MONO-carbonyl functionalized semiconductors

Abstract

The invention is related to a novel asymmetric mono-carbonyl functionalization approach for the synthesis of new highly soluble [1]benzothieno[3,2‐b][1]benzothiophene (BTBT)-based molecular semiconductors. Some examples of such compounds can exhibit very high solubility in organic solvents, including green solvents, and they can exhibit high p-type carrier mobility and good current modulation characteristics in organic field-effect transistors.

Description

[0001] DESCRIPTION

[0002] MONO-CARBONYL FUNCTIONALIZED SEMICONDUCTORS

[0003] Technical Field

[0004] The invention is related to a novel asymmetric mono-carbonyl functionalization approach for the synthesis of new highly soluble [l]benzothieno[3,2-b][l]benzothiophene (BTBT)-based molecular semiconductors. Some examples of such compounds can exhibit very high solubility in organic solvents, including green solvents, and they can exhibit high p-type carrier mobility and good current modulation characteristics in organic field-effect transistors.

[0005] State of the Art

[0006] Small molecules based on coplanar diacene-fused thienothiophene 7t-scaffolds have emerged as one of the most appealing organic semiconductor family in the past decade.1,2[l]Benzothieno[3,2-Z>][l]benzothiophene (BTBT) (Figure 1) 7t-system in this family enables large frontier orbital coefficients on the sulfur atoms and forms a favorable solid-state electronic structure for efficient hole transport.3,4As a direct result of their phene-like 7t-electronic structure, BTBTs have much larger band gaps (>3.5 eV) and deeper HOMO levels (< -5.5 eV) than the majority of the high performance molecular semiconductors reported to date.5Today, BTBT remains an unprecedented 7t-framework enabling facile synthetic modification and good solubility in common organic solvents, and showing optical transparency and ambient-stable high hole mobility.6In addition, from a materials production standpoint, the synthesis of BTBTs could typically be performed in a small number of steps with convenient chromatographic purifications, which makes these semiconductors quite attractive for industrial scale applications.

[0007] Over the past decade, a large variety of 7t-electron rich BTBT semiconductors (Figure 1) have been developed including mono- and di-alkyl substituted BTBTs (e.g., (mono)-C13-BTBT7and C6 / 8-BTBT4), di-aryl substituted BTBTs (e.g., DPh-BTBT3), and mono-aryl / mono-alkyl substituted BTBTs (e.g., Cn-BTBT-Ph8and BTBT-Ph-C6 / 129,10) for use in / ?-channel organic field-effect transistors (OFETs). In these semiconductors, although the BTBT 7t-core is the active charge-transporting moiety, an alkyl and / or aryl substitution has been employed to realize proper semiconductor thin-film formation with efficient hole transport and solid-state characteristics.10Among these BTBTs, some structures have been reported to have good solubility in common organic solvents, and their synthetic purification and thin-filmfabrication were carried out using solution-based techniques. Typically, medium-length linear alkyl chain (-n-CnH2n+1(n = 3-8)) substitution has been employed to realize proper solutionprocessability, and the highest reported solubility was for dialkyl-substituted BTBTs (Cs-BTBT’s4) with values up to 90 mg mL'1, followed by solubilities of up to 9-11 mg mL'1for Cn-BTBT-Ph’s8, both reported at room temperature.

[0008] With the goal of expanding further the versatility of the BTBT 7t-scaffold, a di-functioalization approach was employed and explored with electron withdrawing units.

[0009] D(PhFCO)-BTBT (Figure 1) showed μe= 0.57 cm2 / V·s and D(C7CO)-BTBT (Figure 1) showed μh= 0.03 cm2 / V·s in recent publications by our research group.11 12D(PhFCO)-BTBT was the first example of an electron-transporting ( / / -type) BTBT in the field of organic semiconductors. These two molecules are the only known examples of dicarbonyl functionalized BTBT semiconductors that are reported to show charge carrier mobilties in organic thin-films until today. However, dicarbonyl-functionalized BTBT semiconductors were either insoluble or have a very low solubility value in common organic solvents, and their corresponding thin-film semiconductor devices were deposited by using only physical vapor deposition (PVD) methods. It is important to note that during the development of novel semiconductor structures in the past few decades, dicarbonyls have typically been used either to realize electron transport13-15or to reduce the HOMO level of 7t-electron rich oligothiophenes16for ambient-stable hole transport. However, most of these semiconductors are either insoluble or have a low solubility (<10 mg mL'1) in common organic solvents at room temperature. Therefore, as far as solution-processibility is concerned, dicarbonyl functionalization was considered in only a limited number of examples for BTBTs, both giving practically insoluble semiconductor solids as explained above.

[0010] Therefore, a critical scientific and technological question remains as to whether carbonyl functionalization would be useful in realizing a solution-processable, high performance BTBT-based semiconductor. Novel carbonyl functionalization approaches that can introduce a large solubility to the fused BTBT 7t-core, along with unique molecular and electronic properties, could also facilitate eco-friendly green solvent processing and enhance BTBT-based semiconductor molecules processing and functionality versatility in (optoe)electronics.Figures

[0011] Figure 1. The chemical structures of the [l]Benzothieno[3,2-Z>][l]benzothiophene (BTBT) n- core, previously developed alkyl / aryl substituted BTBT semiconductors (mono)-Ci3- BTBT, BTBT-Ph-C6 / 12, DPh-BTBT, Cn-BTBT-Ph, and C6 / 8-BTBT, and previously developed dicarbonyl-functionalized BTBT semiconductors D(PhFCO)-BTBT and D(C7CO)-BTBT.

[0012] Figure 2. NMR spectra of m-C6PhCO-BTBT (top) and the parent BTBT (bottom) molecules in CDCh showing the non-exchangeable aromatic protons “a-i” and the downfield shifts for “e and g” (AS ~ +0.5 ppm). Inset shows the photo of the gram-scale m-C6PhCO-BTBT solid.

