Stable diradical monomolecular devices containing anchoring groups and methods of synthesis

Abstract

The application provides a stable double free radical monomolecular device containing an anchoring group and a synthesis method, which comprises a nitrogen free radical (-N • ) formed by oxidizing -NH by an oxidant, an Au-N • -p bridge-N • -Au monomolecular junction, a pyridine (-Py) anchoring group, and the nitrogen free radical is located in the middle of the pyridine (-Py) anchoring group and the Au-N • -p bridge-N • -Au monomolecular junction. Based on the technical scheme of the application, a monomolecular junction based on a nitrogen free radical is constructed, has the advantages of simple preparation, high junction rate and good stability, and lays a good foundation for efficiently and stably constructing a double free radical monomolecular device.

Description

TECHNICAL FIELD

[0001] The application relates to the field of micro-nano electronics of the new generation information technology industry, in particular to a stable diradical monomolecular device containing an anchoring group and a synthesis method. BACKGROUND

[0002] The original intention of single-molecule electronics is to use single molecules, which are extremely small and precisely controllable in size, as functional units of electronic devices to cope with the miniaturization process of semiconductor devices. Since the first experimental test of single-molecule conductance, single-molecule electronics has undergone 25 years of development, and has gradually branched out into two research routes: one is to continue the original intention of this field, to realize logic operation and even molecular computing chips by using single molecules to construct semiconductor devices; the other is to open up a new research field, to use single-molecule electronics technology as a characterization method and research tool for single-molecule scale physical and chemical processes.

[0003] Molecular electronics originated in the 1950s. In order to realize the design and manufacture of electronic devices of extreme size, there was an idea of using single molecules to construct electronic devices. Colonel C.H. Lewis of the US Air Force first proposed the term molecular electronics. In 1965, Moore's Law described the trend of miniaturization of electronic devices, that is, the number of transistors in a semiconductor chip doubles every 18 months, and the device size is halved accordingly. Under the driving of this trend, in 1974, Aviram and Ratner proposed the idea of using asymmetric donor-acceptor molecules as single-molecule diodes, which is considered by most people as the beginning of the field of molecular electronics, and also made molecular electronics truly from a concept to a multi-disciplinary frontier research field.

[0004] The research object of molecular electronics is very rich. From the current research status, the specific system studied by molecular electronics is the molecular junction system composed of electrode-molecule-electrode. A series of problems derived from this system can be divided into three aspects: the problem of how to construct the electrode-molecule-electrode junction, the problem of the electrical transport properties of the electrode-molecule-electrode junction, and the problem of using external fields to control the electrical transport properties of the electrode-molecule-electrode junction.

[0005] Single-molecule devices refer to devices that use single molecules as active electronic components to manufacture electronic circuits, especially optoelectronic devices. Generally, a single molecule is connected to two electrodes through an anchoring group to realize charge transport in the device. In single-molecule devices, there are many key factors that affect the electrical properties, such as electrodes, anchoring groups, used molecules, and preparation methods.

[0006] In 1982, Binnig and Rohrer invented the scanning tunneling microscope (STM) at IBM Zurich Laboratory, Switzerland. This technique measures the tunneling current between a tip and a substrate to feedback the distance between the tip and the substrate, thus obtaining the topography and atomic arrangement of the sample surface. In addition, the manipulation of single atoms or molecules can be achieved by modification of the tip. Therefore, STM technology plays a crucial role in the research of nanoscience and molecular electronics.

[0007] In 1987, Gimzewski et al. first reported the construction of metal atomic scale contacts using STM. Although the phenomenon of metal quantum dot contact was not observed due to the limitations of experimental conditions at that time, this method was widely used and developed, and the characterization of quantum conductance of Au, Pt, Ni and other different metals was achieved, thus laying the foundation for the scanning tunneling microscope break junction (STMBJ) technology. In 2003, Tao et al. first proposed the STMBJ technology and successfully measured the conductance of 4,4'-bipyridine molecular junction. By controlling the tip to approach the sample surface until the two collide and form a contact, the tip is lifted in the opposite direction when the preset contact conductance value is reached. Due to the ductility of metal materials, the contact area will gradually decrease, and finally experience a single atom point contact configuration. Continue to lift the tip, and the single atom point contact will break, forming a gap. When the gap size matches the length of the target molecule at a certain moment, a metal / molecule / metal structure can be formed. When the gap continues to increase, the molecular junction breaks. Through repeated movement of the tip, a large number of nanogaps can be dynamically constructed, and the conductance-time curve of this process is recorded. By screening the data curves containing molecular junctions and statistically analyzing their conductance, the conductance value of a single molecule can be obtained.

