electrodes and the substrate during evaporation, which could lead to detachment in subsequent steps. The four small cross-shaped marks were used as calibration markers for further exposure, improving exposure accuracy. The CAD design was then imported into the DY2000A, and the number of exposure layers and exposure sequence were set.

[0040] (2) Fabrication of gold electrodes

[0041] A gold electrode made of graphene was prepared using a double-layer photoresist release process. Two layers of electron beam photoresist were spin-coated onto a substrate. The lower layer has a smaller molecular weight and is more sensitive to electron beams, while the upper layer has a larger molecular weight and is slightly less sensitive. Therefore, when exposed for the same exposure time, the lower layer has a wider pattern and forms a trapezoidal shape at the cross-section. Compared to a single layer of photoresist, the eluent can more easily penetrate the gap between the metal and the photoresist, which is beneficial for metal release. The first layer of photoresist (MicroChem 495KA6) was pre-spinned at 600 rpm for 5 s, then forward spinned at 4500 rpm for 45 s, and baked on a hot stage at 180°C for 2 min. The second layer of photoresist (PMMA, MicroChem 950KA6) was pre-spinned at 600 rpm for 5 s, then forward spinned at 4000 rpm for 45 s, and baked on a hot stage at 180°C for 2 min. Exposure was performed using a field emission scanning electron microscope (FEI NovaNanoSEM 430) equipped with a pattern generator. After exposure, development was performed at room temperature (developer: methyl isobutyl ketone: isopropanol = 1:3) for approximately 20 seconds, followed by fixing in isopropanol for approximately 10 seconds. The sample was then rinsed with deionized water and dried with nitrogen. Chromium was then deposited using a thermal evaporation system. gold

[0042] Since subsequent etching of graphene and chemical reactions are required, electron beam evaporation was used to deposit 400nm silicon dioxide on top of thermal evaporation to protect the metal electrode. Silicon dioxide can prevent the aggregation of metal atoms during the continuous annealing process, maintaining the integrity of the electrode morphology. After evaporation, the electrode was immersed in acetone overnight, and then rinsed with acetone to obtain the photoresist, with attached... Figure 2 This is an optical microscope image of a metal electrode structure on graphene.

[0043] (3) Fabrication of graphene triangular point electrodes

[0044] Anisotropic etching of graphene can be achieved through remote hydrogen plasma etching. A high-temperature tube furnace is installed 48 cm away from the hydrogen plasma flow direction. The recombination rate of the high-temperature hydrogen plasma is greater than that of hydrogen atoms. After long-distance transport, the ionic component is negligible, and the majority of the active components passing through the tube furnace are hydrogen atoms. First, the furnace is evacuated to below 0.5 Pa, and then repeatedly purges with a high flow rate of hydrogen while maintaining a low pressure within the furnace. During etching, the hydrogen flow rate is maintained at 9.7 sccm, the etching temperature is 500℃, and the etching power is 30 W. During etching, a purple glow appears in the RF power supply area, extending to both ends of the quartz tube. Upon reaching the high-temperature region, the purple glow largely disappears.

[0045] The fabrication process of triangular point electrodes requires precise control over the lattice orientation of graphene. Therefore, the graphene is first pre-etched, as shown in the attached figure. Figure 3As shown, the direction of the hexagonal sides corresponds to the zigzag lattice direction of graphene, which is significant in determining the etching direction of graphene before the actual etching.

[0046] The cross-shaped marked area was photographed using a 100x optical microscope, and pre-etching experiments were performed on the graphene region outside the electrode channel area. A pre-etching pattern was designed in a DY2000A, the exposure sequence was set, and electron beam exposure was performed using the template in the DY2000A. Then, oxygen plasma etching was used to artificially introduce defect sites into the graphene. The template was removed by soaking in acetone overnight, and the perforated graphene was etched for approximately 30 minutes using a remote hydrogen plasma etching system. This produced a hexagonal porous structure in the graphene. The lattice orientation of the pre-etched graphene was measured in AutoCAD to determine its lattice orientation.

