A2-a1-d-a1-a3 type narrow-band-gap conjugated small molecules based on dithienoindacene and applications thereof

Abstract

The application belongs to the field of organic functional small molecule materials, and discloses a A2-A1-D-A1-A3 type narrow-band gap conjugated small molecule based on dithiophene and indathieno and application thereof. The A2-A1-D-A1-A3 type conjugated small molecule material designed by an asymmetric end group strategy has electron-withdrawing end groups of different structures, increases the polarity and dipole moment of the molecule, and further enhances the intramolecular charge transfer effect. Compared with the existing asymmetric small molecule acceptor and the reported same type symmetric small molecule, the asymmetric small molecule prepared in the application contains benzothiadiazole and cyano indanedione double strong acceptor units, forms a strong donor-acceptor exchange performance with the intermediate core, and is beneficial to widening the spectral absorption range. On the other hand, the preparation operation of the application is simple, the product is easy to separate and purify, and the solubility is good, so that the application is expected to be used as an active layer acceptor material of an organic solar cell.

Description

Technical Field

[0001] This invention relates to the field of organic functional small molecule materials, and in particular to an A2-A1-DA based on dithiophene and induction-dependent class. 1- A3-type asymmetric narrow bandgap conjugated small molecules, their preparation methods, and applications. Background Technology

[0002] Organic solar cells (OSCs) possess significant advantages such as abundant raw materials, lightweight, semi-transparency, and the ability to fabricate large-area flexible devices, making them promising candidates for applications in wearable flexible electronics, building-integrated photovoltaics (BIPV), and photovoltaic agriculture. Acceptor materials, as crucial raw materials for OSCs, play a vital role in the photoelectric conversion process. Various molecular design strategies, including side-chain engineering, conjugation extension, isomerization, and asymmetry, are widely used to fine-tune the optical absorption, electrochemical properties, dipole moment, and electron mobility of acceptor molecules. Generally, broadening the absorption spectrum of acceptor materials is beneficial for achieving higher photocurrent and energy conversion efficiency in devices. Extended conjugation is a promising strategy to promote the ICT effect, achieving greater redshift absorption. In 2015, Zhan Xiaowei's team reported the ADA-type fused-ring small molecule acceptor, ITIC, achieving absorption at nearly 800 nm (Adv. Mater., 2015, 27, 1170–1174). In 2017, Zou Yingping's team designed and synthesized a small molecule called BZIC, whose nitrogen-substituted core exhibited a red-shifted absorption curve (ACS Appl. Mater. Interfaces, 2017, 9, 37, 31985–31992). Subsequently, a series of A-DA'DA type fused-ring electron acceptors with narrow band gaps and absorption windows located in the NIR region (absorption edges close to 1000 nm) were developed. To date, the power conversion efficiency (PCE) of OSCs using these acceptor materials has exceeded 19%, achieving significant results (Nat. Mater., 2022, 21, 656–663; Joule, 2022, 6, 171–184; Adv. Mater., 2021, 33, 2102420), but there is still a certain performance gap compared to inorganic solar cells.

[0003] Small molecule receptors can be classified into symmetrical and asymmetrical molecules based on their chemical structure. Compared to symmetrical molecules, asymmetrical receptor molecules have attracted relatively less attention. Although their performance has been greatly improved, a wider variety of small molecules still need to be designed to further capture NIR absorption. In recent years, researchers have conducted a series of asymmetrical strategy studies based on ADA-type and A-DA'DA-type fused-ring electron acceptors. These molecules can be divided into three categories: asymmetrical end-group types, asymmetrical central core types, and asymmetrical side-chain types. For example, Professor Yang Chuluo's team developed three isomerized small molecule receptors (ThPy5, IDTP-4F, and ThPy6) by systematically moving subunits of the central core. From ThPy5 to IDTP-4F and then to ThPy6, the absorption spectra of the molecules gradually red-shift (~825nm, ~875nm, 902nm), and finally, the OSC based on PM6:ThPy6 achieved a highest device efficiency of 16.11% (Adv. Funct. Mater., 2022, 2203200). Researchers led by Professor Lu Shirong designed and developed a novel Y6-type asymmetric acceptor, BTP-FCl-FCl. BTP-FCl-FCl possesses F and Cl disubstituted end groups, providing a locally asymmetric structure. Spectroscopic data show that the main absorption peaks of BTP-2F-2Cl and BTP-FCl-FCl are located at 835.5 nm and 845.5 nm, respectively, with an optical gap of 1.33 eV for both (Adv. Sci., 2021, 8, 2004262). A review article on the research progress of asymmetric fused-ring electron acceptors (Adv. Funct. Mater., 2022, 32, 2205115) reveals that existing asymmetric central nucleotype molecules have a significant redshift effect on the absorption edge, but their synthesis is cumbersome. Meanwhile, the reported asymmetric end-group small molecules, which are relatively simple to synthesize, have a negligible effect on absorption. The molecular structures of these asymmetric acceptors based on different end groups are mainly of the A1-D-A2 type and the A1-DA'D-A2 type.

