Donor-acceptor type compounds based on isatin blue derivatives, preparation methods, molecular wires and molecular electric switches

Abstract

The present invention belongs to the technical field of materials science, and specifically discloses a donor-acceptor type compound based on an isoindigo derivative, a preparation method, a molecular wire and a molecular electric switch. The donor-acceptor type compound based on an isoindigo derivative is shown in Formula I: [formula content not provided in the original]. The present invention also discloses a preparation method of the donor-acceptor type compound based on an isoindigo derivative. The synthesis method of the present invention is simple, the raw material cost is low, the process is easy to industrialize, and the product purification is efficient and convenient. A series of donor-acceptor type compounds prepared based on isoindigo derivatives have different energy band gaps and play an important role as molecular wires in single-molecule electron transport materials. Through bias voltage regulation, the molecular conductance of the molecular wire can be reversibly regulated, playing an important role in practical application fields such as molecular electric switches.

Description

Technical Field

[0001] The present invention relates to the technical field of materials science, and particularly to donor-acceptor type compounds based on isoindigo derivatives, preparation methods, molecular wires and molecular switches. Background Art

[0002] A switch is a basic component of a functional molecular device. Integrating a switching module into a logic circuit provides the possibility of performing complex logical operations. So far, strategies for regulating single-molecule conductance include molecular structure design, chemical stimuli, mechanical force, light irradiation, and electrochemical gating, etc. (W. Hong et al, Angew. Chem. Int. Ed. 2017, 56 , 13061-13065; B. W. Mao et al, J. Am. Chem. Soc. 2018, 140 , 17685-17690). However, through the above regulation means, the configuration of the molecule has changed to a large extent, and external factors such as chemical substances, light sources, and counter electrodes need to be introduced. This reduces the stability of the functional device and increases the integration difficulty of the circuit. According to the Landauer principle, a more effective method for regulating electron transport is to regulate the energy level difference between the molecular frontier orbital energy level and the Fermi energy level of the electrode by adjusting the bias voltage between the source electrode and the drain electrode. In this way, the electron transmission probability at the Fermi energy level can be changed T ( E ), and then reversibly regulate the single-molecule conductance. In addition, the electron coupling between the molecular orbit and the electrode has been proven to be bias-dependent, so the change of the bias voltage will inevitably affect the electron coupling strength, which is a key parameter affecting the molecular conductance (J.B. Neaton et al, J. Phys. Chem. C 2017, 121 , 21136-21144). Based on the above considerations, the energy band gap between the frontier orbital and the Fermi energy level and the molecule-electrode coupling strength can be regulated by bias modulation, and then the reversible regulation of single-molecule conductance can be realized. This is very different from the traditional switch regulation method. It can show reversible and instant response at room temperature, and is a non-destructive conductance regulation mode, which is crucial for further application in electronic devices.

[0003] Currently, most π-conjugated molecules usually have a relatively large energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which requires a relatively high bias voltage to adjust the energy level difference between the molecular frontier orbitals and the Fermi level of the electrode. A relatively large bias voltage will increase the instability of the molecular junction and the possibility of local overheating. In contrast, π-conjugated molecules with a narrow bandgap can more easily achieve the regulation of the energy level difference under the action of a bias voltage, thereby obtaining a large on-off ratio within a limited bias voltage range. Currently, the common method to obtain narrow-bandgap molecules is to introduce electron-donating and electron-withdrawing groups into the π-conjugated backbone to construct donor-acceptor (D-A) type conjugated molecules. This method has been widely applied in organic optoelectronic materials. At the same time, the molecular engineering design of electron-donating groups provides an opportunity to study the relationship between bias voltage and molecular conductance from the perspective of interfacial electron coupling.

[0004] Combined with the above research background, the development of a narrow-bandgap donor-acceptor type compound is of great significance for the design of molecular wires and bias-responsive molecular electrical switches, and is an important step towards future circuit integration. Using isoindigo (ISO) as the electron-withdrawing group, different bandgap molecules can be obtained by modifying different electron-donating groups, which also provides an opportunity to study the interaction between the molecule-electrode interface. Therefore, through reasonable molecular design, it is of great significance to carry out the preparation of donor-acceptor type compounds of isoindigo derivatives and the application research of electrical switches in single-molecule devices. Summary of the Invention

[0005] In order to overcome the defects existing in the prior art, the present invention provides a donor-acceptor type compound based on isoindigo derivatives, a preparation method, a molecular wire and a molecular electrical switch.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0007] The first aspect of the present invention is to provide a donor-acceptor type compound based on isoindigo derivatives, and the donor-acceptor type compound based on isoindigo derivatives is shown in Formula I:

[0008]

[0009] Wherein, R1 is one of hydrogen, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl;

[0010] R2 is one of the structures shown in Formula a, Formula b, Formula c, Formula d,

[0011]

[0012] In Formula a, Formula b, Formula c, Formula d, the positions marked by the curves are the substitution positions.

[0013] As a further description of the above solution, the structure of the donor-acceptor type compound is one of Formula I-1, Formula I-2, Formula I-3, and Formula I-4

[0014] .

[0015] The second solution of the present invention is to provide a preparation method of a donor-acceptor type compound based on isatin derivatives, and the preparation method is used to prepare the above-mentioned donor-acceptor type compound based on isatin derivatives.

