Method for capturing singlet split bitriplet excitons and application

Abstract

The invention provides a method for capturing singlet splitting (SF) bitriplet excitons and application of the method. By adopting the method provided by the invention, on one hand, collection of two triplet excitons generated by the SF material can be realized, and on the other hand, the collected triplet excitons can be applied to generation of superoxide free radicals (O2 <.->) and catalysis of subsequent reaction taking O2 <.-> as an active species. The result of the embodiment shows that the SF triplet state quantum yield in the SF-based composite material prepared by the method disclosed by the invention reaches 120%, the triplet state energy transfer efficiency reaches 97%, and the overall quantum yield reaches 115%. The O2 <.-> generation capacity of the composite material is obviously enhanced, and the degradation rate of the composite material to a model pollutant methyl orange is obviously higher than that of a single component (4.20% min <-1 > vs.0.45% min <-1 >). The method is simple and convenient to operate and implement, can be used for capturing and applying the triplet excitons of the SF material so as to realize efficient conversion and utilization of solar energy, and can provide a new thought for photocatalytic application of an inorganic-organic system based on the SF material.

Description

Technical Field

[0001] The invention relates to the technical field of optical functional materials, in particular to a method for capturing two triplet excitons generated by singlet fission and a method for promoting the generation of superoxide free radicals and photocatalytic reactions. Background Art

[0002] Solar energy is the largest green energy on earth. The spectrum of sunlight covers a wide spectral range from ultraviolet to infrared, but the actual available spectrum of sunlight is very narrow. Expanding the light absorption range of the device is the key to improving the energy conversion efficiency of solar devices. Photon modulation (including upconversion and downconversion) is to adapt the absorption of light by solar devices by modulating the wavelength of sunlight, so it can improve the utilization rate of solar energy. Singlet fission (SF) is the only efficient and controllable photon down-conversion pathway in organic materials. It can make the photoelectric conversion quantum efficiency of solar cells at a specific wavelength exceed 100%, showing great development potential, and thus become the research frontier in the field of photoelectric conversion. At present, the research on SF and the design and development of materials are relatively mature, but its application in optoelectronic devices has not achieved the expected results. This is mainly due to the existence of competitive processes such as triplet annihilation in the process of two triplet transfer extraction, which limits the improvement of the efficiency of the light-driven process. Efficiently capturing the two triplet excitons generated by iSF is the bottleneck of SF material development. In addition, the subsequent applications of acceptor materials after capturing the two triplet excitons generated by SF are relatively limited, especially the application of SF materials in the field of photocatalysis has rarely been reported. Therefore, how to achieve efficient capture of two triplet states while ensuring fast and efficient SF and further promote its application in the field of photocatalysis is a key issue that needs to be solved urgently.

[0003] Superoxide radical anion (O 2Singlet oxygen (¹O₂) is a highly efficient reactive oxygen species that has been widely used in photodynamic therapy (PDT) and photo-driven synthesis of important chemical intermediates. Patent CN 117362330 A discloses a method for sensitizing singlet oxygen generation from singlet fission materials. This invention prepared a metal-free bianthracene dimer with high yield (~164%) and long-lived triplets (>300 μs), and used it to generate singlet oxygen. Compared with existing traditional photosensitizers based on intersystem crossing (ISC), the singlet oxygen yield reached an unprecedented ~140%. However, this patent can only achieve the purpose of sensitizing singlet oxygen generation from singlet fission materials, and it is difficult to generate other reactive oxygen species (such as superoxide radicals) in the absence of electron donors. Quantum dots (QDs), also known as inorganic semiconductor nanocrystals, have excellent optical stability, tunable and continuous electronic structures, high absorption cross-sections, high photoluminescence quantum yields, and high absorption spectra. Quantum dots are good triplet energy acceptors and show good research prospects in triplet energy transfer. Therefore, they can be potential acceptors for singlet fission (SF) triplet exciton extraction. Moreover, quantum dots as inorganic semiconductors (such as PbS QDs, PbSe QDs, etc.) often also have the ability to sensitize the generation of superoxide radical anions (O 2 ₂·-). Summary of the Invention