[0008] Organic radicals are small organic molecules or polymers containing unpaired electrons. Because these unpaired electrons reside in the outermost molecular orbitals, they are highly susceptible to gaining or losing electrons, resulting in typically reactive organic radicals that readily undergo oxidation, polymerization, and other chemical reactions, leading to short lifespans for most. However, protecting the radical center with bulky substituents can prolong the existence of unpaired electrons, potentially leading to the formation of stable organic radicals. In 1900, Moses Gomberg of the University of Michigan discovered the triphenylmethyl radical, the first stable organic radical to be discovered and confirmed. Since then, numerous stable radicals have been discovered and reported, and many new organic radicals are still being developed and studied by scientists today. Due to the presence of unpaired electrons, organic radicals possess unique properties not found in closed-shell organic molecules, namely magnetism caused by the interaction of unpaired electrons. Furthermore, organic radicals have smaller band gaps, resulting in broader absorption and emission spectra, making them valuable for applications in magnetism, electronics, optoelectronics, and biology.

[0009] Currently, constructing stable radical single-molecule junctions requires not only introducing anchoring groups at both ends of the bridging molecule but also introducing unpaired electrons at other sites on the bridging molecule to form radical molecules. This not only increases the difficulty of constructing radical single-molecule devices but also hinders direct research into the influence of unpaired electrons on the electrical transport properties of single-molecule junctions. For example... Figure 1 As shown, oligomeric p-phenylacetylene (OPE) radical molecular junctions (a: Au-OPE-Au molecular junction; b: Au-TEMPO-OPE-Au molecular junction) were constructed using Au as the metal electrode, methyl sulfide (-SMe) as the anchoring group, and OPE as the bridging molecule. It is important to emphasize that to construct a radical monomolecular junction, additional TEMPO radical molecules need to be introduced from the side group sites. To construct biradical or even multiradical monomolecular junctions, even more sites are required. Summary of the Invention

[0010] To address the problems in the prior art, this application proposes a stable biradical single-molecule device containing an anchoring group, comprising a nitrogen radical (-N) formed by oxidizing -NH with an oxidant. • Au-N constructed using STMB technology • -p bridge- N • -Au unimolecular junction, pyridine (-Py) anchoring group; nitrogen radical located between the pyridine (-Py) anchoring group and Au-N • -p bridge- N • -Au unimolecular junction in the middle.

[0011] Optionally, a stable biradical monomolecular device containing anchoring groups is constructed, and the biradical molecule is named N,N-biPh2MeR, Au-N • -p bridge-N • The Au monomolecular junction contains two symmetrical pyridines, and each pyridine ring has two chlorine atoms.

[0012] The application also relates to a synthesis method of the stable biradical monomolecular device containing anchoring groups, which comprises the following steps: under a nitrogen atmosphere, 4,4'-diamino-2,2'-dimethylbiphenyl, 3,5-dichloro-4-bromopyridine, tris(dibenzylideneacetone)dipalladium, tri-tert-butylphosphine tetrafluoroborate and sodium tert-butoxide are added into a container; after nitrogen degassing, toluene is added as a solvent; the mixture is heated in an oil bath, condensed and refluxed, and then slowly cooled to room temperature after stirring; precipitates are removed by filtration, the reaction solution is extracted with dichloromethane and saturated brine, and the solvent is removed by evaporation under reduced pressure to obtain a crude product; the crude product is further purified by using a silica gel chromatographic column, and the solvent is evaporated under reduced pressure to obtain the product N,N-biPh2Me; at room temperature, N,N-biPh2Me is taken out, dissolved in dichloromethane, and then lead dioxide is added, and the product N,N-biPh2MeR is obtained after stirring and filtration.

[0013] Optionally, the eluent for purification is a mixed solvent of ethyl acetate and n-hexane.

[0014] Optionally, the reaction container is a double-mouth bottle.

