N-Benzoyl dithieno[3,2-b:2′,3′-d]pyrrole-based hyperbranched polymers by direct arylation polymerization
© The Author(s) 2017
Received: 6 July 2017
Accepted: 14 December 2017
Published: 21 December 2017
Although poly(N-acyl dithieno[3,2-b:2′,3′-d]pyrrole)s have attracted great attention as a new class of conducting polymers with highly stabilized energy levels, hyperbranched polymers based on this monomer type have not yet been studied. Thus, this work aims at the synthesis of novel hyperbranched polymers containing N-benzoyl dithieno[3,23,2-b:2′,3′-d]pyrrole acceptor unit and 3-hexylthiophene donor moiety via the direct arylation polymerization method. Their structures, molecular weights and thermal properties were characterized via 1H NMR and FTIR spectroscopies, GPC, TGA, DSC and XRD measurements, and the optical properties were investigated by UV–vis and fluorescence spectroscopies.
Hyperbranched conjugated polymers containing N-benzoyl dithieno[3,23,2-b:2′,3′-d]pyrrole acceptor unit and 3-hexylthiophene donor moiety, linked with either triphenylamine or triphenylbenzene as branching unit, were obtained via direct arylation polymerization of the N-benzoyl dithieno[3,23,2-b:2′,3′-d]pyrrole, 2,5-dibromo 3-hexylthiophene and tris(4-bromophenyl)amine (or 1,3,5-tris(4-bromophenyl)benzene) monomers. Organic solvent-soluble polymers with number-average molecular weights of around 18,000 g mol−1 were obtained in 80–92% yields. The DSC and XRD results suggested that the branching structure hindered the stacking of polymer chains, leading to crystalline domains with less ordered packing in comparison with the linear analogous polymers. The results revealed that the hyperbranched polymer with triphenylbenzene as the branching unit exhibited a strong red-shift of the maximum absorption wavelength, attributed to a higher polymer stacking order as a result of the planar structure of triphenylbenzene.
Conjugated polymers have received significant attention in fundamental and applied research owing to their interesting optical and optoelectronic properties. Thus, they have been used in many electronic applications such as light emitting diode (OLED), polymeric solar cells (PSCs), electrochromic devices, organic field-effect transistors (OFETs), chemo-and biosensors [1–4]. In these extensive applications, the donor–acceptor (D–A) type of conjugated polymers, consisting of both electron donor and electron acceptor substituents along the conjugated backbone with excellent electron mobility, broad absorption spectrum and properly matched energy levels, has generated significant interest in the field of PSCs [5–10]. Especially, conjugated polymers composed of various thiophene-based electron donating units have shown promising properties to be suitable as hole-transporting materials in electro-optical devices [11–13].
On the other hand, N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole belongs to a new class of dithieno[3,2-b:2′,3′-d]pyrroles incorporating N-acyl groups with highly stabilized energy levels, which have been studied for some years . Evenson and Rasmussen  have reported for the first time the synthesis of the N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole and analogous monomers via copper-catalyzed amidation. N-octanoyl dithieno[3,2-b:2′,3′-d]pyrrole was further electropolymerized, resulting in poly(N-octanoyl dithieno[3,2-b:2′,3′-d]pyrrole) with a polymeric bandgap of 1.60 eV . An N-substituted benzoyl dithieno[3,2-b:2′,3′-d]pyrrole was copolymerized with 4,7-dithieno-2,1,3-benzothiadiazole to give a polymer with a low band gap of 1.44 eV, the PSC of which had a power conversion efficiency (PCE) of 3.95% . Poly(N-alkanoyl dithieno[3,2-b:2′,3′-d]pyrrole-alt-quinoxaline)s have been shown to afford PSCs with high open-circuit voltages and PCEs up to 4.81% . More recently, Busireddy et al.  have reported the synthesis of a small molecule containing dithieno[3,2-b:2′,3′-d]pyrrole (DTP) and butylrhodanine as donor and acceptor moieties. PSCs fabricated from this donor material and -phenyl-C71-butyric acid methyl ester as acceptor reached a PCE of 6.54% .