[0004] In view of this, the present invention provides a method and application for capturing singlet fission dual triplet excitons to promote superoxide radical generation and photocatalytic applications to overcome the deficiencies of the prior art. Using the method provided by the present invention, on the one hand, two triplet excitons generated by singlet fission materials can be collected, and on the other hand, the collected triplet excitons can be used to generate superoxide radicals and catalyze subsequent reactions with superoxide radicals as active species. To achieve the above invention objectives, the present invention provides the following technical solutions:

[0005] The present invention provides a method for capturing singlet fission dual triplet excitons, which includes:

[0006] Mixing a carboxyl (or mercapto, amino)-functionalized SF molecule with quantum dots and stirring for a certain period of time to carry out a ligand exchange reaction to obtain a mixed material liquid;

[0007] Adding acetone to the mixed material liquid and centrifuging for solid-liquid separation, washing the obtained solid product with n-hexane / acetone and centrifuging, and repeating this operation until the free organic ligand molecules in the supernatant are completely removed to obtain an inorganic-organic composite material based on quantum dots;

[0008] The occurrence of the SF process and the triplet energy transfer process from SF molecules to quantum dots are characterized by steady-state / transient absorption spectroscopy, steady-state / transient fluorescence spectroscopy, and photoluminescence quantum yield tests. The triplet quantum yield and energy transfer efficiency of SF are calculated to prove that the two triplet excitons generated by singlet fission are successfully captured by the quantum dots.

[0009] Preferably, the SF molecules include any one or more of tetracene, pentacene, fluoranthene, perylene diimide, pyrene, pyrrolopyrrole dione, etc., and their derivatives and oligomer molecules.

[0010] Preferably, the quantum dots include any one or a combination of several of quantum dots such as lead sulfide, selenium sulfide, silver telluride, etc.

[0011] Preferably, in the obtained mixed feed liquid, the concentration of the quantum dots is 1 g / L to 2000 g / L.

[0012] Preferably, in the mixed feed liquid containing the mixture, the molar ratio of the SF molecules to the quantum dots is (1 to 500):1.

[0013] Preferably, the stirring time of the mixed feed liquid is 30 min to 12 h.

[0014] The present invention provides a method for capturing singlet fission dual triplet excitons for superoxide radical generation, which includes:

[0015] Placing an equimolar amount of quantum dots or the above-mentioned inorganic-organic composite materials based on quantum dots in a solvent in an air / oxygen-rich atmosphere, and measuring the amount of superoxide radicals generated by the composite materials relative to the quantum dots through spectrophotometric / fluorescent probes (such as nitroblue tetrazolium chloride, etc.) or electron paramagnetic resonance (EPR).

[0016] The embodiments of the present invention also provide an application of capturing singlet fission triplet excitons for superoxide radical generation in the field of photocatalysis.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0018] The present invention innovatively proposes a strategy for efficiently capturing the dual triplet excitons of SF molecules through a quantum dot-SF molecule composite system, and the collected triplets can generate superoxide radicals through quantum dot sensitization, effectively improving the superoxide radical yield and the subsequent catalytic reaction efficiency. The operation of the present invention is simple and convenient, and can be used for the capture and application of triplet excitons of SF materials to achieve the efficient conversion and utilization of solar energy. At the same time, it can provide a new idea for the research and development of optical devices and photocatalytic applications of inorganic-organic systems based on SF materials. Description of the Drawings

[0019] To describe the technical solution of the present invention in more detail, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 Transmission electron microscope images and particle size distribution diagrams of lead sulfide quantum dots and tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention;

[0021] Figure 2 Steady-state absorption spectra and fluorescence emission spectra of tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention;

[0022] Figure 3 Fluorescence decay kinetics diagram of tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention;

[0023] Figure 4 Femtosecond transient absorption spectra diagram of tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention;

[0024] Figure 5 Electron paramagnetic resonance spectra diagram of lead sulfide quantum dots and tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention.

