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Multicomponent Tandem Polymerizations of Aromatic Diynes, Terephthaloyl Chloride, and Hydrazines toward Functional Conjugated Polypyrazoles Xiaojuan Tang,† Chao Zheng,† Yizhao Chen,† Zujin Zhao,† Anjun Qin,† Rongrong Hu,*,† and Ben Zhong Tang*,†,‡ †

State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China

‡

S Supporting Information *

ABSTRACT: Multicomponent tandem polymerizations (MCTPs) of alkynes enjoying concise procedure, operational simplicity, synthetic efficiency, large structural diversity, high atom economy, and environmental benefit are recently developed as efficient strategies to synthesize functional conjugated polymers, which have attracted much attention from polymer scientists. In this work, through combination of Sonogashira coupling−Michael addition−cyclocondensation reactions in a one-pot procedure, an efficient three-component tandem polymerization of alkyne, carbonyl chloride, and hydrazine hydrate was reported to proceed smoothly under mild conditions at room temperature, affording polypyrazoles with high molecular weights (Mw up to 19 400 g/mol) in excellent yields (up to 95%). This MCTP also applies to various aromatic diynes and aromatic hydrazines, producing polypyrazoles with improved solubility and processability, higher Mws of up to 30 700 g/mol, and high yields. Structural characterization of the polymers such as IR, 1H NMR, and 13C NMR spectra suggested total consumption of monomers and complete conversion of the polymer intermediate, proving the desired well-defined structure of polypyrazoles. These polypyrazoles generally enjoy good solubility and film-forming ability, high thermal stability, high light refractivity, and luminescence behavior. Such MCTPs are not just a simple reaction to connect functional units together in a polymer chain; they can also build functional units such as the newly formed multisubstituted heterocyclics embedded in the polymer main chain at the same time.

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INTRODUCTION

isocyanide, aldehyde, carboxylic acid, and amine are extensively studied to produce diversely substituted polyamides.5,6 Besides isocyanide, alkyne is another promising monomer for the development of efficient MCPs because of its rich chemical property and potential unsaturated product structure from its extensively reported multicomponent reactions.7,8 A few alkyne-based MCPs have been reported recently.9 For example, two metal-catalyzed A3-coupling polymerizations of diyne, amine, and dialdehyde have reported to produce poly(propargylamines);10,11 Cu(I)-catalyzed MCP of diynes, azides, and diamines/dialcohols have been reported to generate libraries of poly(N-sulfonylamidines) or poly(N-sulfonylimidates) with high yields, large Mws and great structural diversity;4,12 a metal-free MCP of diynes, five-membered cyclic dithiocarbonate, and diamines is reported to produce polythiourethane;13 and a catalyst-free MCP of diynes,

The exploration of efficient polymerizations is of great scientific importance which is crucial to the development of new generation of functional polymer materials. Of all the polymerization strategies, multicomponent polymerization (MCP) with three or more monomers react together in a one-pot fashion to afford polymer product with well-defined structures is an emerging field which has attracted much attention among polymer scientists.1 MCP has inherited the advantages of multicomponent reactions such as large structural diversity, high efficiency and convenience, simple and cheap reactants, atom and step economy, simple operation, and environmental benefits.2,3 However, development of efficient MCPs remains to be challenging because of the narrow monomer scopes, various side reactions among multiple functional groups, defects in the polymer structure, limited molecular weight, and solubility issue of the polymer products.4 Among the reported MCPs, the isocyanide-based threecomponent Passerini polymerization of aldehyde, isocyanide, and carboxylic acid and four-component Ugi polymerization of © XXXX American Chemical Society

Received: October 8, 2016 Revised: November 25, 2016

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DOI: 10.1021/acs.macromol.6b02192 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Chemical Reactions between Alkynone and Hydrazine Hydrate or Phenylhydrazine

Scheme 2. Synthetic Routes of (A) P1−2, and (B) P3a−d

elemental sulfur, and diamines is reported to generate soluble polythioamides with well-defined structures.14 MCPs of alkynes also bring the opportunity to construct conjugated polymers efficiently and conveniently. We have successfully developed a series of multicomponent tandem polymerizations (MCTPs) which combine multiple steps into a one-pot procedure, avoiding the isolation and purification of the reactive intermediates, and afford conjugated polymers with well-defined structures compactly.15 Through combing the Sonogashira coupling reaction of alkynes and carbonyl chlorides, and a following hydrothiolation/hydroamination reaction of the reactive alkynone intermediates with thiols/ amines, heteroatom-containing conjugated polymer products can be obtained through such one-pot, two-step, threecomponent MCTPs under mild polymerization condition near room temperature.16−18

