Strongly conjugated organic small molecule material and preparation method and application thereof

Abstract

The present invention belongs to the field of organic semiconductor photocatalysts, and specifically relates to strongly conjugated organic small molecule materials, preparation methods and applications. The strongly conjugated organic small molecule material is used as a photocatalyst, with a pyrene-based structure having strong conjugation characteristics as an electron donor unit, and different numbers of electron acceptor units are introduced through a Sonogashira‑coupling reaction. The obtained material produces hydrogen by splitting water under visible light illumination. The strongly conjugated organic small molecule material has the advantages of simple and easy synthesis method, abundant reserves of constituent monomers, short carrier migration distance, simple and easy to design structure, and high photocatalytic efficiency, which makes it have unique advantages in the field of photocatalytic hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the field of organic semiconductor photocatalysis in the field of photocatalysis, and more specifically, relates to strongly conjugated organic small molecule materials and preparation methods and applications thereof. Background Art

[0002] In recent years, the research and development and utilization of organic semiconductor photocatalysts have been developing rapidly, among which organic conjugated polymer photocatalysts have become emerging materials in the field of photocatalytic hydrogen production by water splitting. Compared with inorganic semiconductor photocatalysts such as TiO2, organic conjugated polymer photocatalysts such as conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), covalent triazine frameworks (CTFs), etc., have unique advantages in the field of photocatalytic hydrogen production due to their simple and easy synthesis methods and abundant reserves of constituent monomers. This type of polymer is usually polymerized by two monomers with different structures through a condensation reaction. Due to the difference in the electron donation / withdrawal ability between the monomers, an alternating combination unit (DA) of electron donors (Donor, D) and electron acceptors (Acceptor, A) is formed, which is more conducive to electron migration; at the same time, due to the molecular orbital hybridization between donors / acceptors, intramolecular charge transfer can be formed in the low energy region of the spectrum, making this type of DA conjugated polymer have stronger visible light absorption ability and higher carrier separation efficiency.

[0003] However, this type of polymer in the prior art still has the disadvantages of uncontrollable degree of polymerization, unclear structure and poor performance in photocatalytic hydrogen production. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a strongly conjugated organic small molecule material and its application as a photocatalyst. Specifically, a pyrene-based structure with a strong conjugation property is used as an electron donor unit, and different numbers of acceptor units with electron-withdrawing ability are introduced through a Sonogashira-coupling reaction. The strongly conjugated organic small molecule material prepared by the method is applied to the field of photocatalysis, thereby solving the problems of the prior art such as long migration distance of photogenerated carriers, easy recombination of electrons and holes, uncertain degree of polymerization and unclear structure-activity relationship.

[0005] The study of strongly conjugated organic small molecules can conduct a more in-depth and systematic study of the relationship between structure and performance at the molecular level. On the one hand, since the structure of strongly conjugated organic small molecules is relatively simple, there are more selectivities for structural design. At the same time, the migration distance of their photogenerated carriers is short, which can effectively reduce the recombination of electrons and holes, and significantly improve their photocatalytic performance. On the other hand, the chemical structure of strongly conjugated organic small molecules is clear and easy to purify, which has significant advantages in determining the structure-activity relationship. At the same time, designing monomers with strongly conjugated structures to increase the overall conjugation of the molecule can effectively solve the problems of stability, light absorption and recyclability of organic small molecules, and provide a new direction for building a more efficient photocatalytic system.

[0006] To achieve the above object, according to one aspect of the present invention, a strongly conjugated organic small molecule material is provided, wherein the strongly conjugated organic small molecule material has a structural formula as described in Formula I:

[0007]

[0008] Formula I

[0009] Wherein D is the electron donor unit, A is the electron acceptor unit, and n≥1.

[0010] The strongly conjugated organic small molecule material is obtained by a Sonogashira-coupling reaction between an electron donor unit and an electron-withdrawing acceptor unit. The D and / or A contain at least one ethynyl group.

[0011] Preferably, the electron donor unit is ethynylpyrene and its derivatives.

[0012] More preferably, the electron donor unit is 1,3,6,8-tetraethynylpyrene.

[0013] Preferably, the electron acceptor unit is bromobenzene and its derivatives.