[0015] Optionally, the amounts of the reactants are as follows: 4,4'-diamino-2,2'-dimethylbiphenyl 212 mg, 1 mmol, 1.0 eq; 3,5-dichloro-4-bromopyridine 545 mg, 2.4 mmol, 2.4 eq; tris(dibenzylideneacetone)dipalladium 92 mg, 0.1 mmol, 0.1 eq; tri-tert-butylphosphine tetrafluoroborate 44 mg, 0.15 mmol, 0.15 eq; and sodium tert-butoxide 192 mg, 2 mmol, 2 eq.

[0016] The above technical features can be combined in various suitable manners or replaced by equivalent technical features, as long as the purpose of the application can be achieved.

[0017] Compared with the prior art, the stable biradical monomolecular device containing anchoring groups provided by the application has at least the following beneficial effects:

[0018] (1) The monomolecular junction is simple to prepare: the amino group (-NH2) and the bromine atom (-Br) undergo a substitution reaction to form a biradical molecule precursor; and then the -NH is oxidized by an oxidant PbO2 to form a nitrogen biradical (-N •). Finally, using STMB technology, a high-efficiency and stable Au-N • -p bridge-N • -Au single-molecule junction.

[0019] (2) Anchoring group: pyridine (-Py) is selected as the anchoring group. Due to the high binding energy, pyridine exhibits relatively high conductivity, high junction formation rate and stability in single-molecule devices.

[0020] (3) Nitrogen radical: -NH is oxidized by an oxidant PbO2, that is, a nitrogen radical (-N • ) is formed. In addition, the nitrogen radical is located between the anchoring group and the central p bridge molecule, and the unpaired electrons can better delocalize on the entire conductive path, efficiently participate in charge transport, and are more conducive to exploring the influence of unpaired electrons on the electrical transport properties of single-molecule junctions.

[0021] (4) Chlorine atom: The introduction of a chlorine atom with large steric hindrance not only improves the lifetime of the radical, but also increases its solubility.

[0022] (5) A single-molecule junction based on a nitrogen radical is constructed, which has the advantages of simple preparation, high junction formation rate and good stability, and lays a good foundation for the construction of a high-efficiency and stable double-radical single-molecule device.

[0023] The target molecule N,N-biPh2MeR was optimized at the uM06-2X / 6-311G(d) theoretical level, and at the same optimization level, the resonance frequency was calculated to ensure that the optimized structure is an accurate minimum point structure. The spin density distribution map was drawn using Multiwfn and VMD programs. All calculations were completed on Gaussian 16. Some important calculation results are as follows:

[0024] (1) The molecular length is 1.58 nm, which matches the test results of single-molecule devices, proving the stable formation of the double-radical single-molecule junction;

[0025] (2) The double-radical characteristic y = 0.12, and the spin density distribution map as shown in Figure 4 proves the existence of unpaired electrons, and the unpaired electrons can better delocalize on the conductive path;

[0026] (3) The theoretical calculation single-triplet energy difference DE s-t = -2.54 kcal / mol, which is consistent with the ESR test results. BRIEF DESCRIPTION OF DRAWINGS

[0027] In the following, the application will be described in more detail based on the embodiments and with reference to the accompanying drawings. Among them:

[0028] Figure 1 To form an oligo (p-phenylenevinylene) (OPE) based radical molecular junction;

[0029] Figure 2 The technical solutions adopted by the present application are as follows:

[0030] Figure 3 Au-N • -biPh2Me-N • -Au molecular junction;

[0031] Figure 4 Spin density distribution map (Isovalue = 0.001.) of the molecule N,N-biPh2MeR;

[0032] Figure 5 Synthesis route of the molecule N,N-biPh2MeR;

[0033] Figure 6 Synthesis route of the molecule N,N-biPh2MeR;

[0034] Figure 7 NMR hydrogen spectrum of the molecule N,N-biPh2MeR;

[0035] Figure 8 Maldi-Tof mass spectrum of the molecule N,N-biPh2MeR;

[0036] Figure 9 Variable temperature solid ESR of the molecule N,N-biPh2MeR;

[0037] Figure 10 Secondary integral data and fitting curve of the solid ESR of the molecule N,N-biPh2MeR;

[0038] Figure 11 UV-visible-near infrared absorption spectrum of the molecules N,N-biPh2Me and N,N-biPh2MeR;

[0039] Figure 12 One-dimensional conductance histogram, two-dimensional conductance-displacement statistical diagram (inset: displacement distribution histogram). Embodiment

[0040] The present application will be further described below with reference to the accompanying drawings.

