WO2018170851A1

WO2018170851A1 - Imide-containing ladder tpye heteroarenes: synthesis and ralated organic semiconductor devices

Info

Publication number: WO2018170851A1
Application number: PCT/CN2017/077923
Authority: WO
Inventors: Xugang GUO; Yingfeng Wang; Han GUO; Shaohua LING
Original assignee: South University Of Science And Technology Of China
Priority date: 2017-03-23
Filing date: 2017-03-23
Publication date: 2018-09-27

Abstract

Small molecule and polymer semiconductors and their preparation methods are provided. These compounds are of formula I-III, and can be used in high-mobility organic thin-film transistors and bulk heterojunction polymer solar cells.

Description

IMIDE-CONTAINING LADDER TPYE HETEROARENES：SYNTHESIS AND RALATED ORGANIC SEMICONDUCTOR DEVICES

FIELD

The present disclosure relates to a field of semiconductor technology, in particular to organic semiconductor compounds, organic semiconductor polymers, organic semiconductor films, organic thin-film transistors, organic solar cells, and semiconductor devices.

BACKGROUND

Organic π-conjugated materials are emerging semiconductors for next-generation optoelectronic devices, such as organic thin-film transistors (OTFTs) and organic photovoltaic devices (OPVs) owing to the advantages of low-cost, light-weight, mechanical flexibility, and well-tailored properties.

The device performance of organic semiconductors is mainly determined by their conjugated backbones. Ladder-type molecules with high degree of backbone coplanarity, well-delocalized π-system, and strong intermolecular interaction have attracted a great deal of attention as small molecule semiconductors and building blocks for polymers and molecular wires. For example, the fused pentacenes show substantial hole mobility in OTFTs； and thieonacenes, benzothieno [3, 2-b] [1] benzothiophene and dinaphtho [2, 3-b: 2', 3'-f] thieno [3, 2-b] thiophene exhibit remarkable mobility with excellent device stability. To date most ladder-type conjugated molecules typically exhibit electron-rich characteristics and the synthesis of electron-deficient analogues with tunable conjugation length and good solubility remains a great challenge due to the decreased chemical reactivity. Whilst such electron-deficient build blocks are desired for constructing donor-acceptor dyads and developing organic semiconductors using the in-chain donor-acceptor strategy, hence it is highly imperative to develop electron-deficient ladder-type π-conjugated systems.

SUMMARY

To this end， the invention of new ladder type electron-deficient molecule and building blocks with improved solubility, high stability and well-tailored opto-electrical properties plays a critical role.

The present invention provides a strategy to employ strategically imide-functionalized ladder-type heteroarenes as acceptors for molecule and polymer materials. In order to achieve this purpose, the present invention employs the following technical solutions:

Accordingly, a first object of the present disclosure is to provide a series of compounds as follows:

wherein

A is selected from the group consisting of H, F, Cl, Br, CN, CF_3, and following formula:

B is selected from the group consisting of H, F, Cl, Br, CN, CF₃ and following formula:

R is selected from the group consisting of ethylhexyl, Butyl-1-octyloxy, propylheptan-1-oloxy and undecanol, nonanol.

In another aspect, the present invention provides a homopolymer of the electron-deficient building block described herein having Formula

wherein

In another aspect, the present invention provides a preparation method of the homopolymer described above, comprising:

(1) adding an electron-deficient monomer, tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) , and tris (o-tolyl) phosphine (P (o-tolyl) ₃) into a reaction vessel, and subjecting the reaction vessel and the mixture to an inert gas；

(2) adding an organic solvent； sealing the reaction vessel under an inert gas flow and then stirring while heating；

(3) optionally, adding 2- (tributylstanny) thiophene and stirring the reaction mixture while heating； then adding 2-bromothiophene and stirring the reaction mixture while heating；

(4) after cooling to room temperature, dripping the reaction mixture into methanol containing hydrochloric acid；

(5) drying the solid precipitate obtained in step (4) to give the crude product, and then extracting the crude product using a series of solvents depending on the polymer molecular weight and polymer solubility；

(6) after final extraction, concentrating the polymer solution, and then being dripped into methanol, collecting the polymer and drying to give the polymeric semiconductor.

Preferably, the mole ratio of the tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) to tris (o-tolyl) phosphine (P (o-tolyl) ₃) is 1: 4-15, for example, 1: 6, 1: 9, 1: 13 and so on, preferably 1: 6-10, more preferably 1: 8； the Pd loading is 0.005-0.1 equiv, preferably 0.01-0.06 equiv.

Preferably, the reaction vessel and the mixture are subjected to 1-5 pump/purge cycles with Ar.

Preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them.

Preferably, in step (2) , the organic solvent is selected from any one of anhydrous toluene, benzene, chlorobenzene, DMF, or a mixture of at least two of them, preferably anhydrous toluene.

Preferably, the ratio of the organic solvent to the acceptor monomer is 10-50 mL/mmol, preferably 15-30 mL/mmol.

Preferably, the heating is conducted at 50-170 ℃ for 1-72h, preferably at 80-150 ℃ for 3-50h.

Preferably, the heating is conducted using oil bath or microwave.

Preferably, the heating is conducted by 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation.

Preferably, in step (3) , the heating is conducted at 80-170 ℃ for more than 0.2 h, preferably at 100-160 ℃for more than 0.4 h.

Preferably, the heating is conducted using oil bath or microwave.

Preferably, the heating is conducted under microwave irradiation at 140 ℃ for 0.5 h.

Preferably, the heating after adding 2-bromothiophene is conducted at 140 ℃ for another 0.5 h.

In step (3) , the 2- (tributylstanny) thiophene may be added or not added, which does not have much impact on the results. If added, the amount thereof is preferably sufficient such that the bromine groups in the product obtained from the electron-deficient monomer can be replaced completely.

Also, the 2-bromothiophene may be added or not added, which does not have much impact on the results. If added, the amount thereof is preferably sufficient such that the Sn-in the product obtained in the previous step can be replaced completely.

The amount of the methanol is adjusted according to the amount of the reaction mixture. Preferably, the volume ratio of the methanol to the reaction mixture is about 20-200: 1, preferably 40-150: 1. For example, when the amount of the reaction mixture is about 2-5mL, the amount of the methanol may be about 200-300mL.

Preferably, the methanol contains 12 mol/L hydrochloric aci； preferably contains 1 mL HCl/100 mL methanol.

Preferably, the dripping is conducted under vigorous stirring, preferably the strirring is continued for at least 0.5 h, preferably at least 1 h.

Preferably, in step (5) , the extracting is conducted by Soxhlet extraction with the solvent combinations depending on the solubility and molecular weight of the particular polymer. The adding sequence for used solvents for Soxhlet extraction is: methanol, acetone, hexane, dichloromethane, chloroform, and chlorobenzene.

Preferably, in step (6) , the polymer solution is concentrated to less than 10 ml, preferably 4-8 mL.

Preferably, the dripping is conducted under vigorous stirring.

Preferably, the collecting is conducted by filtration.

Preferably, the drying is conducted under reduced pressure.