[0016] As a further description of the above solution, the preparation method includes the following steps:

[0017] (1) Add compound II and sodium methyl mercaptide to N,N-dimethylformamide, stir at a temperature of 60 o °C to 110 o °C for 24 hours, rotary evaporate to remove the solvent, and purify the obtained crude product by recrystallization to obtain compound III, wherein compound II is one of 6-fluoro isatin, 6-chloro isatin, 6-bromo isatin, and 6-iodo isatin, preferably 6-chloro isatin; the molar ratio of compound II to sodium methyl mercaptide is 1:(1-5), preferably 1:2;

[0018] (2) Dissolve compound III and sodium hydride in a tetrahydrofuran / N,N-dimethylformamide solution, react at room temperature for 30 minutes, then add a halogenated alkane, stir at a temperature of 60-140°C for 24 hours, rotary evaporate to remove the solvent, and purify the obtained product by column chromatography to obtain compound IV, wherein the molar ratio of compound III to sodium hydride is 1:(1-3), preferably 1:1.5; the molar ratio of compound III to the halogenated alkane is 1:(0.8-3), preferably 1:1;

[0019] (3) Mix compound IV with hydrazine hydrate, heat up to 60-120°C, reflux for three hours until the solution is clear, rotary evaporate to remove the solvent, acidify with hydrochloric acid, stir for three hours, remove the solvent, and purify the obtained product by column chromatography to obtain compound V, wherein the molar ratio of compound IV to hydrazine hydrate is 1:(2-20), preferably 1:10;

[0020] (4) Dissolve compound IV, compound V, and p-toluenesulfonic acid compound in glacial acetic acid, react at a temperature of 60-120°C for 7 hours, rotary evaporate to remove the solvent, and purify the obtained crude product by recrystallization to obtain the donor-acceptor type compound based on isatin derivatives shown in Formula I-1, wherein the molar ratio of compound IV, compound V, and p-toluenesulfonic acid compound is 1:(1-3):(0.1-1), preferably 1:1:0.275.

[0021] Specifically, the synthetic route corresponding to the above preparation method is as follows:

[0022] 。

[0023] As a further description of the above solution, in step (2), the haloalkane is one of the halo compounds corresponding to hydrogen, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, preferably the halo compound corresponding to 2-ethylhexyl; in step (4), the p-toluenesulfonic acid compound is one of p-toluenesulfonic acid and p-toluenesulfonic acid monohydrate, preferably p-toluenesulfonic acid monohydrate.

[0024] The second solution of the present invention also provides another preparation method of a donor-acceptor type compound based on an isoindigo derivative, including the following steps:

[0025] Dissolve compound VI, 4-methylthiophenylboronic acid compound, and carbonate in a mixed solution of toluene and water, add tetrakis(triphenylphosphine)palladium, heat to 20~110 °C, and react for 24 hours under an argon atmosphere. Remove the organic solvent, and purify the obtained product by column chromatography to obtain the donor-acceptor type compound based on the isoindigo derivative shown in formula I-2, wherein the molar ratio of compound VI, 4-methylthiophenylboronic acid compound, and carbonate is 1: (1~6): (1~6), preferably 1: 2.5: 6; the molar ratio of compound VI to tetrakis(triphenylphosphine)palladium is 100: (1~20), preferably 100: 5;

[0026] Alternatively, the above preparation method includes the following steps:

[0027] Dissolve compound VI and 5-methylthiophene compound in N, N-dimethylformamide, add tetrakis(triphenylphosphine)palladium, heat to 25~110 °C, and react for 24 hours under an argon atmosphere. Remove the organic solvent by rotary evaporation, and purify the obtained product by column chromatography to obtain the donor-acceptor type compound based on the isoindigo derivative shown in formula I-3, wherein the molar ratio of compound VI to 5-methylthiophene compound is 1: (1~6), preferably 1: 2; the molar ratio of compound VI to tetrakis(triphenylphosphine)palladium is 100: (1~20), preferably 100: 5;

[0028] Alternatively, the above preparation method includes the following steps:

[0029] Compound VI and a 5-methylthio-3,4-ethylenedioxythiophene compound are dissolved in N,N-dimethylformamide. Tetrakis(triphenylphosphine)palladium is added, and the temperature is raised to 25 - 110 °C. The reaction is carried out for 24 hours under an argon atmosphere. The organic solvent is removed by rotary evaporation, and the obtained product is purified by column chromatography to obtain a donor-acceptor type compound based on an isoindigo derivative shown in Formula I-4. Among them, the molar ratio of Compound VI to the 5-methylthio-3,4-ethylenedioxythiophene compound is 1:(1 - 6), preferably 1:4; the molar ratio of Compound VI to tetrakis(triphenylphosphine)palladium is 100:(1 - 20), preferably 100:5.

[0030] Among them, Compound VI in the above three preparation methods is one of 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo and 6,6'-diiodo-N,N'-(2-ethylhexyl)-isoindigo, preferably 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo.

[0031] As a further description of the above scheme, the 4-methylthiobenzeneboronic acid compound is one of 4-methylthiobenzeneboronic acid and 4-methylthiophenylboronic acid pinacol ester, preferably 4-methylthiobenzeneboronic acid; the 5-methylthiothene compound is one of 2-tributylstannyl-5-methylthiothene and 2-trimethylstannyl-5-methylthiothene, preferably 2-tributylstannyl-5-methylthiothene; the 5-methylthio-3,4-ethylenedioxythiophene compound is one of 2-tributylstannyl-5-methylthio-3,4-ethylenedioxythiophene and 2-trimethylstannyl-5-methylthio-3,4-ethylenedioxythiophene, preferably 2-tributylstannyl-5-methylthio-3,4-ethylenedioxythiophene.