[0013] Figure 3.

[0014] (a) Solvatochromic optical absorption spectra of m-C6PhCO-BTBT in different solvents with increasing polarity (hexanes (f (e,n) = 0.001) —> acetonitrile (f (e,n) = 0.305)) and solid- state optical absorption spectrum of spin-coated thin-film (annealed at 120 °C) on glass showing vibronic structure.

[0015] (b) Cyclic voltammograms of m-CePhCO-BTBT and Cs-BTBT (measured in house for comparison) showing oxidation and reduction peaks in 0.1 M TBAPF6 / CH2Cl2solution vs. Ag / AgCl (3.0 M NaCl) at a scan rate of 100 mV / s.

[0016] (c) The experimental HOMO and LUMO energy levels, frontier orbital topographies (DFT / B3LYP / 6-31G**), and optical / electrochemical band gaps.

[0017] Figure 4. Tapping mode atomic force microscopy (AFM) topographic images (a) and 0-29 out-of-plane X-ray diffraction (Bragg-Brentano configuration) scans with the assigned planes (b) for p++-Si / SiO2(300 nm) / PS-brush (Mn= 5 kDa) / m-C6PhCO-BTBT (40-50 nm) thin-films that are spin-coated from four different green solvents (2- methyltetrahydrofuran, ethyl acetate, acetone, and ethoxybenzene), and annealed at 120 °C (for 30 min). Figure 5(a)-inset shows the measured step-height profile (~2.5><n nm (n (integer) > 1)) of the 2D terraced multi-layer molecular islands. In the top XRD scan, the spin-coated sample without thermal annealing (gray solid line) is also provided for comparison.

[0018] (c) Transfer (VDS = -100 V) characteristics for p++-Si / SiO2(300 nm) / PS-brush (Mn= 5 kDa) / m-C6PhCO-BTBT (40-50 nm) / Au (50 nm) OFET devices processed from four different green solvents. The IDS1 / 2vs. VGplots (dashed curves) are used for hole mobility calculations. The inset shows a representative top-view image of an OFET device during measurement.

[0019] (d) The molecular arrangement in the out-of-plane

[0100] direction based on the main (100) diffraction peak and the step-height profile of the 2D crystalline domains.

[0020] (e) The morphological change from small nodular grains to micron-sized domains with sharp edges, as observed during thermal annealing process for an unfinished sample.Detailed Description of the Invention

[0021] Herein presented a unique molecular design on the BTBT 7t-system by employing monocarbonyl functionalization with varied alkyl and aryl substituents, and demonstrate the design, synthesis, and characterization of a new class of asymmetric functionalized BTBT semiconductors. The new molecules could be produced in gram-scale through a two-step transition-metal-free synthesis, and the detailed structural, physicochemical, and (opto)electronic characterizations are herein reported. Mono-carbonyl functionalization stabilizes frontier molecular orbitals (AEHOMO ~ -0.3 eV vs. AELUMO ~ -0.7 eV) and induces an asymmetric ^-electronic structure having a large ground state molecular dipole moment (μg) of >3 D. The new BTBT molecule examples show excellent solubility behavior at room temperature (max. solubilities up to 176.0 mg mL'1in chloroform) in varied organic solvents (e.g., chloroform, methylene chloride, toluene), including a number of eco-friendly green solvents (e.g., 2-methyltetrahydrofuran, ethyl acetate, ethoxybenzene, ethanol, acetone). One of our examples, m-C6PhCO-BTBT, exhibits prompt dissolution at room temperature in chloroform, displaying a remarkable room temperature solubility of 176.0 mg mL'1(0.41 M). This solubility represents the highest solubility ever reported for a high-performance organic semiconductor. The impressive solubility of m-C6PhCO-BTBT even allowed for the preparation of semiconductor solutions (solubility up to -12.5 mg mL'1at room temperature) in eco-friendly green solvents such as 2-methyltetrahydrofuran, ethyl acetate, ethoxybenzene, acetone, and ethanol, suitable for thin-film solution-processing. The Hansen solubility parameters of this most soluble example, m-C6PhCO-BTBT, is determined to be δD= 18.9 MPa1 / 2, δP= 5.7 MPa1 / 2, and δH= 5.8 MPa1 / 2(R0= 8.0 MPa1 / 2), which indicates a very small solid-solvent interaction distance of 3.36 MPa1 / 2with respect to chloroform, confirming m-CePhCO-BTBT’s extremely high solubility. The charge-transport characteristics of the mono-carbonyl BTBT molecules developed in this invention were studied in solution-processed top-contact / bottom-gate (TC / BG) OFETs, and all small molecules showed p-type semiconductivity. The maximum saturation hole mobility were achieved for m-C6PhCO-BTBT thin-films spin-coated from 2-methyltetrahydrofuran (μhmax= 1.87 cm2 / V·s, μhavg= 1.21 cm2 / V·s (Ion / Ioff= 107-108)) and ethyl acetate (μhmax= 0.62 cm2 / V·s, μhavg= 0.41 cm2 / V·s (Ion / Ioff= 106-107)) solutions.