[0014] More preferably, the electron acceptor unit is bromobenzene, or 4-bromobenzonitrile, or 4-bromo-2,1,3-benzothiadiazole.

[0015] More preferably, the electron donor unit is 1,3,6,8-tetraethynylpyrene, and the electron acceptor unit is 4-bromobenzonitrile.

[0016] The method for preparing the strongly conjugated organic small molecule material comprises uniformly dispersing an electron donor material, an electron acceptor material and a catalyst in a solvent, and reacting them at 60-100° C. in an inert atmosphere.

[0017] Preferably, the solvent is tetrahydrofuran (THF) and / or triethylamine (TEA).

[0018] Preferably, the inert atmosphere is nitrogen or argon.

[0019] According to another aspect of the present invention, the strongly conjugated organic small molecule material is used for photolysis of water to produce hydrogen.

[0020] The conditions for producing hydrogen by photolysis of water are: using a triethanolamine aqueous solution with a volume fraction of 10% as a dispersant, 3wt% Pt as a co-catalyst, exhausting the air from the reaction system with an inert gas, using the strongly conjugated organic small molecule material as a catalyst, and performing a photolysis of water reaction under visible light illumination of λ≥420nm.

[0021] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0022] The invention introduces electron donor units into different numbers of acceptor units with electron-withdrawing ability through Sonogashira-coupling reaction, and when the electron donor units are used as photocatalysts, the photocatalytic efficiency is relatively high.

[0023] The preparation method of the strongly conjugated organic small molecule material used as a photocatalyst proposed in the present invention has the advantages of easy design and simple structure, is more conducive to the study of structure-activity relationship, plays a vital role in the study of high-efficiency photocatalyst structure design, and is a mild and widely applicable preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the reaction formula of the strongly conjugated organic small molecule material obtained in Example 1;

[0025] Figure 2 is the reaction formula of the strongly conjugated organic small molecule material obtained in Example 2;

[0026] Figure 3 is the reaction formula of the strongly conjugated organic small molecule material obtained in Example 3;

[0027] Figure 4 This is a Fourier infrared spectrum of the strongly conjugated organic small molecule material obtained in Example;

[0028] Figure 5 This is the UV-visible diffuse reflectance spectrum of the strongly conjugated organic small molecule material obtained in Example 1;

[0029] Figure 6 This is the UV-visible diffuse reflectance spectrum of the strongly conjugated organic small molecule material obtained in Example 2;

[0030] Figure 7 This is the UV-visible diffuse reflectance spectrum of the strongly conjugated organic small molecule material obtained in Example 3;

[0031] Figure 8 This is the electrochemical impedance spectrum of the strongly conjugated organic small molecule material obtained in Example;

[0032] Fig. 9 A synthetic route map for the polymer;

[0033] Fig.10 The results of photolysis of water to produce hydrogen from the materials obtained in the examples and the corresponding polymer materials. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The invention proposes that the electron donor unit is introduced into different numbers of acceptor units with electron-withdrawing ability through a Sonogashira-coupling reaction, and when the electron donor unit is used as a photocatalyst, the photocatalytic efficiency is higher.

[0036] The present invention uses a pyrene structure with strong conjugation characteristics as an electron donor unit, introduces different numbers of acceptor units with electron-withdrawing ability through a Sonogashira-coupling coupling reaction, and applies the DA-type strongly conjugated organic small molecule material prepared by the method to the field of photocatalysis. Preferably, the electron donor unit is preferably pyrene and its derivatives. The acceptor unit is preferably one or more of bromobenzene and its derivatives, bromobenzonitrile and its derivatives, 4-bromo-2,1,3-benzothiadiazole and its derivatives. The temperature of the coupling reaction is 60-100°C.

[0037] The present invention applies the DA type strongly conjugated organic small molecule material prepared according to the above preparation method to photolysis of water to produce hydrogen. The condition for photolysis of water to produce hydrogen is under the irradiation of one or more light sources of ultraviolet light or visible light.