[0032] Specifically, the synthetic routes corresponding to the above three preparation methods are as follows:

[0033] 。

[0034] The third solution of the present invention provides a molecular wire, which includes the above-mentioned donor-acceptor type compound based on isoindigo derivative, specifically as follows: The donor-acceptor type compound based on isoindigo derivative has ultraviolet band-edge absorptions at different wavelengths in a tetrahydrofuran solution, forming donor-acceptor type organic semiconductor materials with different energy levels. The band-edge absorption of the donor-acceptor type compound corresponding to Formula I-1 in the tetrahydrofuran solution is 633 nm, the band-edge absorption of the donor-acceptor type compound corresponding to Formula I-2 in the tetrahydrofuran solution is 641 nm, the band-edge absorption of the donor-acceptor type compound corresponding to Formula I-3 in the tetrahydrofuran solution is 664 nm, and the band-edge absorption of the donor-acceptor type compound corresponding to Formula I-4 in the tetrahydrofuran solution is 682 nm. By enhancing the electron-donating property of the electron-donating group, the band-edge absorption of the donor-acceptor type compound based on isoindigo derivative continuously redshifts, obtaining a series of donor-acceptor type compounds based on isoindigo derivative with different band gaps. Through molecular self-assembly, coordination bonds are respectively formed between both ends of the molecule and the Au electrode to construct a single-molecule wire. A constant bias voltage is applied across both ends of the metal electrode to form a circuit, and an I-V converter with a sampling rate of 10 kHz is used to record the real-time conductance, and the molecular conductance of this molecular wire can be obtained. Due to different molecular band gaps and different electron tunneling barriers, the donor-acceptor type compounds based on isoindigo derivative exhibit different single-molecule conductances. Taking the donor-acceptor type compound corresponding to Formula I-3 as an example: at a bias voltage of 0.1 V in trichlorobenzene solvent, the single-molecule conductance of the donor-acceptor type compound corresponding to Formula I-3 is 10 -4.37 G 0. The above-mentioned donor-acceptor type compounds based on isoindigo derivative can all exhibit stable molecular conductance in a single-molecule junction, can be applied to the preparation of stable molecular wires, and are used for charge transport in single-molecule devices.

[0035] The fourth solution of the present invention provides a molecular electric switch, which includes the above-mentioned donor-acceptor type compound based on isoindigo derivative, specifically as follows: By changing the bias voltage applied across the electrodes, the energy level difference between the molecular frontier orbit and the Fermi level of the metal electrode will change, and the electron coupling strength between the molecule and the electrode also changes, thereby affecting the charge transport performance of the molecule, achieving the purpose of regulating the single-molecule conductance by bias voltage. Taking the donor-acceptor type compound corresponding to Formula I-3 as an example: in trichlorobenzene solvent, at 0.1 V, the single-molecule conductance value of the donor-acceptor type compound corresponding to Formula I-3 is 10 -4.37 G 0. After the bias voltage is increased by 0.6 V, the single-molecule conductance rises to 10 -3.17 G 0, and the molecular conductance increases by 15.8 times. After the bias voltage is reduced to 0.1 V, the single-molecule conductance can return to the initial value again, showing reversible and real-time response, and can be applied to the molecular electric switch with bias voltage regulation in a single-molecule junction.

[0036] The present invention has at least one of the following beneficial effects:

[0037] 1. The donor-acceptor type compound based on isoindigo derivatives of the present invention has a simple synthesis method, low raw material cost, easy industrial production process, and high-efficiency and convenient product purification. It can be directly anchored to a metal electrode through molecular self-assembly, and the device preparation is simple, playing an important role in practical application fields such as single-molecule electron transport materials and single-molecule electrical switches.

[0038] 2. The donor-acceptor type compound based on isoindigo derivatives of the present invention is easy to modify, and donor-acceptor type compounds with different energy levels can be obtained through molecular engineering design. At the same time, this type of compound has single-molecule charge transport properties. The introduction of methylthio groups enables it to directly form a single-molecule wire with an Au electrode, realizing the direct measurement of the conductance properties at the single-molecule scale and can be applied in molecular wires. By adjusting the bandgap, the constructed molecular wires can exhibit different magnitudes of single-molecule conductance. In addition, the present invention can also regulate the intramolecular charge transport under different bias voltage stimuli, resulting in changes in conductivity. Such bias-responsive donor-acceptor narrow-bandgap compounds play a very important role in molecular electronics and can be used to prepare molecular wires, single-molecule electrical switches, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the ultraviolet absorption spectrum of compound I-1 prepared in Example 1 of the present invention.

[0040] Figure 2 It is a schematic diagram of the conductance regulation of compound I-1 prepared in Example 2 of the present invention under different bias voltages.

[0041] Figure 3 It is a schematic diagram of the ultraviolet absorption spectrum of compound I-2 prepared in Example 3 of the present invention.

[0042] Figure 4 It is a schematic diagram of the conductance regulation of compound I-2 prepared in Example 3 of the present invention under different bias voltages.

[0043] Figure 5 It is a schematic diagram of the ultraviolet absorption spectrum of compound I-3 prepared in Example 4 of the present invention.

[0044] Figure 6 It is a schematic diagram of the conductance regulation of compound I-3 prepared in Example 4 of the present invention under different bias voltages.

[0045] Figure 7 It is a schematic diagram of the ultraviolet absorption spectrum of compound I-4 prepared in Example 5 of the present invention.