[0004] Therefore, this invention reports a novel asymmetric small molecule based on dithiophene and indole-dependent terminal groups, with a molecular structure of A2-A1-D-A1-A3, a configuration not previously reported. This type of molecule is not only simple to prepare and easy to isolate and purify, but also contains a dual strong acceptor unit of benzothiadiazole and cyanoindanedione, forming a strong donor-acceptor exchange property with the intermediate nucleus, which can greatly broaden the spectral absorption range. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a narrow bandgap conjugated small molecule of type A2-A1-D-A1-A3 based on dithiophene and its preparation method.

[0006] The A2-A1-D-A1-A3 conjugated small molecules based on dithiophene and inducible provinces provided by this invention have asymmetric end groups, resulting in non-uniform charge distribution throughout the conjugated backbone. This is beneficial for increasing molecular polarity and dipole moment, thereby enhancing the ICT effect, extending absorption, and inducing tight and ordered molecular stacking. This results in conjugated small molecule materials with a wide absorption range and suitable energy levels, thus meeting the requirements of high-efficiency organic solar cells for acceptor materials.

[0007] To achieve the objectives of the invention described above, the technical solution of the present invention is as follows:

[0008] A series of A2-A1-D-A1-A3 type conjugated small molecules based on dithiophene and indahedron: 2-((Z)-2-((7-(7-(7-((E)-(3-ethyl-4-oxo-2-thiazolidine-5-ylidene)methyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4,9,9-tetra(4-hexylphenyl)-4,9-dihydro-s-indo[1,2-b:5,6-b']dithiophene-2-yl)benzo[c][1,2,5]thiazol-4-yl)methylene)-3-oxo-2,3-dihydro-1H-indo-1-yl)malonitrile, named IDTBRIC, have the structure shown in formula (1);

[0009]

[0010] 2-((Z)-2-((7-(7-(((E)-(3-ethyl-4-oxo-2-thiazolin-5-ylidene)methyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4,9-tetra(4-hexylphenyl)-4,9-dihydro-s-indo[1,2-b:5,6-b']dithiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)-5,6-difluoro-3-oxo-2,3-dihydro-1H-indo-1-ylidene)malonitrile, named IDTBRIC2F, has the structure shown in formula (2);

[0011]

[0012] 2-((Z)-2-((7-(7-(((E)-(3-ethyl-4-oxo-2-thiazolin-5-ylidene)methyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4,9-tetraoctyl-4,9-dihydro-s-indo[1,2-b:5,6-b']dithiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)-3-oxo-2,3-dihydro-1H-indo-1-yl)malonitrile, named O-IDTBRIC, has the structure shown in formula (3);

[0013]

[0014] 2-((Z)-2-((7-(7-((E)-(3-ethyl-4-oxo-2-thiazolin-5-ylidene)methyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4,9-tetraoctyl-4,9-dihydro-s-indo[1,2-b:5,6-b']dithiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)-5,6-difluoro-3-oxo-2,3-dihydro-1H-indo-1-yl)malonitrile, named O-IDTBRIC2F, has the structure shown in formula (4).

[0015]

[0016] The synthetic route for the A2-A1-D-A1-A3 type narrow bandgap conjugated small molecules based on dithiophene and indole is as follows:

[0017]

[0018] The A2-A1-D-A1-A3 type narrow bandgap conjugated small molecule based on dithiophene and indole-dependent molecule developed in this invention has the following advantages:

[0019] (1) The molecular structure and molecular weight are determined, making it easy to synthesize and purify with high batch reproducibility.