Hyperbranched conjugated polymers with highly branched molecular structure can effectively suppress aggregation and therefore are attractive due to good solubility and processability, low viscosity as well as facile one-pot synthesis and tunable electrical properties. Despite extensive research on the synthesis of hyperbranched conducting polymers in the past [19–21], in the last couple of years considerable effort has been put into the development of hyperbranched conjugated structures based on new compositional units. The Cu(I)-catalyzed azide–alkyne click reaction was used to synthesize an ethynyl-capped hyperbranched conjugated polytriazole . Zhou et al.  employed Suzuki coupling polymerization to obtain hyperbranched polymers based on alkyl-modified 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine and fluorene units with high molecular weights and enhanced two-photon absorption as compared with their unsubstituted analogues. The Suzuki polymerization was also used to one-pot synthesize a hyperbranched conjugated polymer bearing dimethylamino groups to be used as a PSC cathode interlayer . Sen et al.  synthesized hyperbranched conjugated polymers based on 4,4′‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) via Sonogashira cross coupling polymerization reactions. The polymers showed red shifts in absorption and emission maxima upon contact with toluene and benzene vapors. Very recently, hyperbranched thiophene-flanked diketopyrrolopyrrole (TDPP)-based polymers with narrow bandgaps were prepared by direct arylation polymerization method . Knoevenagel condensation and Sonogashira coupling methods were used to synthesize different hyperbranched conjugated polymers, which were tested as chemosensors for detecting nitroaromatic compounds [27–29]. The base-catalyzed reactions between α,β-unsaturated ester and aldehyde was employed to synthesize hyperbranched conjugated polymers containing 1,3-butadiene repeating units and carboxylic ester side groups for sensing metal ion Fe3+ .
To the best of our knowledge, N-acyl dithieno[3,2-b:2′,3′-d]pyrrole-based hyperbranched conjugated polymers have not yet been studied. In this research, we present the synthesis of hyperbranched polymers having N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole and 3-hexylthiophene monomer units, linked with triphenylamine or triphenylbenzene as chain extender, via the direct arylation polycondensation . Besides the role of branch-forming units, triphenylamine and triphenylbenzene are also typical donor moieties in conjugated polymeric materials for optoelectronic devices [32–37]. The optical and thermal properties and the nanostructures of the obtained hyperbranched polymers were characterized, and the effect of polymer aggregation on optical properties was investigated.
Results and discussion
Tris(4-bromophenyl)amine was synthesized via bromination using N-bromosuccinimide, according to a procedure previously reported . On the other hand, 1,3,5-tris(4-bromophenyl)benzene was synthesized from 4-bromoacetophenone using H2SO4 (conc.) and K2S2O7 as the catalytic system following the procedure reported by Prasad et al. . N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole (monomer 3) was prepared via an amidation reaction by using copper(I) iodide and DMEDA as the catalytic system in the presence of K2CO3 at the reflux temperature for 24 h .
Direct arylation polycondensation
Characteristics of hyperbranched conjugated polymers prepared via direct arylation polycondensation of monomers 1, 3 and 4 (PBDP3HTTPA)a, and of monomers 2, 3 and 4 (PBD3HTTBP)b
Mn (g mol−1)d
Mw/M n d
3HT: BD: TPA (TPB) molar ratioe (r)
The polymer structures were characterized by transmission FT-IR and 1H NMR spectroscopies. The FT-IR spectra of PBDP3HTTPA and PBDP3HTTPB displayed several bands between 2850 and 3060 cm−1 asigned to CH stretching modes of n-hexyl groups and ring C–H stretching vibrations. The bands at 1585 and 1492 cm−1 are ascribed to the aromatic C=C stretching and aromatic C–H deformation vibrations, respectively, while the bands at 1323 and 1274 cm−1 are assigned to the C–N stretching of triphenylamine units. The appearance of a strong absorption band at 1700 cm−1 indicates the existence of C=O group of the N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole moiety in the polymer structure. The bands at 696 and 628 cm−1 are ascribed to the thiophene C–S–C bending and S–C stretching vibrations, respectively.