Among conjugated polymers, heterocyclic-containing conjugated polymers possess great potential in organic solar cells,19 organic light-emitting diodes,20 and chemical sensors21 for their potential semiconducting properties. The current synthetic approach for heterocyclic-containing conjugated polymers are predominantly transition-metal-catalyzed polycouplings which generally suffer from tedious synthesis and modification of heterocyclic-containing monomers, limited structural diversity, time-consuming procedures, and solubility issue of intermediates and products.22,23 There are hence great demand to develop efficient synthetic strategies to synthesize heterocycliccontaining conjugated polymers from simple monomers. We have reported an efficient three-component tandem polymerization of alkyne, carbonyl chloride, and ethyl 2-mercaptoacetate through sequential Sonogashira coupling−Michael addition−Fiesselmann cyclocondenstation three-step reaction to construct functional poly(arylene thiophenylene) with newly B


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Macromolecules formed multisubstituted thiophene rings in the polymer backbone, high Mw, and excellent yield.18 Pyrazole is another important heterocyclic with wide applications as blue fluorophores,24 optical brighteners,25 ligands for metal−organic frameworks,26 building blocks for liquid crystalline displays,27 and intermediates for biological molecules.28 Polypyrazoles are also promising materials with potential blue emission;29,30 however, there are still lack of efficient synthetic methods.31,32 Alkynone can react with hydrazines to form pyrazole rings after cascade addition− cyclocondensation reactions (Scheme 1).33 A similar strategy of combining Sonogashira coupling−Michael addition−cyclocondensation reactions is adopted to synthesize multisubstituted pyrazoles in good to excellent yields in moderate condition with good regioselectivity and wide substrate applicability.34,35 In this work, we explored the MCTP of aromatic diyne, terephthaloyl chloride, and hydrazine hydrate/phenylhydrazine and developed it into an efficient polymerization for the preparation of functional conjugated polypyrazoles with high molecular weight in high yield. This MCTP does not just serve as a simple connection method to link monomer units in a polymer chain; most importantly, it can also build new functional units in situ, which greatly simplifies the synthetic routes of functional polymers.

Table 1. Effect of Solvent Used in the Addition− Cyclocondensation Reaction on the Polymerization of 1a, 2, and 3a entry

solvent

yield (%)

Mwb (g/mol)

Mw/Mnb

1 2 3 4

THF MeCN MeOH DMF

89 81 94 95

14200 14500 13500 19400

1.54 2.03 1.59 2.30

a Monomer 1a was reacted with 2 at room temperature in 4 mL of THF under nitrogen in the presence of Pd(PPh3)2Cl2, CuI, and Et3N for 1 h, prior to the addition of 3 and 1 mL of solvent, which then reacted at room temperature for 12 h. [1a] = [2] = 0.05 M, [Et3N] = 0.1 M, [Pd(PPh3)2Cl2] = 0.002 M, [CuI] = 0.004 M, and [3] = 3[1a]. b Estimated by GPC in THF on the basis of a linear polystyrene calibration.

Table 2. Effect of Monomer Concentration on the Polymerization of 1a, 2, and 3a entry

[1a] (M)

yield (%)

Mwb (g/mol)

Mw/Mnb

1 2 3c 4

0.02 0.03 0.05 0.07

69 79 95 gel

6100 9400 19400

1.44 1.59 2.30

a Monomer 1a was reacted with 2 at room temperature in 4 mL of THF under nitrogen in the presence of Pd(PPh3)2Cl2, CuI, and Et3N for 1 h, prior to the addition of 1 mL of DMF and 3, which then reacted at room temperature for 12 h. [1a]:[2]:[Et3N]:[3] = 1:1:2:3, [Pd(PPh3)2Cl2] = 0.04[1a], [CuI] = 0.08[1a]. bEstimated by GPC in THF on the basis of a linear polystyrene calibration. cData taken from Table 1, entry 4.