[0020] (2) The A2-A1-D-A1-A3 type conjugated small molecule material designed by the present invention through the asymmetric end-group strategy has different structures of double strong electron-withdrawing end groups (A2-A1 / A1-A3), and their charge-pulling ability is not the same. Therefore, the asymmetric end groups cause the non-uniformity of charge distribution in the entire conjugated skeleton. While increasing the molecular polarity and dipole moment, it also improves the intramolecular charge transfer effect, thereby significantly broadening the absorption spectrum range. All of these are beneficial to obtaining a larger photocurrent.

[0021] (3) The A2-A1-D-A1-A3 type conjugated small molecules designed by the asymmetric end-group strategy of this invention have excellent π-π conjugated system, strong donor-acceptor exchange performance, and good solubility.

[0022] (4) The A2-A1-D-A1-A3 type conjugated small molecules designed based on the asymmetric end-group strategy provided by this invention have suitable LUMO energy levels and high HOMO energy levels, which are beneficial for matching with the classic polymer donor P3HT. Therefore, this type of material can be widely used as an acceptor material in organic solar cells. Attached Figure Description

[0023] Figure 1 The 1H NMR spectrum of compound 3 (R = hexylphenyl) is shown.

[0024] Figure 2 The 1H NMR spectrum of compound 5 (R = hexylphenyl) is shown.

[0025] Figure 3 The hydrogen NMR spectrum of the asymmetric conjugated small molecule IDTBRIC;

[0026] Figure 4 The hydrogen NMR spectrum of the asymmetric conjugated small molecule IDTBRIC2F;

[0027] Figure 5 The 1H NMR spectrum of compound 3 (R = n-octyl) is shown.

[0028] Figure 6 The 1H NMR spectrum of compound 5 (R = n-octyl) is shown.

[0029] Figure 7 The image shows the carbon NMR spectrum of compound 5 (R = n-octyl);

[0030] Figure 8 The hydrogen NMR spectrum of the asymmetric conjugated small molecule O-IDTBRIC;

[0031] Figure 9 The hydrogen NMR spectrum of the asymmetric conjugated small molecule O-IDTBRIC2F;

[0032] Figure 10 The UV-Vis absorption spectra of the asymmetric conjugated small molecule IDTBRIC in chloroform solution and thin film.

[0033] Figure 11 UV-Vis absorption spectra of the asymmetric conjugated small molecule IDTBRIC2F in chloroform solution and thin film state;

[0034] Figure 12 The UV-Vis absorption spectra of the asymmetric conjugated small molecule O-IDTBRIC in chloroform solution and thin film state;

[0035] Figure 13 The UV-Vis absorption spectra of the asymmetric conjugated small molecule O-IDTBRIC2F in chloroform solution and thin film state;

[0036] Figure 14 Cyclic voltammetry curves for asymmetric conjugated small molecules IDTBRIC and IDTBRIC2F;

[0037] Figure 15 Cyclic voltammetry curves for asymmetric conjugated small molecules O-IDTBRIC and O-IDTBRIC2F;

[0038] Figure 16 Comparison of the UV-Vis absorption spectra of the asymmetric conjugated small molecules IDTBRIC and IDTBRIC2F of this invention with the symmetric small molecule IDT-2BR reported in the literature;

[0039] Figure 17 This is a comparison of the UV-Vis absorption spectra of the asymmetric conjugated small molecule O-IDTBRIC2F of this invention and the symmetric small molecule O-IDT2BR reported in the literature. Detailed Implementation

[0040] The present invention will be further described below through specific embodiments, but these specific embodiments do not limit the scope of protection of the present invention in any way.

[0041] Example 1: Synthesis of the asymmetric conjugated small molecule IDTBRIC as shown in formula (1)

[0042] 1.1 Synthesis of (7,7'-(4,4,9,9-tetra(4-hexylphenyl)-4,9-dihydro-s-indeno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-4-carboxaldehyde) (compound 3, R = hexylphenyl)

[0043]

[0044] Under nitrogen protection, compound 1 (3.00 g, 2.43 mmol), compound 2 (1.48 g, 6.08 mmol), tetrakis(triphenylphosphine)palladium (200 mg), and 150 mL of toluene were added sequentially to a 250 mL single-necked flask. The system was refluxed in an oil bath at 110 °C for 24 hours, then the reaction was stopped and cooled to room temperature. Toluene was removed by rotary evaporation. The crude product was passed through a silica gel column (eluent: petroleum ether: dichloromethane = 1:2, v / v) and recrystallized from dichloromethane / anhydrous methanol to give dark purple crystalline compound 3 (2.23 g, yield: 74.6%).

