WO2019037107A1

WO2019037107A1 - A novel imide building block, a copolymer thereof and their preparation methods, as well their uses in organic semiconductor devices

Info

Publication number: WO2019037107A1
Application number: PCT/CN2017/099122
Authority: WO
Inventors: Xugang GUO; Yongqiang Shi; Han GUO; Yuxi Wang; Jiuyang ZHAO
Original assignee: South University Of Science And Technology Of China
Priority date: 2017-08-25
Filing date: 2017-08-25
Publication date: 2019-02-28

Abstract

The invention relates to organic and polymeric semiconductor filed, in particular to a novel imide building block, a copolymer thereof and their preparation methods, as well their uses in organic semiconductor devices.

Description

A Novel Imide Building Block, A Copolymer Thereof And Their Preparation Methods, As Well Their Uses In Organic Semiconductor Devices

FIELD

BACKGROUND

Organic and polymeric semiconductors have attracted a great deal of attention from both academia and industry in the last two decades due to their applications in various opto-electrical devices, such as organic light-emitting diodes (OLEDs), organic thin-film transistors (OTFTs), and organic solar cells (OSCs) .

In comparison to the conventional inorganic-based semiconductors, organic semiconductors demonstrate great advantages, showing solution-based processability, enabling device fabrication in cost-effective and high throughput fashion, and affording devices with new functionalities and features, such as light-weight and mechanical flexibility/strechability. The advancement of organic electronics field is mainly driven by materials development, which highly relies on the design and synthesis of novel building blocks with favored geometries and well-tailored opto-electrical properties. Their incorporation in to conjugated backbones leads to the resulting semiconductors with precisely controlled physicochemical property, favored self-assembly characteristics, and desired film morphology and microstructure. Therefore, materials innovation combined with device engineering greatly improved the OTFT performance in the last decade. In spite of the remarkable progress in organic electronics, the device performance of n-type semiconductors lags behind that of p-type materials and organic semiconductors with large electron mobility and good device air-stability are essential for the implementation of p-n junction and as the electron-acceptor layer in solar cells.

The development of high-performance n-type semiconductors highly relies on the innovation of electron-deficient units with optimized geometry and favorable physicochemical property. Among various electron-deficient building blocks reported to date, diimide-functionalized arenes show remarkable success for enabling high-performance organic semiconductors. The incorporation of naphthalene diimide (NDI) and perylene diimide (PDI) results in a large number of n-type polymer semiconductors with the most promising device performance in both OTFTs and OSCs. Monoimide-functionalized arenes, such as thieno [3, 4-c] pyrrole-4, 6-dione (TPD), lead to the resulting polymers with highly promising p-channel performance in OTFTs and remarkable power conversion efficiencies (PCEs) as the electron-donor layer in OSCs. In spite of its great success in organic electronics, TPD is mainly used for constructing p-type semiconductors. In order to achieve n-channel performance, the TPD homopolymers are synthesized, however the polymers show limited conjugation and amorphous film morphology, hence the polymers are inactive in OTFTs. For alleviating the steric and/or electronic repulsion between the consecutive building blocks, Marks and co-workers designed and synthesized a novel electron-deficient N-alkyl-2, 2'-bithiophene-3, 3'-dicarboximide (a.k.a. bithiophene imide, BTI, ) with highly planar backbone, close intermolecular stacking, high electron-deficiency, and good materials solubilities. Although BTI has shown great success for enabling high-performance polymer semiconductors with tunable charge carrier polarity in OTFTs, the electron-rich character of thiophene core can lead to BTI and the derived polymer semiconductors with high-lying frontier molecular orbitals (FMOs) , which are detrimental to the transistor stability and limit the open-circuit voltages in solar cells. Through a variety of materials and device characterization techniques, the chemical structure-materials property-device performance correlations of these novel imide-functionalized thiazole-based polymer semiconductors are elucidated, which afford useful insights into materials innovation in organic electronics.

SUMMARY

In order to promote n-channel performance in OTFTs, less electron rich group or more electron-deficient group is need to lower the FMOs without sacrificing good solubility, close packing and so on. The present invention provides the design and synthesis of the novel imide-functional unit and that its incorporation into copolymers affords semiconductors with good solubilizing ability, extended π conjugation length, close π-π stacking, and appropriate electron withdrawing ability and lower-lying FMOs.

In order to achieve this purpose, the present invention employs the following technical solutions:

The novel imide-functional unit of Formula I:

Formula I

wherein

R is a straight or branched alkyl, preferably having 2-30 carbon atoms, and more preferably having 7-24 carbon atoms,

X₁ is O, S or Se atom',

X₂ is O or S atom,

Y₁ is H or N, atom, and

Y₂ is N atom.

The detailed structures are as follows:

wherein R is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms.

To verify the above materials design strategy, The 2, 5-bis (trimethylstanny) thiophene and 3, 4-difluoro-2, 5-bis (trimethylstanny) thiophene are chosen as the electron-rich comonomers due to the smallest thiophene number, which should lead to lower-lying FMOs, thus suppress p-channel performance, and promote n-channel characteristics in OTFTs. It will be seen that the resulting DTzTI-based polymers exhibit promising device performance in n-channel organic thin-film transistors, with electron mobility (μ_e) up to 1 cm² V^-1 s^-1 and current modulation ratio (I_on/I_off) of 10⁶-10⁷. These results demonstrate that DTzTI is an efficient building block for enabling polymer semiconductors with unipolar n-channel OTFT performance. Materials structure-property-device performance correlations are established here, and offer useful insights into organic electronics materials design. We believe that more promising performance can be realized by optimizing the chemical structures of DTzTI-based materials.

DTzTI

Compared to the BTI unit, the imide-functional unit bithiazole imide (BTzI) or thienylthiazole imide dimer (DTzTI) replaces the thiophene moiety, which should lower the HOMO level and suppress p-channel performance in OTFTs for the resulting polymers. Combining the advantages of TPD and BTI by attaching additional thiazole group, the new building block BTzI and DTzTI should lead to the derived polymer semiconductors with lower-lying FMOs versus the polymer analogues based on the amide-functionalized BTzI and DTzTI. Single crystal structure of BTzI and DTzTI indicates that the imide-functional unit features a high degree of planarities having a small dihedral angle of 1.38° and 5.91°. between the two thiazole planes and between the thiazole and thiophene, respectively. The angle is comparable to that (4.32°) between the two thiophene planes in the previously reported BTI model compound. The flanked thiophenes with the central BTzI in the model compound BTzI-C6-2T show small torsion angles (2-6°, b) , the distances between the S atom of thiophene and the N atom of thiazole are

and

Both distances are smaller than the sum

of the van der Waals radii of these two atoms, which in combination with the smaller torsion angles indicates intramolecular non-covalent interaction between the S atom of thiophene and the N atom of thiazole. The non-covalent N…Sinteraction can lock the backbone to achieve a highly planar conformation in polymer semiconductors. In addition, the dithiazole imide cores in the model compound BTzI-C6-2T exhibit very short π-stacking distances of 3.23 or

depending on the stacking directions (c), which are greatly smaller than that

in the BTI-based analogous model compound. The highly planar backbone in combination with the close intermolecular interaction should be beneficial to polymer chain packing. The distance between N and S atoms is

in the model compound DTzTI-C8 (e) , and such non-covalent N…S interaction leads to completely planar backbone, showing a torsion angle of 180° between two neighboring thienylthiazole imides. This is due to two N…S interactions between the two neighboring thiazoles. In addition, DTzTI-C8 also exhibits a close intermolecular π-stacking distance of ～

(2f) . On the basis of the single crystal structures of the model compounds, both BTzI and DTzTI feature highly planar cores with close intermolecular π-stacking distance. The thiazole leads to the new building blocks with reduced steric hindrance with the neighboring arenes due to the replacement of C-H with N. In addition, the heteroatom N on the thiazole moiety promotes intramolecular non-covalent N…S interaction and such conformation locks are beneficial to polymer backbone planarity and charge carrier delocalization Such close intermolecular π-π stacking is beneficial to intermolecular charge transport. See Fig. 2.