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RESULTS AND DISCUSSION Polymerization. To develop one-pot, three-step, threecomponent tandem polymerizations for the synthesis of conjugated polymer products with newly built pyrazole rings in the polymer main chain, modified Sonogashira coupling of alkyne and carbonyl chloride, addition of hydrazine on alkynone, and the following cyclocondensation were combined in a one-pot polymerization. Monomers 1a−d and 2−4 are commercially available or can be facilely synthesized according to the literature. 36,37 The polymerization of bis(4ethynylphenyl)dimethylsilane (1a), terephthaloyl dichloride (2), and hydrazine hydrate (3) was first investigated. 1a was selected because of its nonconjugated structure and flexibility on the Si bridge, which may hamper possible π−π stacking interaction and hence improve the solubility of the resultant polymer product.38 Under the catalysis of Pd(PPh3)2Cl2 and CuI, 1a and 2 can react at room temperature and afford polyalkynone P1 after 1 h under nitrogen.39 The typical MCTP procedure is based on the Sonogashira coupling reaction through direct addition of the third component, monomer 3, as well as additional solvent into the polymerization system to further proceed the addition and cyclocondensation reactions for an additional 12 h at room temperature, affording polypyrazole P2 through such one-pot polymerization (Scheme 2). The solvent used in the addition−cyclocondensation reaction was first studied (Table 1). When THF or acetonitrile was used as the solvent, precipitates were observed in the polymerization system and the yield and Mw were relatively low. When methanol or DMF was used as the solvent which may possess better solubility considering the polarity and the potential hydrogen bonding formation of the polymer, high yields were obtained. Of all the tested solvents, MCTP in the presence of DMF afforded the best polymerization result with a high yield of 95% and a Mw of 19 400 g/mol. Monomer concentration is another crucial aspect of the MCTP (Table 2). When the concentrations of 1a and 2 were gradually increased from 0.02

to 0.05 M, the yield and Mw of the polymers gradually increased. Gelation was observed in the polymerization system when the monomer concentration was increased to 0.07 M, owing to the solubility limitation of polymer intermediate P1. Direct dilution of the concentrated reaction system could dissolve the gel and make the polymerization continue to obtain satisfactory results. The effect of reaction time for the addition−cyclocondensation reaction was also investigated, which does not show significant influence on the polymerization results (Table S1). Under such optimized polymerization condition, the MCTP of 1b−d, 2, and 3 were studied, which could not afford satisfactory results because of the poor solubility of the expected polymer structure. The N−H and the sp2 nitrogen atom in the newly formed pyrazole rings may interact with each other through hydrogen bonds, which may cause interchain tanglement and poor solubility. The third component of the MCTP was then replaced by phenylhydrazine (4) to avoid potential interchain hydrogen bonds in the polymer products and hence increase the solubility of polymer. The reaction temperature for the addition−cyclocondensation reaction was raised to 70 °C because phenylhydrazine is less reactive compared with 3. Protonated solvent methanol was added to facilitate the polymerization by forming hydrogen bonds between solvent and alkynones.40 The MCTPs of 1a−d, 2, and 4 all went smoothly and produced P3a−d with Mws of up to 30 700 g/ mol and high yields up to 95% (Table 3). These polyphenylpyrazoles generally possess better solubility than polypyrazoles. In particular, P3b with fully conjugated structure enjoys the best polymerization results, mainly because of the twisted structure of tetraphenylethene units which hampered the C


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Macromolecules Table 3. Monomer Exploration of the MCTPa entry polymer 1 2d 3 4 5 6

P1 P2 P3a P3b P3c P3d

monomers

yield (%)

Mwb (g/mol)

Mw/Mnb

Sc

1a + 2 1a + 2 + 3 1a + 2 + 4 1b + 2 + 4 1c + 2 + 4 1d + 2 + 4

97 95 95 87 72 63

15700 19400 18400 30700 10500 5900

2.16 2.30 2.43 2.17 1.90 1.58

√ √ √ √ Δ Δ

crystal XRD analysis proved the expected regioselective structure in Scheme 3 (Table S2). Compound 7 takes a butterfly shape. The molecular packing mode revealed the existence of intermolecular C−H···N interaction and C−H···π interaction. All the monomers, model compounds, and polymers are fully characterized by the standard spectroscopic techniques, giving satisfactory analysis results. Through the comparison of the spectra of monomers, model compounds, and the polymers, the chemical structures of the polypyrazoles are confirmed as those shown in Scheme 2. The IR spectra of 1a, 4, 7, P1, and P3a are compared in Figure 1 for example. The C−H and CC stretching vibrations of monomer 1a at 3293 and 2102 cm−1, respectively, the N−H stretching vibration of monomer 4 at 3338 cm−1, and the CC and CO stretching vibrations of intermediate P1 at 2194 and 1644 cm−1, respecitvely, have all disappeared in the spectra of P3a, suggesting the total consumption of monomers and complete conversion of the intermeditate. Meanwhile, the IR spectra of model compound 7 and P3a are very much alike, suggesting the expected chemical structure and regioselective product in the polymer backbone. Similarly, the IR spectra comparison of model compound 6 and P2 are shown in Figure S3; the representative peaks of the monomers and polymer intermediates have all disappeared, and the IR spectrum of polymer product matches well with that of the model compound, suggesting the desired polymer structure of P2. The 1H NMR spectra of 1a, 4, 7, P1, and P3a were also compared to reveal more structure details (Figure 2). The resonance peak of C−H of 1a at δ 3.10 is absent in the spectra of both 7 and P3a, indicating that the monomer has