[0045] The proton NMR spectrum analysis of compound 3 is as follows: 1 H NMR (400MHz, CDCl3) δ10.69(s,2H),8.23(s,2H),8.20(d,J=7.6Hz,2H),7.98(d,J=7.6Hz,2H),7.59(s,2H),7.26(d,J=7 .5Hz,8H),7.12(d,J=8.2Hz,8H),2.62-2.53(m,8H),1.64-1.55(m,8H),1.30(t,J=7.8Hz,24H),0.86(t,J=6.7Hz,12H).

[0046] Synthesis of 1,2(E)-7-(7-(((3-ethyl-4-oxo-2-thiooxythiazolin-5-ylidene)methyl)benzo[c][1,2,5]thiadiazole-4-yl)-4,4,9-tetra(4-hexylphenyl)-4,9-dihydro-s-indeno[1,2-b:5,6-b']dithiophene-2-yl)benzo[c][1,2,5]thiadiazole-4-carboxaldehyde (compound 5, R = hexylphenyl)

[0047]

[0048] Under nitrogen protection, compound 3 (0.78 g, 0.63 mmol) and 3-ethyl-2-thiazolidin-4-one (compound 4) (91.89 mg, 0.57 mmol) were added to 180 mL of chloroform. Piperidine (0.5 mL) was added at 35 °C, and the mixture was stirred overnight at 35 °C. After cooling to room temperature, the mixture was poured into 45 mL of water and extracted with dichloromethane. The combined organic phases were dried over anhydrous magnesium sulfate, filtered, and the organic solvent was removed by vacuum distillation. The crude product was passed through a silica gel column (eluent: petroleum ether: dichloromethane = 1:1, v / v) to give blue compound 5 (0.50 g, yield: 57.7%).

[0049] The proton NMR spectrum analysis of compound 5 is as follows: 1 H NMR (400MHz, CDCl3) δ10.69(s,1H),8.50(s,1H),8.20(dd,J=15.8,8.5Hz,3H),7.97(dd,J=15.0,7.6Hz,2H),7.68(d,J=7.6Hz,1H),7.58(d,J=3.5Hz,2H ),7.26(d,J=7.9Hz,8H),7.12(d,J=7.9Hz,8H),4.24(d,J=7.2Hz,2H),2.66- 2.50(m,8H),1.71-1.49(m,8H),1.40-1.16(m,24H),0.86(t,J=6.3Hz,12H).

[0050] 1.3 Synthesis of the asymmetric conjugated small molecule IDTBRIC

[0051]

[0052] Under nitrogen protection, compound 5 (0.17 g, 0.12 mmol), 2-(3-oxo-2,3-dihydro-1H-inden-1-yl)malononitrile (96 mg, 0.49 mmol), and 50 mL of chloroform were added sequentially to a 100 mL two-necked flask. The reaction system was then placed in a 65 °C oil bath, and pyridine (0.5 mL) was added all at once. The mixture was refluxed and stirred overnight at 65 °C. After cooling to room temperature, the product precipitated in acetone solution. After filtration, the crude product was recrystallized from chloroform to give the blue-green target small molecule IDTBRIC (103 mg, yield: 55.2%).

[0053] The proton NMR spectrum analysis of the conjugated small molecule IDTBRIC is as follows: 1 H NMR (400MHz, CDCl3) δ9.56 (s, 1H), 9.24 (d, J = 8.0Hz, 1H), 8.72 (d, J = 7.8Hz, 1H), 8.48 (s, 1H), 8.28 (s,1H),8.18(s,1H),8.01(d,J=8.0Hz,1H),7.97-7.90(m,2H),7.83-7.74(m,2H),7.66(d,J=7.8H z,1H),7.59(d,J=7.0Hz,2H),7.27(dd,J=8.2,2.0Hz,5H),7.12(dd,J=8.4,2.3Hz,8H),4.23(q,J= 7.1Hz,2H),2.58(t,J=7.7Hz,8H),1.63-1.58(m,8H),1.39-1.22(m,30H),0.86(t,J=6.7Hz,12H).