[0047] In the DY2000A, the etching sites for the electrode channel region are designed. The graphene lattice orientation obtained from pre-etching determines the positive etching defect sites. After a period of etching, triangular point electrodes can be obtained. To overcome the influence of stress, a semi-free channel is designed. First, an electron beam lithography is used to create windows on the photoresist. Then, oxygen plasma etching is used to create artificial defects, i.e., the starting sites for positive etching, in the graphene. After the operation is completed, acetone is used to remove the photoresist. Then, hydrogen plasma etching is used, with the positive etching conditions consistent with the pre-etching conditions, ultimately producing regular triangular point electrodes with a defined edge configuration, as shown in the attached figure. Figure 4 As shown, it exhibits a regular triangular point electrode structure.

[0048] The etching rate of hydrogen plasma can be controlled by adjusting the video power, etching time, and etching temperature, maintaining a rate of 1 nm / min. The reaction conditions are mild and clean, enabling the fabrication of graphene point electrodes with controllable electrode gaps and clear edge configurations. The etching endpoint is determined by electrical detection. As the endpoint approaches, the current decreases. When tunneling current appears on the IV curve between the electrode pairs, the electrode gap is less than 5 nm, making direct characterization by scanning electron microscopy or atomic force microscopy impossible. Simmons tunneling simulation can be used to fit the IV curve and estimate the electrode gap.

[0049]

[0050] In the formula, A is the electron tunneling area, and e is the electron charge. To reduce Planck's constant, φ b Let A be the insulator barrier height, d be the gap between the graphene electrode pairs, m be the electron mass, and V be the applied voltage. The final results are A = 0.098 nm², Φb = 0.7 eV, and d = 1.5 nm, indicating that the tunneling distance is approximately the length of a molecule, and the apex of the graphene triangular point electrode region has the conditions for fabricating single-molecule devices.

[0051] (4) Construction of a single-molecule photodetector based on molecule 1

[0052] First, the prepared silicon wafers with graphene-based triangular point electrodes were placed in a drying oven at 100°C to remove moisture from the substrate. A dried 100mL flat-bottomed two-necked flask was then fixed onto an iron stand, which was placed in a fume hood during the experiment. Several silicon wafers with graphene-based triangular point electrodes were taken out, and 0.1–1.5 mg of A–D–A type molecule 1 was weighed and added to 50 mL of tetrahydrofuran. The graphene-based triangular point electrodes and A–D–A type molecule began to self-assemble. After the reaction was completed and allowed to stand for 48–72 hours, the silicon wafers were removed, rinsed several times with acetone solution and deionized water, and then dried for later use. The structure is as follows:

[0053]

[0054] (5) Electrical testing of single-molecule photodetectors

[0055] Single-molecule electronic devices constructed from the aforementioned molecules were selected, and their electrical properties were tested using an Agilent B1500A semiconductor parameter analyzer and a TTPX cryogenic probe platform. Bias voltages ranging from -1 to 1V were applied to the devices, and the current changes of the single-molecule field-effect devices under different bias voltages were measured, as shown in the attached figure. Figure 5 As shown, the current value of the device increases under illumination compared to in darkness. Using a comprehensive property testing system, the temperature dependence of the device was characterized, and the current change of a single-molecule electronic device with a temperature range of 80K–300K at a gate voltage of 0V was obtained, as shown in the attached figure. Figure 6 As shown, the device exhibits significant switching changes under alternating light and darkness.

[0056] By applying light of different wavelengths to the device, the photocurrent generated by the device for different wavelengths of light was measured and evaluated, resulting in a gain of 10. 7 This single-molecule detector has great application potential.