[0046] Figure 8Schematic diagram of the conductance regulation of Compound I-4 prepared in Example 5 of the present invention under different bias voltages.

[0047] Figure 9 Schematic diagram of the comparison of the ultraviolet absorption spectra of Compounds I-1, I-2, I-3, and I-4 prepared in Examples 1-5 of the present invention. Detailed implementation manners

[0048] The following further illustrates the detailed implementation manners of the present invention with reference to the accompanying drawings. It should be noted here that the description of these implementation manners is used to help understand the present invention, but does not limit the present invention.

[0049] The donor-acceptor type compound based on isoindigo derivatives provided by the present invention is shown in Formula I:

[0050]

[0051] Among them, R1 is one of hydrogen, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl;

[0052] R2 is one of the structures shown in Formula a, Formula b, Formula c, and Formula d,

[0053]

[0054] In Formula a, Formula b, Formula c, and Formula d, the positions marked by the curves are the substitution positions.

[0055] The structures of the above corresponding donor-acceptor type compounds are one of Formula I-1, Formula I-2, Formula I-3, and Formula I-4

[0056] .

[0057] The following further illustrates the donor-acceptor type compounds corresponding to Formula I-1, Formula I-2, Formula I-3, and Formula I-4 through specific examples.

[0058] Example 1

[0059] The synthesis route of the donor-acceptor type compound I-1 based on isoindigo derivatives is as follows:

[0060]

[0061] Raw materials such as 6-chloroindirubin and sodium methyl mercaptide are commercial products.

[0062] (1) 6-Chloroindirubin (3.00 g, 16.5 mmol), namely Compound II-1, was added to a 50 mL solution of N,N-dimethylformamide. An aqueous solution of sodium methanethiolate (11.58 g, 33 mmol, note: since an aqueous solution of sodium methanethiolate was used, sodium methanethiolate accounted for 20% of the aqueous solution of sodium methanethiolate) was added at room temperature and the temperature was gradually raised to 100 o °C, and the mixture was stirred for 24 h. After the reaction was completed, the temperature was lowered to room temperature. The reaction solution was extracted with ethyl acetate, washed with water three times, the organic phases were combined, and dried over anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, the crude product was recrystallized from dichloromethane to obtain 2.3 g of Compound III-1 with a yield of 72%.

[0063] 1 H NMR (400 MHz, d6-DMSO) δ 11.00 (s, 1H), 7.41 (d, J = 8.0 Hz, 1H), 6.90 (dd, J = 8.1, 1.6 Hz, 1H), 6.68 (d, J = 1.4 Hz, 1H), 2.56 (s, 4H). 13 C NMR(100 MHz, d6-DMSO) δ 182.92, 160.69, 153.30, 151.63, 125.28, 119.08, 114.71, 107.80, 14.39.]

[0064] (2) Compound III-1 (1.00 g, 5.18 mmol) was added to a 20 ml solution of tetrahydrofuran / N,N-dimethylformamide (volume ratio of tetrahydrofuran / N,N-dimethylformamide 1:1). Sodium hydride (0.186 g, 7.75 mmol) was added in portions. After reacting at 25 °C for 30 minutes, 2-ethylhexyl bromide (1.00 g, 5.18 mmol) was added to the reaction solution, and the temperature was raised to 100 °C and stirring was continued for 24 hours. After the reaction was completed, the temperature was lowered to room temperature. The reaction solution was extracted with ethyl acetate and washed with water three times. After combining the organic phases, it was dried over anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, it was purified by column chromatography (eluent was a mixture of petroleum ether:dichloromethane = 1:1) to obtain 0.9 g of Compound IV-1 with a yield of 57%.

[0065] 1 H NMR (400 MHz, CDCl3) δ 7.50 (d, J = 8.0 Hz, 1H), 6.87 (dd, J ​​= 8.0, 1.4 Hz, 1H), 6.64 (d, J = 1.3 Hz, 1H), 3.64 - 3.53 (m, 2H), 1.82 - 1.76 (m, 1H), 1.42 - 1.29 (m, 8H), 0.94 (t, J = 7.4 Hz, 3H), 0.90 (t, J = 6.8 Hz, 3H). 13 C NMR (100 MHz, CDCl3) δ 181.71, 159.48, 153.76, 151.69, 125.40, 118.70, 114.22, 106.24, 44.23, 37.53, 30.62, 28.64, 24.01, 23.01, 14.77, 14.04, 10.62.]

[0066] (3) Dissolve compound IV - 1 (0.3 g, 0.98 mmol) in 3.5 mL of hydrazine hydrate (60%), reflux at 100 °C for three hours until the solution becomes clear, and then cool to room temperature after the reaction is completed. Extract the reaction solution with ethyl acetate, wash it three times with water, combine the organic phases, and dry them with anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, add 8 ml of hydrochloric acid solution (6 N), stir at room temperature for another three hours, then extract the crude product with ethyl acetate, wash it three times with water, combine the organic phases, and dry them with anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, purify it by column chromatography (the eluent is a mixture of petroleum ether:dichloromethane = 1:3) to obtain 0.26 g of compound V - 1 with a yield of 91%.

[0067] 1 H NMR (400 MHz, CDCl3) δ 7.16 (d, J = 7.7 Hz, 1H), 6.92 (dd, J = 7.7, 1.6 Hz, 1H), 6.72 (d, J = 1.3 Hz, 1H), 3.63 - 3.52 (m, 2H), 3.49 (s, 2H), 2.50 (s, 3H), 1.85 - 1.75 (m, 1H), 1.36 - 1.29 (m, 8H), 0.92 (t, J = 7.4 Hz, 3H), 0.89 (t, J = 7.1 Hz, 3H). 13 ​13C NMR (100 MHz, CDCl3) δ 175.46, 145.66, 138.22, 124.58, 121.63, 120.07, 107.35, 44.11, 37.38, 35.40, 30.67, 28.70, 24.04, 23.05, 16.31, 14.06, 10.67.