a

[1] = [2] = 0.05 M, [Et3N] = 0.1 M, [Pd(PPh3)2Cl2] = 0.002 M, [CuI] = 0.004 M, and [3] = 3[1a]. Monomer 1 was reacted with 2 in 4 mL of THF under nitrogen in the presence of Pd(PPh3)2Cl2, CuI, and Et3N for 1 h (entry 1), prior to the addition of 1 mL of DMF and 3, which then reacted at room temperature for 12 h (entry 2), or prior to the addition of 1 mL of methanol and 4, which then reacted at 70 °C for 12 h (entries 3−6). bEstimated by GPC in THF on the basis of a linear polystyrene calibration. cSolubility (S) tested in organic solvents, such as chloroform, THF, and DMF: √ = completely soluble, Δ = partially soluble. dData taken from Table 1, entry 4.

intermolecular interaction and enlarged the interchain distance, resulting in good solubility. The Mws of polypyrazoles are relatively smaller compared with that of the previously reported polythiophene,18 mainly because the solubility limitation of these polypyrazoles. The first step polycoupling time is decreased from 3 to 1 h in this work to ensure soluble product. Structural Characterization. To characterize the polymer structure, two model compounds 6 and 7 were synthesized through similar one-pot, three-step, three-component tandem reaction in 89% yield (Scheme 3, Figures S1 and S2). Needleshaped single crystals of 7 were obtained in the mixed solvents of THF/acetonitrile/methanol (v/v/v = 1/1/3), and the single

Scheme 3. (A) Synthetic Routes of Model Compounds 6 and 7, (B) Single Crystal Structure, and (C) Molecular Packing of Model Compound 7

D


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Macromolecules

Figure 3. 1H NMR spectra of (A) 1a, (B) 6, and (C) P2 in DMSO-d6. The solvent peaks are marked with asterisks.

Figure 1. FT-IR spectra of (A) 1a, (B) 4, (C) 7, (D) P1, and (E) P3a.

the spectrum of 6, which further splitted into two small peaks, indicating the existence of a fast proton transfer isomerization. The aromatic proton on the newly formed pyrazole ring of 6 resonances at δ 7.20. These two representative peaks of pyrazole rings exist in the spectra of P2 at δ 13.44 and 7.25, respectively, which is in good accordance with the model compound. The structure of P3a was further confirmed by 13C NMR spectra (Figure 4). In the 13C NMR spectra of P3a, the resonances of the terminal acetylene carbon of 1a at δ 78.01 and 83.76 disappear; the resonances of the internal acetylene carbon of P1 at δ 87.50 and 94.37 and the resonances of carbonyl groups of P1 at δ 177.16 are all absent. Instead, new resonances at δ 105.55, 143.71, and 152.15, which represent the aromatic carbons of the newly formed pyrazole rings in 7, have

Figure 2. 1H NMR spectra of (A) 1a, (B) 4, (C) 7, (D) P1, and (E) P3a in CDCl3. The solvent peaks are marked with asterisks.

been completely consumed. Compared with the spectrum of intermediate P1, the aromatic proton of P1 close to the carbonyl group which resonances at δ 8.33 has totally disappeared in the spectrum of P3a. Meanwhile, the other two aromatic protons of P1 resonance at δ 7.67 and 7.57 have shifted to the downfield at δ 7.91 and 7.62, respectively, in the spectrum of P3a, proving that no alkynone structure exists in the polymer product. Compared with the spectrum of model compound 7, the aromatic proton on the newly formed pyrazole rings resonances at δ 6.87 emerges in the spectrum of P3a, while sharing similar spectrum profile with that of 7, proving the desired polymer structure. The 1H NMR spectra of 6 and P2 are compared in DMSOd6 solution, considering the solubility of the polymer (Figure 3). Similar analytical results can be summarized, except that an active pyrazole N−H proton resonances at δ 13.39 and 13.41 in