[0057] In this embodiment, the synthetic route for molecule 1 is as follows:

[0058]

[0059] 1 g of compound (1) (0.92 mmol) and 0.84 g of monofluorosubstituted naphthalene compound (3.22 mmol) were dissolved in 20 mL of trichloroethane solution under a nitrogen atmosphere. Then, 0.6 mL of pyridine was added to the system, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the reactants were poured into water and the reaction system was extracted twice with 30 mL of trichloroethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, and then further purified by column chromatography and recrystallized to obtain compound (2) (0.43 g, 30%), i.e., molecule 1. 1 HNMR(500MHz,Chloroform-d)δ7.86(dt,J=8.1,1.6Hz,1H),7.51–7.44(m,3H),2.12(dt,J=12.4,7.0Hz,2H),1 .88(t,J=6.9Hz,2H),1.80(dt,J=12.4,7.0Hz,2H),1.46–1.31(m,12H),1.31–1.20(m,23H),0.94–0.84(m,9H). 13 C NMR (125MHz, Common NMR) Solvents)δ184.74,161.15,153.71,142.45,139.63,138.42,134.67–13 4.40(m),134.24,133.34,132.95,132.32,131.21,130.51,129.11(d,J=2 .9Hz),127.26,126.69,122.46,119.27(d,J=10.0Hz),116.14,115.93,11 4.55,84.72,66.26,33.88,32.61,29.82–29.42(m),26.79,23.91,14.19. HRMS(TOF-ESI+)(m / z):C 105 H 120 F2N4O2S2, m / z = 1571.89.

[0060] Example 2: Constructing a single-molecule detector based on molecule 2.

[0061] (1) Preparation of graphene

[0062] Same as Example 1.

[0063] (2) Preparation of metal electrodes

[0064] Same as Example 1.

[0065] (3) Fabrication of graphene triangular point electrodes

[0066] Same as Example 1.

[0067] (4) Construction of a single-molecule photodetector based on molecule 2

[0068] First, the prepared silicon wafers with graphene-based triangular point electrodes were placed in a 100°C drying oven to remove moisture from the substrate. A dried 100mL flat-bottomed two-necked flask was then fixed onto an iron stand, which was placed in a fume hood during the experiment. Several silicon wafers with graphene-based triangular point electrodes were taken out, and 0.1–1.5 mg of A–D–A type molecule 2 was weighed and added to 50 mL of tetrahydrofuran. The graphene-based triangular point electrodes and A–D–A type molecules began to self-assemble. After the reaction was completed and allowed to stand for 48–72 hours, the silicon wafers were removed, rinsed several times with acetone solution and deionized water, and then dried for later use. The structural formula is as follows:

[0069]

[0070] (5) Electrical testing of single-molecule photodetectors

[0071] Same as Example 1.

[0072] In this embodiment, the synthetic route for molecule 2 is as follows:

[0073]

[0074] 1 g of compound (1) (0.92 mmol) and 0.90 g of difluorosubstituted naphthalene compound (3.22 mmol) were dissolved in 20 mL of trichloroethane solution under a nitrogen atmosphere. Then, 0.6 mL of pyridine was added to the system, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the reactants were poured into water and the reaction system was extracted twice with 30 mL of trichloroethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, and then further purified by column chromatography and recrystallized to obtain compound (3) (0.52 g, 35%), i.e., molecule 2. 1 HNMR(500MHz,Chloroform-d)δ8.38(dd,J=9.3,1.5Hz,1H),7.51–7.44(m,2H),7.32(dddd,J=20.8,8.1,5.1,1.6Hz,1H), 2.12(dt,J=12.4,7.0Hz,1H),1.88(t,J=6.9Hz,1H),1.80(dt,J=12.4,7.0Hz,1H),1.46–1.20(m,18H),0.94–0.84(m,5H). 13C NMR(125MHz,CommonNMR Solvents)δ184.74,153.71,151.00,150.14,142.45,139.63,139.38,134.67–134.40(m),134.17(d,J=18.6Hz),133.45,132.92,132.32,130.51 ,129.11(d,J=2.9Hz),126.69,120.39,119.27(d,J=10.0Hz),118.71,11 4.55,84.72,66.26,33.88,32.61,29.82–29.42(m),26.79,23.91,14.14. HRMS(TOF-ESI+)(m / z):C 105 H 118 F4N4O2S2, m / z = 1607.87.