In still another aspect, the present invention provides use of the polymeric semiconductor according to the present invention in thin-film transistor or polymer solar cell.

In another aspect, the present invention provides a copolymer semiconductor material described herein having the following Formula:

wherein

R is selected from the group consisting of C₁-C₂₀ alkyl.

In another aspect, the present invention provides a preparation method of the copolymer described above, comprising:

(1) adding an acceptor monomer and a donor monomer, tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) , and tris (o-tolyl) phosphine (P (o-tolyl) 3) into a reaction vessel, and subjecting the reaction vessel and the mixture to an inert gas；

Preferably, the mole ratio of the acceptor monomer to the donor monomer is 1: 0.8-1.3, for example, 1: 0.9, 1:1.2 and so on, preferably 1: 0.9-1.1, more preferably 1: 1.

Preferably, the inert gas is selected from any one of Ar, N2, He, Ne, or a mixture of at least two of them.

Preferably, the heating is conducted using oil bath or microwave.

Also, the 2-bromothiophene may be added or not added, which does not have much impact on the results. If added, the amount there of is preferably sufficient such that the Sn-in the product obtained in the previous step can be replaced completely.

Preferably, in step (5) , the extracting is conducted by Soxhlet extraction with the solvent combinations depending on the solubility and molecular weight of the particular polymer. The adding sequence for used solvent for Soxhlet extraction is: methanol, acetone, hexane, dichloromethane, chloroform, and chlorobenzene.

Preferably, the dripping is conducted under vigorous stirring.

Preferably, the collecting is conducted by filtration.

Preferably, the drying is conducted under reduced pressure.

In summary, we have successfully synthesized a series of novel imide-functionalized ladder-type (fused) heteroarenes and corresponding polymers. These fused novel arenes show excellent solubilities, high degree of backbone coplanarity, substantial crystallinity, and tunable conjugation length and optoelectrical properties. In comparison to most of fused arenes, these imide-functionalized bithiophene derivatives are electron-deficient. Some small molecules and polymers are incorporated into organic thin-film transistors and show promising electron transport property. The results herald the great potential of these imide-functionalized ladder-type heteroarenes for small molecule semiconductors and as a class of building blocks for high-performance polymer semiconductors.

The raw material used in above preparation method can be prepared by known method in the art or by the following method described below or buying on the market.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows absorption spectra of small molecules in a solution (top) and a film (bottom) of the present invention.

Figure 2 shows TGA curves of a small molecule of the present invention at a scan rate of 20 ℃ min^-1 under nitrogen atmosphere.

Figure 3 shows cyclic voltammograms of small molecules of the present invention measured in 0.1 M (n-Bu) ₄ N^. PF₆ acetonitrile solution at scan rate of 50 mV s^-1.

Figure 4 shows (a) output and (b) transfer characteristics of small molecule (BIT5) of thin-film transistors of the present invention. The active layer was deposited from solution.

Figure 5 shows Tapping-mode (a) AFM height, (b) phase image and (c) XRD pattern of small molecules in the present invention film deposited on Si/SiO₂ (aand b) and Si (c) substrate, respectively.

Fig. 6A: ¹H NMR spectrum of compound 2 (r.t., in DMSO-d6) .

Fig. 6B: ¹³C NMR spectrum of compound 2 (r.t., in DMSO-d6) .

Fig. 6C: ¹H NMR spectrum of compound 3 (r.t., in CDCl3) .

Fig. 6D: ¹³C NMR spectrum of compound 3 (r.t., in CDCl3) .

Fig. 6E: ¹H NMR spectrum of compound 13 (r.t., in CDCl3) .

Fig. 6F: ¹³C NMR spectrum of compound 13 (r.t., in CDCl3) .

Fig. 6G: ¹H NMR spectrum of compound 4 (r.t., in CDCl3) .

Fig. 6H: ¹³C NMR spectrum of compound 4 (r.t., in CDCl3) .

Fig. 6I: ¹H NMR spectrum of compound 18 (r.t., in CDCl3) .

Fig. 6J: ¹³C NMR spectrum of compound 18 (r.t., in CDCl3) .

Fig. 6K: ¹H NMR spectrum of compound 14 (r.t., in CDCl3) .

Fig. 6L: ¹³C NMR spectrum of compound 14 (r.t., in CDCl3) .

Fig. 6M: ¹H NMR spectrum of compound 15 (r.t., in DMSO-d6) .

Fig. 6N: ¹³C NMR spectrum of compound 15 (r.t., in DMSO-d6) .

Fig. 6O: ¹H NMR spectrum of compound 17, BTI2 (r.t., in CDCl3) .

Fig. 6P: ¹³C NMR spectrum of compound 17, BTI2 (r.t., in CDCl3) .

Fig. 6Q: ¹H NMR spectrum of compound 5 (r.t., in CDCl3) .

Fig. 6R: ¹³C NMR spectrum of compound 5 (r.t., in CDCl3) .

Fig. 6S: ¹H NMR spectrum of compound 19 (r.t., in CDCl3) .

Fig. 6T: ¹³C NMR spectrum of compound 19 (r.t., in CDCl3) .

Fig. 6U: ¹H NMR spectrum of compound 20 (r.t., in CDCl3) .

Fig. 6V: ¹³C NMR spectrum of compound 20 (r.t., in CDCl3) .

Fig. 6W: ¹H NMR spectrum of compound 21 (r.t., in DMSO-d6) .

Fig. 6X: ¹³C NMR spectrum of compound 21 (r.t., in DMSO-d6) .

Fig. 6Y: ¹H NMR spectrum of compound 23, BTI3 (r.t., in CDCl3) .

Fig. 6Z: ¹³C NMR spectrum of compound 23, BTI3 (r.t., in CDCl3) .

Fig. 7A: ¹H NMR spectrum of compound 24 (r.t., in CDCl3) .

Fig. 7B: ¹³C NMR spectrum of compound 24 (r.t., in CDCl3) .

Fig. 7C: ¹H NMR spectrum of compound 25 (r.t., in CDCl3) .

Fig. 7D: ¹³C NMR spectrum of compound 25 (r.t., in CDCl3) .

Fig. 7E: ¹H NMR spectrum of compound 26 (r.t., in CDCl3) .

Fig. 7F: ¹³C NMR spectrum of compound 26 (r.t., in CDCl3) .

Fig. 7G: ¹H NMR spectrum of compound 27 (r.t., in CDCl3) .

Fig. 7H: ¹³C NMR spectrum of compound 27 (r.t., in CDCl3) .

Fig. 7I: ¹H NMR spectrum of compound 28 (r.t., in DMSO-d6) .

Fig. 7J: ¹³C NMR spectrum of compound 28 (r.t., in DMSO-d6) .

Fig. 7K: ¹H NMR spectrum of compound 30, BTI4 (120 ℃, in C2D2Cl4) .

Fig. 7L: ¹H NMR spectrum of compound 6 (r.t., in CDCl3) .

Fig. 7M: ¹³C NMR spectrum of compound 6 (r.t., in CDCl3) .