Figure 4. 13C NMR spectra of (A) 1a, (B) 4, (C) 7, (D) P1, and (E) P3a in CDCl3. The solvent peaks are marked with asterisks. E


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Macromolecules emerged in the spectra of P3a.34 All the spectroscopic analysis suggests the complete conversion of polymer intermediate and well-defined product structure. Kinetic Study on the Polymerization of 1a, 2, and 4. The time course study of the first step and the addition− cyclocondensation step of the MCTP of 1a, 2, and 4 was then conducted. The effect of the reaction time for the first coupling reaction is shown in Table S3. When the reaction time increased from 5 to 60 min, the Mw of P1 gradually increased. The 1H NMR spectra of P1 obtained in 5, 15, 30, and 60 min suggested that the polymerization is very fast, and after 5 min, most of the monomers have converted to P1 (Figure S4). The terminal alkyne peak at δ 3.10 and the dimethylsilyl peak at δ 0.55 of 1a were gradually decreased and eventually disappeared after 60 min reaction. Instead, the resonances of the dimethylsilyl groups in P1 emerged at δ 0.62, which has increased along the reaction time. The reaction time of the Michael addition−cyclocondensation reaction was also investigated from 1 to 12 h, and the Mw as well as 1H NMR spectra of the polymers were recorded (Table S4 and Figure S5). The reaction time shows little influence on Mw of P3a. The comparison of the 1H NMR spectra of P3a obtained after 1, 3, 5, and 12 h and P1 suggested that P1 has consumed rapidly in 1 h, and the conversion from P1 to P3a was completed in 12 h. Solubility and Thermal Stability. Despite the rigid polymer backbone structure, P2 and P3a−d generally possess satisfactory solubility in common organic solvents such as chloroform, THF, DMF, or DMSO. In particular, P2 is less soluble compared with P3a because of the existence of the N− H groups which might form an intermolecular hydrogen bond. These polypyrazoles can be fabricated into tough thin films by spin-coating their solutions, demonstrating good film-forming ability. Moreover, the polymers generally possess high thermal stability, with their decomposition temperature under nitrogen at a 5% weight loss ranging from 355 to 467 °C (Figure 5). High carbon residue rate of up to 85% still remained at 800 °C, demonstrating high thermal resistance. Transmittance and Refractive Index. Despite their conjugated structure, the thin films of these polypyrazoles show high transmittance. As shown in Figure 6A, P1−2 and P3a−d absorb little light in the visible spectral region and allow the light beyond 400 nm to transmit through, suggesting their

excellent optical transparency. Because of the existence of the large number of polarizable pyrazole and benzene rings, the refractive indices of their spin-coated thin films are investigated (Figure 6B and Table S5). P1 and P3a−d possess high RI values (n = 1.8100−1.6394 for P1, 1.7605−1.6556 for P3a, 1.6810−1.6385 for P3b, 1.8161−1.6199 for P3c, and 1.7667− 1.6494 for P3d) in a wide wavelength region (400−1700 nm), which are much higher than those of the commercially important optical plastics (e.g., n = 1.49 for poly(methyl methacrylate), n = 1.59 for polycarbonate and polystyrene). Their Abbé number (vD), which is defined as vD = (nD − 1)/(nF − nC), where nD, nF, and nC are the n values at Fraunhofer D, F, and C lines of 589.3, 486.1, and 656.3 nm, respectively,41 and the modified Abbé number (vD′), which is defined as vD′ = (n1319 − 1)/(n1064 − n1550) calculated from the n values at the nonabsorbing wavelengths of 1319, 1064, and 1550 nm, are summarized in Table S5. The chromatic dispersion of the polymers defined as D′ = 1/vD′ are in the range 3.5 × 10−3−2.4 × 10−2, which are generally smaller than those of the commercial optical plastics and show great potential in the optical applications.42 Photophysical Properties. Luminescence behavior of the small molecular model compounds 6 and 7 is observed. The photophysical properties of the model compounds and polymers are summarized in Figure 7 and Table S6. The absorption maxima of 6 and 7 in dilute THF solutions are located at 268 and 269 nm, respectively, while that of the polymers generally shifted to 278−333 nm, demonstrating the enlongated conjugation. The molar absorptivities of the polymers (24 800−56 000 L mol−1 cm−1) are generally smaller compared with that of the model compounds (54 400−59 600 L mol−1 cm−1). The emission maxima of 6 and 7 in THF solution are located at 332 and 371 nm, respectively, with the fluorescence quantum efficiencies (ΦFs) of 45.7% (6) and 11.0% (7). The polymer intermediate P1 is almost nonemissive in solution with a low ΦF of 0.4%. After it was converted to polypyrazoles P2 and P3a−d, the emission maxima generally located at 354−500 nm with the ΦFs in the range of 3.2%− 33.2%.