[0075] Example 3: Constructing a single-molecule detector based on molecule 3.

[0076] (1) Preparation of graphene

[0077] Same as Example 1.

[0078] (2) Preparation of metal electrodes

[0079] Same as Example 1.

[0080] (3) Fabrication of graphene triangular point electrodes

[0081] Same as Example 1.

[0082] (4) Construction of a single-molecule photodetector based on molecule 3

[0083] First, the prepared silicon wafers with graphene-based triangular point electrodes were placed in a drying oven at 100°C to remove moisture from the substrate. A dried 100mL flat-bottomed two-necked flask was then fixed onto an iron stand, which was placed in a fume hood during the experiment. Several silicon wafers with graphene-based triangular point electrodes were taken out, and 0.1–1.5 mg of A–D–A type molecule 3 was weighed and added to 50 mL of tetrahydrofuran. The graphene-based triangular point electrodes and A–D–A type molecules began to self-assemble. After the reaction was completed and allowed to stand for 48–72 hours, the silicon wafers were removed, rinsed several times with acetone solution and deionized water, and then dried for later use. The structural formula is as follows:

[0084]

[0085] (5) Electrical testing of single-molecule photodetectors

[0086] Same as Example 1.

[0087] In this embodiment, the synthetic route for molecule 3 is as follows:

[0088]

[0089] 1 g of compound (4) (1.67 mmol) and 1.64 g of difluorosubstituted naphthalene compound (5.85 mmol) were dissolved in 20 mL of trichloroethane solution under a nitrogen atmosphere. Then, 0.6 mL of pyridine was added to the system, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the reactants were poured into water and the reaction system was extracted twice with 30 mL of trichloroethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, and then further purified by column chromatography and recrystallized to obtain compound (5) (0.71 g, 38%), i.e., molecule 3. 1 HNMR(500MHz,Chloroform-d)δ8.46(d,J=1.4Hz,1H),8.38(d,J=1.6Hz,1H),7.94(d,J=1.2Hz,1H), 7.90(s,1H),7.67(dd,J=7.5,1.5Hz,1H),7.59–7.50(m,2H),7.28(ddd,J=8.1,5.0,1.5Hz,1H),6.93 (t,J=1.1Hz,1H),5.42(d,J=1.1Hz,1H),3.74(d,J=1.1Hz,2H),1.93(dt,J=12.4,6.9Hz,1H),1.83( dt,J=12.4,6.9Hz,1H),1.46–1.39(m,2H),1.39–1.30(m,2H),1.30–1.21(m,8H),0.94–0.84(m,3H). 13 C NMR (125MHz, Common NMR Solvents)δ203.09,157.92,151.70,150.49,149.75(dd,J=20.0,9.3Hz),148.48,144.46,140 .83(d,J=12.9Hz),137.71,135.89,134.60,134.29,132.37–132.01(m),131.50(d,J=15.0Hz), 126.03,122.84(d,J=3.1Hz),122.10,121.30(d,J=16.0Hz),118.16,117.28–116.89(m),114.6 1,82.13,74.93,53.43,39.70,36.19,32.63,29.41(d,J=10.5Hz),28.16,25.84,23.66,14.30. HRMS(TOF-ESI+)(m / z):C75 H 58 F4N4O2, m / z = 1122.45.

[0090] Example 4: Constructing a single-molecule detector based on molecule 4.

[0091] (1) Preparation of graphene

[0092] Same as Example 1.

[0093] (2) Preparation of metal electrodes

[0094] Same as Example 1.

[0095] (3) Fabrication of graphene triangular point electrodes

[0096] Same as Example 1.