[0038] The following are examples:

[0039] Example 1

[0040] A strongly conjugated organic small molecule material, the structural formula is Figure 1As shown in. The preparation method comprises the following steps: 1,3,6,8-tetraethynylpyrene (149 mg 0.5 mmol), bromobenzene (345 mg 2.2 mmol), cuprous iodide CuI (3 mg), and catalyst palladium Pd(PPh3)4 (30 mg 0.04 mmol) are weighed and transferred into a 100 ml three-necked flask, 30 ml of tetrahydrofuran (THF) and 30 ml of triethylamine (TEA) are added, nitrogen is exhausted for 20 min to keep the system in a nitrogen atmosphere, the temperature is raised to 80 ° C and refluxed and stirred for 12 h, after the reaction is completed, the reaction is cooled to room temperature, and the solid product is filtered under reduced pressure to obtain a solid product, the product is rinsed with methanol, and then stirred and washed twice with methanol and dichloromethane 9:1 (V:V), each time with an interval of 4 h, and a reddish brown solid product is obtained after reduced pressure filtration, which is placed in a freeze dryer and dried overnight to obtain 174 mg of an organic small molecule PB.

[0041] Example 2

[0042] A strongly conjugated organic small molecule material, the structural formula is Figure 2 As shown in. The preparation method comprises the following steps: 1,3,6,8-tetraethynylpyrene (149 mg 0.5 mmol), 4-bromobenzonitrile (400 mg 2.2 mmol), cuprous iodide CuI (3 mg), and catalyst palladium Pd(PPh3)2Cl2 (30 mg 0.04 mmol) are weighed and transferred into a 100 ml three-necked flask, 30 ml of tetrahydrofuran (THF) and 30 ml of triethylamine (TEA) are added, nitrogen is exhausted for 20 min to keep the system around nitrogen, the temperature is raised to 80 ° C, refluxed and stirred for 12 h, the reaction is cooled to room temperature after completion, and the solid product is filtered under reduced pressure, the product is rinsed with methanol, and then stirred and washed twice with methanol and dichloromethane 9:1 (V:V), each time with an interval of 4 h, and a reddish brown solid product is obtained after reduced pressure filtration, which is placed in a freeze dryer and dried overnight to obtain 189 mg of an organic small molecule PBN.

[0043] Take 25 mg of the product of Example 2, add it to 100 mL of 10 vol% triethanolamine (TEOA) aqueous solution, and ultrasonicate for 7 min to evenly disperse the organic small molecule catalyst in the solution to form a suspension. Use nitrogen exhaust for 30 min to remove the air in the reaction system, use a 300 W xenon lamp as the light source, and measure the amount of hydrogen generated by gas chromatograph after each 30 min of illumination.

[0044] Example 3

[0045] A DA-type strongly conjugated organic small molecule material, the structural formula is as follows Figure 3As shown in. The preparation method comprises the following steps: 1,3,6,8-tetraethynylpyrene (75mg 0.25mmol), 4-bromo-2,1,3-benzothiadiazole (258mg 1.2mmol), cuprous iodide CuI (3mg), and catalyst palladium Pd(PPh3)2Cl2 (30mg 0.04mmol) are weighed and transferred to a 100ml three-necked flask, 30ml of tetrahydrofuran (THF) and 30ml of triethylamine (TEA) are added, nitrogen is exhausted for 20min to keep the system around nitrogen, the temperature is raised to 80℃ and refluxed and stirred for 12h, the reaction is cooled to room temperature after completion, and a solid product is obtained by vacuum filtration, the product is rinsed with methanol, and then stirred and washed twice with methanol and dichloromethane 9:1 (V:V), each time with an interval of 4h, and a reddish-brown solid product is obtained after vacuum filtration, which is placed in a freeze dryer and dried overnight to obtain 189mg of an organic small molecule PBT.

[0046] The strongly conjugated organic small molecule materials obtained in Examples 1-3 were subjected to the following tests and analyses:

[0047] 1) Fourier infrared spectrum Figure 4 As shown in -1 The infrared vibration characteristic absorption peak of acetylene group can be clearly observed, proving that the small molecule catalyst material has been successfully obtained;

[0048] 2) The UV-Vis diffuse reflectance spectra of Examples 1-3 are as follows: Figure 5-7 As shown in , the spectral adsorption sidebands of the three small molecule catalyst materials are all over 600nm, indicating that the three materials have the ability to absorb visible light;

[0049] 3) Electrochemical impedance spectroscopy Figure 8 As shown in , the impedance curve radius of PBN is the smallest among the three materials, indicating that the PBN structure is more conducive to the migration and transmission of photogenerated charges.