[0041] As Figure 2 shown, the present application provides a stable biradical molecular device containing an anchoring group, which comprises a nitrogen radical (-N • ) formed by oxidizing -NH with an oxidizing agent, and an Au-N • -p bridge-N • -Au molecular junction (Au-N• -biPh2Me-N • -Au unimolecular junction, Figure 3 ), pyridine (-Py) anchoring group; nitrogen radical located between pyridine (-Py) anchoring group and Au-N • -p bridge- N • -Au unimolecular junction in the middle.

[0042] In one embodiment, such as Figure 5 As shown, the synthesis of molecule N,N-biPh2Me is as follows: Under a nitrogen atmosphere, 4,4'-diamino-2,2'-dimethylbiphenyl (212 mg, 1 mmol, 1.0 eq), 3,5-dichloro-4-bromopyridine (545 mg, 2.4 mmol, 2.4 eq), tris(dibenzylacetone)dipalladium(0) (92 mg, 0.1 mmol, 0.1 eq), tritert-tert-butylphosphine tetrafluoroborate (44 mg, 0.15 mmol, 0.15 eq), and sodium tert-butoxide (192 mg, 2 mmol, 2 eq) were added to a 50 mL double-necked flask. After degassing with nitrogen for 15 minutes, 10 mL of toluene was added as a solvent. The mixture was heated to 100°C (oil temperature) in an oil bath, refluxed, and stirred for 24 hours. It was then slowly cooled to room temperature, filtered to remove the precipitate, and the reaction mixture was extracted with dichloromethane and saturated brine. The solvent was evaporated under reduced pressure to obtain the crude product. The crude product was further purified using a silica gel column chromatography with a mixture of ethyl acetate and n-hexane as the eluent. Evaporation of the solvent under reduced pressure yielded 333 mg of the product N,N-biPh₂Me, a pale yellow solid, in 66% yield.

[0043] Preparation of molecular N,N-biPh2MeR: such as Figure 6 As shown, at room temperature, N,N-biPh2Me (5 mg, 0.01 mmol, 1.0 eq) was dissolved in dichloromethane, followed by the addition of lead dioxide (120 mg, 0.5 mmol, 50.0 eq). After stirring for 10 min, the mixture was filtered to obtain 4.7 mg of the product N,N-biPh2MeR, a wine-red solid with a yield of 94%.

[0044] In one embodiment, the obtained molecular structure was confirmed by nuclear magnetic resonance and mass spectrometry.

[0045] like Figure 7 The 1H NMR spectrum of molecule N,N-biPh2Me is shown below: 1 H NMR (400 MHz, DMSO- d 6) δ8.48 (s, 4H), 8.47 (s, 2H), 6.94 (d, J= 8.1 Hz, 2H), 6.77 (d, J = 2.4 Hz, 2H), 6.69 (dd, J = 8.1, 2.4 Hz, 2H), 1.95 (s, 6H).

[0046] like Figure 8 As shown, the mass spectrum of molecule N,N-biPh2MeR: Maldi-Tof MS: [M]+: 502.04 (calculated value: 502.22).

[0047] In one embodiment, electron spin resonance (ESR) characterization is performed by solid-state temperature-varying ESR testing of the free radical N,N-biPh2MeR using an electron spin resonance analyzer. Figure 9 Electron spin resonance intensity I With current temperature T Perform a second integral and plot the results. I*T-T Scatter plot, and the singlet triplet energy difference (DE) is fitted using the Blaney-Bowers equation. s-t The value is -1.37 kcal / mol. Figure 10 This indicates that the molecule N,N-biPh2MeR is a diradical and that its ground state is a singlet state.

[0048] In one embodiment, UV-Vis-NIR absorption spectra of the molecule N,N-biPh2Me and its radical N,N-biPh2MeR were measured at room temperature and in air. All samples were prepared to a concentration of 1×10⁻⁶. -5 A mol / L dichloromethane solution. All measured data were normalized. Figure 11 The maximum absorption peak of N,N-biPh2Me solution is located at 297 nm, while that of N,N-biPh2MeR is located at 483 nm, a redshift of about 186 nm. This is consistent with the phenomenon of redshift in absorption spectrum after the introduction of unpaired electrons, and further confirms that N,N-biPh2MeR is a free radical molecule.