Fig. 7N: ¹H NMR spectrum of compound 7 (r.t., in CDCl3) .

Fig. 7O: ¹³C NMR spectrum of compound 7 (r.t., in CDCl3) .

Fig. 7P: ¹H NMR spectrum of compound 8 (r.t., in CDCl3) .

Fig. 7Q: ¹³C NMR spectrum of compound 8 (r.t., in CDCl3) .

Fig. 7R: ¹H NMR spectrum of compound 9 (r.t., in CDCl3) .

Fig. 7S: ¹³C NMR spectrum of compound 9 (r.t., in CDCl3) .

Fig. 7T: ¹H NMR spectrum of compound 10 (r.t., in DMSO-d6) .

Fig. 7U: ¹³C NMR spectrum of compound 10 (r.t., in DMSO-d6) .

Fig. 7V: ¹H NMR spectrum of compound 12, BTI5 (120 ℃, in C2D2Cl4) .

DETAILED DESCRIPTION

To facilitate understanding of the present invention, the embodiments of the present invention are exemplified as follows. An artisan skilled in the art should appreciate that the embodiments are merely used to help understand the present invention and should not be regarded as specific limits on the invention.

Materials and Instruments

All reagents and chemicals were commercially available and were used without further purification unless otherwise stated. Anhydrous THF, ether, and toluene were distilled from Na/benzophenone under argon, whereas anhydrous dichloromethane was distilled from calcium hydride. Unless otherwise stated, all reactions were carried out under inert atmosphere using standard Schlenk line techniques. The known BTI1 was synthesized following the published procedures. 2 NMR spectra were measured on Bruker Ascend 400 MHz spectrometer in CDCl3 or DMSO-d6. High-temperature NMR spectra were recorded on Bruker asend 3 400 MHz spectrometers in C2D2Cl4 at 120 ℃. Chemical shifts were referenced to the residual protio-solvent signals. Mass spectra were measured on Bruker Daltonics autoflexTM speed MALDI-TOF and high-resolution mass spectrometry were obtained on Thermo Scientific^TM Q-Exactive. Elemental analyses (EA) of compounds were performed at Shenzhen University (Shenzhen, Guangdong) . UV-vis absorption spectra of solution and film were collected on a Shimadzu UV-3600 UV-VIS-NIR spectrophotometer. Cyclic voltammetry measurements of BTI-BTI5 were carried out under argon atmosphere using a CHI760 Evoltammetric workstation with N2-saturated solution of 0.1 M tetra-n-butylammoniumhexafluorophosphate (Bu4NPF6) in acetonitrile (CH3CN) as the supporting electrolyte. A platinum disk working electrode, a platinum wire counter electrode, and a silver wire reference electrode were employed, and the ferrocenium/ferrocene redox couple (Fc/Fc+) was used as the internal reference for all measurements. The scanning rate was 50 mV S^-1. Thermogravimetric (TGA) measurements were carried out with a METTLER TOLEDO (TGA 1 STARe System) apparatus at a heating rate of 20 ℃ min^-1 under N2. AFM measurements of thin films were performed by using a Dimension Icon Scanning Probe Microscope (Asylum Research, MFP-3D-Stand Alone) in tapping mode. X-ray diffraction (XRD) of thin films was recorded on X-ray diffractometer (Rigaku, Smartlab 9KW) .

Source-drain electrodes (3 nm Cr and 30 nm Au) were patterned on borosilicate glass substrates by photolithography. The substrates were subsequently cleaned by sonication in acetone, isopropanol followed by UV-ozone and oxygen plasma treatment. The semiconductor layers were spin-coated from 3 mg mL^-1 anhydrous tetrahydrofuran (THF) solutions and then were thermally annealed at various temperatures for 10 min. Dielectric layers were spin coated from diluted CYTOP solutions (CTL-809M: CT-SOLV180 ＝ 2: 1 (v: v) , Asahi Glass Co., Ltd. ) , then they were annealed at 80 ℃ for 1 h. Finally, 50 nm Al was evaporated on top as the gate electrode. The devices were characterized with Keithley 4200 semiconductor characterization system. All device fabrication and characterization were carried out in N2-filled glove box.

Molecule and Polymer Synthesis:

Example 1. Synthesis of BTI2-BTI5.

Synthesis of thieno [3, 2-b] thiophene-3, 6-dicarboxylic acid 2. To a solution of n-BuLi (1.6 M in hexane, 14 mL, 22.4 mmol) in THF (30 mL) , the

compound

1, 3, 6-dibromothieno [3, 2-b] thiophene (2.98 g, 10.0 mmol) , in 20 mL anhydrous THF was added dropwise over the period of 0.5 h at -78 ℃. The resulting solution was stirred 2 h at -78 ℃. Then to the mixture was added dry ice (3.5 g, 80 mmol) at -78 ℃ and gradually warmed to room temperature. After stirring for 12 h at room temperature, the reaction was quenched with methanol, and the solvent was removed under reduced pressure. The residual solid was dissolved in 200 mL of water, acidified with 6 M HCl (aq) , and the resulting white solid (2.2g, 96％) is isolated by filtration. ¹H NMR (400 MH_Z, DMSO-d₆) δ： 8.47 (s, 2H) . ¹³C NMR (100 MHz, DMSO-d₆) δ： 163.20， 138.41， 137.69， 126.78.

Synthesis of diethyl thieno [3, 2-b] thiophene-3, 6-dicarboxylate 3. To a solution of thieno [3, 2-b] thiophene-3, 6-dicarboxylic acid 2 (2.28 g, 10 mmol) in 200 mL ethanol was added 2.5 mL sulfuric acid. Then, the reaction mixture was refluxed overnight. After cooling to room temperature, the white solid was collected by filtration, washed with another ethanol, and dried in vacuum at 50 ℃ overnight. The resulting white crystals (2.23 g, 78％) were used for the following reaction without further purification. ¹H NMR (400 MH_Z, CDCl₃) δ： 8.27 (s， 2H) ， 4.47-4.41 (q, 4H) , 1.47-1.44 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.80， 138.23， 136.55, 125.98, 61.27, 14.34.

Synthesis of diethyl 2, 5-dibromothieno [3, 2-b] thiophene-3, 6-dicarboxylate 13. To a solution of diethyl thieno [3, 2-b] thiophene-3, 6-dicarboxylate 3 (568 mg, 2.0 mmol) in 50 mL chloroform, Br₂ (640 mg, 4.0 mmol) and iron (III) chloride (5 mg) were added successively. The reaction was stirred at room temperature in the dark overnight. Na₂SO₃ aqueous solution was added to the reaction mixture and stirred for 0.5 h. Then the solvent was removed by evaporation to afford a white solid, which was purified by column chromatography on silica gel with petroleum ether: dichloromethane (3: 1) as the eluent to give 13 (841 mg, 95％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 4.49-4.44 (q, 4H) , 1.57-1.47 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 160.6， 135.8， 123.6， 123.5， 61.7， 14.2.