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CONCLUSIONS In this work, a one-pot, three-step, three-component tandem polymerization was developed for the convenient preparation of heterocyclic-containing conjugated polymers through combination of the Sonogashira coupling reaction of alkynes and teraphthaloyl chloride, the Michael addition reaction of alkynone intermediates and hydrazines, and the following cyclocondensation reaction in a sequential manner. The polymerization can proceed efficiently at room temperature, affording desired polypyrazoles with high regioselectivity, high molecular weight, and high yield. The single crystal structure of model compound together with the spectroscopic analysis of model compounds and polymers suggested that the monomers were fully transformed to the desired polymers without structure of intermediate observed in the polymer chain. Furthermore, this MCTP demonstrates general applicability to various aromatic diynes and hydrazines, producing functional polypyrazoles with good solubility and processability, high thermal stability, high light transparency and refractivity, and unique luminescence behavior. With the compelling advantages of MCTPs, their great potential in the construction of functional conjugated polymers, especially heterocyclic-containing semiconducting polymers, can be foreseen.

Figure 5. TGA thermograms under nitrogen with a heating rate of 10 °C/min. F


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Macromolecules

Figure 6. (A) Light transmission spectra of thin films of polymers P1−2 and P3a−d. (B) Wavelength-dependent refractive indices of the thin films of P1 and P3a−d.

Figure 7. (A) Absorption spectra of 6, 7, P1−2, and P3a−d in THF solutions. (B) Normalized PL spectra of 6, 7, P1−2, and P3a−d in THF solutions. Concentration: 10 μM.

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Refractive indices (RI) of polymer films were estimated by a J.A. Woolam V-VASE spectroscopic ellipsometer in a wavelength range of 400−1700 nm. Synthetic Procedures. All the reactions and polymerizations were conducted under nitrogen according to the standard Schlenk procedures. Bis[4-(3-phenyl-1H-pyrazol-5-yl)phenyl]dimethylsilane (6): Compound 1a (260 mg, 1.0 mmol), Pd(PPh3)2Cl2 (28 mg, 0.02 mmol), and CuI (15 mg, 0.04 mmol) were added into a 50 mL two-neck round-bottom flask equipped with a magnetic stir bar under nitrogen. 20 mL of distilled tetrahydrofuran was injected into the flask, followed by the addition of benzoyl chloride 5 (0.24 mL, 2.1 mmol) and triethylamine (0.29 mL, 2.1 mmol). The reaction mixture was stirred at room temperature for 1 h. After that, hydrazine hydrate (3) (0.36 mL, 3.0 mmol) and 5 mL of DMF were injected into the mixture and further stirred for 12 h at room temperature. The reaction was terminated by pouring the mixture into 50 mL of water and extracting with dichloromethane for three times (30 mL × 3), after which the organic phases were combined. After evaporation of the solvent, crude product was obtained, which was purified through silica-gel chromatography using petroleum/ethyl acetate (v/v = 10/1) as the eluent. A white solid was obtained in 89% yield. IR (KBr thin film), v (cm−1): 3200, 2923, 2855, 1665, 1636, 1575, 1459, 1257, 1114, 966, 809, 764, 690, 512. 1H NMR (500 MHz, DMSO), δ (TMS, ppm): 13.40 (d, J = 9.6 Hz, 2H), 7.88 (d, 4H), 7.81 (d, J = 6.9 Hz, 4H), 7.62 (dd, J = 19.3, 7.2 Hz, 4H), 7.51−7.39 (m, 4H), 7.40−7.28 (m, 2H), 7.20 (s, 2H), 0.60 (s, 6H). 13C NMR (125 MHz, DMSO), δ (TMS, ppm): 151.37, 151.22, 143.41, 143.26, 138.00, 137.74, 136.86, 136.62, 134.58, 134.30, 133.62, 131.97, 129.98, 129.29, 129.01, 128.64, 128.15,