[0022] Methods for Synthesis: Friedel-Crafts acylation reactions were conducted under nitrogen atmosphere with conventional Schlenk techniques and all reagents were used as received without any purifications. Chromatographic purification was carried out using 230-400 meshsize silica gel.1H and13C NMR spectroscopy characterizations were carried out on Bruker 400 spectrometer (' H, 400 MHz;13C, 100 MHz). Atmospheric pressure chemical ionization mass spectra (APCI-MS) were recorded by using molecular solid sample on Advion-ExpressionL-CMS instrument. Thermogravimmetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were performed under nitrogen (heating rate ~ 10 °C / min) using Mettler Toledo-TGA / STDA 851 and Mettler Toledo-DSC 822e model instruments, respectively. Conventional melting temperatures were recorded on Electrothermal IA9000 instrument. Cyclic voltammograms were recorded on the BAS-Epsilon potentiostat / galvanostat system (Bioanalytical Systems Inc. (Lafayette, IN) equipped with a C3-cell stand electrochemical station) using ferrocene / ferrocenium redox couple (Fc / Fc+: E1 / 2= +0.40 V) as the internal standard. Pt wire was used as the working and the counter electrodes, and the reference electrode was Ag / AgCl (3 M NaCl). The. UV-vis absorption studies were performed on a Shimadzu UV-1800 spectrophotometer.

[0023] Scheme 1 shows the general structure (I) of mono-carbonyl BTBT semiconductor molecules of the invention where R is selected from a linear or branched, alkyl or alkoxy group of 1-20 carbon atoms with or without alkene or alkyne functional groups. R is also selected from an aryl group of 6-20 carbon atoms with or without one or more alkyl or alkoxy substituents of 1-20 carbon atoms with or without alkene or alkyne functional groups, and a heteroaryl group of 5-20 ring atoms with or without one or more alkyl or alkoxy substituents of 1-20 carbon atoms with or without alkene or alkyne functional groups.

[0024]

[0025] (I)

[0026] The following examples of this mono-carbonyl BTBT semiconductor molecule family are synthesized and characterized in this invention: m-MeCO-BTBT, m-PhCO-BTBT, m-PhFCO-BTBT, m-C7CO-BTBT, m-C6PhCO-BTBT, m-t-BuPhCO-BTBT, m-NaphCO-BTBT, and m-BisPhCO-BTBT (Scheme 2)AICI3, DCM AICIj, DCM -78 °C to RT -78 °C to RT o m-MeCO-BTBT m-C6PhCO-BTBT

[0027] AICI3, DCM o m-PhCO-BTBT m-t-BuPhCO-BTBT

[0028] DCM AICI3, DCM -78 °C to RT ■78 °C to RT O m-NaphCO-BTBT m-PhFCO-BTBT C7His-<fCl / \ J AICI3, DCM AICI-, DCM O -78 °C to RT -78 °C to RT o

[0029]

[0030] m-C7CO-BTBT m-BisPhCO-BTBT

[0031] Scheme 2

[0032] Syntheses, chemical characterizations, and thermal properties

[0033] Scheme 2 shows the chemical structures and the syntheses of the mono-carbonyl functionalized BTBT semiconductor examples developed in this invention. The monocarbonyl functionalized BTBTs were synthesized on a several-hundred-mg scale via regioselective Friedel-Crafts acylation, in the presence of AlCl3Lewis acid catalyst, at 2-position of the BTBT 7t-core using different alkyl- or aryl -acyl chloride reagents. For example, 4-w-hexylbenzoyl chloride was used in the case of -CePhCO-BTBT, benzoyl chloride was used in the case of m-PhCO-BTBT, and 4-w-octanoylchloride was used in the case of m-C7CO-BTBT. As the new molecules were found to have excellent solubility (vide infra) in common organic solvents, the purifications were performed via column chromatography to yield the final pure solids on a several-hundred-mg scale as single batches. The molecular structure and the chemical purity of the new molecules were characterized by using1H and13C NMR spectroscopies, and atmospheric-pressure chemical ionization mass spectrometry (APCI-MS). As shown in Figure 2, the chemical shifts of the non-exchangeable aromatic protons “e, g” in -CePhCO-BTBT, which are on the outer phenyl ring adjacent to the 4- / 7-hexylbenzoyl unit, show downfield shifts of ~0.5 ppm relative to those of the unfunctionalized BTBT. However, the other outer phenyl ring protons “a-d” show minimal changes in their chemical shifts. This indicates a reduced electron density (^-electron deficiency) on one side of the BTBT unit due to the asymmetric electron withdrawing effect of the mono-carbonyl functionalization. The 7t-density on the other outer phenyl side remainssimilar to that of the parent BTBT 7t-system. As another indicator of asymmetric electronic structure, for example, -CePhCO-BTBT shows a large ground state molecular dipole moment (μg= 3.17 D). On the basis of the thermogravimetric analysis, the new monocarbonyl BTBTs exhibit high thermolysis onset temperatures (Tonset~ 5% weight loss) of >300 °C and nearly quantitative decomposition behavior. All of the new molecules show one major endothermic transition at the melting temperature, which corresponds to transitions to an isotropic liquid phase, as confirmed via conventional melting point measurements.

[0034] The syntheses and chemical characterization details are given below:

[0035] Synthesis of l-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)ethanone (m-MeCO-BTBT): AlCl3(0.31 g, 2.33 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.56 g, 2.33 mmol) in anhydrous dichloromethane (50 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. Acetyl Chloride (0.18 g, 2.33 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, organic layer was dried with ISfeSC, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform as mobile phase. After column, MeOH leaching was carried out to afford the final product as a white solid (427 mg, 65% yield). Melting point: 222-223 °C;1H NMR (400 MHz, CDCl3), 8 (ppm): 8.55 (s, 1H), 8.07 (d, 1H, J = 8.0 Hz), 8.05 (d, 3H, J = 8.0 Hz), 7.51-7.47 (t, 2H, J = 16.0 Hz), 2.73 (s, 3H);13C NMR (100 MHz, CDCl3), δ (ppm): 197.1, 142.8, 142.2, 137.0, 136.4, 133.9, 132.9, 132.8, 125.9, 125.1, 124.9, 124.8, 124.2, 122.1, 121.5, 121.4, 26.7; MS (Mass Spec.) m / z calcd for C16H10OS2: 282.02[M+]; found: 282.487[M+].