Synthesis of diethyl 2-bromothieno [3, 2-b] thiophene-3, 6-dicarboxylate 4. To a solution of diethyl thieno [3, 2-b] thiophene-3, 6-dicarboxylate 3 (2.23 g, 8.0 mmol) in 80 mL chloroform, Br₂ (1.28 g, 8.0 mmol) and iron (III) chloride (10 mg) were added successively. The Br₂ addition was completed in 5 times by partly quantitative injection. The reaction was stirred at room temperature in dark overnight. Na₂SO₃ aqueous solution was then added to the reaction mixture and stirred for 0.5 h. After the removal of solvent, the residual white solid was purified by column chromatography on silica gel with petroleumether: dichloromethane (3: 1) as the eluent to give 4 as the product (1.12g, 39％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 8.27 (s， 1H) ， 4.49-4.45 (q, 2H) , 4.45-4.40 (q, 2H) , 1.50-1.47 (t, 3H) , 1.47-1.44 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.51， 160.94， 137.65， 136.13, 135.03, 125.78, 123.86, 123.72, 61.60, 61.45, 14.34, 14.27.

Synthesis of ethyl 2- (trimethylstannyl) thiophene-3-carboxylate 18. To a solution of thiophene-3-carboxylic acid (12.8 g, 100 mmol) in 250 mL ethanol was added 3 mL sulfuric acid. Then the reaction mixture was refluxed overnight. After cooling to room temperature, the solvent was removed using rotary evaporator. The resulting yellow oil was purified by column chromatography on silica gel using dichloromethane as the eluent to give ethyl thiophene-3-carboxylate as a colorless oil. To a solution of diisopropyl amine (2.88 mL, 20 mmol) in 100 mL dry ether at -78 ℃, n-BuLi (2.4 M in hexane, 8.3 mL, 20 mmol) was added dropwise under argon to form lithiumdiisopropylamide (LDA) . A solution of ethyl thiophene-3-carboxylate (3.12 g, 20 mmol) in 10 mL dry ether was then added dropwise to the formed LDA over the period of 20 min. The resulting solution was stirred at -78 ℃ for 1 h. To the reaction mixture was added trimethyltinchloride (44 mL, 44 mmol) in one portion via syringe injection at -78 ℃. Then the cooling bath was removed and the mixture was gradually warmed to room temperature. After stirring for 4 h at room temperature, the reaction solution was quenched with H₂O. The solvent was then evaporated under reduced pressure, and the crude product was purified by column chromatography on silica gel using dichloromethane as the eluent to give 18 as a colorless oil (5.4 g, 84.6 ％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.72-7.70 (d, 1H) , 7.58-7.56 (d, 1H) , 4.39-4.34 (q, 2H) , 1.42-1.39 (t, 3H) , 0.49-0.35 (t, 9H) . ¹³C NMR (100 MHz, CDCl₃) δ： 164.28， 150.81， 139.74， 131.21， 129.58， 60.65， 14.47， -7.19.

Synthesis of diethyl 2, 5-bis (3- (ethoxycarbonyl) thiophen-2-yl) thieno [3, 2-b] thiophene-3, 6-dicarboxylate 14. To a two-neck flask equipped with a condenser was added 13 (1.10 g, 2.5 mmol) , 18 (3.19 g, 10 mmol) , Pd (PPh₃) ₂Cl₂ (87.7 mg, 0.125 mmol) , and 50 mL dry toluene and 5 mL DMF. The reaction mixture was refluxed under argon for 48 h. After cooling to room temperature, the solvent was evaporated under reduced pressure and the crude product was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (4: 1) as the eluent to give 14 as a white solid (726 mg, 49％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.62-7.60 (d, 2H) , 7.44-7.3 (d, 2H) , 4.28-4.23 (q, 4H) , 4.21-4.16 (q, 4H) , 1.25-1.22 (t, 6H) , 1.18-1.14 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 162.52, 161.51, 143.15, 139.30, 137.75, 132.44, 129.64, 126.36, 123.59, 61.16, 60.61, 13.99, 13.91.

Synthesis of 2, 5-bis (3-carboxythiophen-2-yl) thieno [3, 2-b] thiophene-3, 6-dicarboxylic acid 15. To a solution of 14 (710 mg, 1.2 mmol) in 20 mL THF was added NaOH (800 mg) , 20 mL EtOH and 5 mL H₂O. The mixture was refluxed for overnight. Then the reaction was cooled to room temperature, and the solvent was evaporated under reduced pressure. The remaining solid was dissolved in 100 mL H₂O, acidified with 6 M HCl (aq) , and the resulting white precipitate (550mg, 95％) was isolated by filtration. ¹H NMR (400 MH_Z, DMSO-d₆) δ： 7.79-7.77 (d, 2H) , 7.50-7.49 (d, 2H) . ¹³C NMR (100 MHz, DMSO-d₆) δ： 163.82， 163.01， 142.55， 138.66， 137.51, 133.52, 130.17, 128.24, 124.62.

Synthesis of compound 16. Compound 15 (550 mg, 1.14 mmol) was stirred in 25 mL of acetic anhydride under reflux for 12 h. After cooling to room temperature, the resulting solid was collected by filtration, washed with methanol, and dried in vacuum overnight. A yellow solid (498 mg, 98％) was obtained as the product, which will be used for the following reaction without further purification.

Synthesis of compound 17. To a suspension of anhydride 16 (111 mg, 0.25 mmol) in 50 mL dichloromethane was added a solution of 2-octyldodecyl amine (1.05 g, 3.0 mmol) in 30 mL dichloromethane. After addition, the reaction solution was stirred at reflux for overnight. Upon removal of solvent, 10 mL thionyl chloride was added in one portion, and the mixture was refluxed for overnight. The excess thionyl chloride was then removed under reduced pressure, and the residue was purified by column chromatography on silica gel with petroleum ether: dichloromethane (1: 1) as the eluent to give 17 as a yellow solid (170 mg, 76.5％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.84-7.82 (d, 2H) , 7.34-7.33 (d, 2H) , 4.35-4.33 (d, 4H) , 1.99 (m, 2H) , 1.37-1.24 (m, 64H) , 0.9-0.85 (m, 12H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.33， 161.20， 141.26， 138.04， 137.90， 134.00， 133.48， 125.28， 124.30， 49.31, 42.60, 36.24, 31.93, 31.92, 31.61, 30.12, 29.69, 29.66, 29.64, 29.59, 29.37, 29.35, 26.42, 22.69, 14.12. Calcd MW for C₅₈H₈₇O₄N₂S₄: 1003.5543. Found: HRMS, 1003.5544. MALDI-TOF, 1003.218. Elem. Anal. calcd. for C₅₈H₈₇O₄N₂S₄: C, 69.42； H, 8.64； N, 2.79； S, 12.78； Found: C, 69.32； H, 8.33； N, 2.77； S, 12.68.