In another aspect, the present invention provides copolymers of the electron-deficient building block described herein as follows:

In another aspect, the present invention provides a preparation method of the imide-functional unit of Formula I:

(1) adding Methyl 5-bromothiazole-4-carboxylate, methyl 2- (trimethylstannyl) thiophene-3-carboxylate， an organic solvent into a reaction vessel, and purging the mixture with an inert gas；

(2) adding Pd (PPh₃) ₄ and then purging an inert gas, heating the mixture to 80-140℃；

(3) adding alkali carbonate, an organic solvent or water to the mixture and refluxing the mixture at 40-90℃；

(4) adding SOCl₂ into a reaction vessel；

(5) adding alkyl amine and heating the mixture to 140-160 ℃；

(6) adding LiHMDS and BrCCl₂CCl₂Br at -78℃；

(7) extracting the reaction mixture and washing；

(8) concentrating the organic layer and purifying to give the imide-functional unit.

Preferably, on the basis of the technical solution provided by the present invention, in step (1), the mole ratio of the Methyl 5-bromothiazole-4-carboxylate to methyl 2- (trimethylstannyl) thiophene-3-carboxylate is 1: 2-4, preferably 1: 2.2-3, more preferably 1: 2.5；

preferably, the ratio of the organic solvent to the Methyl 5-bromothiazole-4-carboxylate is 2-10 mL/mmol, preferably 3-7 mL/mmol；

preferably, the organic solvent is selected from THF, DMF, toluene or a mixture thereof；

preferably, time of the purging is more than 10 minutes, preferably more than 20 minutes, more preferably 30 minutes；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture thereof；

preferably, in step (2), the mole ratio of the Pd (PPh₃) ₄ to Methyl 5-bromothiazole-4-carboxylate is 1: 5-20, preferably 1: 8-15, more preferably 1: 10；

preferably, time of the purging is more than 5 minutes, preferably more than 10 minutes, more preferably 20 minutes；

preferably, the mixture is heated to 80-140 ℃； preferably to 140 ℃；

preferably, the heating is conducted under microwave irradiation；

preferably, in step (3), preferably, the alkali carbonate is selected from K₂CO₃, Na₂CO₃, Li₂CO₃, LiOH, NaOH, KOH or a mixture thereof；

preferably, the organic solvent is selected from THF, EtOH, dioxane, DMF or a mixture thereof；

preferably, the mixture is refluxed at 70 ℃；

preferably, in step (4) , the ratio of SOCl₂ is 1-5 mL/mmol, preferably 2-4 mL/mmol；

preferably, the ratio of alkyl amine to chlorocarbonyl is 1: 1.5, preferably 1: 1, more preferably 1: 0.7；

preferably, the mixture is heated to 140-160 ℃； preferably to 150 ℃；

preferably, in step (6) , the mixture is cooled to -80 ℃； preferably to -78 ℃；

preferably, in step (7) , the reaction mixture is extracted with an organic solvent, preferably with DCM；

preferably, the washing is conducted with water and brine；

preferably, in step (8) , the concentrating is conducted under reduced pressure；

preferably, the purifying is conducted by column chromatography using petroleum ether as an eluent；

preferably, R in the imide-functional unit of Formula I is a branched alkyl.

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

(1) adding the imide-functional unit of claim 1, an aromatic unit material, tris (di-benzylideneacetone) 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) 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；

(6) after the extracting, concentrating the polymer solution, and then being dripped into methanol, collecting the solid and drying to obtain the copolymer.

Preferably, the mole ratio of the electron-donating unit of the invention to the aromatic unit material is 1: 0.5-2, for example, 1: 0.8, 1: 1.2, 1: 1.8 and so on, preferably 1: 0.8-1.5, more preferably 1: 1.

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.

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 thereof.

Preferably, in step (2) , the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture thereof.

Preferably, the organic solvent is selected from any one of anhydrous toluene, benzene, chlorobenzene, DMF, or a mixture thereof.

Preferably, the ratio of the organic solvent to the electron-donating unit is 10-75 mL/mmol, preferably 5-50 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 under microwave irradiation.

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 under microwave irradiation.

Preferably, the heating is conducted under microwave irradiation at 140 ℃ for 0.5 h, then adding 2-bromothiophene and stirring the reaction mixture at 140 ℃ for another 0.5 h.

Preferably, the mole ratio of the 2- (tributylstanny) thiophene to the electron-donating unit is 0.1-0.5: 1, for example, 0.2: 1, 0.4: 1 and so on, preferably 0.2: 0.4-1.

Preferably, the mole ratio of the 2-bromothiophene to the electron-donating unit is 0.2-1.5: 1, for example, 0.4: 1, 0.8: 1, 1.3: 1 and so on, preferably 0.4: 0.8-1； preferably, in step (4) , the methanol contains 0.5-10mL hydrochloric acid， preferably 0.5-10mLof 5-20 mol/L hydrochloric acid.

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

Preferably, in step (6) , 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 a use of the copolymer according to the present invention in n-channel thin-film transistor.

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.

We report herein the design and synthesis of a novel imide-functionalized building block, (BTzI) or thienylthiazole imide dimer (DTzTI) replaces the thiophene moiety, which should lower the HOMO level and suppress p-channel performance in OTFTs for the resulting polymers. Combining the advantages of TPD and BTI by attaching additional thiazole group, the new building block BTzI and DTzTI should lead to the derived polymer semiconductors with lower-lying FMOs versus the polymer analogues based on the amide-functionalized BTzI and DTzTI. Single crystal structure of BTzI and DTzTI indicates that the imide-functional unit features a high degree of planarities having a small dihedral angle of 1.38° and 5.91°. between the two thiazole planes and between the thiazole and thiophene, respectively. The angle is comparable to that (4.32°) between the two thiophene planes in the previously reported BTI model compound. The flanked thiophenes with the central BTzI in the model compound BTzI-C6-2T show small torsion angles (2-6°, b) , the distances between the S atom of thiophene and the N atom of thiazole are

and

Both distances are smaller than the sum

depending on the stacking directions (c) , which are greatly smaller than that

(2f) . On the basis of the single crystal structures of the model compounds, both BTzI and DTzTI feature highly planar cores with close intermolecular π-stacking distance. The thiazole leads to the new building blocks with reduced steric hindrance with the neighboring arenes due to the replacement of C-H with N. In addition, the heteroatom N on the thiazole moiety promotes intramolecular non-covalent N…S interaction and such conformation locks are beneficial to polymer backbone planarity and charge carrier delocalization Such close intermolecular π-π stacking is beneficial to intermolecular charge transport.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1. The chemical structure of BTzI and DTzTI-based polymers.

Fig. 2. Top view (a, d) , side view (b, e) , and intermolecular arrangements (c, f) of the BTzI-C6-2T and DTzTI-C8 single crystals.

Fig. 3. Optimized geometries of BTzI and DTzTI-based polymers with 3 repeat units. The DFT calculation was performed at B3LYP/6-31G*level.

Fig. 4. The TGA curves of BTzI andDTzTI-based polymers.

Fig. 5. The DSC curves of BTzI and DTzTI-based polymers.

Fig. 6. The UV-vis absorption spectra of BTzI and DTzTI-based polymers in chloroform solution (1 × 10^-5 M) and in film states (spin coated from 5 mg mL^-1 chloroform solution) .

Fig. 7. The cyclic voltammograms of BTzI and DTzTI-based polymer films in 0.1 M (n-Bu) ₄N. PF₆ acetonitrile solution with the Fc/Fc⁺ as the internal standard.

Fig. 8. Transfer (up) and output (down) characteristics of PBTzI3T (a, f) , PBTzI3T-2F (b, g) , PDTzTIT (c, h) , PDTzTIT-2F (d, i) , and PDTzTI (e, j) of OTFTs in n-channel regime at the optimized annealing temperature (250, 220, and 250 ℃, respectively) with Au source/drain electrodes. The transfer and output characteristics of based DTzTI polymers OTFTs at the optimized annealing temperature (250 ℃) with Al source/drain electrodes, the OTFTs show unipolar n-channel performance.