To reach more insights into the polymer structures, the unit ratio of 3-hexylthiophene (3HT) versus N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole (BD) was calculated based on the integration values of the thiophene-CH2 proton signal at 2.6 ppm (peak f, Fig. 2a) and the benzoyl ortho proton signal of N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole at 7.7 ppm (peak o, Fig. 3a). Taking into account that the molar ratio between the total number of 3HT and BD units versus the number of TPA units is 1.5, a compositional molar ratio (r) between BD, 3HT and TPA units of 1:1.18:1.45 was determined. In the case of PBDP3HTTPB, r was calculated based on the integration ratio between the thiophene-CH2 proton signal at 2.6 ppm (peak f, Fig. 3b) and the overlapping shift range of aromatic proton signals around 7.75 ppm of BD (peak q corresponding to 1 proton, Fig. 2b) and triphenylbenzene (peak l, m, n corresponding to 3 protons, Fig. 3b) moieties, taking into acount the molar ratio between the total number of 3HT and BD units versus the number of TPB units being 1.5. PBDP3HTTPB had a compositional molar ratio (r) between BD, 3HT and TPB units of 1:1.38:1.59. The characteristics of the obtained hyperbranched conjugated polymers are presented in Table 1. However, we could not determine the degree of branching by the use of 1H NMR integration, since the chemical shifts of branching, terminal, and linear units could not be differentiated.
In addition to the NMR results, which indirectly confirm the formation of hyperbranched structures, controlled experiments were also performed. Accordingly, one reactive site of the monomer 3-hexylthiophene (monomer 4) was blocked with a carbaldehyde (–CHO) group to give in 3-hexylthiophene-2-carbaldehyde. Direct arylation reaction between 3-hexylthiophene-2-carbaldehyde and tris(4-bromophenyl)amine (compound 1) was then conducted. Attributed to the non-participation of the carbaldehyde group in the direct arylation reaction, no hyperbranched structure was obtained, as indicated by the low molecular weight (below 1000 g mol−1) of the product determined by GPC and mass spectroscopic analysis. The 1H and 13C NMR results also indicated a corresponding star-structure formed from 3-hexylthiophene-2-carbaldehyde and tris(4-bromophenyl)amine. These results suggest that a hyperbranched structure could only be generated with the participation of both reactive sites of the monomer.
It should also be noted that in other controlled experiments, the direct arylation reaction between tris(4-bromophenyl)amine and N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole provided a polymer product with a poor solubility, suggesting that a hyperbranched structure was formed. On the other hand, the direct arylation reaction between tris(4-bromophenyl)amine and 3-hexylthiophene resulted in a polymer product with Mn of around 15,000 g mol−1 and Đ of 2.1.
In the case of PBDP3HTTPB, an absorption maximum at around 410–420 nm was observed in CHCl3, THF as well as toluene. However, an addition absorption peak at 750 nm was found for PBDP3HTTPB in THF and toluene, indicating the co-existence of a small fraction of polymer molecules in a more aggregated form. In solid film, besides an absorption maximum at 410 nm, PBDP3HTTPB exhibited an absorption peak at 700 nm, broadening to 850 nm. This reveals that PBDP3HTTPB has a high aggregation degree than PBDP3HTTPA in the solid state, which is in agreement with the DSC and XRD results.