Synthesis of tetraethyl [2, 2'-bithieno [3, 2-b] thiophene] -3, 3', 6, 6'-tetracarboxylate 5. To a solution of 4 (1.09 g, 3 mmol) in 10 mL DMF, Ni (COD) ₂ (454 mg, 1.65 mmol) was added in one portion under nitrogen. The reaction mixture was heated at 50 ℃ for 12 h. Then the solvent was removed under reduced pressure, and the residue was purified by column chromatography on silica gel with petroleum ether: ethyl acetate (4: 1) as the eluent to give product 5 as a yellow solid (688 mg, 81％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 8.31 (s， 2H) ， 4.417-4.41 (q, 4H) , 4.29-4.23, (q, 4H) , 1.47-1.43 (t, 6H) , 1.22-1.18 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.68， 161.50， 142.81， 139.32, 137.09, 136.30, 125.83, 124.35, 61.42, 61.21, 14.36, 13.92.

Synthesis of tetraethyl 5, 5'-dibromo- [2, 2'-bithieno [3, 2-b] thiophene] -3, 3', 6, 6'-tetracarboxylate 19. To a solution of 5 (375 mg, 0.66 mmol) in 30 mL chloroform, bromine (284 mg, 2.4 mmol) and iron (III) chloride (2 mg) were added successively. The reaction mixture was stirred in the dark for 12 h at room temperature. Na₂SO₃ aqueous solution was added to the reaction mixture and stirred for 0.5 h. Then the solvent was removed by evaporation to afford a yellow solid, which was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (4: 1) as the eluent to give coumpund 19 as the product (412 mg, 86％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 4.50-4.45 (q, 4H) , 4.28-4.23 (q, 4H) , 1.50-1.46 (t, 6H) 1.24-1.21 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.18， 160.78, 141.29, 137.39, 136.86, 124.52, 123.99, 123.62, 61.75, 61.42, 14.27, 13.95.

Synthesis of tetraethyl 5, 5'-bis (3- (ethoxycarbonyl) thiophen-2-yl) - [2, 2'-bithieno [3, 2-b] thiophene] -3, 3', 6, 6'-tetracarboxylate 20. To a two-neck flask equipped with a condenser were added 19 (362 mg, 0.5 mmol) , 18 (640 mg, 2 mmol) , Pd (PPh₃) ₂Cl₂ (60 mg) , 20 mL dry toluene and 1 mL DMF. The reaction mixture was refluxed under argon for 48 h. After cooling to room temperature, the solvent was removed under reduced pressure. The crude product was purified by column chromatography on silica gel with petroleum ether: ethyl acetate (4: 1) as the eluent to give 20 as a yellow solid (241 mg, 55 ％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.63-7.61 (d, 2H) , 7.46-7.44 (d, 2H) , 4.31-4.24 (m, 8H) , 4.22-4.17 (q, 4H) , 1.27-1.23 (m, 12H) , 1.19-1.16 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 162.51， 161.48, 161.43, 143.56, 142.36, 139.19, 138.29, 137.90, 132.51, 129.66, 126.44, 124.03, 123.67, 61.27, 61.24, 60.65, 14.02, 14.00, 13.91.

Synthesis of 5, 5'-bis (3-carboxythiophen-2-yl) - [2, 2'-bithieno [3, 2-b] thiophene] -3, 3', 6, 6'-tetracarboxylic acid 21. To a solution of 20 (831 mg, 0.95 mmol) in 20 mL THF were added NaOH (430 mg) , 20 mL EtOH (20 mL) , and 5 mL H₂O. The mixture was refluxed for overnight and then cooled to room temperature. The solvent was removed under reduced pressure. The remaining solid was dissolved in 100 mL H₂O and acidified with 6 M HCl (aq) , and the resulting pale yellow precipitate (637 mg, 90％) was isolated by filtration. ¹H NMR (400 MH_Z, DMSO-d₆) δ： 7.80-7.79 (d, 2H) , 7.51-7.50 (d, 2H) . ¹³C NMR (100 MHz, DMSO-d₆) δ： 163.83， 163.00， 162.93， 143.06, 141.50, 138.55, 138.25, 137.48, 133.59, 130.20, 128.38, 125.39, 124.69.

Synthesis of compound 22. Compound 21 (637 mg, 0.9 mmol) was stirred in 20 mL acetic anhydride under reflux for 12 h. After cooling to room temperature, the solid was collected by filtration, washed with methanol, and dried in vacuum overnight to afford a dark red solid (580 mg, 98％) as the product 22, which will be used for the following reaction without further purification.

Synthesis of compound 23. To a solution of 22 (391.2 mg, 0.6 mmol) in 80 mL dichloromethane was added a solution of 2-octyldodecyl amine (536.4 mg, 1.8 mmol) in 30 mL dichloromethane dropwise. After addition, the reaction solution was stirred under reflux overnight. Upon the removal of solvent, 20 mL thionyl chloride was added, and the reaction mixture was refluxed for overnight. The excess thionyl chloride was removed under reduced pressure and the residue was purified by column chromatography on silica gel using petroleum ether: dichloromethane (1: 1) as the eluent to give 23 as a dark red solid (460 mg, 49.6％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.52-7.51 (d, 2H) , 7.05-7.04 (d, 2H) , 4.43-4.42 (d, 2H) , 4.34-4.32, (d, 4H) , 2.16 (s, 1H) , 2.03 (s, 2H) , 1.43-1.26 (m, 96H) , 0.88-0.83 (m, 18H) . ¹³C NMR (100 MHz, CDCl₃) δ： 160.89， 160.16， 159.98， 140.77, 140.51, 138.58, 138.13, 137.04, 133.87, 133.44, 124.73, 124.21, 123.79, 49.81, 49.49, 36.45, 36.19, 31.98, 31.83, 31.74, 30.39, 30.34, 29.83, 29.80, 29.77, 29.75, 29.71, 29.47, 29.44, 29.41, 26.57, 22.71, 22.70, 14.13, 14.10. Calcd MW for C₈₆H₁₂₈O₆N₃S₆: 1490.8122. Found: HRMS, 1490.8112. MALDI-TOF, 1490.273. Elem. Anal. calcd. for C₈₆H₁₂₈O₆N₃S₆: C, 69.26； H, 8.58； N, 2.82； S, 12.90； Found: C, 69.14； H, 8.88； N, 2.77； S, 12.57.

Synthesis of diethyl 2, 5-bis (trimethylstannyl) thieno [3, 2-b] thiophene-3, 6-dicarboxylate 24. To a solution of diisopropyl amine (1.73 mL, 12 mmol) in 100 mL dry THF at -78 ℃ was added n-BuLi (2.4 M in hexane； 5 mL, 12 mmol) dropwise under argon to yield lithiumdiisopropylamide (LDA) . A solution of 3 (1.42 g, 5 mmol) in 10 mL dry THF was then added dropwise over 20 min and the resulting solution was stirred at -78 ℃ for 1 h. To the mixture was added trimethyltinchloride (1.0 M in hexane, 12 mL, 12 mmol) in one portion at -78 ℃. Then, the cooling bath was removed, and the mixture was gradually warmed to room temperature. After stirring for 4 h, the reaction mixture was quenched with H₂O. The solvent was removed under reduced pressure, and the crude product was purified by recrystallization using hexane to give 24 as a brown solid (2.2 g, 72 ％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 4.48-4.42 (q, 4H) , 1.49-1.46 (t, 6H) , 0.53-0.38 (t, 18) . ¹³C NMR (100 MHz, CDCl₃) δ： 163.35， 156.51, 146.50, 130.25, 61.17, 14.49, -7.19.

