Synthesis of DA-type organic small molecules with fulvalene-like structures and their application in photocatalytic hydrogen evolution

Abstract

The present invention discloses the synthesis of D-A type organic small molecules with a fulvalene-like structure and their application in photocatalytic hydrogen evolution, belonging to the field of organic material technology. This type of organic small molecule photocatalyst has many advantages: 1) the photogenerated excitons of the D-A type structure are easily delocalized within the molecule, which is beneficial for the separation of electrons and holes; 2) the fulvalene-like structure does not contain unstable vinylidene protons, which is beneficial for improving the light and chemical stability of the material; 3) the molecular structure is simple, easy to synthesize, and low in cost; 4) compared with polymers, no palladium (Pd) catalyst is used in the synthesis process. The D-A type organic small molecule with a fulvalene-like structure of the present invention was successfully used in photocatalytic hydrogen production experiments and obtained good hydrogen production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic materials, and in particular relates to the synthesis of DA-type organic small molecules with a fulvalene-like structure and their application in photocatalytic hydrogen evolution. Technical Background

[0002] Since the discovery of TiO2 photocatalysts, inorganic semiconductor photocatalysts have been rapidly developed for photocatalytic hydrogen evolution due to their appropriate electronic structure and high activity. However, due to the weak absorption of visible light by inorganic photocatalysts, achieving high photocatalytic activity remains a challenge [Chem. Soc. Rev. 2019, 48, 2109-2125]. Therefore, the development of new materials with diverse structures, broad absorption spectra, stable photochemical properties, low cost, and high efficiency is essential for the commercialization of photocatalytic hydrogen production technology.

[0003] In recent years, organic polymer semiconductors have attracted increasing interest due to their diverse synthesis methods, tunable electronic structures, and ease of functionalization of the polymer backbone, which significantly impacts their photocatalytic activity. To date, numerous polymer photocatalysts for hydrogen evolution have been developed, primarily based on linear conjugated polymers, covalent organic frameworks (COFs), graphitic carbon nitride polymers (g-C3N4), conjugated microporous polymers (CMPs), and covalent triazine framework polymers. These organic semiconductor photocatalysts exhibit excellent performance, particularly in the visible light region, demonstrating superior hydrogen production, a property not achievable by many inorganic semiconductors.

[0004] Although organic polymer semiconductors have many advantages, the synthesis of polymers usually requires multiple steps and is costly. The synthesis of polymers is characterized by batch differences, and high-performance batches are not easy to repeat. The polymerization process usually requires a metal palladium catalyst to catalyze the polymerization reaction, which is costly and causes residual palladium in the organic polymer, interfering with the study of hydrogen production performance and being very unfavorable for accurately studying the relationship between the structure and performance of organic semiconductors.

[0005] Compared with organic polymers, organic small molecule semiconductor materials have advantages such as a defined molecular structure, a defined molecular weight, high purity without batch variation, low cost, and easy synthesis. In recent years, ADA (Acceptor-Donor-Acceptor) type small molecule acceptor materials have been used for photocatalytic hydrogen production [Angew. Chem., Int. Ed. 2022, 61, e202114234], with high performance, but these molecules have vinylidene protons and are unstable in light and chemical environments [Adv. Funct. Mater. 2023, 33, 2304752; Dyes Pigments 2020, 175, 108182]. In addition, the synthesis of such molecules requires many steps and the cost is still high. Therefore, the development of photocatalytic materials with good stability, low cost, and excellent performance remains a great challenge. Summary of the Invention

[0006] In order to overcome the above technical defects, the present invention provides a synthesis of a DA-type organic small molecule semiconductor material with a fulvalene-like structure, which improves the light and chemical stability and catalytic performance of the organic semiconductor material.

[0007] This type of DA-type small molecule semiconductor material has a fulvalene-like structure: 1) The photogenerated excitons of the DA-type structure are easily delocalized and transferred within the molecule, which is beneficial to the separation of electrons and holes; 2) The fulvalene-like structure does not contain unstable vinylidene protons, which is beneficial to improving the optical and chemical stability of the material; 3) The molecular structure is simple, easy to synthesize, and low in cost; 4) Compared with polymers, no palladium catalyst is used in the synthesis process, which avoids residual palladium in the catalytic process as a co-catalyst to interfere with the actual performance of the material, which is conducive to understanding the true structure-activity relationship between molecular structure and performance.

[0008] To achieve the above object, the present invention is implemented by the following scheme: a fulvalene-like DA-type organic small molecule has the following structure:

[0009]

[0010] Among them, the electron-withdrawing unit is a conjugated unit, and the electron-donating unit is a conjugated unit.