UV–vis absorption and fluorescence emission maximum wavelengths, and the fluorescence quantum yields (ϕ F ) of PBDP3HTTPA and PBDP3HTTPB
380, 475, 520
460, 500, 560
380, 475, 520
We have demonstrated the successful synthesis of novel hyperbranched conjugated polymers containing N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole and 3-hexylthiophene monomer units, linked with the triphenylamine or triphenylbenzene moiety (PBDP3HTTPA and PBDP3HTTPB, respectively), via direct arylation polycondensation in 80–90% yields. The molecular weights of the obtained polymers were 18,000 g mol−1 for PBDP3HTTPA and 16,700 g mol−1 for PBDP3HTTPB. Both polymers exhibited high structural order in thin films, which can be promising for organic solar cell applications. The UV–vis absorption of PBDP3HTTPB containing triphenylbenzene as branching unit was red-shifted as compared with PBDP3HTTPA, as a result of a higher chain packing degree. Generally, the results proved that the optical properties of these hyperbranched conjugated polymers could be controlled via alteration of the branching unit, which is useful for potential application as optoelectronic materials.
3-Hexylthiophene (3HT) was purchased from TCI (Tokyo, Japan). triphenylamine, benzo [c] [1,2,5] thiadiazole, tetrahydrofuran (99.9%) and N-bromosuccinimide were purchased from Acros Organics. Palladium(II) acetate (Pd(OAc)2) (98%), tricyclohexylphosphine tetrafluoroborate (97%, PCy3·HBF4), 3,3′dibromo-2,2′bithiophene, benzamide, N,N′-dimethylethylenediamine (85%, DMEDA) and pivalic acid (PivOH) were purchased from Sigma-Aldrich. Potasium acetate (KOAc), sodium carbonate (99%), magnesium sulfate (98%), and copper iodine (CuI) were purchased from Acros and used as received. Chloroform (CHCl3, 99.5%), toluene (99.5%), and dimethylacetamide (DMAc, 99%) were purchased from Fisher/Acros and dried using molecular sieves under N2. Dichloromethane (99.8%), n-heptane (99%), methanol (99.8%), ethyl acetate (99%) and diethyl ether (99%) were purchased from Fisher/Acros and used as received.
1H NMR spectra were recorded in deuterated chloroform (CDCl3) with TMS as an internal reference, on a Bruker Avance 300 MHz. Fourier transform infrared (FT-IR) spectra, collected as the average of 64 scans with a resolution of 4 cm−1, were recorded from KBr disk on the FT-IR Bruker Tensor 27. Size exclusion chromatography (SEC) measurements were performed on a Polymer PL-GPC 50 gel permeation chromatograph system equipped with an RI detector, with tetrahydrofuran as the eluent at a flow rate of 1.0 mL min−1. Molecular weight and molecular weight distribution were calculated with reference to polystyrene standards. UV–vis absorption spectra of polymers in solution and polymer thin films were recorded on a Shimadzu UV-2450 spectrometer over a wavelength range of 300–700 nm. Fluorescence spectra were measured on a HORIBA IHR 325 spectrometer. Differential scanning calorimetry (DSC) measurements were carried out with a DSC 204 F1—NETZSCH instruments under nitrogen flow (heating rate 10 °C min−1). Thermogravimetric analysis (TGA) measurements were performed under nitrogen flow using a STA 409 PC Instruments with a heating rate of 10 °C min−1 from ambient temperature to 800 °C. Wide-angle powder X-ray diffraction (XRD) patterns were recorded at room temperature on a Bruker AXS D8 Advance diffractometer using Cu-Kα radiation (k = 0.15406 nm), at a scanning rate of 0.05 degrees per second. The data were analyzed using DIFRAC plus Evaluation Package (EVA) software. The d-spacing was calculated from peak positions using Cu-Kα radiation and Bragg’s law.