Synthesis of hexaethyl [2, 2': 5', 2”-terthieno [3, 2-b] thiophene] -3, 3', 3”, 6, 6', 6”-hexacarboxylate 25. To a two-neck flask equipped with a condenser was added 24 (2.13 g, 3.5 mmol) , 4 (3.8 g, 10.5 mmol) , Pd (PPh₃) ₂Cl₂ (122 mg) , 50 mL dry toluene, and 5 mL DMF. The reaction mixture was refluxed under argon for 48 h. After cooling to room temperature, the solvent was removed under reduced pressure. The crude product was purified by column chromatography on silica gel using dichloromethane as the eluent to give 25 as a pale yellow solid (1.2 g, 40％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 8.32 (d， 2H) ， 4.48-4.43 (q, 4H) , 4.32-4.24 (m, 8H) , 1.48-1.45 (t, 6H) , 1.28-1.20 (m, 12H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.67， 161.49， 161.33， 143.01， 142.44， 139.45， 138.24， 137.22, 136.33, 125.86, 124.45, 124.06, 61.42, 61.31, 61.24, 14.36, 14.00, 13.94.

Synthesis of

hexaethyl

5, 5”-dibromo- [2, 2': 5', 2”-terthieno [3, 2-b] thiophene] -3, 3', 3”, 6, 6', 6”-hexacarboxylate 26. To a solution of 25 (1.1 g, 1.3 mmol) in 50 mL chloroform were added Br₂ (416 mg, 2.6 mmol) and iron (III) chloride (2 mg) , successively. The reaction mixture was stirred in the dark for 12 h at room temperature. Na₂SO₃ aqueous solution was added to the reaction mixture and stirred for 30 minutes. Then the solvent was removed under reduced pressure to afford a pale yellow solid, which was purified by column chromatography on silica gel using dichloromethane as the eluent to give product 26 (1.3 g, 99％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 4.51-4.46 (q, 4H) , 4.31-4.24 (m, 8H) , 1.51-1.47 (t, 6H) 1.28-1.21 (m, 12H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.31， 161.21， 160.81, 142.29, 141.66, 138.40, 137.42, 136.89, 124.54, 124.12, 123.98, 123.63, 61.78, 61.45, 61.39, 14.29, 14.02, 13.99.

Synthesis of

hexaethyl

5, 5”-bis (3- (ethoxycarbonyl) thiophen-2-yl) - [2, 2': 5', 2”-terthieno [3, 2-b] thiophene] -3, 3', 3”, 6, 6', 6”-hexacarboxyl ate 27. To a two-neck flask equipped with a condenser, was added 26 (1.31 g, 1.3 mmol) , 18 (1.65 g, 5.2 mmol) , Pd(PPh₃) ₂Cl₂ (46 mg) , 50 mL dry toluene, and 2 mL DMF. The reaction mixture was then refluxed under argon for 48 h. After cooling to room temperature, the solvent was removed under reduced pressure and the ccrude product was purified by column chromatography on silica gel using dichloromethane as the eluent to give product 27 as a pale yellow solid (630 mg, 41 ％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.63-7.62 (d, 2H) , 7.46-7.45 (d, 2H) , 4.32-4.25 (m, 12H) , 4.23-4.18 (q, 4H) , 1.28-1.23 (m, 18H) , 1.20-1.16 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 162.51, 161.48, 161.42, 161.40, 143.62, 142.76, 142.23, 139.18, 138.42, 138.34, 137.89, 132.51, 129.67, 126.47, 124.07, 123.66, 61.36, 61.32, 61.26, 60.66, 14.21, 14.04, 14.02, 13.92.

Synthesis of 5, 5”-bis (3-carboxythiophen-2-yl) - [2, 2': 5', 2”-terthieno [3, 2-b] thiophene] -3, 3', 3”, 6, 6', 6”-hexacarboxylic acid 28. To a solution of 27 (578.5 mg, 0.5 mmol) in 20 mL THF were added NaOH (800 mg) , EtOH (20 mL) and 5 mL H₂O. The mixture was refluxed for overnight. The reaction was then cooled to room temperature, and the solvent was removed under reduced pressure. The remaining solid was dissolved in 100 mL H₂O and acidified with 6M HCl (aq) , and the resulting brown precipitate 28 (460 mg, 99％) was isolated by filtration. ¹H NMR (400 MH_Z, DMSO-d₆) δ： 7.80-7.79 (d, 2H) , 7.51-7.50 (d, 2H) . ¹³C NMR (100 MHz, DMSO-d₆) δ： 163.83， 163.00， 162.92, 143.10, 141.98, 141.34, 138.53, 138.31, 138.19, 137.47, 133.59, 130.21, 128.42, 125.45, 124.69.

Synthesis of compound 29. Compound 28 (460mg, 0.5 mmol) was stirred in 25 mL acetic anhydride under reflux for 12 h. After cooling to room temperature, the solid was collected by filtration, washed with methanol, and dried in vacuum overnight. The resulting dark brown solid 29 (420 mg, 98％) was used for the following reaction without further purification.

Synthesis of compound 30. To a solution of 29 (129 mg, 0.15 mmol) in 150 mL dichloromethane was added a solution of 2-octyldodecyl amine (178.5 mg, 0.6 mmol) in 30 mL dichloromethane dropwise. After addition, the reaction mixture was stirred under reflux for overnight. Upon the removal of solvent, 10 mL thionyl chloride was added and the mixture was refluxed for overnight. The excess thionyl chloride was removed under reduced pressure and the resulting residue was purified by column chromatography on silica gel using petroleum ether: dichloromethane (2: 3) as the eluent to give product 30 as a dark purple solid (110 mg, 37％) . ¹H NMR (400 MH_Z, C₂D₂Cl₄, 120 ℃) δ： 7.72 (d, 2H) , 7.23 (d, 2H) , 4.59-4.57 (d, 4H) , 4.47-4.46 (d, 4H) , 2.27 (s, 2H) , 2.21 (s, 2H) , 1.57-1.38 (m, 128H) , 0.98-0.96 (m, 24H) . Calcd MW for C₁₁₄H₁₆₈O₈N₄S₈: 1978.0701. Found: HRMS, 1978.0726. MALDI-TOF, 1978.066. Elem. Anal. calcd. for C₁₁₄H₁₆₈O₈N₄S₈: C, 69.19； H, 8.56； N, 2.83； S, 12.96； Found: C, 69.25； H, 8.34； N, 2.81； S, 12.46.