[0036] Synthesis of benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl(phenyl)methanone (m-PhCO-BTBT): AlCl3(0.27 g, 2.0 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.40 g, 1.66 mmol) in anhydrous dichloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. Benzoyl Chloride (1.17 g, 8.32 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, the organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gelusing chloroform as mobile phase. After column, MeOH leaching was carried out to afford the final product as a pale yellow solid (354 mg, 62% yield). Melting point: 223-224 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.41 (s, 1H), 7.96-7.93 (t, 4H, J = 12.0 Hz), 7.87-7.86 (d, 2H, J = 4.0 Hz), 7.65 (t, 1H, J = 16.0 Hz), 7.54-7.49 (m, 4H);13C NMR (100 MHz, CDCl3), δ (ppm): 196.4, 142.9, 141.9, 137.9, 136.9, 136.1, 134.0, 133.1, 132.8, 132.4, 130.1, 128.5, 126.9, 126.8, 125.9, 125.2, 124.2, 122.2, 121.2; MS (Mass Spec.) m / z calcd for C21H12OS2: 344.03[M+]; found: 344.540[M+].

[0037] Synthesis of benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl(perfluorophenyl)methanone (m-PhFCO-BTBT): AlCl3(0.24 g, 1.83 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.40 g, 1.66 mmol) in anhydrous dichloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. Perfluorobenzoyl Chloride (0.42 g, 1.83 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, the organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform: hexane (1:1) as mobile phase. After the column, MeOH leaching was carried out to afford the final product as a pale yellow solid (280 mg, 39% yield). Melting point: 234-235 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.41 (s, 1H), 7.98-7.97 (m, 4H), 7.51 (m, 2H);13C NMR (100 MHz, CDCl3), δ (ppm): 184.1, 143.2, 142.4, 138.6, 137.8, 133.0, 132.5, 132.4, 126.6, 126.4, 126.0, 125.8, 125.3, 124.2, 122.3, 121.9; MS (Mass Spec.) m / z calcd for C21H7F5OS2: 433.99[M+]; found: 434.568[M+]. Synthesis of 1-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)octan-1-one (m-C7CO-BTBT): AlCl3(0.31 g, 2.33 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.56 g, 2.33 mmol) in anhydrous dichloromethane (50 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. Octanoyl chloride (0.38 g, 2.33 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, the organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform as mobile phase to afford the final product as a white solid (623 mg, 73% yield). Melting point: 175-176 °C; 'H NMR (400 MHz, CDCh), 6 (ppm): 8.56 (s, 1H), 8.06(d, 1H J = 8.0 Hz), 7.97-7.95 (t, 3H, J = 8.0 Hz), 7.51-7.46 (m, 2H), 3.10-3.06 (t, 2H, J = 16.0 Hz), 1.82-1.79 (m, 2H), 1.40-1.32 (m, 8H), 0.92 (t, 3H, J = 16.0 Hz);13C NMR (100 MHz, CDCl3), δ (ppm): 199.7, 142.8, 142.2, 136.8, 136.2, 133.7, 133.0, 132.8, 125.8, 125.1, 124.8, 125.5, 124.2, 122.1, 121.4, 38.8, 31.4, 29.4, 28.7, 24.6, 22.6, 14.1; MS (Mass Spec.) m / z calcd for C22H22OS2: 366.11[M+]; found: 366.469[M+].

[0038] Synthesis of benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl(4-hexylphenyl)methanone (m-CePhCO-BTBT): AlCl3(1.21 g, 9.07 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.40 g, 1.66 mmol) in anhydrous dichloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. 4-Hexylbenzoyl Chloride (1.86 g, 8.30 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, the organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform as mobile phase and after column, MeOH leaching was carried out to afford the final product as a white solid (595 mg, 83% yield). Melting point: 145-146 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.40 (s, 1H), 7.97 (m, 4H), 7.81-7.79 (d, 2H, J = 12.0 Hz), 7.53-7.47 (m, 2H), 7.35-7.33 (d, 2H, J = 8.0 Hz), 2.74-2.71 (t, 2H, J = 12.0 Hz), 1.69 (m, 2H), 1.35 (m, 6H), 0.91 (m, 3H);13C NMR (100 MHz, CDCl3), δ (ppm): 195.8, 148.2, 142.8, 141.9, 136.7, 135.9, 135.3, 134.4, 133.0, 132.8, 130.3, 128.4, 126.8, 126.5, 125.8, 125.2, 124.1, 122.1, 121.2, 36.1, 31.8, 31.3, 28.8, 22.7, 14.1; MS (Mass Spec.) m / z calcd for C27H24OS2: 428.13[M+]; found: 428.440[M+].