EXPERIMENTAL SECTION

Materials. Alkynes 1a−d were prepared according to the reported literature.36,37 Pd(PPh3)2Cl2 and phenylhydrazine (4) were purchased from TCI, terephthaloyl dichloride (2) and hydrazine hydrate (3) were purchased from Alfa Aesar, CuI was purchased from Energy Chemical, and benzoyl chloride (5) was purchased from SigmaAldrich. All these commercial available reactants were used as obtained without further purification. All the organic solvents were dried and distilled before use. Instruments. 1H NMR and 13C NMR spectra were measured on a Bruker Avance 500 MHz NMR spectrometer using deuterated dimethyl sulfoxide or deuterated chloroform (tetramethylsilane as internal reference) as solvent. FT-IR spectra were recorded on a Bruker Vector 33 FT-IR spectrometer. High resolution mass spectrometry measurements were tested on a GCT premier CAB 048 mass spectrometer. The number- (Mn) and weight-average (Mw) molecular weights and polydispersity indices (PDI = Mw/Mn) of polymers were estimated by a Waters Associates 515 gel permeation chromatography (GPC) system. THF was utilized as eluent at a flow rate of 0.5 mL/min. A set of monodispersed linear polystyrenes covering the Mw range of 103−107 g/mol were utilized as standards for molecular weight calibration. Thermogravimetric analysis was performed on a NETZSCH TG 209 F1 under nitrogen with a heating rate of 10 °C/min. UV−vis absorption spectra and fluorescence spectra were recorded on a SHIMADZU UV-2600 spectrophotometer and a Horiba Fluoromax-4 fluorescence spectrophotometer, respectively. The absolute fluorescence quantum yields were recorded on a Hamamarsu C11347-11 Quantaurus-QY. G


Article

Macromolecules 127.48, 125.14, 124.59, 124.50, 99.80, −2.65. HRMS: m/z 497.2145 (M + H+, calcd 497.2161). Bis[4-(1,5-diphenylpyrazol-3-yl)phenyl]dimethylsilane (7): Compound 1a (260 mg, 1.0 mmol), Pd(PPh3)2Cl2 (28 mg, 0.02 mmol), and CuI (15 mg, 0.04 mmol) were added into a 50 mL two-neck round-bottom flask equipped with a magnetic stir bar under nitrogen. 20 mL of distilled tetrahydrofuran was injected into the flask, followed by the addition of benzoyl chloride 5 (0.24 mL, 2.1 mmol) and triethylamine (0.29 μL, 2.1 mmol). The reaction mixture was reacted at room temperature for 1 h, and then 5 mL of MeOH and phenylhydrazine (4) (0.30 mL, 3.0 mmol) were injected into the mixture, which was further reacted at 70 °C for 12 h. The reaction mixture was cooled to room temperature, poured into 50 mL of water, and extracted with dichloromethane for three times (30 mL × 3), after which the organic phases were combined. After evaporation of the solvent, crude product was obtained, which was purified through silica gel chromatography using petroleum/ethyl acetate (v/v = 10/1) as the eluent. A white solid was obtained in 89% yield. IR (KBr thin film), v (cm−1): 3058, 2957, 1596, 1493, 1352, 1111, 816, 762, 690, 531, 496. 1 H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.91 (d, J = 8.1 Hz, 4H), 7.61 (d, J = 8.1 Hz, 4H), 7.37−7.28 (m, 20H), 6.83 (s, 2H), 0.60 (s, 6H). 13C NMR (125 MHz, CDCl3), δ (TMS, ppm): 152.00, 144.46, 140.24, 138.03, 134.73, 133.82, 130.69, 129.01, 128.87, 128.58, 128.40, 127.53, 125.42, 125.27, 105.47, −2.14. HMRS: m/z 649.2775 (M + H+, calcd 649.2787). P1: 1a (52 mg, 0.20 mmol), 2 (41 mg, 0.20 mmol), Pd(PPh3)2Cl2 (6 mg, 0.008 mmol), and CuI (3 mg, 0.016 mmol) were added into a 10 mL Schlenk tube equipped with a magnetic stir bar under nitrogen. 4 mL of THF and triethylamine (56 μL, 0.20 mmol) were injected into the mixture, and the solution was stirred at room temperature for 1 h. The polymerization was terminated by dropping the reaction mixture into 200 mL of hexane/THF (v/v = 10/1) mixed solvent through a cotton filter. The polymer product was allowed to precipitate and stand overnight. After filtration, the crude product was washed with hexane and dried under vacuum overnight. A yellow solid was obtained in 97% yield. Mw = 15 700 g/mol, Mw/Mn = 2.16. IR (KBr thin film), v (cm−1): 3064, 2955, 2194, 1644, 1495, 1403, 1284, 1207, 1104, 1003, 800, 707, 542. 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 8.33, 7.67, 7.57, 0.62. 13C NMR (125 MHz, CDCl3), δ (TMS, ppm): 177.16, 141.91, 140.63, 134.47, 132.46, 129.82, 120.74, 94.37, 87.50, −2.68. P2: 1a (52 mg, 0.20 mmol), 2 (41 mg, 0.20 mmol), Pd(PPh3)2Cl2 (6 mg, 0.008 mmol), and CuI (3 mg, 0.016 mmol) were added into a 10 mL Schlenk tube equipped with a magnetic stir bar under nitrogen. 4 mL of THF and triethylamine (56 μL, 0.20 mmol) were injected into the reaction mixture, and the solution was stirred at room temperature for 1 h. Afterward, 1 mL of DMF and hydrazine hydrate (3) (0.6 mmol, 98 μL) were added to the reaction mixture and stirred at room temperature for another 12 h. The polymerization was terminated by dropping the reaction mixture into 200 mL of hexane/ THF (v/v = 10/1) mixed solvent through a cotton filter. The polymer product was allowed to precipitate and stand overnight. After filtration, the crude product was washed with hexane and dried under vacuum overnight. A gray solid was obtained in 96% yield. Mw = 19 400 g/mol, Mw/Mn = 2.30. IR (KBr thin film), v (cm−1): 3414, 3224, 2955, 1664, 1605, 1494, 1114, 964, 811, 525. 1H NMR (500 MHz, DMSO), δ (TMS, ppm): 13.44, 7.92, 7.85, 7.62, 7.25, 0.59. The typical procedure for the polymerizations of 1a−d, 2, and 4 was introduced below by taking the polymerization of 1a, 2, and 4 for example. 1a (52 mg, 0.20 mmol), 2 (41 mg, 0.20 mmol), Pd(PPh3)2Cl2 (6 mg, 0.008 mmol), and CuI (3 mg, 0.016 mmol) were added into a 10 mL Schlenk tube equipped with a magnetic stir bar under nitrogen. 4 mL of THF and triethylamine (56 μL, 0.20 mmol) were then injected into the reaction mixture and stirred at room temperature for 1 h. Afterward, 1 mL of MeOH and phenylhydrazine (4) (60 μL, 0.60 mmol) were injected into the mixture and further reacted at 70 °C for 12 h. The polymerization was terminated by dropping the mixture into 200 mL of hexane/THF (v/v = 10/1) mixed solvent through a cotton filter. The polymer product was allowed to precipitate and stand