[0050] The performance of the three strongly conjugated organic small molecule materials prepared in Examples 1-3 and the corresponding polymers for photocatalytic hydrogen production from water was compared. First, the three polymers were prepared by the following method:

[0051] like Fig. 9As shown, 1,3,6,8-tetraethynylpyrene (150 mg 0.50 mmol), p-dibromobenzene (472 mg, 2.0 mmol, for synthesizing PB-polymer), [or 2,5-dibromobenzonitrile (522 mg, 2.0 mmol, for synthesizing PBN-polymer) or 4,7-dibromo-2,1,3-benzothiadiazole (588 mg, 2.0 mmol, for synthesizing PBT-polymer)], cuprous iodide CuI (trace), catalyst palladium Pd(PPh3)2Cl2 (60 mg 0.08mmol) was transferred into a 250ml three-necked flask, 60ml of tetrahydrofuran (THF) and 60ml of triethylamine (TEA) were added, and nitrogen was used to exhaust for 20min to keep the system around nitrogen. The temperature was raised to 80℃ and refluxed with stirring for 12h. After the reaction was completed, it was cooled to room temperature and filtered under reduced pressure to obtain a solid product. The product was rinsed with methanol, and then washed twice with methanol and dichloromethane in a ratio of 9:1 (V:V) with stirring, each time with an interval of 4h. After reduced pressure filtration, a reddish-brown solid product was obtained, which was placed in a freeze dryer and dried overnight to obtain the corresponding three polymer materials PB-polymer, PBT-polymer, and PBN-polymer.

[0052] Photocatalytic water splitting hydrogen production performance test:

[0053] Take 25mg of small molecules and polymers, add them to 100mL of 10vol% triethanolamine (TEOA) aqueous solution, and load 3wt% Pt co-catalyst, ultrasonicate for 7min to make the organic small molecule catalyst evenly dispersed in the solution to form a suspension. Use nitrogen exhaust for 30min to remove the air in the reaction system, use a 300W xenon lamp as the light source, and perform photolysis water test under visible light (λ≥420nm). After 30min of illumination, the amount of hydrogen generated is measured by gas chromatograph.

[0054] The test results are as follows Fig.10 As shown in the results, the photocatalytic hydrogen production activity of the three organic small molecule materials is significantly better than that of the polymer materials with the same structure, and the photocatalytic hydrogen production performance is improved by nearly two times, which fully proves that strongly conjugated small molecules have significant advantages in improving photocatalytic performance.

[0055] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of strongly conjugated organic small molecule materials, characterized in that: The structural formula of the strongly conjugated organic small molecule material is as shown in Formula I: or or Formula I The strongly conjugated organic small molecule material is used for photolysis of water to produce hydrogen. The conditions for photolysis of water to produce hydrogen are: a 10% triethanolamine aqueous solution by volume fraction is used as a dispersant, 3 wt% Pt is used as a co-catalyst, the air in the reaction system is exhausted with an inert gas, the strongly conjugated organic small molecule material is used as a catalyst, and a photolysis reaction of water is carried out under visible light illumination of λ ≥ 420 nm.

2. The use of the strongly conjugated organic small molecule material according to claim 1, characterized in that: The preparation method of the strongly conjugated organic small molecule material is to uniformly disperse the electron donor material, the electron acceptor material and the catalyst in a solvent, and react them at 60-100° C. in an inert atmosphere; the catalyst is CuI and Pd(PPh3)2Cl2; The electron donor material is 1,3,6,8-tetraethynylpyrene; the electron acceptor material is bromobenzene or 4-bromobenzonitrile or 4-bromo-2,1,3-benzothiadiazole.

3. The use of the strongly conjugated organic small molecule material according to claim 2, characterized in that: The solvent is tetrahydrofuran and / or triethylamine.

4. The use of the strongly conjugated organic small molecule material according to claim 2, characterized in that: The inert atmosphere is nitrogen or argon.

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