Synthesis of tetraethyl 5-bromo- [2, 2'-bithieno [3, 2-b] thiophene] -3, 3', 6, 6'-tetracarboxylate 6. To a solution of 5 (1.98 g, 3.5 mmol) in 50 mL chloroform were added Br₂ (560 mg, 3.5 mmol) and iron (III) chloride (6 mg) , successively. The Br₂ addition was completed in five times by partly quantitative injection. The reaction mixture was stirred in dark for 12 h at room temperature. Na₂SO₃ aqueous solution was then added to the reaction mixture and stirred for 0.5 h. Then the solvent was removed under reduced pressure to afford a yellow solid, which was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (4: 1) as the eluent to give product 6 (1.16 g, 51％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 8.32 (s, 1H) , 4.49-4.42 (m, 4H) , 4.28-4.23 (m, 4H) , 1.49-1.44 (m, 6H) 1.23-1.20 (m, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.65， 161.45， 161.22， 160.77， 142.07， 142.02, 139.40, 137.32, 137.20, 136.76, 136.34, 125.84, 124.44, 124.43, 123.93, 123.60, 61.72, 61.43, 61.37, 61.24, 14.35, 14.26, 13.95, 13.92.

Synthesis of octaethyl [2, 2': 5', 2”: 5”, 2”'-quaterthieno [3, 2-b] thiophen] -3, 3', 3”, 3”', 6, 6', 6”, 6”'-octacarboxylate 7. To a solution of 6 (1.74 g, 2.7 mmol) in 15 mL DMF was added Ni (COD) ₂ (409 mg, 1.49 mmol) in one portion under nitrogen. The reaction mixture was heated at 50 ℃ for 12 h. Then the solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (3:1) as the eluent to give product 7 as a pale yellow solid (1.4 g, 91％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 8.32 (s， 2H) , 4.47-4.42 (m, 4H) , 4.32-4.25, (m, 12H) , 1.48-1.43 (t, 6H) , 1.28-1.21 (m, 18H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.68， 161.51， 161.37， 161.35， 143.06， 142.63， 142.40， 139.45， 138.36， 137.22， 136.39， 125.84， 124.45， 124.12, 124.06, 61.45, 61.38, 61.36, 61.27, 14.37, 14.02, 13.96.

Synthesis of

octaethyl

5, 5”'-dibromo- [2, 2': 5', 2”: 5”, 2”'-quaterthieno [3, 2-b] thiophen] -3, 3', 3”, 3”', 6, 6', 6”, 6”'-octacarboxylate 8. To a solution of 7 (1.4g, 1.23 mmol) in 50 mL chloroform were added Br₂ (787.2 mg, 4.92 mmol) and iron (III) chloride (4 mg) , successively. The reaction mixture was stirred in dark for 12 h at room temperature. Na₂SO₃ aqueous solution was added to the reaction mixture and stirred for 0.5 h. Then the solvent was removed under reduced pressure to afford a yellow solid, which was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (3: 1) as the eluent to give product 8 (1.37 g, 86.4％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 4.51-4.46 (q, 4H) , 4.33-4.25 (m, 12H) , 1.51-1.48 (t, 6H) 1.29-1.22 (m, 18H) . ¹³C NMR (100 MHz, CDCl₃) δ： 161.33, 161.22, 160.80, 142.66, 142.29, 141.67, 138.44, 138.43, 137.44, 136.90, 124.52, 124.14, 124.01, 123.64, 61.77, 61.45, 61.40, 14.29, 14.03, 13.98.

Synthesis of

octaethyl

5, 5”'-bis (3- (ethoxycarbonyl) thiophen-2-yl) - [2, 2': 5', 2”: 5”, 2”'-quaterthieno [3, 2-b] thiophen] -3, 3', 3”, 3”', 6, 6', 6”, 6”'-octacarboxylate 9. To a two-neck flask equipped with a condenser was added 8 (1.29 g, 1 mmol) , 18 (1.28 g, 4 mmol) , Pd (PPh₃) ₂Cl₂ (70 mg) , 40 mL dry toluene, and 3 mL DMF. The reaction mixture was refluxed under argon for 48 h. After cooling to room temperature, the solvent was evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel using petroleum ether: ethyl acetate (3: 1) as the eluent to give product 9 as a yellow solid (480 mg, 33.3 ％) . ¹H NMR (400 MH_Z, CDCl₃) δ： 7.63-7.62 (d, 2H) , 7.46-7.45 (d, 2H) , 4.34-4.27 (m, 16H) , 4.25-4.18 (q, 4H) , 1.30-1.24 (m, 24H) , 1.20-1.17 (t, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ： 162.52， 161.49， 161.42， 161.40， 161.39， 143.63， 142.82， 142.63， 142.21， 139.17， 138.48， 138.42， 138.36, 137.90, 132.52, 129.66, 128.30, 126.48, 124.24, 124.09, 123.68, 61.39, 61.39, 61.33, 61.26, 60.67, 14.04, 14.01, 13.92.

Synthesis of 5, 5”'-bis (3-carboxythiophen-2-yl) - [2, 2': 5', 2”: 5”, 2”'-quaterthieno [3, 2-b] thiophen] -3, 3', 3”, 3”', 6, 6', 6”, 6”'-octa carboxylic acid 10. To a solution of 9 (431.7 mg, 0.3 mmol) in 20 mL THF were added NaOH (500 mg) , 20 mL EtOH, and 6 mL H₂O. The mixture was refluxed for overnight. Then the reaction was cooled to room temperature, the solvent was evaporated under reduced pressure. The remaining solid was dissolved in 100 mL H₂O, acidified with 6 M HCl (aq) , and the resulting brown precipitate (340 mg, 97％) was isolated by filtration as the product 10. ¹H NMR (400 MH_Z, DMSO-d₆) δ： 7.81-7.79 (d, 2H) , 7.52-7.50 (d, 2H) . ¹³C-NMR (100 MHz, DMSO-d₆) δ： 163.84, 163.01, 162.93, 143.12, 142.04, 141.86, 141.35, 138.53, 138.32, 138.27, 138.22, 137.49, 133.60, 130.22, 128.41, 125.53, 125.48, 125.46, 124.70.

Synthesis of compound 11. ^aCompound 10 (340 mg, 0.29 mmol) was stirred in 20 mL acetic anhydride under reflux for 12 h. After cooling to room temperature, the solid was collected by filtration, washed with methanol, and dried in vacuum overnight. The resulting black solid 11 (282 mg, 90％) was used for the following reaction without further purification.

Synthesis of compound 12. To a solution of 11 (128 mg, 0.12 mmol) in 80 mL toluene was added a solution of 2-octyldodecyl amine (178 mg, 0.6 mmol) in 30 mL toluene dropwise. After addition, the reaction solution was stirred under reflux for overnight. Upon the removal of solvent under reduced pressure, 10 mL thionyl chloride was added and the mixture was refluxed for overnight. The excess thionyl chloride was then removed under reduced pressure and the residue was purified by column chromatography on silica gel using petroleum ether: dichloromethane (2: 3) as the eluent to give product 12 as a dark purple solid (60 mg, 20％) . ¹H NMR (400 MH_Z, C₂D₂Cl₄, 120 ℃) δ： 7.62 (d, 2H) , 7.11 (d, 2H) , 4.58 (d, 6H) , 4.47 (d, 4H) , 2.30 (d, 2H) , 2.19 (d, 3H) , 1.4 (m, 160 H) , 0.97-0.96 (m, 30H) . Calcd MW for C₁₄₂H₂₀₉O₁₀N₅S₁₀: 2465.3279. Found: HRMS, 2465.3354. MALDI-TOF, 2465.656. Elem. Anal. calcd. for C₁₄₂H₂₀₉O₁₀N₅S₁₀: C, 69.14； H, 8.54； N, 2.84； O, S, 13.00； Found: C, 69.42； H, 8.31； N, 2.81； S, 12.53.