Synthesis of tris(4-bromophenyl)amine (1)
N-bromosuccinimide (2.17 g, 12.2 mmol) and triphenylamine (1 g, 4.08 mmol) were added to anhydrous THF (10 mL) at 0 °C under nitrogen. The mixture was stirred at 50 °C for 1.5 h. After completion of the reaction, 10 mL of distilled water was added to the reaction mixture, which was extracted with dichloromethane. The organic layer was washed with 10% solution of Na2S2O3 and 10% solution of KOH, dried over anhydrous MgSO4 and concentrated. The product was precipitated in cold n-heptane and dried under vacuum to give a white powder (Rf = 0.6; yield: 67%). 1H NMR (300 MHz, CDCl3), δ (ppm): 7.35 (d, 6H), 6.95 (d, 6H). 13C NMR (125 MHz, CDCl3): (ppm): 146.10, 132.42, 125.68, 116.17. MS m/z (M+) 478. Analysis calculated for C18H12Br3N: C, 45.1; H, 2.51; Br, 49.49; N, 2.92. Found: C, 45.35; H, 2.41; Br, 49.35; N, 2.89.
Synthesis of 1,3,5-tris(4-bromophenyl)benzene (2)
4-Bromoacetophenone (5 g, 25.13 mmol), 0.25 mL of H2SO4 (conc.) and K2S2O7 (6.6 g, 26.14 mmol) were heated at 180 °C for 16 h under a nitrogen atmosphere. The resulting crude solid was cooled to room temperature and refluxed in 25 mL of dry ethanol (EtOH) for 1 h and then cooled to room temperature. The solution was filtered and the resulting solid was refluxed in 25 mL of H2O to give a pale yellow solid that was then filtered. The crude product was dried under vacuum giving 7.5 g of dried product, which was recrystallized from CHCl3 (yield 55%). 1H NMR (300 MHz, CDCl3), (ppm): 7.51 (d, 6H), 7.60 (d, 6H), 7.68 (s, 3H). 13C NMR (125 MHz, CDCl3): (ppm): 139.82, 137.60, 130.23, 122.72, 121.43. MS m/z (M+) 539. Analysis calculated for C24H15Br3: C, 53.34; H, 2.77; Br, 43.89. Found: C, 53.25; H, 2.69; Br, 44.06.
Synthesis of N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole monomer (BD) (3)
To a 50 mL rounded-bottomed flask equipped with a magnetic stirrer was added copper iodide (0.19 g, 1 mmol), DMEDA (1.728 mL, 8 mmol), potassium carbonate (4.15 g, 30 mmol) in the nitrogen atmosphere. Then, toluene and a small amount of distilled water (1 equiv.) were added to the reaction mixture and the solution was stirred for 30 min. Benzamide (12 mmol) was added, followed by 3,3′-dibromo-2,2′-bithiophene (3.24 g, 10 mmol). The reaction mixture was stirred for 24 h at 110 °C. The reaction was cooled to the room temperature, then washed with distilled water (3 × 20 mL) and extracted with chloroform (3 × 20 mL). The organic phase was dried by anhydrous K2CO3. The solvent was removed by rotary evaporation. The crude product was purified by silica column chromatography (eluent: heptane/ethyl acetate: 4/1) to give the isolated product as a white crystalline solid (3.82 g, Rf = 0.75, yield: 45.3%). 1H NMR (500 MHz, CDCl3), δ (ppm) 7.73 (d, 2H), 7.65 (t, 1H), 7.55 (t, 2H), 7.1 (d, 2H), 6.85 (s, 2H). 13C NMR (125 MHz, CDCl3): (ppm): 167.0, 143.1, 134.5, 132.4, 128.7, 124.4, 121.8, 116.4; MS m/z [MNa]+: 306.04.