[0097] (4) Construction of a single-molecule photodetector based on molecule 4

[0098] First, the prepared silicon wafers with graphene-based triangular point electrodes were placed in a 100°C drying oven to remove moisture from the substrate. A dried 100mL flat-bottomed two-necked flask was then fixed onto an iron stand, which was placed in a fume hood during the experiment. Several silicon wafers with graphene-based triangular point electrodes were taken out, and 0.1–1.5 mg of A–D–A type molecule 4 was weighed and added to 50 mL of tetrahydrofuran. The graphene-based triangular point electrodes and A–D–A type molecules began to self-assemble. After the reaction was completed and allowed to stand for 48–72 hours, the silicon wafers were removed, rinsed several times with acetone solution and deionized water, and then dried for later use. The structural formula is as follows:

[0099]

[0100] (5) Electrical testing of single-molecule photodetectors

[0101] Same as Example 1.

[0102] In this embodiment, the synthetic route for molecule 4 is as follows:

[0103]

[0104] 1 g of compound (6) (2.58 mmol) and 2.50 g of methyltriphenylphosphine (9.03 mmol) were dissolved in 20 mL of trichloroethane solution under a nitrogen atmosphere. Then, 0.6 mL of pyridine was added to the system, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the reactants were poured into water and the reaction system was extracted twice with 30 mL of trichloroethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, and then further purified by column chromatography and recrystallized to obtain compound (7) (0.48 g, 45%). 1H NMR(500MHz,Chloroform-d)δ8.46(d,J=7.3Hz,1H),8.41(d,J=7.5Hz,1H),7.55(dd,J=7.5,2.2H z, 1H), 7.51 (d, J = 7.5Hz, 1H), 7.22 (d, J = 2.2Hz, 1H), 5.88 (q, J = 6.3Hz, 1H), 2.17 (d, J = 6.3Hz, 3H). 13 C NMR (125MHz, Common NMR Solvents)δ154.45,132.45(d,J=6.2Hz),128.23,128.04,127.51,126.67,12 6.33, 124.85, 124.43 (d, J = 19.3Hz), 124.11, 123.03, 120.05, 110.90, 15.91. HRMS(TOF-ESI+)(m / z):C 30 H 20 O2,m / z=412.15.

[0105] 1 g of compound (7) (2.43 mmol) and 2.38 g of difluorosubstituted naphthalene compound (8.51 mmol) were dissolved in 20 mL of trichloroethane solution under a nitrogen atmosphere. Then, 0.6 mL of pyridine was added to the system, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the reactants were poured into water and the reaction system was extracted twice with 30 mL of trichloroethane. The organic phase was dried with anhydrous sodium sulfate for 2 hours, and then further purified by column chromatography and recrystallized to obtain compound (8) (0.64 g, 28%), i.e., molecule 4. 1 HNMR(500MHz,Chloroform-d)δ8.69(d,J=1.4Hz,1H),8.47(d,J=7.5Hz,1H),8.42(d, J=7.5Hz,1H),8.37(d,J=1.4Hz,1H),7.56(ddd,J=8.1,5.2,1.7Hz,1H),7.50(dd,J=7 .5,2.2Hz,1H),7.43(d,J=7.5Hz,1H),7.28(ddd,J=8.0,5.2,1.7Hz,1H),6.68(dd,J= 2.3, 1.0Hz, 1H), 5.88 (q, J = 6.4Hz, 1H), 4.44 (d, J = 1.1Hz, 1H), 2.15 (d, J = 6.4Hz, 3H). 13C NMR (125MHz, Common NMR Solvents)δ204.15,156.30,150.61(d,J=9.3Hz),149.72,149.56,148.59(d,J=9.3Hz),1 39.79,138.89,134.19,132.84(d,J=7.9Hz),132.51(dd,J=10.6,3.0Hz),132.17,130.20, 129.98,129.59,129.26,128.84,127.21,125.48(d,J=6.2Hz),124.92–124.58(m),124.3 0,122.74(d,J=2.9Hz),121.47,120.42,117.34–116.95(m),113.71,81.36,75.11,15.88. HRMS(TOF-ESI+)(m / z):C 62 H 28 F4N4O2, m / z = 936.21.