[0068] (4) Compound V-1 (0.234 g, 0.80 mmol), compound IV-1 (0.245 g, 0.80 mmol) and p-toluenesulfonic acid monohydrate (0.042 g, 0.22 mmol) were dissolved in 15 mL of glacial acetic acid and refluxed at 115 °C for seven hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was extracted with ethyl acetate, washed three times with water, and the organic phases were combined and dried over anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, the crude product was recrystallized with petroleum ether to obtain 0.31 g of compound I-1, with a yield of 67%.

[0069] [ 1 1H NMR (400 MHz, CDCl3) δ 9.07 (d, J J = 8.5 Hz, 2H), 6.86 (dd, J J = 8.6, 1.6 Hz, 2H), 6.61 (d, J J = 1.6 Hz, 2H), 3.71 - 3.59 (m, 4H), 2.54 (s, 6H), 1.86 - 1.80 (m, 2H), 1.42 - 1.25 (m, 16H), 0.93 (t, J J = 7.4 Hz, 6H), 0.89 (t, J J = 7.3 Hz, 6H). 13 13C NMR (100 MHz, CDCl3) δ 168.86, 145.26, 144.32, 131.20, 129.55, 118.71, 118.21, 105.02, 44.10, 37.71, 30.75, 28.81, 24.13, 23.09, 15.09, 14.10, 10.77. HRMS (EI-TOF): C 34 H 46 N2O2S2 m / z [M + calcd for 578.3001 found: 578.3008.

[0070] Example 2

[0071] Spectral properties of the donor-acceptor type compound I-1 based on isoindigo derivatives:

[0072] Dissolve the compound I-1 prepared in Example 1 in tetrahydrofuran to prepare a tetrahydrofuran solution with a concentration of 20 μmol∙L -1 In a quartz cuvette with dimensions of 1 cm×1 cm×4 cm, add 3.0 mL of the solution to be measured, and use a UV-Vis spectrophotometer to measure the absorption spectrum. Figure 1 This is a schematic diagram of the UV absorption spectrum of the compound I-1 prepared in Example 1 of the present invention. The abscissa is the wavelength, and the ordinate is the absorbance. π-π * transition absorption peaks and intramolecular charge transfer (ICT) peaks are shown at 420 nm and 530 nm, respectively. The band-edge absorption of the molecule is 633 nm, and the optical band gap E opt g = 1240 / λ onset = 1.96 eV.

[0073] Conductance regulation of the donor-acceptor type compound I-1 based on isoindigo derivatives:

[0074] The donor-acceptor type compound of the isoindigo derivative forms a molecular wire with the gold electrode through self-assembly in the nanogap. By changing the bias voltage applied across the electrodes, the energy level difference between the frontier orbitals of the molecule and the Fermi level of the metal electrode will change, and the change in the bias voltage will affect the coupling strength between the molecule and the electrode, thereby affecting the charge transport performance of the molecule, achieving the purpose of bias voltage regulation of molecular conductance. Making full use of the above characteristics, the present invention uses bias voltage to regulate molecular conductance and prepares a series of molecular switches / wires with bias voltage regulation properties. The conductance performance of its single-molecule device is characterized by using the tunneling scanning break junction (STM-BJ) technique. The STM-BJ technique is one of the effective methods to construct a metal-molecule-metal single-molecule junction (Metal-Molecule-Metal Junction) and measure the conductance of a single molecule under normal temperature, normal pressure, and common solution environments. Its data is based on statistical analysis, so it has significant advantages in terms of measurement reliability. Prepare an STM probe by burning a gold wire (diameter 0.25 mm, 99.99%) with a hydrogen flame to expose the (111) plane. Use ~20 / 200 nm Cr / Au at 1 Ås -1The rate is used to slowly evaporate on the silicon wafer to prepare the Au substrate. A 0.1 mM target molecule solution is prepared using trichlorobenzene (TCB) as the solvent, and 5 μL of the above solution is dropped onto the Au substrate. First, the STM probe is controlled by a stepper motor so that the distance between the STM probe and the Au matrix is less than 1 μm; subsequently, through piezoelectric control, the STM probe is approximated to the gold-coated substrate until impact occurs, and then the probe is retracted at a certain speed (15 nm / s). As the STM probe is retracted, first, an Au-Au point contact is formed, and its conductance is the conductance quantum ( G 0 = 2e 2 / h = 77.5 μS). The STM probe continues to retract, and the Au-Au point contact breaks, and the target molecule and the two end electrodes form an Au-Molecule-Au molecular junction through self-assembly. At this time, a plateau appears below G 0 in the conductance-displacement trace, indicating the formation of the molecular junction. During the process of disconnecting and forming the junction, the bias voltage is kept at a constant value, and a custom I-V converter with a sampling rate of 10 kHz is used to record the real-time conductance. Due to the excellent stability of the single-molecule device and the test platform, this process can be repeated thousands of times to obtain a large number of statistically significant valid data. In the present invention, thousands of conductance-displacement traces are collected for each device and plotted into a two-dimensional conductance-displacement histogram and a one-dimensional conductance histogram to ensure the statistical reproducibility of the conductance. Figure 2 is a schematic diagram of the conductance regulation of the donor-acceptor type compound I-1 of the isoindigo derivative in Example 2 under different bias voltages. At a bias voltage of 0.1 V, the conductance of compound I-1 is 10 -2.79 G 0; when the bias voltage is increased to 0.6 V, the conductance of compound I-1 increases to 10 -2.49 G 0, and the molecular conductance increases by two times.