Synthesis of hyperbranched polymer based on N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole, 3-hexylthiophene and tris(4-bromophenyl)amine monomer moieties (PBDP3HTTPA) (5)
In a glove box, 28.34 mg (0.1 mmol) of N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole, 64.27 mg (0.133 mmol) of tris(4-bromophenyl)amine and 16.83 mg (0.1 mmol) of 3-hexylthiophene were dissolved in 3 mL of DMAc. To the solution, 1.03 mg (0.0048 mmol) of Pd(OAc)2, 3.46 mg (0.009 mmol) of PCy3.HBF4, 9.43 mg (0.09 mmol) of PivOH and 38.3 mg of K2-CO3 were added to the monomer solution. The vial was sealed with a rubber cap and then removed from the glove box. The vial was heated in a 100 °C oil bath for 24 h. After being cooled to room temperature, the reaction mixture was diluted with 30 mL of chloroform. The obtained organic layer was passed through Celite to remove the Pd catalyst and the insoluble polymer fraction, subsequently washed with 10% solution of Na2S2O3 and distilled water, dried over Na2CO3, concentrated and finally poured into a large amount of cold n-heptane to precipitate the polymer. The resulting polymer was isolated by filtration, washed with acetone to remove oligomers, and finally dried under reduced pressure at 50 °C for 24 h. A yield of 82% was obtained. FT-IR (cm−1): 3057, 2925, 2852, 1700, 1585, 1492, 1436, 1323, 1273, 1182, 1116, 1026, 825, 750, 721, 696, 606, 628, 542. 1H NMR (500 MHz, CDCl3), δ (ppm) 7.73 (d, 12H), 2.65 (s, 2H), 0.8–1.95 (m, 11H). 13C NMR (125 MHz, CDCl3): 167.0; 143.3, 141.0, 135.8, 132.7, 129.6, 128.7, 127.0, 126.2, 124.4, 122.1, 116.4, 32.1, 30.7, 29.0, 22.5, 14.0. GPC: M n = 18,000 g mol−1. Đ = M w /M n = 2.1
Synthesis of hyperbranched polymer based on N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole, 3-hexylthiophene and 1,3,5-tris(4-bromophenyl)benzene monomer moieties (PBDP3HTTPB) (6)
In a glove box, 28.34 mg (0.1 mmol) of N-benzoyl dithieno[3,2-b:2′,3′-d]pyrrole, 72.45 mg (0.133 mmol) of 1,3,5-tris(4-bromophenyl)benzene and 16.83 mg (0.1 mmol) of 3-hexylthiophene were dissolved in 3 mL of DMAc. To the solution, 1.03 mg (0.0048 mmol) of Pd(OAc)2, 3.46 mg (0.009 mmol) of PCy3.HBF4, 9.43 mg (0.09 mmol) of PivOH and 38.3 mg of K2-CO3 were added to the monomer solution. The vial was sealed with a rubber cap and then removed from the glove box. The vial was heated in a 100 °C oil bath for 24 h. After being cooled to room temperature, the reaction mixture was diluted with 30 mL of chloroform. The obtained organic layer was passed through Celite to remove the Pd catalyst and the insoluble polymer fraction, subsequently washed with 10% solution of Na2S2O3 and distilled water, dried over Na2CO3, concentrated and finally poured into a large amount of cold n-heptane to precipitate the polymer. The resulting polymer was isolated by filtration, washed with acetone to remove oligomers, and finally dried under reduced pressure at 50 °C for 24 h. A yield of 90% was obtained. FT-IR (cm−1): 3059, 2917, 2851, 1700, 1584, 1560, 1490, 1436, 1319, 1274, 1183, 1117, 1011, 825, 753, 721, 696, 628, 542. 1H NMR (500 MHz, CDCl3), δ (ppm) 7.85–6.9 (d, 13H), 2.65 (s, 2H), 0.8–1.95 (m, 11H). 13C NMR (125 MHz, CDCl3): 167.0; 143.3, 141.0, 135.8, 131.5, 129.0, 127.3, 120.2, 124.4, 122.1, 116.4, 32.1, 30.7, 29.0, 22.5, 14.0. GPC: M n = 16,700 g mol−1. Đ = M w /M n = 2.3.