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, substitutions, etc., made within the principles and spirit of this application are included within the scope of protection of this application.

Claims

1. A single-molecule photoelectric detection device with single-photon sensitivity, characterized in that: It includes graphene electrodes, atomically precise molecular heterostructures, and A–D–A organic optoelectronic functional molecules. The graphene electrodes are configured as triangular point electrodes. The interaction between the A–D–A organic optoelectronic functional molecules and graphene is a π–π interaction. Strong π–π interactions are formed between the strong electron-withdrawing groups at the ends of the A–D–A organic optoelectronic functional molecules and graphene, resulting in a stable connection. The A–D–A organic optoelectronic functional molecule is one of the types shown in Formula A. Formula A.

2. The single-molecule photoelectric detection device with single-photon sensitivity according to claim 1, characterized in that: The thickness of the atomically precise molecular heterostructure is 1 nm.

3. The single-molecule photoelectric detection device with single-photon sensitivity according to claim 1, characterized in that: It also includes a substrate; the substrate is a silicon wafer coated with silicon dioxide, silicon nitride, or mica.

4. The method for fabricating a single-molecule photoelectric detection device with single-photon sensitivity according to any one of claims 1-3, characterized in that: Includes the following steps: 1) Constructing a graphene device, wherein the graphene device includes a source, a drain, and a conductive channel, wherein the conductive channel is graphene; 2) Fabrication of metal electrodes on graphene using electron beam lithography and vapor deposition techniques; 3) Electron beam exposure is performed in the region outside the graphene channel to prepare a pre-etched pattern, and the lattice orientation of the graphene is prepared and confirmed by remote hydrogen plasma etching technology. 4) Electron beam exposure is performed in the channel of graphene to prepare a positive etching pattern, and nanoscale controllable graphene point electrodes are prepared along the direction determined by the pre-etching by remote hydrogen plasma etching technology. 5) The graphene point electrodes described in step 4) are self-assembled into single-molecule bridges through π–π interactions; 6) Evaluate the electrical properties of this single-molecule photoelectric detection device; Step 5) involves assembling A–D–A type molecules to the ends of graphene point electrodes via electrostatic and π–π interactions assisted by an electric field. The A–D–A type molecule is one of the A–D–A organic optoelectronic functional molecules represented by formula A in claim 1, and is obtained through the following synthetic routes: 。 5. The preparation method according to claim 4, characterized in that, Step 2) includes: drawing electrode patterns on the graphene using AutoCAD software, preparing electrode patterns using electron beam exposure, and depositing chromium, gold and silicon dioxide protective films on the graphene using thermal evaporation. The thickness of the chromium is 6–10 nm; the thickness of the gold is 60–100 nm; and the thickness of the silicon dioxide is 20–60 nm.

6. The preparation method according to claim 4, characterized in that: The pre-etching described in step 3) involves constructing hexagonal holes along the graphene lattice orientation by electron beam exposure and remote hydrogen plasma etching of the graphene electrode layer.

7. The preparation method according to claim 4, characterized in that, Step 4) includes: constructing an electrode gap of less than 5 nm by positive etching of the graphene to obtain a graphene electrode pair with controllable gap and well-defined configuration.

8. The preparation method according to claim 4, characterized in that, Step 5) includes: immersing the graphene device in a solution of a compound having structural formula A, wherein the solvent is any one of tetrahydrofuran, pyridine, dimethyl sulfoxide, or dichloromethane, with a solvent volume of 50–100 mL and a molecular weight of 0.1–1.5 mg. The solution is allowed to stand at room temperature in the dark for 48 h. After the reaction is complete, the device is rinsed multiple times with alternating amounts of dichloroethane, acetone, and water, and then dried.

9. The preparation method according to claim 4, characterized in that: During the self-assembly of molecules, an electrostatic-assisted method is used to apply a positive bias voltage to both ends of the graphene to improve the assembly efficiency of negatively charged groups. The graphene electrode layer was obtained through mechanical exfoliation.

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