[0011] Furthermore, in the above technical solution, the electron-donating conjugated unit is one of the following chemical structures:

[0012]

[0013] Wherein: X is N, O, S, Se or Te; R1-R 12The groups are independently hydrogen, halogen, C1-C30 alkyl, or a group in which one or more carbon atoms in the C1-C30 alkyl are substituted by halogen, oxygen, alkenyl, alkynyl, aryl, hydroxyl, amino, carbonyl, carboxyl, ester, cyano, or nitro.

[0014] Furthermore, in the above technical solution, the electron-withdrawing conjugated unit is one of the following chemical structures:

[0015]

[0016] Wherein: R1-R6 are independently hydrogen, NH2, N(Me)2, Me, Et, CN or halogen, C1-C30 alkyl, a group formed by replacing one or more carbon atoms in the C1-C30 alkyl with halogen, oxygen, alkenyl, alkynyl, aryl, hydroxyl, amino, carbonyl, carboxyl, ester, cyano or nitro.

[0017] The present invention also provides the use of the DA-type organic small molecules with the fulvalene-like structure in photocatalytic hydrogen production.

[0018] Furthermore, in the above technical solution, during the catalytic hydrogen production process, the catalytic performance is not interfered by metal palladium.

[0019] The present invention also provides a method for preparing the DA-type organic small molecule having a fulvalene-like structure, comprising the following steps:

[0020]

[0021] 1. Dissolve the electron-donating unit, electron-withdrawing unit and pyridine in tetrahydrofuran (THF) solution;

[0022] 2. Pyridine and titanium tetrachloride were added to the reaction system respectively. After the reaction was completed, the target compound was separated by column chromatography and then dried at 80° C. for 24 hours to obtain an organic small molecule compound.

[0023] Furthermore, in the above technical solution, the molar ratio of the electron donating unit, the electron withdrawing unit, pyridine and titanium tetrachloride is 1:2:5:3, the reaction temperature is 80° C., and the reaction time is 1 hour.

[0024] Furthermore, in the above technical solution, the mixture is heated to 80° C. and dried for 24 hours.

[0025] The present invention characterizes the thermodynamic stability of small molecule materials by thermogravimetric analysis, the structure of small molecule materials by nuclear magnetic resonance (NMR), the spectral properties of polymer materials by ultraviolet spectrophotometry, the electrochemical properties by cyclic voltammetry, and the photocatalytic performance by at the same time.

[0026] The present invention has the following beneficial effects:

[0027] 1) The photogenerated excitons of DA-type small molecules are easily delocalized and transferred within the molecule, which is conducive to the separation of electrons and holes;

[0028] 2) The fulvalene-like structure does not contain unstable vinylidene protons, which helps to improve the photo- and chemical stability of the material;

[0029] 3) Simple molecular structure, easy to synthesize and low cost;

[0030] 4) No palladium catalyst is used in the synthesis process to avoid the possibility that residual palladium in the catalytic process will act as a co-catalyst to interfere with the actual performance of the material, which is conducive to understanding the true structure-activity relationship between molecular structure and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a thermogravimetric graph of the organic small molecule material obtained in Examples 1-3 of the present invention;

[0032] Figure 2 This is an absorption spectrum of the organic small molecule material obtained in Examples 1-3 of the present invention in chloroform solution;

[0033] Figure 3 The absorption spectra of the organic small molecule material films obtained in Examples 1-3 of the present invention are shown;

[0034] Figure 4 The electrochemical properties of the organic small molecule materials obtained in Examples 1-3 of the present invention are shown;

[0035] Figure 5 This is a graph showing the hydrogen production efficiency of the organic small molecule materials obtained in Examples 1-3 of the present invention under irradiation with ultraviolet-visible light (greater than 300 nm). DETAILED DESCRIPTION

[0036] The practice of the present invention can adopt the conventional techniques of organic synthetic chemistry within the art. In the following examples, efforts have been made to ensure the accuracy of the numbers used (including amounts, temperatures, reaction times, etc.), but some experimental errors and deviations should be considered. The temperatures used in the following examples are expressed in ° C. and the pressures are atmospheric pressure or near atmospheric pressure. All solvents were purchased at analytical or chromatographic grade, and all reactions were carried out under an inert atmosphere of nitrogen. Unless otherwise noted, all reagents were commercially available.

[0037] Example 1:

[0038] The small molecule compound 1-a was synthesized by the following reaction formula:

[0039]

[0040] In a 100 mL three-necked flask, fluorenone (500 mg, 2.77 mmol), 1,3-indandione (811 mg, 5.54 mmol), and tetrahydrofuran (30 mL) were added to the reaction flask. The mixture was stirred and the nitrogen atmosphere was purged three times. Pyridine (1.08 mL, 2.38 mmol) was added dropwise to the reaction solution, followed by titanium tetrachloride (0.93 mL, 8.31 mmol). The reaction was allowed to react at 80°C for 1 hour. The mixture was extracted with dichloromethane, washed with brine, dried over anhydrous sodium sulfate, and separated by column chromatography using dichloromethane / methanol / petroleum ether as the eluent to obtain the target compound 1-a in a 91% yield. 1 H NMR (400MHz, CDCl3) δ8.77(d,J=8.0,2H),8.03-8.01(m,2H),7.84-7.81(m,2H),7.50(d,J=4.0,2H),7.41-7.37(m,2H),7.28-7.22(m,2H).