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

Fig. 10: ¹³C NMR spectrum of compound 1 (r.t., in CDCl₃) .

Fig. 11: ¹H NMR spectrum of compound 3 (r.t., in CDCl₃) .

Fig. 12: ¹³C NMR spectrum of compound 3 (r.t., in CDCl₃) .

Fig. 13: ¹H NMR spectrum of compound 5 (r.t., in DMSO-d₆) .

Fig. 14: ¹³C NMR spectrum of compound 5 (r.t., in DMSO-d₆) .

Fig. 15: ¹H NMR spectrum of compound 7 (r.t., in CDCl₃) .

Fig. 16: ¹³C NMR spectrum of compound 7 (r.t., in CDCl₃) .

Fig. 17: ¹H NMR spectrum of compound 8 (r.t., in DMSO-d₆) .

Fig. 18: ¹³C NMR spectrum of compound 8 (r.t., in CDCl₃) .

Fig. 19: ¹H NMR spectrum of compound 9 (r.t., in CDCl₃) .

Fig. 20: ¹³C NMR spectrum of compound 9 (r.t., in CDCl₃) .

Fig. 21: ¹H NMR spectrum of compound 10 (r.t., in CDCl₃) .

Fig. 22: ¹³C NMR spectrum of compound 10 (r.t., in CDCl₃) .

Fig. 23: ¹H NMR spectrum of compound 13 (r.t., in CDCl₃) .

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

Fig. 25: ¹H NMR spectrum of compound 14 (r.t., in DMSO-d₆) .

Fig. 26: ¹³C NMR spectrum of compound 14 (r.t., in DMSO-d₆) .

Fig. 27: ¹H NMR spectrum of compound 16 (r.t., in CDCl₃) .

Fig. 28: ¹³C NMR spectrum of compound 16 (r.t., in CDCl₃) .

Fig. 29: ¹H NMR spectrum of compound 17 (r.t., in CDCl₃) .

Fig. 30: ¹³C NMR spectrum of compound 17 (r.t., in CDCl₃) .

Fig. 31: ¹H NMR spectrum of compound 18 (r.t., in CDCl₃) .

Fig. 32: ¹³C NMR spectrum of compound 18 (r.t., in CDCl₃) .

Fig. 33: ¹H NMR spectrum of compound 19 (r.t., in CDCl₃) .

Fig. 34: ¹³C NMR spectrum of compound 19 (r.t., in CDCl₃) .

Fig. 35: ¹H NMR spectrum of PBTzI3T (120 ℃, in C₂D₂Cl₄) .

Fig. 36: 1H NMR spectrum of PBTzI3T-2F (120 ℃, in C₂D₂Cl₄) .

Fig. 37: 1H NMR spectrum of PDTzTIT (120 ℃, in C₂D₂Cl₄) .

Fig. 38: 1H NMR spectrum of PDTzTIT-2F (120 ℃, in C₂D₂Cl₄) .

Fig. 39: 1H NMR spectrum of PDTzTI (120 ℃, in C₂D₂Cl₄) .

DETAILED DESCRIPTION

All solvents, reagents, and chemicals were commercially available and were used without further purification unless otherwise stated. Toluene and tetrahydrofuran were distilled from Na/benzophenone, and anhydrous dichloromethane and acetonitrile were distilled from CaH₂. 2, 5-Bis (trimethylstannyl) thiophene, (3, 4-difluoro-2, 5-thiophenediyl) bis [trimethylstannane] , and 2-bromothiazole, were purchased from SunaTech Inc. (Suzhou, China) . Hexabutylditin was purchased from Sigma-Aldrich. Methyl 5-bromothiazole-4-carboxylate was purchased from Shuya Pharmaceutical Technology Co., Ltd (Shanghai, China) . Unless otherwise stated, all manipulations and reactions were carried out under argon using standard Schlenk line techniques. Polymerizations were carried out on Initiator⁺ Microwave Synthesizer (Biotage, Sweden) . ¹H and ¹³C NMR spectra were recorded on a Bruker Ascend 400MHz and 500MHz spectrometer, and chemical shifts were referenced to residual protio-solvent signals. C, H, N, and S elemental analyses (EA) of monomers and polymers were performed at Shenzhen University (Shenzhen, China) . Polymer molecular weights were characterized on Polymer Laboratories GPC-PL220 high temperature GPC/SEC system (Agilent Technologies) at 150 ℃ vs polystyrene standards using trichlorobenzene as the eluent. DSC curves were recorded on a differential scanning calorimetry in nitrogen (Mettler, STARe, heating ramp: 10 ℃/min) , and TGA curves were collected on a TA Instrument (Mettler, STARe) . UV-Vis data were recorded on a Shimadzu UV-3600 UV-VIS-NIR spectrophotometer. Cyclic voltammetry measurements of polymer films were carried out under argon atmosphere using a CHI760E voltammetric analyzer with 0.1 M tetra-n-butylammonium hexafluorophosphate in acetonitrile as the supporting electrolyte. A platinum disk working electrode, a platinum wire counter electrode, and a silver wire reference electrode were employed, and the ferrocene/ferrocenium (Fc/Fc⁺) was used as the internal reference for all measurements. The scan rate was 100 mV/S. Polymer films were drop-coated from chloroform solutions on a Pt working electrode (2 mm in diameter) . The supporting electrolyte solution was thoroughly purged with argon before all CV measurements. AFM measurements of polymer films were performed by using a Dimension Icon Scanning Probe Microscope (Asylum Research, MFP-3D-Stand Alone) in tapping mode.

Molecule and Polymer Synthesis:

Scheme 1. Synthetic route to (a) the dibrominated bithiazole imide and its thiophene franked derivative and (b) the dibrominated thienylthiazole imide dimer.

Synthesis of 2- (triisopropylsilyl) thiazole (1) .

2-Bromothiazole (11.82 g, 72.0 mmol, 1 equiv) was added dropwise to n-BuLi (49.5 mL, 79.2 mmol, 1.1 equiv) in 190 mL THF at –78 ℃. The resulting solution was allowed to stir for 1 h, and then triisopropylsilyltriflate (20.0 mL, 93.6 mmol, 1.3 equiv) was added dropwise. The solution was stirred at –78 ℃ for 1 h and then allowed to warm to room temperature. The reaction was diluted with ethyl acetate and then washed with saturated NaHCO₃, and brine, dried over MgSO₄. After filtration, the reaction mixture was concentrated under reduced pressure, and the residue was purified by flash chromatography using petroleum ether as the eluent to give 2-triisopropylthiazole 1 (12.88 g, 74％) . ¹H NMR (CDCl₃, 400 MHz) δ: 8.18 (d, 1H) , 7.56 (d, 1H) , 1.53 (sept, J ＝ 7.2 Hz, 3H) , 1.16 (d, J ＝ 7.2 Hz, 18H) ； ¹³C NMR (CDCl₃, 100 MHz) δ: 169.78, 145.38, 121.03, 18.46, 11.67.

Synthesis of 2, 2'-Bis-triisopropylsilyl-4, 4'dibromo-5, 5'-bithiazole (3) .