[0075] This donor-acceptor type compound based on the isoindigo derivative is easy to modify, and donor-acceptor type compounds with different energy levels can be obtained through molecular engineering design. At the same time, this type of compound has the property of single-molecule charge transport. The introduction of methylthio groups enables it to directly form a single-molecule wire with the Au electrode, realizing the direct measurement of the conductance properties at the single-molecule scale and can be applied in molecular wires. Through bandgap regulation, the constructed molecular wires can exhibit different magnitudes of single-molecule conductance. In addition, the present invention can also regulate the intramolecular charge transport under different bias voltage stimuli, resulting in changes in conductivity. This type of bias-responsive donor-acceptor narrow-bandgap compound plays a very important role in molecular electronics and can be used to prepare molecular wires, single-molecule electric switches, etc. It is not only a good single-molecule device itself but also provides ideas for designing new molecular electric switches.

[0076] Example 3

[0077] The synthetic route of the donor-acceptor type compound I-2 based on isoindigo derivatives is as follows:

[0078]

[0079] Raw materials such as 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo and 4-(methylthio)phenylboronic acid used are commercial products.

[0080] Compound VI-1, namely 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo (0.1 g, 0.155 mmol), 4-(methylthio)phenylboronic acid (0.065 g, 0.388 mmol), potassium carbonate (0.128 g, 0.93 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.009 g, 0.00776 mmol) were added to a 100 mL Schlenk tube under argon protection. Deoxygenated toluene (10 mL) and deionized aqueous solution (2 mL) were successively added to the reaction solution, and the mixture was stirred at 95 o °C for 24 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was extracted with ethyl acetate and washed three times with water. After combining the organic phases, it was dried over anhydrous sodium sulfate. After removing the organic solvent using a rotary evaporator, it was purified by column chromatography (the eluent was a mixture of petroleum ether:dichloromethane = 2:1) to obtain 0.091 g of compound I-2 with a yield of 80%.

[0081] 1 1H NMR (600 MHz, CDCl3) δ 9.20 (d, J J = 8.34 Hz, 2H), 7.57 (d, J J = 8.46Hz, 4H), 7.34 (d, J J = 8.46 Hz, 4H), 7.26 (dd, J J = 8.4, 1.74 Hz, 2H), 6.92 (d, J J =1.32 Hz, 2H), 3.75 - 3.64 (m, 4H), 2.53 (s, 6H), 1.91 - 1.85 (m, 2H), 1.46 -1.28 (m, 16H),0.95 - 0.88 (m, 12H). 13 ​13C NMR (150 MHz, CDCl3) δ 168.67, 145.74, 144.15, 139.09, 137.09, 132.36, 130.15, 127.26, 126.71, 120.88, 120.37, 106.14, 44.17, 37.73, 30.79, 28.84, 24.18, 23.12, 15.67, 14.14, 10.82. MALDI-TOF-MS: C 46 H 54 N2O2S2 m / z [M+H + calcd for 731.3699 found: 731.3017.]

[0082] Figure 3 Schematic diagram of the ultraviolet absorption spectrum of compound I-2 prepared in Example 3 of the present invention. Compound I-2 exhibits π-π * transition absorption peaks and intramolecular charge transfer (ICT) peaks at 420 nm and 530 nm, respectively. The band-edge absorption of the molecule is 641 nm, and the optical band gap E opt g = 1240 / λ onset = 1.93 eV. Figure 4 Schematic diagram of the conductance regulation of the donor-acceptor type compound I-2 of the isoindigo derivative at different bias voltages in Example 3. At a bias voltage of 0.1 V, the conductance of compound I-2 is 10 -4.53 G 0; when the bias voltage is increased to 0.6 V, the conductance of compound I-2 increases to 10 -4.08 G 0, and the molecular conductance increases by 2.8 times.

[0083] Example 4

[0084] The synthetic route of the donor-acceptor type compound I-3 based on the isoindigo derivative is as follows:

[0085]

[0086] Raw materials such as 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo and 2-tributylstannyl-5-methylthiophene used are commercial products.

[0087] Compound VI-1, namely 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo (0.1 g, 0.155 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.009 g, 0.00776 mmol) were added into a 50 mL Schlenk tube under argon protection. Deoxygenated N,N-dimethylformamide (5 mL) was added to the reaction mixture, and the mixture was stirred at 80 o °C for 30 minutes. Subsequently, 2-tributylstannyl-5-methylthiothene (0.13 g, 0.310 mmol) was added to the reaction mixture by syringe, and the mixture was stirred for another 24 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction mixture was extracted with ethyl acetate and washed with water three times. The organic phases were combined and dried over anhydrous sodium sulfate. After removing the organic solvents by rotary evaporation, the residue was purified by column chromatography (eluent: a mixture of petroleum ether:dichloromethane = 5:1) to obtain 0.1 g of compound I-3 with a yield of 87%.