[0025] Figure 6 Photocatalytic degradation efficiency diagram of methyl orange by lead sulfide quantum dots and tetracene dimer / lead sulfide quantum dot composites obtained in a typical Embodiment 1 of the present invention. Detailed implementation manners

[0026] In view of the defects of the prior art, the inventors of this case proposed the technical solution of the present invention, which mainly uses quantum dots with energy level matching and SF molecules to construct a quantum dot-SF molecule composite system. The quantum dots capture the triplet excitons generated by SF and are used to sensitize the generation of superoxide radicals, which can then be further applied to photocatalytic reactions with superoxide radicals as active substances. The following will further explain the technical solution, its implementation process and principle.

[0027] One aspect of the embodiments of the present invention provides a method for capturing singlet fission triplet excitons, including:

[0028] Mixing carboxyl (or mercapto, amino)-functionalized SF molecules with quantum dots and stirring for a certain period of time for ligand exchange reaction to obtain a mixed material liquid;

[0029] Acetone was added to the mixture solution and centrifuged for solid-liquid separation. The obtained solid product was washed with n-hexane / acetone and centrifuged. This operation was repeated until the free organic ligand molecules in the supernatant were completely removed, and an inorganic-organic composite based on quantum dots was obtained.

[0030] The occurrence of the SF process and the energy transfer process from SF molecules to the triplet state of quantum dots were characterized by steady-state / transient absorption spectroscopy, steady-state / transient fluorescence spectroscopy, and photoluminescence quantum yield measurement. The SF triplet quantum yield and energy transfer efficiency were calculated to prove that the two triplet excitons generated by singlet fission were successfully captured by the quantum dots.

[0031] Furthermore, the SF molecules include any one or several of tetracene, pentacene, perylene, perylene diimide, pyrene, pyrrolopyrrole dione, etc., and their derivatives and oligomer molecules.

[0032] Furthermore, the source of the SF molecules: synthesized in the laboratory or purchased commercially.

[0033] Furthermore, the quantum dots include any one or several combinations of quantum dots such as lead sulfide, selenium sulfide, silver telluride, etc.

[0034] Furthermore, the source of the quantum dots: synthesized in the laboratory or purchased commercially.

[0035] Furthermore, in the obtained mixture solution, the concentration of the quantum dots is 1 g / L to 2000 g / L.

[0036] Furthermore, in the mixture solution containing the SF molecules and the quantum dots, the molar ratio of the SF molecules to the quantum dots is (1 to 500):1.

[0037] Furthermore, the stirring time of the mixture solution is 30 min to 12 h.

[0038] On the other hand, the present invention provides a method for capturing singlet fission triplet excitons for superoxide radical generation, including:

[0039] An equimolar amount of quantum dots or the above-mentioned inorganic-organic composite based on quantum dots was placed in a solvent in an air / oxygen-rich atmosphere, and the amount of superoxide radicals generated by the composite relative to the quantum dots was measured by a spectrophotometric probe (such as nitroblue tetrazolium chloride, etc.) or electron paramagnetic resonance (EPR).

[0040] The present invention also provides an application of capturing singlet fission triplet excitons for superoxide radical generation in the field of photocatalysis.

[0041] Moreover, the method provided by the present invention for capturing singlet fission triplet excitons for superoxide radical generation has broad application prospects in the fields of photocatalysis and the like, providing a new way to improve the photocatalytic reaction efficiency with superoxide radicals as the active species.

[0042] To better understand the purpose and characteristics of the present invention, the technical solutions of the present application will be described in more detail below in conjunction with the accompanying drawings and several embodiments. It should be noted that the content of the following embodiments is illustrative and not a limiting embodiment, and does not limit the scope of the present application. Additionally, unless otherwise specified, various raw materials, reaction methods, etc. used in the following embodiments are known in the art.

[0043] Example 1

[0044] 1. Preparation of Tetracene Dimer (TC 2 COOH) / Lead Sulfide Quantum Dot (PbS QDs) Composite and Study on Triplet Energy Transfer Process

[0045] The molecular structure formula of the tetracene dimer is as follows:

[0046]

[0047] Source of the tetracene dimer molecule: synthesized in the laboratory or purchased commercially.