[0054] Example 2: Synthesis of the asymmetric conjugated small molecule IDTBRIC2F as shown in formula (2)

[0055]

[0056] Under nitrogen protection, compound 5 (0.19 g, 0.14 mmol), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-yl)malononitrile (47.7 mg, 0.21 mmol), and 27 mL of chloroform were added sequentially to a 100 mL two-necked flask. The reaction system was then placed in a 65 °C oil bath, and pyridine (0.3 mL) was added at once. The reaction was continued to be refluxed at 65 °C overnight. After cooling to room temperature, the organic solvent was removed by vacuum distillation. The crude product was rapidly passed through a silica gel column (eluting with chloroform) and recrystallized from chloroform / acetone to give the blue-green target small molecule IDTBRIC2F (140 mg, yield: 63.1%).

[0057] The proton NMR spectrum analysis of the conjugated small molecule IDTBRIC2F is as follows: 1 HNMR(400MHz, CDCl3)δ9.59(s,1H),9.24(d,J=8.0Hz,1H),8.58(dd,J=9.8,6.5Hz,1H),8.49(s,1H) ,8.29(s,1H),8.17(s,1H),8.02(d,J=8.1Hz,1H),7.94(d,J=7.8Hz,1H),7.73(t,J=7.5Hz,1H),7.6 7(d,J=7.8Hz,1H),7.59(d,J=8.8Hz,2H),7.29-7.21(m,5H),7.12(dd,J=8.4,2.2Hz,8H),4.24(q,J =7.1Hz,2H),2.58(t,J=7.7Hz,8H),1.60-1.55(m,8H),1.40-1.22(m,30H),0.86(t,J=6.8Hz,12H).

[0058] Example 3: Synthesis of the asymmetric conjugated small molecule O-IDTBRIC as shown in formula (3)

[0059] Synthesis of 3.17,7'-(4,4,9,9-tetraoctyl-4,9-dihydro-s-indeno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-4-carboxaldehyde) (compound 3, R = n-octyl)

[0060]

[0061] Under nitrogen protection, compound 1 (2.00 g, 1.92 mmol), compound 2 (1.08 g, 4.42 mmol), tetrakis(triphenylphosphine)palladium (200 mg), and 150 mL of toluene were added sequentially to a 250 mL single-necked flask. The system was refluxed in an oil bath at 110 °C for 24 hours, then the reaction was stopped and cooled to room temperature. Toluene was removed by rotary evaporation, and the crude product was purified by silica gel column chromatography (eluent: petroleum ether: dichloromethane = 1:2, v / v) to give compound 3 (1.83 g, yield: 91.7%) as a purple solid.

[0062] The proton NMR spectrum analysis of compound 3 is as follows: 1H NMR (400MHz, CDCl3) δ10.72(s,2H),8.27(s,2H),8.24(d,J=7.6Hz,2H),8.05(d,J=7.6Hz,2H),7.45(s,2H),2.12(t d,J=13.2,4.7Hz,4H),1.97(td,J=13.2,4.7Hz,4H),1.24-1.07(m,40H),1.04-0.82(m,8H),0.77(t,J=6.9Hz,12H).

[0063] 3.2 Synthesis of ((E)-7-(7-(((3-ethyl-4-oxo-2-thiooxythiazolin-5-ylidene)methyl)benzo[c][1,2,5]thiadiazole-4-yl)-4,4,9,9-tetraoctyl-4,9-dihydro-s-indeno[1,2-b:5,6-b']dithiophene-2-yl)benzo[c][1,2,5]thiadiazole-4-carboxaldehyde (compound 5, R = n-octyl)

[0064]

[0065] Under nitrogen protection, compound 3 (0.80 g, 0.68 mmol) and 3-ethyl-2-thiazolidin-4-one (compound 4) (109.1 mg, 0.68 mmol) were added to 150 mL of chloroform. Piperidine (0.5 mL) was added at 35 °C, and the mixture was stirred overnight at 35 °C. After cooling to room temperature, the mixture was poured into 45 mL of water and extracted with dichloromethane. The combined organic phases were dried over anhydrous magnesium sulfate, filtered, and the organic solvent was removed by vacuum distillation. The crude product was passed through a silica gel column (eluent: petroleum ether: dichloromethane = 1:2, v / v) to give blue compound 5 (0.45 g, yield: 56.0%).