[0049] In one embodiment, single-molecule conductivity tests of N,N-biPh2Me and N,N-biPh2MeR were performed using a scanning tunneling microscope split-junction apparatus. Figure 12 In the single-molecule conductivity tests, the following parameters were used: applied bias voltage of 100 mV, sampling frequency of 20000 Hz, and piezoelectric change rate of the piezoelectric ceramic of 1 V / s. For all single-molecule conductivity tests, more than 2000 single-molecule conductivity data points were collected to ensure the authenticity and reliability of the test data. All samples were dissolved in anhydrous 1,2,4-trichlorobenzene (TCB) to prepare a solution of 1×10⁻⁶.-4 mol / L of the solution to be tested.

[0050] For the molecule N,N-biPh2Me, no obvious conductance peak can be seen in the one-dimensional conductance histogram, which is due to the low conductance value of the molecule, which is close to the limit of the resolution of the instrument under the testing condition, and overlaps with the background noise. Meanwhile, no obvious "conductance cloud" can be observed from the two-dimensional conductance-displacement histogram. For the radical molecule N,N-biPh2MeR, the conductance value is 10 -5.24 G 0, and a clear "conductance cloud" can also be seen from the two-dimensional conductance-displacement histogram, with the fitting result of the displacement distribution being 1.55 nm, which can match the theoretical value of 1.58 nm. The conductance of N,N-biPh2MeR is greatly improved compared to the non-radical state of N,N-biPh2Me, while the molecular structure does not change greatly, so such a huge improvement can be attributed to the influence of the unpaired electron in the single-molecule junction.

[0051] While the application has been described with reference to particular embodiments, it will be understood that the examples are merely illustrative of the principles and applications of the present application. It will be understood that various modifications can be made to the illustrative embodiments, and other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It will be understood that the features of the various embodiments can be combined with each other, in different ways than as described herein. It will be understood that features described with reference to individual embodiments can be used in other described embodiments.

Claims

1. A stable biradical single-molecule device containing an anchoring group, characterized in that, diradical molecules are .

2. The method for synthesizing a stable biradical single-molecule device containing an anchoring group according to claim 1, characterized in that, Includes the following steps: Under a nitrogen atmosphere, 4,4'-diamino-2,2'-dimethylbiphenyl, 3,5-dichloro-4-bromopyridine, tris(dibenzylacetone)dipalladium, tri-tert-butylphosphine tetrafluoroborate, and sodium tert-butoxide were added to a container. After degassing with nitrogen, toluene was added as a solvent. The mixture was heated in an oil bath, refluxed, stirred, and slowly cooled to room temperature. The precipitate was removed by filtration, and the reaction solution was extracted with dichloromethane and saturated brine. The solvent was removed by evaporation under reduced pressure to obtain the crude product. The crude product was further purified using a silica gel column chromatography, and the solvent was evaporated under reduced pressure to obtain the intermediate N,N-biPh2Me. ; At room temperature, N,N-biPh₂Me was dissolved in dichloromethane, then lead dioxide was added, the mixture was stirred, and filtered to obtain the product. .

3. The method for synthesizing a stable biradical single-molecule device containing an anchoring group according to claim 2, characterized in that, The eluent used for purification is a mixed solvent of ethyl acetate and n-hexane.

4. The method for synthesizing a stable biradical single-molecule device containing an anchoring group according to claim 2, characterized in that, The reaction vessel is a double-necked flask.

5. The method for synthesizing a stable biradical single-molecule device containing an anchoring group according to claim 2, characterized in that, The reactants were used in the following amounts: 4,4'-diamino-2,2'-dimethylbiphenyl 212 mg, 1 mmol, 1.0 eq; 3,5-dichloro-4-bromopyridine 545 mg, 2.4 mmol, 2.4 eq; tris(dibenzylacetone)dipalladium 92 mg, 0.1 mmol, 0.1 eq; tritert-butylphosphine tetrafluoroborate 44 mg, 0.15 mmol, 0.15 eq; sodium tert-butoxide 192 mg, 2 mmol, 2 eq.

Images