[0048] Source of the lead sulfide quantum dots: synthesized in the laboratory or purchased commercially

[0049] Preparation of the model tetracene dimer / lead sulfide quantum dot composite system material:

[0050] Mix the carboxyl-functionalized tetracene dimer molecule with lead sulfide quantum dots and stir for 12 h for ligand exchange reaction to obtain a mixed solution;

[0051] Add acetone to the mixed solution and centrifuge for solid-liquid separation. Wash the obtained solid product repeatedly with n-hexane / acetone and then suspend it in toluene solution for storage to obtain the tetracene dimer / lead sulfide quantum dot composite material (QD-TC 2 ); Characterize the structure of the QD-TC 2 composite material by transmission electron microscopy ( Figure 1 B, D).

[0052] In this example, the ultraviolet-visible absorption spectrum, steady-state fluorescence emission spectrum, and fluorescence decay kinetics of the QD-TC 2 composite material can be referred to Figure 2 and Figure 3 respectively. The transient absorption test technique is used to further verify the triplet energy transfer kinetics ( Figure 4 ). The results show that in the QD-TC 2In the composite system, TC 2 COOH effectively generates triplets through iSF, with a yield of Φ T = 120 ± 8%, and then transfers the triplet energy to PbS QDs through triplet energy transfer (TET), and the energy transfer efficiency is as high as about 97%. In addition, the total triplet quantum yield can reach 115 ± 3%.

[0053] 2. Tetracene dimer / lead sulfide quantum dot composite sensitizes the generation of superoxide radicals and catalyzes the degradation of methyl orange

[0054] An equimolar amount of quantum dots or the above-mentioned quantum dot-based inorganic-organic composite materials are placed in a solvent in an air / oxygen-rich atmosphere, and the amount of superoxide radicals generated by the composite materials relative to the quantum dots is tested by a spectrophotometric probe (such as nitroblue tetrazolium chloride, etc.) or electron paramagnetic resonance (EPR). The results show that the EPR signal of the tetracene dimer / lead sulfide quantum dot composite is significantly stronger than that of the lead sulfide quantum dot ( Figure 5 ), indicating that the lead sulfide quantum dots in the composite collect the two electrons generated by the SF of the tetracene dimer and are used for the generation of superoxide radicals.

[0055] An equimolar amount of quantum dots or the above-mentioned quantum dot-based inorganic-organic composite materials are placed in a model pollutant (methyl orange, MO) solution in an air / oxygen-rich atmosphere, irradiated for a certain time, and the degradation of the pollutant is detected by ultraviolet-visible absorption spectroscopy or liquid chromatography ( Figure 6 ). The results show that in the presence of QD-TC 2 or PbS QDs, as the light irradiation time prolongs, the concentration of MO gradually decreases, and the degradation rate of QD-TC 2 rapidly increases and tends to be stable after about 10 minutes. At this time, the degradation rate is significantly higher than that of PbS QDs (42% vs. 13%).

[0056] Example 2

[0057] Other conditions are the same as those in Example 1, only changing the type of quantum dots to lead selenide quantum dots (PbSe QD). The morphology of PbSe QD and the composite material is characterized by transmission electron microscopy, and the changes in their photophysical properties are detected by steady-state fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy. The transient absorption test technology is used to further verify the triplet energy transfer kinetics, and the triplet energy transfer process from TC 2 COOH to PbSe QD occurs in the composite system.

[0058] Example 3

[0059] Other conditions are the same as those in Example 1, except that the type of quantum dots is changed to silver telluride quantum dots (AgTe QD). The morphology of AgTe QD and the composite material is characterized by transmission electron microscopy, and the steady-state fluorescence spectrum and ultraviolet-visible absorption spectrum are used to detect the changes in their photophysical properties. The transient absorption test technology is adopted to further verify the triplet energy transfer kinetics, and the triplet energy transfer process from TC 2 COOH to AgTe QD occurs in the composite system.

[0060] Example 4

[0061] Other conditions are the same as those in Example 1, except that the tetracene dimer molecule (TC 2 COOH) is changed to a biphenyl-linked tetracene dimer (TC 2 Ph 2 COOH), and the molecular structure is as follows:

[0062]

[0063] The morphology of PbS QD and the PbS QD-TC 2 composite material is characterized by transmission electron microscopy, and the steady-state fluorescence spectrum and ultraviolet-visible absorption spectrum are used to detect the changes in their photophysical properties. The transient absorption test technology is adopted to further verify the triplet energy transfer kinetics, and the triplet energy transfer process from TC 2 Ph 2 COOH to PbS QD occurs in the composite system.