[0039] Synthesis of benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl(4-(tert-butyl)phenyl)methanone ( / n-t-BuI’hCO-BTBT): AlCl3(0.167 g, 1.25 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.25 g, 1.04 mmol) in anhydrous di chloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. 4-(tert-Butyl)benzoyl chloride (1.02 g, 5.18 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform as mobile phase and after column, MeOH leaching was carried out to afford the final product as a white solid (120 mg,29% yield). Melting point: 224-225 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.42 (s, 1H), 7.98 (m, 4H), 7.97-7.95 (d, 2H, J = 12.0 Hz), 7.57-7.55 (m, 2H), 7.50 (m, 2H, J = 8.0 Hz), 1.41 (m, 9H),;13C NMR (100 MHz, CDCl3), δ (ppm): 195.6, 156.2, 142.8, 141.8, 136.7, 135.9, 135.0, 134.3, 133.0, 132.8, 130.1, 126.7, 126.6, 125.8, 125.1, 124.1, 122.0, 121.2, 35.1, 31.1; MS (Mass Spec.) m / z calcd for C25H20OS2: 400.10[M+]; found: 400.824[M+]. Synthesis of benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl(naphthalen-2-yl)methanone (m-NaphCO-BTBT): AlCl3(0.167 g, 1.25 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.250 g, 1.04 mmol) in anhydrous dichloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. 2-Naphthoyl chloride (0.991 g, 5.2 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, organic layer dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform:hexane (2:1) as mobile phase and after column, MeOH leaching was carried out to afford the final product as a white solid (230 mg, 56% yield). Melting point: 216-217 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.48 (s, 1H), 8.34 (s, 1H), 8.02 (m, 7H), 7.75 (m, 3H, J = 12.0 Hz), 7.51 (m, 2H);13C NMR (100 MHz, CDCl3), δ (ppm): 142.8, 142.0, 136.0, 135.2, 135.1, 134.3, 132.7, 132.3, 131.6, 129.4, 128.4, 127.8, 126.9, 126.7, 125.8, 125.1, 124.2, 122.1, 121.2; MS (Mass Spec.) m / z calcd for C25H14OS2: 394.05[M+]; found: 395.017[M+].

[0040] Synthesis of [l,l'-biphenyl]-4-yl(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)methanone (m-BisPhCO-BTBT): AlCl3(0.167 g, 1.25 mmol) was added into a solution of [l]benzothieno[3,2-b][l]benzothiophene (0.250 g, 1.04 mmol) in anhydrous di chloromethane (40 mL) at -10 °C under nitrogen. The resulting solution was stirred at -10 °C for 30 min. Then, the reaction mixture was cooled down to -78 °C. Biphenyl-4-carbonyl chloride (1.13 g, 5.2 mmol) was subsequently added dropwise, and the mixture was stirred for 1 h at the same temperature. The reaction mixture was allowed to warm to room temperature and stirred for 2 days. After extraction with CHCh, organic layer was dried with Na2SO4, filtered and concentrated to obtain the crude product. The crude was then purified through column chromatography on silica gel using chloroform: hexane (2:1) as mobile phase and after column, MeOH leaching was carried out to afford the final product as a white solid (100 mg, 23% yield). Melting point: 247-248 °C;1H NMR (400 MHz, CDCl3), δ (ppm): 8.46 (s, 1H),8.00-7.97 (m, 6H), 7.78 (d, 2H, J = 12.0 Hz), 7.71 (d, 2H), 7.52-7.74 (m, 5H);13C NMR (100 MHz, CDCl3), 8 (ppm): 195.5, 145.2, 142.8, 141.9, 139.9, 136.9, 136.5, 136.0, 134.1, 133.0, 132.7, 130.7, 129.0, 128.2, 127.3, 126.7, 126.6, 125.8, 125.1, 124.2, 122.1, 121.2; MS (Mass Spec.) m / z cal cd for C27H16OS2: 420.06[M+]; found: 420.731[M+],

[0041] Solubility measurements

[0042] The gravimetric method is employed to determine the solubilities of the new semiconductor molecules. In this method, approximately 10.0-15.0 mg of the semiconductor solid is accurately weighed into a vial. Incremental volumes of the solvent (in 50-100 pL portions) are then added using a micropipette. After each addition, the solution is stirred or sonicated for 10 minutes at room temperature. This process continues until the complete dissolution is visually confirmed. Once dissolution is complete, the semiconductor solution is filtered through a PTFE syringe filter (VWR, part of Avantor, 0.20 pm pore size) and then evaporated to dryness using a rotary evaporator. The gravimetric solubility was determined by calculating the ratio of the recovered semiconductor solid weight (mosc) to the total amount of solvent. (Vsoivent), using the equation “solubility = mOSc / VSoivent”. The solubility values of the new semiconductor molecules in different solvents are given in Table 1. All new semiconductor molecules show solubilities of 4.5-176.0 mg mL'1in chloroform. The new semiconductor molecules also showed reasonable solubilities up to 8.8 mg mL'1in green solvents including ethyl acetate, acetone, ethanol, ethylene carbonate, ethoxybenzene, and 2-methyltetrahydrofuran. Notably, -CePhCO-BTBT shows an instantaneous dissolution behavior at room temperature in chloroform with a remarkable solubility of 176.0 mg mL'1. This corresponds to a molarity of 0.41 M, which, is the highest solubility ever reported for a high performance organic semiconductor.17-23Note that this is >20-40* higher than those of the previously reported Cn-BTBT-Ph’s (solubility < 9-11 mg mL'1)8and BTBT-Ph-Cn’s (solubility « 5-10 mg mL'1)9 10, which carry the same alkyl and phenyl molecular fragments on the BTBT 7t-system. This suggests that our asymmetric mono-carbonyl design is effective in inducing an extremely high solubility in organic solvents, and giving BTBT structures an ability to develop stronger interactions with solvent molecules.Table 1. Solubility values of the new mono-carbonyl BTBT semiconductor molecules (m- CePhCO-BTBT, -PhCO-BTBT, m-I’hiCO-BTBT. m-C CO-BTBT. -t-BuPhCO- BTBT, -NaphCO-BTBT, / n-BisPhCO-BTBT and -MeCO-BTBT) in different solvents.