[0041] Example 2:

[0042] The small molecule compound 1-b was synthesized by the following reaction formula:

[0043]

[0044] In a 100 mL three-necked flask, fluorenone (500 mg, 2.77 mmol), cyanoindanone (1.08 g, 5.54 mmol), and tetrahydrofuran (30 mL) were added to the reaction flask. The mixture was stirred and purged with nitrogen three times. Pyridine (1.08 mL, 2.38 mmol) was then added dropwise to the reaction solution. Titanium tetrachloride (0.93 mL, 8.31 mmol) was then added dropwise to the reaction solution. The mixture was reacted at 80°C for 1 hour. The mixture was extracted with dichloromethane, washed with brine, dried over anhydrous sodium sulfate, and separated by column chromatography using dichloromethane / methanol / petroleum ether as the eluent to obtain the target compound 1-b in 80% yield. This compound has poor solubility.

[0045] Example 3:

[0046] The synthesis of small molecule compound 1-c is as follows:

[0047]

[0048] In a 100 mL three-necked flask, fluorenone (500 mg, 2.77 mmol), cyanoindanone (4.18 g, 5.54 mmol), and tetrahydrofuran (4.27 g, 31.0 mmol) were added to the reaction flask. The mixture was stirred and the nitrogen atmosphere was purged three times. Pyridine (1.08 mL, 2.38 mmol) was added dropwise to the reaction solution, followed by titanium tetrachloride (0.93 mL, 8.31 mmol). The reaction was allowed to react at 80°C for 1 hour. The mixture was extracted with dichloromethane, washed with brine, dried over anhydrous sodium sulfate, and separated by column chromatography using dichloromethane / methanol / petroleum ether as the eluent to obtain the target compound 1-c in an 83% yield. 1 H NMR (400MHz, CDCl3) δ8.91(d,J=8.0,2H),8.82(d,J=8.0,2H),8.15(d,J=8.0,2H),8.7(d,J=8.0,2H),7.97- 7.93(m,2H),7.89-7.85(m,2H),7.55-7.51(m,4H),7.48-7.41(m,4H),7.34-7.30(m,2H),7.28-7.23(m,2H).

[0049] Other small molecule catalysts synthesized in this patent and their yields:

[0050]

[0051] Example 4 Testing of the Hydrogen Production Performance of Organic Conjugated Small Molecule Photocatalysts:

[0052] 5 mg of the small molecule catalyst was dissolved in 5 mL of DMF and then added to 45 mL of 1 M ascorbic acid (AA) solution. The mixture was ultrasonicated for 1 hour and tested using the photocatalytic system CEL-PAEM-D8 produced by Beijing Zhongjiao Jinyuan Company. A xenon lamp was used as the light source, and the ultraviolet-visible light range was greater than 300 nm. The reaction was detected and analyzed by a chromatographic instrument, with a cycle of one hour to obtain the corresponding hydrogen production efficiency.

[0053] Other small molecule catalysts synthesized in this patent and their hydrogen production efficiency:

[0054]

[0055]

[0056] from Figure 1 The thermogravimetric curve of the organic small molecule material shows that the thermal decomposition temperature of the organic small molecule material of the present invention is above 320° C., has good thermal stability, and can be applied to photocatalytic hydrogen production.

[0057] from Figure 2The absorption spectrum of the organic small molecule material in chloroform solution shows that the organic small molecule material of the present invention has a good ability to capture sunlight.

[0058] from Figure 3 The absorption spectrum of the organic small molecule material film shows that the organic small molecule material of the present invention has a good ability to capture sunlight.

[0059] from Figure 4 The electrochemical properties diagram of organic small molecule materials shows that the reduction potentials of the three organic small molecule semiconductor materials 1-a, 1-b, and 1-c all meet the driving force requirements for the reduction of hydrogen protons to hydrogen gas.

[0060] from Figure 5 The hydrogen production performance diagram of organic small molecule materials shows that the hydrogen production efficiency of the DA-type organic small molecule semiconductor materials 1-a / 1-b / 1-c under ultraviolet visible light (greater than 300nm) is 0.65, 1.34, and 0.59mmol, respectively. -1 g -1 h -1 . This shows that this type of material has great research value and application prospects.

[0061] 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 scope of protection of the present invention.

Claims

1. Application of organic small molecules in photocatalytic hydrogen production, characterized in that: The organic small molecule is selected from:

2. The use of the organic small molecules in photocatalytic hydrogen production according to claim 1, characterized in that: During the catalytic hydrogen production process, the catalytic performance is not interfered by metal palladium.

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