[0064] Example 5

[0065] Other conditions are the same as those in Example 4, except that the type of quantum dots is changed to lead selenide quantum dots (PbSe QD). The morphology of PbSe QD and the PbSe QD-TC 2 composite material is characterized by transmission electron microscopy, and the steady-state fluorescence spectrum and ultraviolet-visible absorption spectrum are used to detect the changes in their photophysical properties. The transient absorption test technology is adopted to further verify the triplet energy transfer kinetics, and the triplet energy transfer process from TC 2 Ph 2 COOH to PbSe QD occurs in the composite system.

[0066] Example 6

[0067] Other conditions are the same as those in Example 4, except that the type of quantum dots is changed to silver telluride quantum dots (AgTe QD). The morphology of AgTe QD and the AgTe QD-TC 2The morphology of the composite material was used to detect the changes in its photophysical properties by steady-state fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy. The transient absorption test technique was used to further verify the triplet energy transfer kinetics. The triplet energy transfer process from TC 2 Ph 2 COOH to the triplet state of AgTe QD occurred.

[0068] In summary, the present invention provides a method and application for capturing two triplet excitons generated by singlet fission to promote the generation of superoxide radicals. On the one hand, the method provided by the present invention can achieve the collection of two triplet excitons generated by the singlet fission material. On the other hand, the collected triplet excitons can be used to generate superoxide radicals and catalyze subsequent reactions with superoxide radicals as active species. The operation and implementation of the present invention are simple and convenient, and can be used for the capture and application of triplet excitons of SF materials to achieve the efficient conversion and utilization of solar energy. At the same time, it can provide a new idea for the research and development of optical devices and photocatalytic applications of inorganic-organic systems based on SF materials.

[0069] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for capturing singlet fission (SF) double triplet excitons, characterized in that: The carboxyl (or thiol, amino) functionalized SF molecules are mixed with quantum dots and stirred for a certain period of time to perform a ligand exchange reaction to obtain a mixed liquid; Adding acetone to the mixed liquid and centrifuging for solid-liquid separation, washing the obtained solid product with n-hexane / acetone and centrifuging, repeating this operation until the free organic ligand molecules in the supernatant are completely removed, thereby obtaining an inorganic-organic composite material based on quantum dots; The occurrence of the SF process and the triplet energy transfer process from SF molecules to quantum dots were characterized by steady-state / transient absorption spectroscopy, steady-state / transient fluorescence spectroscopy and photoluminescence quantum yield tests. The SF triplet quantum yield and energy transfer efficiency were calculated, proving that the two triplet excitons produced by singlet fission were successfully captured by quantum dots.

2. The method according to claim 1, characterized in that: The SF molecules include any one or more of tetracene, pentacene, perylene, perylene diimide, pyrene, dione pyrrolopyrrole, etc., and derivatives and oligomer molecules thereof.

3. The method according to claim 1, characterized in that: The quantum dots include any one or a combination of lead sulfide, selenium sulfide, silver telluride and other quantum dots.

4. The method according to claim 1, characterized in that: The concentration of quantum dots is 1 g / L to 2000 g / L.

5. The method according to claim 1, characterized in that: The molar ratio of SF molecules to quantum dots is (1-500):

1.

6. The method according to claim 1, characterized in that: The mixing time of the mixed liquid is 30min to 12h.

7. The present invention also provides a method for capturing singlet fission triplet excitons and applying them to generate superoxide radicals, which comprises: An equal amount of quantum dots or an inorganic-organic composite material based on quantum dots obtained according to the method of claim 1 is placed in a solvent in an air / oxygen-rich atmosphere, and the amount of superoxide free radicals generated by the composite material relative to the quantum dots is tested by a spectrophotometric probe (such as nitro blue tetrazolium chloride, etc.) or electron paramagnetic resonance (EPR).

8. Application of superoxide anion free radicals produced by any one of the methods described in claims 1-6.

9. The use according to claim 8, characterized in that The superoxide anion radicals are applied to photocatalysis or biomedicine.

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