2- (Triisopropylsilyl) thiazole 1 (16.71 g, 69.2 mmol, 1 equiv) was dissolved in 300 mL anhydrous THF under N₂ and the solution was cooled in an acetone/dry ice bath. n-Butyllithium (28.8 mL, 69.2 mmol, 1 equiv) was added dropwise to the reaction solution. The mixture became dark yellow and then precipitates formed. After 15 min stirring, Br₂ (11.06 g, 69.2 mmol, 1 equiv) was added dropwise and a yellowish solution formed. To the reaction, LDA (38.1 mL, 76.1 mmol, 1.1 equiv) was then added dropwise and the reaction mixture was stirred for 10 min and anhydrous CuCl₂ (10.23 g, 76.1 mmol, 1.1 equiv) was added to the solution. After addition of CuCl₂, the reaction mixture turned to yellow brown solution and after 2 h stirring, it was allowed to warm to room temperature. The greenish reaction mixture was diluted with 150 mL hexanes and filtered through silica gel plug using hexanes as the eluent. The solvents were removed under reduced pressure and the residual crude product was recrystallized from ethanol. After filtration, the beige plates were obtained as the target product (15.4 g, 70％) . The solvent was removed from the mother liquor and the residue was recrystallized from ethanol. Additional product was obtained (1.97 g, 9％) as the product. The whole yield for the reaction is 79％. ¹H NMR (CDCl₃, 400 MHz) δ: 1.48 (sept, J ＝ 7.5 Hz, 6H) , 1.17 (d, 36H) ； ¹³C NMR (CDCl₃, 100MHz) δ: 172.45, 130.31, 124.95, 18.44, 11.54.

Synthesis of 2, 2'-Bis-triisopropylsilyl-4, 4'-dicarboxylic acid-5, 5'-bithiazole (4) .

A solution of 3 (4.0 g, 6.26 mmol) in 60 mL anhydrous Et₂O was added dropwise to a stirring solution of n-BuLi (8.0 mL, 18.8 mmol) in 50 mL anhydrous Et₂O at -78 ℃. After the addition, the reaction was then allowed to warm to room temperature for 1 h before bone dry CO₂ was bubbled into the reaction mixture for 1 h. The solvent was then evaporated under reduced pressure. To the residual solid was added 100 mL H₂O, acidified with 6 M HCl (aq) , and filtered to afford a yellow solid, which was dried overnight in vacuum at 65 ℃ to yield the product compound 4 (yield: 95％) .

Synthesis of 4, 4'-dicarboxylic acid-5, 5'-bithiazole (5) .

A solution of 4 in diluted HCl and AcOH was heated to reflux for 3 h. The solvent was then evaporated under reduced pressure and the residue was washed with CHCl₃to yield a brown solid 5 (yield: 99％) . ¹H NMR (400 MHz, DMSO) δ: 9.25 (s, 2H) ； ¹³C NMR (100 MHz, DMSO) δ: 162.50, 155.81, 145.45, 133.46.

Synthesis of N- (2-hexyldecyl) -5, 5'-bithiazole-4, 4'-dicarboximide (7) .

A mixture of compound 5 (0.88 g, 3.44 mmol) , SOCl₂ (20 mL) , and DMF (2 drops) was heated to reflux for 8 h. The solvent was evaporated under reduced pressure to give compound 6. Then a mixture of 2-hexyldecan-1-amine (0.25 g, 2.41 mmol) and intermediate 6 was heated to 140 ℃for 3 h under N₂. The crude product was further purified by column chromatography using petroleum ether/ethyl acetate (3:1) as the eluent to give a pale yellow solid 7 (yield: 27％) . ¹H NMR (400 MHz, CDCl₃) δ: 8.91 (s, 2H) , 4.35 (d, J ＝ 7.2 Hz, 2H) , 2.04-1.95 (m, 1H) , 1.26 (b, 24H) , 0.88 (q, J ＝ 6.8 Hz, 6H) . ¹³C NMR (100 MHz, CDCl₃) δ: 160.26, 152.74, 146.59, 129.94, 50.44, 36.33, 31.93, 31.87, 31.71, 30.03, 29.71, 29.61, 29.33, 26.43, 26.39, 22.69, 22.67, 14.16.

Synthesis of N- (2-hexyldecyl) -2, 2'-dibromo-5, 5'-bithiazole-4, 4'-dicarboximide (8)

The imide 7 (184 mg, 0.57 mmol) and BrCCl₂CCl₂Br (464 mg, 1.43 mmol) was dissolved in anhydrous THF. lithium hexamethyldisilazide (LiHMDS) (1.54 mL, 2.0 mmol) was added slowly at -78℃ and stirred for 20 min under N₂. Then, to the reaction, saturated NH₄Cl aqueous solution was added. The aqueous phase was extracted with dichloromethane and the combined organic phase was evaporated to afford a yellow solid, which was further purified by column chromatography using petroleum ether/ethyl acetate (5:1) as the eluent and recrystallized from isopropanol (yield: 45％) . ¹H NMR (400 MHz, CDCl₃) δ: 4.29 (d, J ＝ 7.1 Hz, 2H) , 1.99-1.90 (m, 1H) , 1.25 (b, 24H) , 0.88 (dd, J ＝ 12.1, 6.8 Hz, 6H) . ¹³C NMR (101 MHz, CDCl₃) δ: 158.77, 145.75, 136.86, 131.87, 50.84, 36.31, 31.94, 31.87, 31.70, 30.03, 29.71, 29.61, 29.34, 26.41, 26.38, 22.71, 22.68, 14.16.

SynthesisofN- (2-hexyldecyl) -2, 2'-bis (3-dodecylthiophene-2-yl) -5, 5'-bithiazole-4, 4'-dicarbox-i mide (9) .

The dibrominated imide 8 (206 mg, 0.33 mmol) , 2-trimethyltinchloride-3-dodecylthiophene (414 mg, 0.99 mmol) , Pd (PPh₃) ₄ (20 mg, 0.016 mmol) , and 3 mL DMF were combined, and the reaction mixture was stirred under microwave irradiation at 150 ℃ for 3h. Then the solvent was removed under reduced pressure to afford a red solid, which was purified by column chromatography over silica gel with CH₂Cl₂/hexane (1: 1) as the eluent to afford an orange solid as the product 9 (yield: 30％) . ¹H NMR (400 MHz, CDCl₃) δ: 7.45 (d, J ＝ 5.1 Hz, 2H) , 7.03 (d, J ＝ 5.1 Hz, 2H) , 4.36 (d, J ＝ 7.2 Hz, 2H) , 3.00 (t, J ＝ 7.6 Hz, 4H) , 2.10-2.01 (m, 1H) , 1.76 (dt, J ＝ 15.2, 7.6 Hz, 4H) , 1.27 (b, 60H) , 0.88 (q, J ＝ 6.6 Hz, 12H) . ¹³C NMR (100 MHz, CDCl₃) δ: 160.25, 159.67, 145.46, 145.05, 130.68, 129.99, 129.08, 128.74, 50.76, 36.34, 31.94, 31.90, 31.75, 30.13, 30.08, 29.95, 29.80, 29.70, 29.62, 29.54, 29.50, 29.39, 26.45, 22.71, 14.14.

SynthesisofN- (2-hexyldecyl) -2, 2'-bis (5-bromo-3-dodecylthiophene-2-yl) -5, 5'-bithiazole-4, 4'-di carboximide (10) .

Br₂ (118 mg, 0.74 mmol) was added to a solution of 9 (238 mg, 0.25 mmol) in CHCl₃/AcOH (5: 1； total volume: 6 mL) in one portion. The reaction mixture was stirred at room temperature for 4 h, and 30 mL H₂O was then added. Next, the reaction mixture was extracted with 30 mL CH₂Cl₂ three times, and the combined organic layer was washed with 50 mL brine, and dried over MgSO₄. After filtration, the solvent was removed under reduced pressure to afford an orange solid, which was purified by column chromatography over silica gel with CH₂Cl₂/hexane (1: 2) as the eluent. The product compound 10 was obtained as an orange solid (yield: 70％) . ¹H NMR (400 MHz, CDCl₃) δ: 7.29 (s, 2H) , 4.33 (d, J ＝ 7.1 Hz, 2H) , 2.91 (t, J ＝ 7.6 Hz, 4H) , 2.02 (s, 1H) , 1.79-1.67 (m, 4H) , 1.28 (b, 60H) , 0.89 (t, J ＝ 6.2 Hz, 12H) . ¹³C NMR (100 MHz, CDCl₃, ppm) δ: 160.25, 158.19, 145.49, 145.29, 133.35, 131.66.128.62, 117.62, 50.76, 36.38, 31.96, 30.13, 29.72, 30.13, 29.58, 29.47, 29.39, 22.71, 14.14. Anal. Calcd for C₅₆H₈₅Br₂N₃O₂S₄ (％) ； C, 60.03； H, 7.65； N, 3.75； S, 11.45. Found (％) : C, 60.22； H, 7.55； N, 3.65； S, 11.57.