[0088] 1 1H NMR (600 MHz, CDCl3) δ 9.08 (dd, J J = 8.34, 0.96 Hz, 2H), 7.23 (d, J J = 3.72 Hz, 2H), 7.19 (dd, J J = 8.34, 1.62 Hz, 2H), 7.04 (d, J J = 3.72 Hz, 2H), 6.81(s, 2H), 3.68 - 3.54 (m, 4H), 2.56 (s, 6H), 1.83 - 1.66 (m, 2H), 1.40 - 1.27 (m, 16H), 0.94 - 0.89 (m, 12H). 13 13C NMR (150 MHz, CDCl3) δ 168.51, 145.62, 145.56, 138.78, 137.18, 131.79, 131.39, 130.22, 124.42, 121.07, 118.79, 104.53, 44.05, 37.76, 30.83, 28.90, 24.25, 23.10, 21.71, 14.16, 10.85. HRMS(EI-TOF):C 42 H 50 N2O2S4 m / z [M + +] calcd for 742.2755 found: 742.2761.]

[0089] Figure 5 ​Schematic diagram of the ultraviolet absorption spectrum of Compound I-3 prepared in Example 4 of the present invention. Compound I-3 exhibits π-π * transition absorption peaks at 447 nm and 560 nm, and an intramolecular charge transfer (ICT) peak. The band-edge absorption of the molecule is 664 nm, and the optical band gap E opt g = 1240 / λ onset = 1.87 eV. Figure 6 Schematic diagram of the conductance regulation of the donor-acceptor type compound I-3 of the isoindigo derivative in Example 4 under different bias voltages. At a bias voltage of 0.1 V, the conductance of Compound I-3 is 10 -4.37 G 0; when the bias voltage is increased to 0.6 V, the conductance of Compound I-3 increases to 10 -3.17 G 0, and the molecular conductance increases by 15.8 times.

[0090] Example 5

[0091] The synthetic route of the donor-acceptor type compound I-4 based on the isoindigo derivative is as follows:

[0092]

[0093] Raw materials such as 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo and 2-tributylstannyl-5-methylthio-3,4-ethylenedioxythiophene used are commercial products.

[0094] Compound VI-1, 6,6'-dibromo-N,N'-(2-ethylhexyl)-isoindigo (0.15 g, 0.23 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.0134 g, 0.0116 mmol) were added to a 50 mL Schlenk tube under argon protection. Deoxygenated N,N-dimethylformamide (5 ml) was added to the reaction solution, and the mixture was stirred at 95 o °C for 30 minutes. Subsequently, 2-tributylstannyl-5-methylthio-3,4-ethylenedioxythiophene (0.444 g, 0.93 mmol) was added to the reaction solution with a syringe, and stirring was continued for 24 hours. After the reaction, the mixture was cooled to room temperature. The reaction solution was extracted with ethyl acetate and washed three times with water. After combining the organic phases, they were dried over anhydrous sodium sulfate. After removing the organic solvent with a rotary evaporator, purification was carried out by column chromatography (the eluent was a mixture of petroleum ether:dichloromethane = 1:1), and 0.15 mg of Compound I-4 was obtained with a yield of 75%.

[0095] 1 1H NMR (600 MHz, CDCl3) δ 9.06 (d, J ​= 8.46 Hz, 2H), 7.26 (dd, J = 8.46, 1.68 Hz, 2H), 7.17 (s, 2H), 4.35 - 4.32 (m, 8H), 3.68 - 3.57 (m, 4H), 2.44 (s, 6H), 1.82 - 1.77 (m, 2H), 1.39 - 1.27 (m, 16H), 0.93 (td, J = 7.32, 3.24 Hz, 6H), 0.89 (td, J = 6.84, 2.04 Hz, 6H). 13 C NMR (150 MHz, CDCl3) δ 168.68, 145.25, 143.48, 139.20, 135.98, 131.61, 129.75, 120.33, 119.46, 118.96, 109.11, 105.25, 64.75, 64.66, 43.91, 37.88, 31.02, 29.00, 24.29, 23.11, 20.99, 14.19, 10.90. MALDI - TOF - MS: C 46 H 54 N2O6S4 m / z [M + H + calcd for 859.2937 found: 859.2593.]

[0096] Figure 7 This is the schematic diagram of the ultraviolet absorption spectrum of compound I - 4 prepared in Example 5 of the present invention. Compound I - 4 exhibits π - π * transition absorption peaks at 466 nm and 580 nm, respectively, and an intramolecular charge transfer (ICT) peak. The band - edge absorption of the molecule is 682 nm, and the optical band gap E opt g = 1240 / λ onset = 1.82 eV. Figure 8 This is the schematic diagram of the conductance regulation of the donor - acceptor type compound I - 4 of the isoindigo derivative in Example 4 under different bias voltages. At a bias voltage of 0.1 V, the conductance of compound I - 4 is 10 -3.86 G 0; when the bias voltage is increased to 0.6 V, the conductance of compound I - 4 increases to 10 -3.21 G 0, and the molecular conductance increases by 4.5 times.

[0097] As can be seen from the above, the preparation methods of the donor-acceptor type compounds I-1, I-2, I-3, and I-4 based on isoindigo derivatives are simple and efficient, with low raw material costs, good economy, easy large-scale industrial production, environmental friendliness, and high-efficiency and convenient product purification. The main intermediates are fully commercialized, inexpensive and easily available, with good economic value, and solve the technical problems of complex synthesis routes and high costs in the prior art, while realizing the multifunctional composite characteristics of the materials.

[0098] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions, and variations to these embodiments still fall within the protection scope of the present invention.