[0066] The proton and carbon NMR spectra of compound 5 are as follows: 1H NMR (400MHz, CDCl3) δ10.72(s,1H),8.52(s,1H),8.28(s,1H),8.24(d,J=7.6Hz,1H),8.2 2(s,1H),8.05(d,J=7.6Hz,1H),8.01(d,J=7.8Hz,1H),7.72(d,J=7.9Hz,1H),7.44(d,J=2 .6Hz,2H),4.25(q,J=7.1Hz,2H),2.12(td,J=12.5,4.1Hz,4H),1.97(td,J=12.7,4.4Hz,4 H),1.33(t,J=7.1Hz,3H),1.21-1.08(m,40H),1.01-0.85(m,8H),0.77(t,J=6.9Hz,12H).

[0067] 13 C NMR (101MHz, CDCl3) δ192.99,188.44,167.54,157.07,156.93,154.57,154.23,154.17,1 53.95,152.22,151.72,147.09,145.98,141.08,140.52,136.58,136.16,134.12,132.95 ,131.31,130.48,127.23,124.84,124.77,124.51,124.27,124.00,123.83,122.70,113.94,109.99,54.38,39.93,39.15,31.79,29.98,29.29,29.20,24.27,22.58,14.04,12.32.

[0068] 3.3 Synthesis of the asymmetric conjugated small molecule O-IDTBRIC

[0069]

[0070] Under nitrogen protection, compound 5 (0.10 g, 0.08 mmol), 2-(3-oxo-2,3-dihydro-1H-inden-1-yl)malononitrile (24.6 mg, 0.13 mmol), and 25 mL of chloroform were added sequentially to a 50 mL two-necked flask. The reaction system was then placed in a 65 °C oil bath, and pyridine (0.5 mL) was added all at once. The mixture was refluxed and stirred at 65 °C for 2 h. After cooling to room temperature, the product precipitated in acetone solution. After filtration, the crude product was purified by silica gel column chromatography (eluting with chloroform) and recrystallized from chloroform / acetone to give the blue-green target small molecule O-IDTBRIC (112 mg, yield: 82.4%).

[0071] The proton NMR spectrum analysis of the conjugated small molecule O-IDTBRIC is as follows: 1 HNMR (400MHz, CDCl3) δ9.62(s,1H),9.33(d,J=7.4Hz,1H),8.75(d,J=7.7Hz,1H),8.53(s,1H),8.32(s,1H ),8.22(s,1H),8.10(d,J=8.0Hz,1H),8.02(d,J=7.7Hz,1H),7.98(d,J=6.4Hz,1H),7.86-7.77(m,2H),7. 73(d,J=7.8Hz,1H),7.45(d,J=7.8Hz,2H),4.25(q,J=7.2Hz,2H),2.13(dt,J=24.8,4.8Hz,4H),1.98(td, J=13.2,4.6Hz,4H),1.33(t,J=7.2Hz,3H),1.23-1.04(m,40H),1.07-0.79(m,8H),0.78(t,J=6.9Hz,12H).

[0072] Example 4: Synthesis of the asymmetric conjugated small molecule O-IDTBRIC2F as shown in formula (4)

[0073]

[0074] Under nitrogen protection, compound 5 (0.10 g, 0.08 mmol), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-yl)malononitrile (29.2 mg, 0.13 mmol), and 25 mL of chloroform were added sequentially to a 100 mL two-necked flask. The reaction system was then placed in a 65 °C oil bath, and pyridine (0.6 mL) was added at once. The reaction was continued to be refluxed at 65 °C overnight. After cooling to room temperature, the organic solvent was removed by vacuum distillation. The crude product was rapidly passed through a silica gel column (eluting with chloroform) and recrystallized from chloroform / acetone to give the blue-green target small molecule O-IDTBRIC2F (117 mg, yield: 84.2%).

[0075] The proton NMR spectrum analysis of the conjugated small molecule O-IDTBRIC2F is as follows: 1H NMR (400MHz, CDCl3) δ9.64(s,1H),9.32(d,J=8.7Hz,1H),8.59(dd,J=9.9,6.5Hz,1H),8.53(s,1H ),8.34(s,1H),8.22(s,1H),8.10(d,J=8.0Hz,1H),8.02(d,J=7.8Hz,1H),7.74(dd,J=11.8,5.2Hz ,1H),7.45(d,J=9.3Hz,1H),4.25(q,J=7.1Hz,1H),2.12(dd,J=15.3,9.6Hz,2H),1.99(dd,J=19.8 ,7.8Hz,2H),1.33(t,J=7.1Hz,2H),1.23-1.06(m,18H),1.03-0.83(m,4H),0.78(t,J=6.9Hz,5H).