Synthesis of 5- (3-methoxycarbonyl-thiophen-2-yl) -thiazole-4-carboxylic acid methyl ester (13) .

To a reaction tube equipped with a stirring bar was added 11 (1.0 g, 4.5 mmol) , 12 (2.06 g, 6.75 mmol) , Pd (PPh₃) ₄ (104 mg, 0.09 mmol) , and DMF (10 mL) . The reaction tube was purged with argon and sealed, and then heated at 150 ℃ for 3 h under microwave irradiation. After cooling to room temperature, the reaction solution was poured into 100 mL H₂O and extracted with 100 mL DCM three times. The combined organic layer was dried over MgSO₄, and 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 compound 13 as a white crystal (yield: 92％) . ¹H NMR (400 MHz, CDCl₃) δ: 8.89 (s, 1H) , 7.59 (d, J ＝ 5.4 Hz, 1H) , 7.46 (d, J ＝ 5.4 Hz, 1H) , 3.85 (s, 3H) , 3.74 (s, 3H) . ¹³C NMR (100 MHz, CDCl₃) δ: 162.77, 161.68, 152.90, 143.73, 136.80, 136.06, 132.10, 129.66, 127.01, 52.43, 51.88.

Synthesis of 5- (3-carboxy-thiophen-2-yl) -thiazole-4-carboxylic acid (14) .

A mixture of compound 13 (800 mg, 2.82 mmol) and sodium hydroxide (451 mg, 11.3 mmol) in THF/water (20 mL/5 mL) was refluxed overnight. The solvent was removed under reduced pressure to 1/4 of its original volume. 50 mL H₂O was added to the solution and the resulting mixture was treated with dilute HCl. The precipitate was filtered and washed with H₂O three times to give product compound 14 (98％) . ¹H NMR (500 MHz, DMSO) δ: 9.18 (s, 1H) , 7.74 (d, J ＝ 5.3 Hz, 1H) , 7.46 (d, J ＝ 5.3 Hz, 1H) . ¹³C NMR (126 MHz, DMSO) δ: 163.74, 162.74, 154.75, 145.04, 136.54, 136.03, 133.17, 130.00, 128.19.

Synthesisof5- (2-hexyldecyl) -4H-thiazolo [4, 5-c] thieno [2, 3-e] azepine-4, 6 (5H) -dione (16) .

A mixture of intermediate 14 (1.74 g, 6.83 mmol) , SOCl₂ (20 ml) , and DMF (2 drops) was heated to reflux for 8 h. The solvent was evaporated to give compound 15. Then a mixture of 2-hexyldecan-1-amine (1.65 g, 6.83 mmol) and intermediate 15 was heated to 140 ℃ for 3h under N₂. The crude product was further purified by column chromatography using petroleum ether/ethyl acetate (3: 1) as the eluent to give a pale yellow oil (51％) . ¹H NMR (400 MHz, CDCl₃) 3: 8.79 (s, 1H) , 7.79 (d, J ＝ 5.3 Hz, 1H) , 7.39 (d, J ＝ 5.3 Hz, 1H) , 4.30 (d, J ＝ 7.2 Hz, 2H) , 1.96 (t, J ＝ 8.1 Hz, 1H) , 1.38–1.17 (m, 24H) , 0.87 (q, J ＝ 6.8 Hz, 6H) . ¹³C NMR (100 MHz, CDCl₃) 3: 161.94, 160.55, 150.82, 145.34, 134.46, 134.15, 133.64, 133.03, 126.45, 49.88, 36.37, 31.91, 31.84, 31.72, 30.04, 29.72, 29.57, 29.31, 26.45, 26.41, 22.68, 22.65, 14.13.

Synthesisof2-bromo-5- (2-hexyldecyl) -4H-thiazolo [4, 5-c] thieno [2, 3-e] azepine-4, 6 (5H) -dione.

Intermediate 16 (184 mg, 0.57 mmol) and BrCCl₂CCl₂Br (464 mg, 1.43 mmol) was dissolved in 30 mL anhydrous THF. lithium hexamethyldisilazide (LiHMDS) (1.54 mL, 2.0 mmol) was added dropwise at -78 ℃ and stirred for 20 min under N₂. Then, to the reaction, saturated NH₄Cl aqueous solution was added. The aqueous phase was extracted with CH₂Cl₂ three times and the combined organic phase was evaporated to afford a yellow solid, which was further purified by column chromatography using petroleum ether/ethyl acetate (10:1) as the eluent and then recrystallized from isopropanol (yield: 57％) . ¹H NMR (500 MHz, CDCl₃) 3: 7.78 (d, J ＝ 5.3 Hz, 1H) , 7.42 (d, J ＝ 5.3 Hz, 1H) , 4.27 (d, J ＝ 7.2 Hz, 2H) , 1.97-1.88 (m, 1H) , 1.41-1.21 (m, 24H) , 0.88 (q, J ＝ 7.0 Hz, 6H) . ¹³C NMR (126 MHz, CDCl₃) δ: 161.63, 159.36, 144.38, 137.59, 134.64, 134.58, 133.76, 131.74, 126.94, 50.08, 36.34, 31.93, 31.86, 31.72, 31.71, 30.05, 29.74, 29.59, 29.33, 26.45, 26.42, 22.70, 22.67, 14.16, 14.14.

Synthesis of N, N'-bis (2-hexyldecyl) -2, 2'-bithiazolethienyl-4, 4', 10, 10'-tetracarboxdiimide 18.

A mixture of 17 (362 mg, 0.67 mmol) and Ni (COD) ₂ (92 mg, 0.33 mmol) was dissolved in 10 mL DMF under N₂. The reaction mixture was heated at 50 ℃ for 6 h. It was then poured into H₂O and extracted with CH₂Cl₂. The combined organic phase was washed with H₂O and dried over Na₂SO₄. After concentrated under reduced pressure, the residue was purified by column chromatography on silica gel using CH₂Cl₂/hexane (1:2) as the eluent to give the product compound 18 as a yellow solid (70％yield) . ¹H NMR (500 MHz, CDCl₃) δ: 7.82 (d, J ＝ 5.3 Hz, 2H) , 7.46 (d, J ＝ 5.3 Hz, 2H) , 4.31 (d, J ＝ 7.3 Hz, 4H) , 2.01-1.94 (m, 2H) , 1.43-1.20 (m, 48H) , 0.88 (td, J ＝ 6.9, 2.7 Hz, 12H) . ¹³C NMR (126 MHz, CDCl₃) δ: 161.75, 160.02, 156.91, 145.41, 136.85, 135.13, 133.91, 132.59, 127.45, 50.16, 36.43, 31.93, 31.86, 31.71, 30.09, 29.77, 29.60, 29.35, 26.46, 26.42, 22.73, 22.70, 22.69, 14.18, 14.14.

Synthesis of N, N'-bis (2-hexyldecyl) -2, 2'-bithiazolethienyl-4, 4', 10, 10'-tetracarboxdiimide 19.