Claims

1. A donor-acceptor type compound based on isoindigo derivatives, characterized in that: As shown in Formula I: Wherein, R1 is one of hydrogen, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl; R2 is one of the structures shown in Formula a, Formula b, and Formula d, In Formula a, Formula b, and Formula d, the positions marked by the curves are the substitution positions; The donor-acceptor type compound based on isatin derivatives can be applied to the preparation of stable molecular wires and molecular electric switches for bias voltage regulation in single molecule junctions.

2. The donor-acceptor type compound based on isoindigo derivatives according to claim 1, characterized in that: The structure of the donor-acceptor type compound is one of Formula I-1, Formula I-2, and Formula I-4 。 3. Preparation method of donor-acceptor type compound based on isoindigo derivative, characterized in that: The preparation method is used to prepare the donor-acceptor type compound based on isatin derivatives as described in Claim 2. The preparation method includes the following steps: (1) Add compound II and sodium methanethiolate to N,N-dimethylformamide, stir at 60 o C to 110 o C for 24 h, remove the solvent by rotary evaporation, and purify the obtained crude product by recrystallization to obtain compound III, wherein the compound II is one of 6-fluoroindole-2,3-dione, 6-chloroindole-2,3-dione, 6-bromoindole-2,3-dione, and 6-iodoindole-2,3-dione, and the molar ratio of the compound II to sodium methanethiolate is 1:(1-5); (2) Dissolve Compound III and sodium hydride in a tetrahydrofuran / N,N-dimethylformamide solution, react at room temperature for 30 minutes, then add the corresponding halide of 2-ethylhexyl, stir at 60-140°C for 24 hours, evaporate the solvent by rotary evaporation, and purify the obtained product by column chromatography to obtain Compound IV. Among them, the molar ratio of Compound III to sodium hydride is 1:(1-3), and the molar ratio of Compound III to the corresponding halide of 2-ethylhexyl is 1:(0.8-3); (3) Mix Compound IV with hydrazine hydrate, heat up to 60-120°C, reflux for three hours until the solution is clear, evaporate the solvent by rotary evaporation, acidify with hydrochloric acid, stir for three hours, remove the solvent, and purify the obtained product by column chromatography to obtain Compound V. Among them, the molar ratio of Compound IV to hydrazine hydrate is 1:(2-20); (4) Dissolve Compound IV, Compound V, and p-toluenesulfonic acid compound in glacial acetic acid, react at 60-120°C for 7 hours, evaporate the solvent by rotary evaporation, and purify the obtained crude product by recrystallization to obtain the donor-acceptor type compound based on isatin derivatives shown in Formula I-1. Among them, the molar ratio of Compound IV, Compound V, and p-toluenesulfonic acid compound is 1:(1-3):(0.1-1); The structural formulas of Compound III, Compound IV, and Compound V are shown in Formula III, Formula IV, and Formula V respectively Wherein, R1 is 2-ethylhexyl, and R2 is the structure shown in Formula a, In Formula a, the positions marked by the curves are the substitution positions.

4. The preparation method of the donor-acceptor type compound based on isoindigo derivatives according to claim 3, characterized in that: In step (4), the p-toluenesulfonic acid compound is one of p-toluenesulfonic acid and p-toluenesulfonic acid monohydrate.

5. The preparation method of the donor-acceptor type compound based on isoindigo derivatives according to claim 3, characterized in that, It includes the following steps: Dissolve Compound VI, 4-methylthiophenylboronic acid compound, and carbonate in a mixed solution of toluene and water, add tetrakis(triphenylphosphine)palladium, heat up to 20-110°C, react under an argon atmosphere for 24 hours, remove the organic solvent, and purify the obtained product by column chromatography to obtain the donor-acceptor type compound based on isatin derivatives shown in Formula I-2. Among them, the molar ratio of Compound VI, 4-methylthiophenylboronic acid compound, and carbonate is 1:(1-6):(1-6), and the molar ratio of Compound VI to tetrakis(triphenylphosphine)palladium is 100:(1-20); Or, it includes the following steps: Dissolve compound VI and 5-(methylthio)-3,4-ethylenedioxythiophene compounds in N,N-dimethylformamide, add tetrakis(triphenylphosphine)palladium, heat the temperature to 25 - 110 °C, react for 24 hours under an argon atmosphere, remove the organic solvent by rotary evaporation, and purify the obtained product by column chromatography to obtain the donor-acceptor type compound based on isatin blue derivative shown in Formula I-4, wherein the molar ratio of compound VI to 5-(methylthio)-3,4-ethylenedioxythiophene compounds is 1:(1 - 6), and the molar ratio of compound VI to tetrakis(triphenylphosphine)palladium is 100:(1 - 20); Compound VI is one of 6,6'-dibromo-N,N'-(2-ethylhexyl)-isatin blue and 6,6'-diiodo-N,N'-(2-ethylhexyl)-isatin blue; The 4-(methylthio)phenylboronic acid compound is one of 4-(methylthio)phenylboronic acid and 4-(methylthio)phenylboronic acid pinacol ester; the 5-(methylthio)-3,4-ethylenedioxythiophene compound is one of 2-trimethylstannyl-5-(methylthio)-3,4-ethylenedioxythiophene and 2-tributylstannyl-5-(methylthio)-3,4-ethylenedioxythiophene.

6. Molecular wire, characterized in that: It includes the donor-acceptor type compound based on isatin blue derivative according to any one of claims 1 - 2.

7. Molecular electric switch, characterized in that: It includes the donor-acceptor type compound based on isatin blue derivative according to any one of claims 1 - 2.

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