[0076] Example 5: Determination of the optical properties of four asymmetric conjugated small molecules

[0077] Figure 10-13 The UV-Vis absorption spectra of four asymmetric conjugated small molecules in chloroform solution and thin film are given, and the corresponding photophysical performance data are listed in Table 1. As can be seen from the figure: (1) In both solution and thin film states, IDTBRIC, IDTBRIC2F, O-IDTBRIC and O-IDTBRIC2F all show two characteristic absorption peaks. The absorption peak at the short wavelength is attributed to the π-π* electronic transition of the small molecule backbone; the maximum absorption peak at the long wavelength is attributed to the charge transfer (ICT) effect from the donor unit to the acceptor unit within the molecule. (2) Compared with the absorption spectrum in chloroform solution, the absorption peaks of the four small molecules in solid film have a redshift broadening of 50-100 nm. This is mainly due to the stronger intermolecular forces and the strong π-π stacking effect caused by the rigid planar structure in solid film state. As shown in Table 1, the absorption peaks of the four small molecules in solid film are broadened by a redshift of 50-100 nm. onset Their optical band gap (E) can be calculated. g opt The values ​​were 1.64 eV, 1.61 eV, 1.54 eV and 1.45 eV, respectively.

[0078] from Figure 16-17 The results show that, compared with the reported symmetrical small molecules IDT-2BR and O-IDTBR, introducing a cyanoindanone derivative end group at one end of the molecule can significantly regulate the planarity and absorption spectrum and optical band gap of the small molecule (significant red shift of the spectrum and obvious broadening of the absorption peak), which is beneficial to improving the utilization rate of sunlight, and thus achieving high photocurrent and high conversion efficiency of solar cells.

[0079] Example 6: Electrochemical performance determination of four asymmetric conjugated small molecules

[0080] The redox processes of four asymmetric conjugated small molecules were determined by electrochemical cyclic voltammetry, yielding their initial redox potentials relative to ferrocene. The frontier orbital energy levels (HOMO and LUMO levels) were then estimated, and the data are listed in Table 1. Figure 14 and 15 It can be seen that the initial reduction potential of IDTBRIC is -1.22V and the oxidation potential is 0.42V. According to the formula LUMO = -(E red,onset +4.8)eV, HOMO=-(E ox,onset The LUMO energy level was estimated to be -3.58 eV and the HOMO energy level to be -5.22 eV based on +4.8 eV. Using the same method, the LUMO energy level of the small molecule IDTBRIC2F was calculated to be -3.68 eV and the HOMO energy level to be -5.29 eV; the LUMO energy level of the small molecule O-IDTBRIC was -3.70 eV and the HOMO energy level to be -5.24 eV; and the LUMO energy level of O-IDTBRIC2F was -3.86 eV and the HOMO energy level to be -5.31 eV. These results ensure its application in non-fullerene photovoltaic devices.

[0081] Table 1. Photophysical and electrochemical properties of four asymmetric conjugated small molecules.

[0082]

[0083] Although the invention has been described in conjunction with preferred embodiments, the invention is not limited to the above embodiments, and it should be understood that the appended claims summarize the scope of the invention. Guided by the inventive concept, those skilled in the art should recognize that any modifications made to the various embodiments of the invention will be covered by the spirit and scope of the claims.

Claims

1. A class of A2-A1-D-A1-A3 type narrow bandgap conjugated small molecule materials based on dithiophene and indole-based materials, characterized in that, Narrow bandgap conjugated small molecule materials are one of the following molecular structural formulas 1-3: ; Formula 1: IDTBRIC ； Formula 2: IDTBRIC2F ; Formula 3: O-IDTBRIC.

2. The application of the A2-A1-D-A1-A3 type narrow bandgap conjugated small molecule material based on dithiophene and indole as described in claim 1, characterized in that, A2-A1-D-A1-A3 type narrow bandgap conjugated small molecule materials based on dithiophene and inducible provinces are used as active layer acceptor materials for organic solar cells.

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