Compound 18 (204 mg, 0.22 mmol) and BrCCl₂CCl₂Br (180 mg, 0.55 mmol) was dissolved in anhydrous THF. lithium hexamethyldisilazide (LiHMDS) (0.84 mL, 1.1 mmol) was added slowly at -78℃ and stirred for 20 min under N₂. Then, to the reaction was added saturated NH₄Cl aqueous solution. The aqueous phase was extracted with DCM and the combined organic phase was evaporated to afford a yellow solid, which was further purified by column chromatography using CH₂Cl₂/hexane (1:2) as the eluent and recrystallized from isopropanol (yield: 40％) . ¹H NMR (400 MHz, CDCl₃) δ: 7.78 (s, 2H) , 4.29 (d, J ＝ 7.2 Hz, 4H) , 1.99-1.92 (m, 2H) , 1.44-1.19 (m, 48H) , 0.89 (dd, J ＝ 6.9, 4.9 Hz, 12H) . ¹³C NMR (126 MHz, CDCl₃) δ: 160.59, 159.65, 156.89, 145.52, 136.02, 135.59, 135.35, 133.69, 115.51, 50.30, 36.39, 31.94, 31.87, 31.66, 30.08, 29.76, 29.61, 29.36, 26.42, 26.40, 22.74, 22.72, 22.69, 14.19, 14.15. Anal. Calcd for C₅₀H₆₈Br₂N₄O₄S₄ (％) : C, 55.75； H, 6.36； N, 5.20； S, 11.91. Found (％) : C, 55.66； H, 6.47； N, 5.31； S, 11.92.

General Procedure for Polymerizations via Stille Coupling for the Synthesis of Polymers PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI.

An glass tube was charged with two monomers (0.1 mmol each) , 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: 0.03-0.05 equiv) . The tube and its contents were subjected to 3 pump/purge cycles with argon, followed by the addition of 3 mL anhydrous toluene via syringe. The tube was sealed under argon flow and then stirred at 80 ℃ for 10 min, 100 ℃ for 10 min, and 140 ℃ for 3 h under microwave irradiation. Then, 0.1 mL 2- (tributylstanny) thiophene was added and the reaction mixture was stirred under microwave irradiation at 140 ℃ for 0.5 h. Finally, 0.2 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 slowly dripped into 100 mL methanol (containing 5 mL 12 N hydrochloric acid) under vigorous stirring. After stirring for 1 h, the solid precipitate was transferred to a Soxhlet thimble. After drying, the crude product was subjected to sequential Soxhlet extraction with the solvent sequence depending on the solubility of the particular polymer. After final extraction, the polymer solution was concentrated to ～20 mL, and then dripped into 100 mL methanol under vigorous stirring. The polymer was collected by filtration and dried under reduced pressure to afford deep colored solid as the product polymer.

PBTzI3T. The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane, and chloroform. The chloroform fraction was concentrated by removing most of solvent and precipitated into methanol. The solid was collected by filtration and dried in vacuum to afford the polymer as a deep colored solid (yield: 53％) . ¹H NMR (400 MHz, CCl₄D₂, 120 ℃) δ: 7.67 (s, 2H) , 7.37 (d, 2H) , 4.39 (d, 2H) , 3.05 (t, 4H) , 2.10 (s, 1H) , 1.79 (m, 4H) , 1.35 (m, 60H) , 0.95 (m, 12H) . M_n ＝ 24 kDa, PDI ＝ 1.7. Anal. Calcd for C₆₀H₈₇N₃O₂S₅ (％) ：C, 69.11； H, 8.41； N, 4.03； S, 15.38. Found (％) : C, 68.98； H, 8.32； N, 4.33； S, 15.21.

PBTzI3T-2F. The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane, and chloroform. The chloroform fraction was concentrated by removing most of solvent and precipitated into methanol. The solid was collected by filtration and dried in vacuum to afford the polymer as a deep colored solid (yield: 62％) . ¹H NMR (400 MHz, CCl₄D₂, 120 ℃) δ: 7.29 (s, 2H) , 4.33 (d, 2H) , 2.91 (t, 4H) , 2.02 (s, 1H) , 1.79-1.67 (m, 4H) , 1.28 (b, 60H) , 0.89 (t, 12H) . M_n ＝ 11 kDa, PDI ＝ 1.2. Anal. Calcd for C₆₀H₈₅F₂N₃O₂S₅ (％) : C, 66.81； H, 7.94； N, 3.90； S, 14.86. Found (％) : C, 66.69； H, 7.82； N, 3.69； S, 14.56.

PDTzTIT. The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane, and chloroform. The chloroform fraction was concentrated by removing most of solvent and precipitated into methanol. The solid was collected by filtration and dried in vacuum to afford the polymer as a deep colored solid (yield: 72％) . ¹H NMR (400 MHz, CCl₄D₂, 120 ℃) δ: 7.58 (s, 2H) , 7.16 (s, 2H) , 4.29 (d, 4H) , 1.99-1.92 (m, 2H) , 1.44-1.19 (m, 48H) , 0.89 (d, 12H) . M_n ＝ 20 kDa, PDI ＝ 1.8. Anal. Calcd for C₅₄H₇₀N₄O₄S₅ (％) : C, 64.89； H, 7.06； N, 5.61； S, 16.04. Found (％) : C, 64.33； H, 7.06； N, 5.08； S, 15.33.

PDTzTIT-2F. The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane, and chloroform. The chloroform fraction was concentrated by removing most of solvent and precipitated into methanol. The solid was collected by filtration and dried in vacuum to afford the polymer as a deep colored solid (70％) . ¹H NMR (400 MHz, CDCl₃, 120 ℃) δ: 7.82 (s, 2H) , 4.29 (d, 4H) , 1.99-1.92 (m, 2H) , 1.44-1.19 (m, 48H) , 0.96 (d, 12H) . M_n ＝ 14 kDa, PDI ＝ 1.2. Anal. Calcd for C₅₄H₆₈F₂N₄O₄S₅ (％) : C, 62.64； H, 6.62； N, 5.41； S, 15.48. Found (％) : C, 62.94； H, 6.62； N, 5.22； S, 15.29.

PDTzTI. The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, and dichloromethane. The dichloromethane fraction was concentrated by removing most of solvent and precipitated into methanol. The solid was collected by filtration and dried in vacuum to afford the polymer as a deep colored solid (86％) . ¹H NMR (400 MHz, CDCl₃, 120 ℃) δ: 7.81 (s, 2H) , 4.37 (d, 4H) , 2.09 (m, 2H) , 1.38 (m, 48H) , 0.96 (d, 12H) . M_n ＝ 7 kDa, PDI ＝ 1.1. Anal. Calcd for C₅₀H₆₈N₄O₄S₄ (％) : C, 65.46； H, 7.47； N, 6.11； S, 13.98. Found (％) : C, 65.28； H, 7.39； N, 5.88； S, 13.97.

After polymerizations, the polymer chains were end-capped with mono-functionalized thiophene. The polymers were collected by precipitation in methanol, which were then subjected to purification via Soxhlet extractions using different solvent sequences, depending on the polymer solubility. The identity and purity of the product polymers were supported by ¹H NMR as well as by elemental analysis. All the polymers exhibit good solubility in common organic solvents for device fabrication. Polymer molecular weights were measured by gel permeation chromatography (GPC) versus polystyrene standards. Number average molecular weight, Mns are summarized in Table 1. Table 1. Molecular Weights, Optical Absorption, and Electrochemical Properties of Polymers PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI.

polystyrene standards, trichlorobenzene as eluent at 150 ℃. ^b Absorption spectra in chloroform solution (1×10^-5 M) . ^c Absorption spectra of pristine film casted from 5 mg/mL chloroform solution. ^d E_HOMO ＝ -e (E_ox ^onset+4.80) eV, and E_ox ^onset determined electrochemically using F_c/F_c ⁺ internal standard. ^e E_LUMO ＝ E_HOMO +E_g ^opt. ^f Optical bandgap estimated from absorption onset of as-cast polymer thin film using the equation: E_g ^opt＝ 1240/λ_onset (eV) .