NMR Spectra of the inventive Compounds.

See Figures 6 and 7.

Example 2. Synthesis of monomer.

To a solution of BTI3 (1.49g, 1.0 mmol) in 50 mL chloroform were added Br₂ (320 mg, 2.0 mmol) and iron (III) chloride (4 mg) , successively. The reaction mixture was stirred in dark for 12 h at room temperature. Na₂SO₃ aqueous solution was added to the reaction mixture and stirred for 0.5 h. Then the solvent was removed under reduced pressure to afford a yellow solid, which was purified by column chromatography on silica gel using petroleum ether: dichloromethane (2: 1) as the eluent to give product 8 (1.5 g, 90％) .

Synthesis of P1.

To an dry glass tube was charged monomer (0.2 mmol ) , tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) , and tris (o-tolyl) phosphine (P (o-tolyl) 3) (1: 8, Pd2 (dba) 3: P (o-tolyl) 3 molar ratio； Pd loading: 0.03 equiv) . The tube and its contents were subjected to 3 pump/purge cycles with argon, followed by the addition of anhydrous toluene (4-5 mL) via syringe. The tube was sealed under argon flow and then stirred at 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation. Then, 0.05 mL 2- (tributylstanny) thiophene was added and the reaction mixture was stirred under microwave irradiation at 140 ℃ for 0.5 h. Finally, 0.10 mL 2-bromothiophene was added and the reaction mixture was stirred at 140 ℃ for another 0.5 h. After cooling to room temperature, the reaction mixture was dripped into 100 mL methanol containing 1 mL 12 N HCl under vigorous stirring. After stirring for 1 h, the polymer precipitate was transferred to a Soxhlet thimble. After drying, the crude product was subjected to sequential Soxhlet extraction with the solvent combinations depending on the solubility of the particular polymer. After the extraction with the final solvent, the polymer solution was concentrated to ～6 mL, and then dripped into 100 mL methanol under vigorous stirring. The polymer was collected by filtration and dried under reduced pressure to afford a deep colored solid as the product.

Physical characterization:

Example 3. Physical characterization of BTI-BTI5.

The optical properties of these ladder-type arenes are investigated by measuring their absorption spectra of solution and thin films and the spectra are shown in Figure 1. The onsets of absorption in CH₂Cl₂ solutions (Figure 1) are gradually bathochromically shifted from 392 nm for BTI to 643 nm for BTI5. The films of these BTI derivatives show similar transition and the optical bandgaps decrease with increasing backbone length. Among the series, BTI5 shows the smallest bandgap of 1.90 eV. From solution to film, all arenes exhibit similar absorption profiles with comparable absorption onsets and peaks, especially for the longer BTI4 and BTI5, which indicate comparable backbone conformation in solution and film enabled by the ladder-type backbone. The extrapolated limit of bandgap is ～1.7 eV, showing the good tunability from wide to medium bandgaps. Thermal properties of these ladder-type materials are investigated by thermogravimetric analysis (TGA) and the TGA curves show excellent thermal stability (Figure 2) with the decomposition temperatures typically larger than ～450 ℃ except BTI. Hence as the conjugation length is increased, the thermal stability is enhanced and then saturated for these ladder-type BTI derivatives.

Electrochemical properties of these ladder-type BTI derivatives were investigated by cyclic voltammetry (CV) referencing to a ferrocene/ferrocium (Fc/Fc+) internal standard (Figure 3) . The onsets of reduction potentials are -2.07, -1.46, -1.21, -1.10, and -0.81 V for BTI, BTI2, BTI3, BTI4, and BTI5, respectively. Hence with the extension of π-conjugated systems, the derived LUMOs of these ladder-type molecules are gradually decreased from -2.29 eV for BTI to -3.55 eV for BTI5, indicating increased electron affinity. The gradual decrement trend of LUMOs are in good accord with the results from theoretical calculation, where a stabilization of ～1 eV is recorded ongoing from BTI to BTI5. The CV data render similar HOMO levels for all BTI derivatives, while a destabilization of the HOMO level of ～0.6 eV is found theoretically from BTI to BTI5. Nevertheless, it seems to be less affected than LUMO with chain lengthening. The results indicate that the bandgap lowering is mainly attributed to the decreased LUMOs of the BTI derivatives with extended conjugation. That contrasts from previous reports where the bandgap lowering is mainly contributed from the HOMO or both HOMO and LUMO in these kinds of ladder-type arenes.

Fabrication and Characterization of Organic Thin-Film Transistors:

Example 4. Organic Thin-Film Transistors of BTI5.

Top-gate bottom-contact OTFTs were fabricated to investigate the potential applications of these building blocks in organic electronics and BTI5 was chosen as the active layer due to its longest backbone and appropriately lying frontier molecular orbitals in the series. The OTFTs show predominant electron transporting characteristics and the representative output and transfer curves are shown in Figure 4. The highest electron mobilities (μ_es) of 0.014 and 0.010 cm²V^-1s^-1 are extracted in the saturation and linear regimes, respectively, and the corresponding average μ_es are 0.013 and 0.0094 cm²V^-1s^-1. The transfer curve of the transistors shows “kink-free” feature, indicative of the reliability of these mobilities. The typical threshold voltages (V_T) are 25-30 V and the current modulation ratios (I_on/I_offs) in the linear region are ～10⁶ with the highest approaching 10⁷, which is benefited from the low off-current (10^-11-10^-12A) . The BTI5 film microstructure and morphology are characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM) . Both XRD data and AFM images (Figure 5) reveal high crystallinity of the BTI5 film. It should be pointed out that the readily soluble BTI5 contains very bulky 2-octyldodecyl side chains, which are likely detrimental to the packing of the molecules, thus with side chain engineering and more intensive device optimization, further improved OTFT performance can be expected.

Claims

A series of compounds having a formula as：

wherein

each A is independently selected from the group consisting of H, F, Cl, CN, CF₃, and following formula:

each B is independently selected from the group consisting of H, F, Cl, CN, CF₃, and following formula:

each R is an alkyl selected from the following formula:
Compounds of claim 1, wherein each R is an alkyl selected from the following formula:
A series of compounds having a formula as：

wherein each R is independently selected from the following formula:
The compound of claim 3， wherein each π is individually selected from the following formula:

wherein each R is C1-20 alkyl independently.
Use of the compounds according to claim 1 to 4 in thin-film transistor or polymer solar cell.