[0043] Melting Point Solubility (mg-mL1)

[0044] Compound Ethyl

[0045] (°C) Chloroform Methylene Toluene Ethanol Acetone Ethylene Chloride Acetate Carbonate m-MeCO-BTBT 222-223 22.5 8.2 4.2 247 0.36 2.43 2.35 m-PhCO-BTBT 223-224 222 6.3 2.37 0.90 ■ 075 0.86 m-PhpCO-BTBT 234-235 364 12.5 22.2 4.2 0.21 342 1.37 m-C CO-BI BI

[0046] 175-176 583 25.1 7.3 1.61 0.10 1.57 0.12 m-CcPhCO- BTBT 145-146 1760 87.5 34.0 8.8 0.24 270 0.36 m-t-BuPhCO- BTBT 224-225 31 3 16.8 5.3 2.21 0.17 156 0.25 m-NaPhCO- BTBT 216-217 26.6 6.4 3.11 1 47 0.16 1.43 0.56 m-BisPhCO- BTBT 247-248 4.5 4.11 1.51 0.35 0.05 0.30 0.19

[0047]

[0048] Hansen solubility parameters and structure-solubility relationships

[0049] To gain insights into molecular design and reveal the key structural components that enable good solubilities of the new semiconductor molecules, especially the record-high solubility behavior of -CePhCO-BTBT, the Hansen solubility parameters for three of these molecules are calculated. The HSPs for -CePhCO-BTBT are determined to be δD= 18.9 MPa1 / 2, δP= 5.7 MPa1 / 2, and δH= 5.8 MPa1 / 2with an interaction radius (Ro) of 8.0 MPa1 / 2. The HSPs for m-PhCO-BTBT are determined to be 5D= 20.5 MPa1 / 2, 5P= 7.7 MPa1 / 2, and 5H= 9.6 MPa1 / 2with an interaction radius (Ro) of 8.9 MPa1 / 2. The HSPs for / M-C7CO-BTBT are determined to be δD= 19.2 MPa1 / 2, δP= 6.9 MPa1 / 2, and δH= 6.5 MPa1 / 2with an interaction radius (Ro) of 6.8MPa1 / 2. On the basis of the calculated HSPs, chloroform, which appears to be the best solvent for all three molecules, gives the closest solute-solvent interaction distances (Ra= (4ΔδD2+ ΔδP2+ ΔδH2)1 / 2), as compared to the rest of the solvents. More importantly, Ravalue gradually decreases as 8.05 MPa1 / 2(for m-PhCO-BTBT), 4.79 MPa1 / 2(for / M-C7CO-BTBT), and 3.36 MPa1 / 2(for -CePhCO-BTBT), which aligns well with the corresponding gradual solubility increase of 0.06 M 0.16 M 0.41 M. Due to the fourfold effect of the difference in dispersion parameters (ΔδD) on Ra, -CePhCO-BTBT with the closest δDvalue to that of chloroform yields the highest solubility. This highlights a key design advantage of alkyl-aryl substitution over either alkyl or aryl substitution alone, particularly in enhancing the molecular solubility of a rigid 7t-system.The excellent solubility of m-Q. PhCO-BTBT is compared with that of previously reported BTBT-Ph-Ce / Ci2 semiconductors, which have exactly the same “7t-7t-o” subunit sequence as the molecule but lack an electron withdrawing carbonyl unit. It is noteworthy that one of these molecules even has a longer alkyl chain (-W-C12H25). In the earlier studies with BTBT-Ph-C6 / C12,9 10the material purifications and OFET thin-film depositions have been performed via non- solvent-based techniques, vacuum sublimation and physical vapor deposition. Therefore, it is evident that the solubility of BTBT-Ph-Ce / C is well below -5-10 mg mL'1, which is typically the minimum requirement for solution processing.23,24This vis-a-vis experimental comparison clearly demonstrates that inserting a mono-carbonyl unit between the 7t-core and the aryl substituent, transitioning from “TC-TC-O” to a “7t-CO-7t-o” configuration, notably enhances molecular solubility. On the other hand, transitioning from m-CTCO-BTBT to D(C7CO)-BTBT, which was synthesized in previous study,12although an additional solubilizing alkyl substituent is introduced, the molecular solubility decreases more than tenfold (58.3 mg mL'1— <3.5 mg mL'1). One may also compare the di-carbonyl semiconductor D(C7CO)-BTBT with the analogous non-carbonyl derivatives of (di)-C7 / 8-BTBT that have the same alkyl substituents.4,12Despite having the same alky substituents, dicarbonyl functionalization significantly decreases molecular solubility (70-80 mg mL'1—> <3.5 mg mL'1). Therefore, it is evident that while mono carbonyl functionalization greatly improves solubility, going from an asymmetric mono-carbonyl to a symmetric di-carbonyl configuration (“7t-CO-substituent” —> “substituent-CO-7r-CO-substituent”) results in a significant decrease in molecular solubility. These findings clearly indicates the advantage of having a monocarbonyl-functionalization on the BTBT 7t-system to enhance solubility in solvents.

[0050] Photophysical and electrochemical properties

[0051] The photophysical and electrochemical properties of the new semiconductor molecules are studied by UV-vis absorption and cyclic voltammetry. All semiconductor molecules show clear optical absorption spectra in the UV-Vis region. For example, as shown in Figure 3(a), consistent with its colorless solution, -CePhCO-BTBT molecule shows two low-energy absorption maxima at 327 / 362 nm with the onset wavelength of 391 nm (Egopt= 3.17 eV) in dichloromethane. The absorption maxima and the onset wavelengths show a significant bathochromic shift (Δλ ~ 40-55 nm) in the spin-coated thin-film, and a typical vibronic structure (-1200 cm'1) of an aromatic 7t-system is formed. This indicates that the “PhCO-BTBT” 7t-scaffold is coplanarized / rigidified in the solid state through intermolecular forces.All semiconductor molecules show clear (quasi)reversible electrochemical oxidation and reduction characteristics. For example, in -CePhCO-BTBT molecule, the cyclic voltammograms in dichloromethane solution shows clear (quasi)reversible oxidation and reduction peaks at +1.64 V and -1.65 V (vs. Ag / AgCl), respectively (Figure 3(b)). Considering that dialkyl-substituted counterpart Cs-BTBT shows only an oxidation peak at +1.35 V (vs. Ag / AgCl) in the same experimental system, the presence of a reduction peak and anodically shifted (ΔE1 / 2ox= +0.29 V) oxidation peak undoubtedly reflect the electronic effects of mono-carbonyl functionalization. As shown in Figure 3(c), HOMO and LUMO energy levels are estimated to be -2.75 eV and -6.04 eV, which falls between those of unfunctionalized (substituted with alkyl chains) and di-carbonyl functionalized BTBT molecules.