Density Functional Theory Calculation

In order to further understand the effect of thiazole incorporation on the polymer physicochemical properties and to establish the chemical structure-materials property correlations, density functional theory (DFT) -based calculations were performed at the B3LYP/6-31G (d) level using the Gaussian 09 program. To reduce computation time, three repeating units were chosen as the simplified models and the 2-hexyldecyl side chains were replaced with methyl groups. The optimized conformations show the dihedral angles between neighboring arenes typically < 5°. The DFT calculation results reveal that all polymers adopt highly planar backbones for the trimers of these thiazole-based polymer repeat units, in good accordance with the single crystal structures of the model compounds. Such planar backbones should in turn benefit charge transport in OTFT devices. Additionally, the DFT results reveal that the torsion angles between the difluorothiophene and the neighboring arene in polymers PBTzI3T-2F and PDTzTIT-2F are smaller than those in the PBTzI3T and PDTzTIT, which is likely attributable to the intramolecular non-covalent S…F interaction. The S…F interactions enhance polymer backbone planarity, thus a higher charge carrier mobilities can be expected for polymers PBTzI3T-2F and PDTzTIT-2F. It is interesting to note that the homopolymer PDTzTI shows the smallest dihedral angles with highly planar backbone among all polymers, which is likely due to the intramolecular non-covalent S…N interaction. The highly planar backbone of PDTzTI combined with its lowest LUMO results in the highest mobility in the series.

Thermal Properties and Materials Crystallinity

Thermal properties of the polymer semiconductors are investigated using thermogravimetric analysis (TGA) in N₂ at a heating ramp of 10 ℃/min. A mass loss of 5％is defined as the threshold for thermal decomposition. All these imide-functionalized polymers show good thermal stability with the decomposition onsets of 348, 323, 329, 328, and 336 ℃ for PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI, respectively. The data indicates that the polymers are sufficiently stable for thermal annealing and device optimization over a wide range. Differential scanning calorimetry (DSC) was used to characterize the thermal transitions of all polymer semiconductors. On the basis of DSC thermograms, all polymers show no distinctive exotherms or endotherms from 50 to 300 ℃, providing no evidence of mesophase transition in the temperature range. Such thermal properties are similar to those of bithiophene imide homopolymers and bithiophene imide-thiophene copolymers

Optoelectronic Properties

The UV-vis absorption spectra of polymers PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F， and PDTzTI in chloroform solution and as thin films are shown in Figure 6 and the corresponding absorption data and bandgaps of the polymers are summarized in Table 1.

In chloroform solution, all polymers exhibit an absorption maximum (λ_max) accompanied by a distinctive absorption shoulder, indicative of a certain degree of polymer chain ordering in solution. From solution to film state, all polymers show a minimal λ_max shift with comparable absorption profile, which is attributed to the polymer aggregation in solution. The strong aggregation of polymer chains is mainly due to the fused imide structure, high degree of polymer backbone planarity, and strong intermolecular interaction, which should be beneficial to intramolecular charge carrier delocalization along single polymer chain and intermolecular hopping between distinct polymer chains. The optical bandgaps (E_g ^opts) of PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI are 1.89, 1.89, 1.91, 2.04, and 2.01 eV, respectively, as determined from the onsets of polymer film absorption. In comparison to the previously reported BTI-based polymer analogues, the incorporation of thiazole into polymer backbone leads to widening of polymer bandaps, which is mainly attributed to the low-lying HOMO (vide infra) . Among the polymers, PDTzTIT-2F and PDTzTI show bandgaps > 2 eV, which are likely due to the reduced electron donating ability of difluorinated thiophene unit in the donor-acceptor copolymer PDTzTIT-2F or the lack of donor-acceptor interaction in homopolymer PDTzTI. Such large bandgaps reflect their very low-lying HOMOs (-5.56 --6.14 eV, Table 1) , which are contrary to other high-performance n-type polymer semiconductors reported to date, such as isoindigo and DPP-based polymer semiconductors, which typically feature narrow bandgaps with high-lying HOMOs.

Electrochemical properties

Organic semiconductors should have appropriate highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) energy levels to facilitate hole (p-type) or electron (n-type) injection, respectively, from source electrodes and to stabilize the generated charge carriers in the conduction channel to increase the device environmental stability. The electrochemical properties of polymer semiconductors are investigated using cyclic voltammetry (CV) . The experimentally measured cyclic voltammograms are shown in Figure 7 and the results are summarized in Table 1. All these imide-functionalized polymer semiconductors exhibit distinctive reduction peaks, indicating their n-type characteristics. From top to down (Figure 7) , the reduction peaks become more pronounced accompanied by gradually weakened oxidation peaks, indicating that the F addition on the thiophene unit and the incorporation of imide dimer DTzTI should lead to improved n-channel and suppressed p-channel performance in OTFTs.

The HOMO levels of the polymers are determined from the onsets of oxidation peaks versus the half-wave potential of the ferrocene/ferrocenium (F_c/F_c ⁺) redox couple as the internal standard. The HOMOs are calculated using the equation: E_HOMO ＝ -e (E_ox ^onset+ 4.80) eV, where E_ox ^onset is the onset oxidation potential versus F_c/F_c ⁺. The onset oxidation potentials of PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI are 1.18, 1.47, 1.51, 1.65, and 1.76V, corresponding to HOMO levels of -5.56, -5.85, -5.89, -6.03, and -6.14 eV for PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI, respectively (Figure 7) . Such very low-lying HOMOs should suppress the hole injection. Compared to the HOMOs of the PBTzI3T and PBTzI3T-2F, the polymers PDTzTIT, PDTzTIT-2F, and PDTzTI HOMOs are further suppressed, which reflects the higher loading of the electron-withdrawing imide group in the backbone of DTzTI-based polymer semiconductors. The LUMOs of PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI, are -3.67, -3.96, -3.98, -3.99, and -4.13 eV, respectively, which are derived from their HOMOs and optical bandgaps using the equation: E_LUMO ＝ E_HOMO +E_g ^opt. On the basis of the LUMOs, the addition of fluorine atoms slightly lowers the polymer LUMOs and the higher loading of imide moiety leads to deeper LUMOs for DTzTI-based polymers versus the BTzI-based polyemrs. Among the polymers, the homopolyemr PDTzTI shows the lowest-lying LUMO of -4.13 eV. In combination with their distinctive reduction peaks, the relatively low-lying LUMOs of PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI should enable them to be promising n-type semiconducting materials, which are in good accordance with the OTFT performance. In comparison to the previous BTI-based polymer analogues, the introduction of thiazole leads to lower-lying HOMOs and LUMOs, which should be beneficial to n-channel OTFT performance.

Device Fabrication and Characterization

The charge carrier transport properties of these novel imide-functionalized thiazole-based polymer semiconductors were investigated by fabricating OTFT devices with a top-gate/bottom-contact (TGBC) configuration. The OTFTs were fabricated on glass substrates, and Cr (3 nm) /Au (30 nm) is patterned by photolithography as the source and drain electrodes. The semiconducting polymer layers are spin-coated onto the substrate from either 3 or 5 mg/mL chlorobenzene (CB) solutions and then annealed in N₂. Either PMMA (polymethylmethacrylate, k ＝ 3.5) or Cytop (k ＝ 2.1) is used as the gate dielectric layer, which is spin-coated onto the semiconductor films. Finally 50 nm Al is deposited by thermal evaporation as the gate electrode to complete the device fabrication. The mobilities are calculated from the slope of the plot of drain/source current (I_S) ^0.5 as afunction of V_GSin the saturation regime.