Synthesis of 3-hexylthiophene-2-carbaldehyde (for controlled experiment)
3-Hexylthiophene-2-carbaldehyde was synthesized according to the procedures reported in the literature [54, 55] with some modification. 3-Hexylthiophene (1 g) was dissolved in 100 mL of anhydrous toluene under nitrogen. DMF (4.6 mL, 59.2 mmol) and phosphorus(V)oxychloride (POCl3) (4.91 mL, 58 mmol) were then added to the solution. The reaction was performed at 75 °C for 24 h. The solution was cooled down to room temperature, followed by the addition of a saturated aqueous solution of sodium acetate. The solution was stirred for 4 h. Then, the compound was extracted with CHCl3 and dried over MgSO4. Then the solution was filtered and evaporated to obtain a crude compound. Finally, the crude compound was purified over silica column with hexane/ethyl acetate (v/v: 5/95) as eluent (Rf = 0.8, 0.9 g). The yield was 77.6%. 1H NMR (500 MHz, CDCl3), δ (ppm): 9.01 (s, 1H), 7.55 (d, 1H), 6.92 (d, 1H), 2.85 (t, 2H), 1.59 (m, 2H), 1.23 (m, 6H), 0.81 (t, 3H). 13C NMR (125 MHz, CDCl3), δ (ppm): 182.1, 152.8, 138.0, 134.6, 130.5, 31.6, 31.2, 29.0, 28.6, 22.6, 14.0. MS m/z (M+) 196, Analysis calculated for C11H16OS: C, 67.30; H, 8.22; O, 8.15; S, 16.33. Found: C, 66.73; H, 9.05; O, 7.85; S, 16.37.
Direct arylation reaction between 3-hexylthiophene-2-carbaldehyde and tris(4-bromophenyl)amine (controlled experiment)
Direct arylation reaction between 3-hexylthiophene-2-carbaldehyde and tris(4-bromophenyl)amine was performed, resulting in star-shaped 5,5′,5″-(nitrilotris(benzene-4,1-diyl))tris(3-hexylthiophene-2-carbaldehyde). Procedure: 0.1 g (0.51 mmol) of 3-hexylthiophene-2-carbaldehyde and 82.15 mg (0.17 mmol) of tris(4-bromophenyl)amine were dissolved in 20 mL DMAc. To the solution, 5.5 mg (0.025 mmol) of Pd(OAc)2, 19.22 mg (0.05 mmol) of PCy3.HBF4, 52.4 mg (0.5 mmol) of PiOH and 212 mg of K2CO3 were added to the monomer solution. The vial was sealed with a rubber cap and was freeze–pump–thaw degassed for several times. Then the reaction was heated in a 100 °C oil bath for 24 h. After being cooled to room temperature, the reaction mixture was diluted with 100 mL of chloroform, washed with brine three times and dried over MgSO4. The obtained organic layer was passed through Celite to remove the Pd catalyst, concentrated and finally purified over silica column with hexane/ethyl acetate eluent (v/v: 20/80) (Rf = 0.7, 113 mg) to give the isolated product as a dark yellow solid. The yield was 80.1%. 1H NMR (500 MHz, CDCl3), δ (ppm): 10.1 (s, 1H), 7.60 (d, 6H), 7.13 (s, 3H), 6.9 (d, 6H), 2.6 (t, 6H), 1.59 (m, 6H), 1.33 (m, 18H), 0.91 (t, 9H). 13C NMR (125 MHz, CDCl3), δ (ppm): 181.7, 152.4, 147.2, 141.0, 127.2, 125.3, 31.6, 29.7, 29.4, 28.0, 22.6, 14.1. MS m/z (M+) 828.4, Analysis calculated for C51H57NO3S3: C, 73.96; H, 6.94; N, 1.69; O, 5.80; S, 11.61. Found: C, 73.46; H, 6.81; N, 1.70; O, 6.60; S, 11.43.
THN, TAN and HMT carried out the synthesis, and characterization of the monomers and polymers. LTTN, ATL, JYL and HTN carried out the acquisition of data, analysis and interpretation of data collected and involved in drafting of manuscript, revision of draft for important intellectual content and give final approval of the version to be published. All authors read and approved the final manuscript.
This research was supported by The Department of Science and Technology (DOST)—Ho Chi Minh City under Grant Number [88/2016/HĐ-SKHCN].
The authors declare that they have no competing interests.
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