[0052] OFET Device Fabrication and Electrical Characterization

[0053] The charge transport characteristics of the new mono-carbonyl functionalized BTBT molecules were explored in top-contact / bottom-gate (TC / BG) OFETs. Top-contact / bottom-gate (TC / BG) organic field effect transistors (OFETs)25,26were fabricated on heavily / ?-doped (100) silicon substrate (p++-Si) having a 300 nm thermally grown silicon dioxide (SiO2) as the gate dielectric layer. The substrates were cleaned via sonication in an ultrasonic bath with hexane, acetone, and ethanol, respectively, for 10 minute each, dried with nitrogen and treated with air plasma for 3 min (Harrick Plasma, 30W). An ultrathin (~3.6 nm) polystyrene brush (PS-brush) layer (grafting density ~ 0.45 chains nm'2) was formed on the p++-Si / SiO2 (300 nm) substrates using hydroxyl-terminated polystyrene (Mn= 5.0 kDa, Mw / Mn= 1.05, Polymer Source Inc.) via a “grafting-to” method, as described in earlier methods.27-29Organic semiconductor films (40-50 nm thick) were spin-coated onto p++-Si / SiO2 (300 nm) / PS-brush (Mn= 5 kDa) substrates from varied solvents including green solvent solutions for some of the semiconductors (e.g., 4 mg mL'1in chloroform, 2-methyltetrahydrofuran, ethyl acetate, ethoxybenzene, and acetone) at 1200 rpm for 60 s. For deposition from ethanol (1 mg mL'1), drop-casting method was used at solution and substrate temperatures of 60 °C. The semiconductor thin films were then annealed at varied temperatures (90-130 °C) under vacuum. The surface morphology and the microstructure of the solution-processed semiconductor thin-films were characterized by using atomic force microscopy (NanoSurf FlexAFM C3000) and X-ray diffraction (Malvern Panalytical Empyrean diffractometer) techniques. Finally, Au source-drain electrodes (50 nm thickness) with variable channel lengths of 30, 40, 50, 60, 80 pm (width = 1000 pm) were deposited via thermal evaporation(growth rate = 0.2 A / s) under high vacuum (~10‘6Torr) using high density deposition masks (Ossila, E322). The electrical characterizations of the OFET devices were performed in an ambient probe station (Everbeing BD-6) using a Keithley 2614B source-measure unit (without excluding natural or fluorescent lighting). Charge carrier mobility (gh) was estimated in the saturation regime from the IDS1 / 2vs. VGStransfer plots based on the conventional metal-oxide-semiconductor field-effect transistor (MOSFET) model using the formula, µsat= (2IDSL) / [WCi(VGS- Vth)2], where IDS is the source-drain current, L is the channel length, PFis the channel width, Ci is the areal capacitance of the gate dielectric with the PS-brush layer (10.4 nF / cm2based on large grafting density of 0.45 chains nm'2and Mn= 5 kDa),30,31VGS is the gate voltage, and Vth is the threshold voltage.

[0054] All semiconductor molecules show p-type OFET characteristics under ambient conditions, and the corresponding data is provided in Table 2. Notably, the electrical characterizations conducted under ambient conditions for m-Ct. PhCO-BTBT revealed that all transistors processed from all different green solvents, exhibit clear p-channel semiconductor behavior with high current-modulation characteristics. The transistors function only under negative gate bias. For example, for the best performing semiconductor molecule m-Q. PhCO-BTBT, the maximum saturation hole mobilities were achieved for thin-films spin-coated from 2-methyltetrahydrofuran (µhmax= 1.87 cm2 / V s, gi / "8= 1.21 cm2 / V s (lon / Ioff = 107-108)) and ethyl acetate (µhmax= 0.62 cm2 / V s, µhavg= 0.41 cm2 / V s (lon / Ioff = 106-107)) solutions (Figures 4(c). Relatively lower gh’s of 0.07-0.11 cm2 / V s (lon / Ioff = 105-106) were realized for spin-coated thin-films from acetone and ethoxybenzene. On the other hand, semiconductor thin-films drop-casted from ethanol, onto p++-Si / SiO2 (300 nm) / PS-brush (Mn= 5 kDa) substrates yielded OFETs with lower µhof ~0.001 cm2 / V·s (lon / Ioff - 104and Vth = -39 V)). On the other hand, the microstructural and morphological characterizations for m-Ct. PhCO-BTBT thin film were performed by atomic force microscopy (AFM) and out-of-plane 9-29 X-ray diffraction (i.e., in Bragg-Brentano geometry) (Figure 4(a) and 4(b)). While poor hole mobilities (µh) of ~10-4cm2 / V·s were measured for the devices with only spin coated semiconductor layers, µhprogressively increased to 0.001 cm2 / V·s and 0.01 cm2 / V·s with thermal annealing at 70 °C and 90 °C, respectively. The highest hole mobility for all green solutions was achieved with the semiconductor thin films annealed at 120 °C (for 20 min). The highly responsive semiconductor behavior of m-Ci. PhCO-BTBT (Δµh≈ 20,000×) to thermal annealing was evident with the morphological characterizations. As shown in Figure 4(e), thermal annealing facilitates a progressive growth of smooth and micron-sized terraced2D islands with sharp edges and well-defined steps, from nanometer-sized (-100-200 nm) small granular domains obtained right after spin-coating process. Also, the crystallinity increases and the molecular packing becomes denser (i.e., decrease in ^ / -spacing) in the out-of-plane direction after thermal annealing (Figure 4(b)-top scans) and the molecules adopt an edge-on orientation on the surface (Figure 4(d)) which is very favorable for semiconductivity and charger transport.