To fully optimize the OTFT performance, we systematically investigated the OTFT performance under various annealing temperatures. It was found that the performance highly depends on the annealing temperature and thermal annealing results in improved performance. The performance parameters of all polymer fabricated under optimal conditions including mobilities, threshold voltages, the I_on/I_offs are summarized in Table 2 (at least 5 devices measured for each sample) . The polymers PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI based OTFT devices all exhibited n-channel dominated or unipolar n-channel transistor characteristic. Figure 8 shows the representative n-channel output and transfer curves for the OTFTs fabricated under the optimal condition. PBTzI3T OTFTs annealed at 250 ℃show improved electronic properties compared to as-cast film with an average electron mobility (μ_e) of 0.015 cm² V^-1 s^-1 and an average hole mobility (μ_h) of 1.9 x 10^-4 cm² V^-1 s^-1. The p-channel performance is due to its highest-lying HOMO (-5.56 eV, Table 1) in the polymer series. In comparison to PBTzI3T, PBTzI3T-2F annealed at 250 ℃exhibit enhanced electron transport properties with an average μ_e of 0.040 cm² V^-1 s^-1 with greatly suppressed μ_h. For the polymer containing thienylthiazole imide dimer DTzTI as the electron-acceptor unit, the OTFTs exhibit unipolar n-channel transport characteristic. After annealing at 250 ℃, OTFTs incorporating PDTzTIT active layer show an average μ_e of 0.17 cm² V^-1 s^-1, and the PDTzTIT-2F-based OTFTs annealed at 200 ℃ exhibit greatly improved n-channel performance with an average μ_e of 0.58 cm²V^-1 s^-1 and high current on/off ratios (I_on/I_offs) of 10⁵ -10⁶. Among all polymers, homopolymer PDTzTI shows the most promising n-channel performance, and the OTFTs annealed at 200 ℃exhibit an average μ_e of 0.78 cm²V^-1 s^-1 with the highest μ_e of 1.04 cm²V^-1 s^-1. In addition PDTzTI OTFTs show small off-current (I_offs) of 10^-11 -10^-12 A and hence remarkable I_on/I_offs of 10⁶-10⁷, which are different from many high mobility n-type polymers, showing high off-current with smaller I_on/I_offs of 10⁴-10⁵. The small off-currents are mainly due to its very low-lying HOMO of -6.14 eV. The improved electron mobility of the OTFTs fabricated from the PDTzTIT-2F and PDTzTI could be partially attributed to their low-lying LUMOs, resulting in efficient electron injection, and highly planar backbone, facilitating charge carrier delocalization. Polymers PDTzTIT-2F and PDTzTI show high degree of film crystallinity, long-range lamellar structure, and close intermolecular π-stacking distance as revealed by AFM and GIWAXD characterization, leading to most promising electron mobility in the series. Table 2. TG/BC OTFT performance parameters of polymers PBTzI3T, PBTzI3T-2F, PDTzTIT, PDTzTIT-2F, and PDTzTI fabricated under the optimal condition.

^a Maximum mobility from at least 5 devices (average value shown in parentheses) ； ^b Average threshold values shown.

Claims

An imide-functional unit of Formula I:

wherein

R is a straight or branched alkyl, preferably having 2-30 carbon atoms, and more preferably having 7-24 carbon atoms,

X₁ is O, S or Se atom,

X₂ is O or S atom,

Y₁ is H or N atom, and

Y₂ is N atom.
The imide-functional unit of claim 1 having a structure selected from the group consisting of the follows:

wherein R is a straight or branched alkyl, preferably having 5-15 carbon atoms.
The imide-functional unit of claim 1 or 2, wherein R is a straight or branched alkyl having 7-12 carbon atoms.
A copolymer comprising the imide-functional unit of any of claims 1-3, which have a structure selected from the group consisting of:

wherein

R is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms.
A Preparation method of the imide-functional unit of any of claims 1-3, comprising the following steps:

(1) adding Methyl 5-bromothiazole-4-carboxylate, methyl 2- (trimethylstannyl) thiophene-3-carboxylate， an organic solvent into a reaction vessel, and purging the mixture with an inert gas；

(2) adding Pd (PPh₃) ₄ and then purging an inert gas, heating the mixture to 80-140℃；

(3) adding alkali carbonate, an organic solvent or water to the mixture and refluxing the mixture at 40-90℃；

(4) adding SOCl₂ into a reaction vessel；

(5) adding alkyl amine and heating the mixture to 140-160 ℃；

(6) adding LiHMDS and BrCCl₂CCl₂Br at -78℃；

(7) extracting the reaction mixture and washing； and

(8) concentrating the organic layer and purifying to give the imide-functional unit.
A preparation method according to claim 5, wherein on the basis of the technical solution provided by the present invention, in step (1) , the mole ratio of the Methyl 5-bromothiazole-4-carboxylate to methyl 2- (trimethylstannyl) thiophene-3-carboxylate is 1: 2-4, preferably 1: 2.2-3, more preferably 1∶ 2.5；

preferably, the ratio of the organic solvent to the Methyl 5-bromothiazole-4-carboxylate is 2-10 mL/mmol, preferably 3-7 mL/mmol；

preferably, the organic solvent is selected from THF, DMF, toluene or a mixture thereof；

preferably, time of the purging is more than 10 minutes, preferably more than 20 minutes, more preferably 30 minutes；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture thereof；

preferably, in step (2) , the mole ratio of the Pd (PPh₃) ₄ to Methyl 5-bromothiazole-4-carboxylate is 1: 5-20, preferably 1: 8-15, more preferably 1∶ 10；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture thereof；

preferably, time of the purging is more than 5 minutes, preferably more than 10 minutes, more preferably 20 minutes；

preferably, the mixture is heated to 80-140 ℃； preferably to 140 ℃；

preferably, the heating is conducted under microwave irradiation；

preferably, in step (3) , preferably, the alkali carbonate is selected from K₂CO₃, Na₂CO₃, Li₂CO₃, LiOH, NaOH, KOH or a mixture thereof；

preferably, the organic solvent is selected from THF, EtOH, dioxane, DMF or a mixture thereof；

preferably, the mixture is refluxed at 70 ℃；

preferably, in step (4) , the ratio of SOCl₂ is 1-5 mL/mmol, preferably 2-4 mL/mmol；

preferably, the ratio of alkyl amine to chlorocarbonyl is 1: 1.5, preferably 1: 1, more preferably 1: 0.7；

preferably, the mixture is heated to 140-160 ℃； preferably to 150 ℃；

preferably, in step (6) , the mixture is cooled to -80 ℃； preferably to -78 ℃；

preferably, in step (7) , the reaction mixture is extracted with an organic solvent, preferably with DCM；

preferably, the washing is conducted with water and brine；

preferably, in step (8) , the concentrating is conducted under reduced pressure；

preferably, the purifying is conducted by column chromatography using petroleum ether as an eluent.
A preparation method of the copolymer of claim 4, comprising:

(1) adding the imide-functional unit of claim 1, an aromatic unit material, tris (di-benzylideneacetone) 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) 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； and

(6) after the extracting, concentrating the polymer solution, and then being dripped into methanol, collecting the solid and drying to obtain the copolymer.
The preparation method according claim 7, wherein the mole ratio of the electron-donating unit of the invention to the aromatic unit material is 1: 0.5-2, for example, 1: 0.8, 1: 1.2, 1: 1.8 and so on, preferably 1: 0.8-1.5, more preferably 1: 1；

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；

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 thereof；

preferably, in step (2) , the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture thereof；

preferably, the organic solvent is selected from any one of anhydrous toluene, benzene, chlorobenzene, DMF, or a mixture thereof；

preferably, the ratio of the organic solvent to the electron-donating unit is 10-75 mL/mmol, preferably 5-50 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 under microwave irradiation；

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 under microwave irradiation；

preferably, the heating is conducted under microwave irradiation at 140 ℃ for 0.5 h, then adding 2-bromothiophene and stirring the reaction mixture at 140 ℃ for another 0.5 h；

preferably, the mole ratio of the 2- (tributylstanny) thiophene to the electron-donating unit is 0.1-0.5: 1, for example, 0.2: 1, 0.4: 1 and so on, preferably 0.2: 0.4-1；

preferably, the mole ratio of the 2-bromothiophene to the electron-donating unit is 0.2-1.5: 1, for example, 0.4: 1, 0.8: 1, 1.3: 1 and so on, preferably 0.4: 0.8-1； preferably, in step (4) , the methanol contains 0.5-10mL hydrochloric acid， preferably 0.5-10mLof 5-20 mol/L hydrochloric acid；

preferably, the dripping is conducted under vigorous stirring, preferably is conducted for at least 0.5 h, preferably at least 1 h；

preferably, in step (6) , the dripping is conducted under vigorous stirring；

preferably, the collecting is conducted by filtration；

preferably, the drying is conducted under reduced pressure.
Use of the imide-functional unit according to any of claims 1-3 in n-channel thin-film transistor.
Use of the copolymer according to claim 4 in n-channel thin-film transistor.