[0055] Table 2. The charge transport characteristics of top-contact / bottom-gate (TC / BG) OFETs for the new mono-carbonyl BTBT semiconductor molecules ( -CePhCO-BTBT, m-PhCO-BTBT, m-PhiCO-BTBT. / n-C CO-BTBT. -t-BuPhCO-BTBT, -NaphCO-BTBT, m-BisPhCO-BTBT and m-MeCO-BTBT) (Maximum hole mobility values (pmax), on / off current rates (lon / Ioff) and threshold voltage values (Vth)).

[0056] Semiconductor Solvent, µhmax, Ln / Ln Vth

[0057] (cnr / V-s) (V) chloroform 0.44 106-23

[0058] 7.

[0059] 2-methyltetrahydrofuran 1.87 107-108-38

[0060] m-C6PhCO- ethyl acetate 0.62 106-107-30 B BT ethoxybenzene 0.11 105-106-26

[0061] acetone 0.07 105-106-12

[0062] ethanol (drop-casting) 0.001 104-39

[0063] m-PhCO-BTBT chloroform 1.46xl0'4102-25

[0064] m-PhtCO-BTBT chloroform 1.83xl0'5103-8

[0065] m-CvCO-BTBT chloroform 1.60xl0'5102-34

[0066] m-t-BuPhCO- - - _

[0067] m-t-BuPhCO-BTBT chloroform 7.00×10-6102-17 m-NaphCO-BTBT chloroform 5.94×10-5103-20 m-BisPhCO-BTBT chloroform 1.04×10-4103-16

[0068]

[0069] DIDI

[0070] m-MeCO-BTBT chloroform 2.91xl0'5102-51

[0071] There are very limited examples of OFETs processed from some of these solvents, especially from ethyl acetate, acetone, and ethanol.32-34Also, this is the first time that a BTBT-based OFET is fabricated from these green solvents. The excellent / ?-channel performances, having high gh’s and lon / Ioff ratios, achieved with 2-methyltetrahydrofuran and ethyl acetate green solvents rank among the highest reported from a green solvent.35,36Among all known high-performance (µh≥ 0.5 cm2 / V·s) -type semiconductors, -CePhCO-BTBT exhibits one of the deepest HOMO energy levels ever recorded at -6.04 eV.1,5,37The p-type semi conductivityof the new molecules, coupled with their wide optical band gaps and excellent processing abilities, suggests that they could find many practical applications in multilayer (opto)electronic devices such as OFETs, OLEDs, OPVs, OPDs, and organic lasers.38-40

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Claims

CLAIMS1. Asymmetric mono-carbonyl [l]benzothieno[3,2-b][l]benzothiophene semiconductor compound expressed by General Formula (I)s(I)where R is selected from a linear or branched, alkyl or alkoxy group of 1-20 carbon atoms with or without alkene or alkyne functional groups, or aryl group of 6-20 carbon atoms with or without one or more alkyl or alkoxy substituents of 1-20 carbon atoms with or without alkene or alkyne functional groups, or a heteroaryl group of 5-20 ring atoms with or without one or more alkyl or alkoxy substituents of 1-20 carbon atoms with or without alkene or alkyne functional groups.

2. A compound according to Claim 1 where R is methyl, phenyl, perfluorophenyl, heptyl, 4- hexylphenyl, 4-(tert-butyl)phenyl, naphthalene, biphenyl.

3. A compound according to Claim 2 where the compound is 1- (benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)ethanone having the chemical structure of:sso4. A compound according to Claim 2 where the compound is benzo[b]benzo[4,5]thieno[2,3- d]thi ophen-2 -yl(phenyl)methanone having the chemical structure of:so5. A compound according to Claim 2 where the compound is benzo[b]benzo[4,5]thieno[2,3- d]thiophen-2yl(perfluorophenyl)m ethanone having the chemical structure of:

6. A compound according to Claim 2 where the compound is 1- (benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)octan-l-one having the chemical structure of:S7. A compound according to Claim 2 where the compound is benzo[b]benzo[4,5]thieno[2,3- d]thiophen-2-yl(4-hexylphenyl)methanone having the chemical structure of:C6H13SO8. A compound according to Claim 2 where the compound is benzo[b]benzo[4,5]thieno[2,3- d]thi ophen-2 -yl(4-(tert-butyl)phenyl)methanone having the chemical structure of:O9. A compound according to Claim 2 where the compound is benzo[b]benzo[4,5]thieno[2,3- d]thi ophen-2 -yl(naphthalen-2-yl)methanone having the chemical structure of:ss10. A compound according to Claim 2 where the compound is [1, l'-biphenyl]-4- yl(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)methanone having the chemical structure of:ss11. An electronic device comprising the semiconductor compound according to any one of claims 1-10.

12. Method of producing [l]benzothieno[3,2-b][l]benzothiophene compound according to any one of claims 1-10 characterized in using regioselective Friedel-Crafts acylation, in the presence of AlCl3Lewis acid catalyst, at 2-position of the [l]benzothieno[3,2- b][l]benzothiophene using alkyl- or aryl-acylchloride reagent.

13. Method according to Claim 12 where, alkyl- or aryl-acylchloride reagent is acetyl chloride, benzoyl chloride, perfluorobenzoyl chloride, octanoyl chloride, 4-hexylbenzoyl chloride, 4-(tert-Butyl)benzoyl chloride, 2-naphthoyl chloride, or biphenyl-4-carbonyl chloride.

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