overnight. After filtration, the crude product was washed with hexane and dried under vacuum overnight. P3a: yellow solid in 95% yield. Mw = 18 400 g/mol, Mw/Mn = 2.43. IR (KBr thin film), v (cm−1): 3058, 2954, 1598, 1495, 1430, 1351, 1252, 1109, 1065, 965, 809, 768, 693, 531. 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.91, 7.62, 7.36, 7.23, 6.87, 0.62. 13C NMR (125 MHz, CDCl3), δ (TMS, ppm): 152.15, 143.71, 140.13, 138.17, 134.77, 133.69, 130.45, 129.11, 128.85, 127.78, 125.51, 125.27, 105.55, −2.14. P3b: yellow solid in 87% yield. Mw = 30 700 g/mol, Mw/Mn = 2.17. IR (KBr thin film), v (cm−1): 3053, 1597, 1497, 1437, 1352, 1021, 845, 797, 697. 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.66, 7.34, 7.19, 7.12, 6.78. 13C NMR (125 MHz, CDCl3), δ (TMS, ppm): 152.02, 143.85, 143.75, 143.68, 140.98, 140.11, 131.92, 131.61, 130.94, 130.43, 129.08, 128.80, 127.93, 127.73, 126.71, 125.43, 125.22, 105.45. P3c: yellow solid in 72% yield. Mw = 10 500 g/mol, Mw/Mn = 1.90. IR (KBr thin film), v (cm−1): 2964, 1601, 1504, 1244, 1179, 1013, 798, 693. 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.92, 7.49, 7.35, 7.22, 7.15, 6.88, 5.07, 1.64. P3d: yellow solid in 63% yield. Mw = 5900 g/mol, Mw/Mn = 1.58. IR (KBr thin film), v (cm−1): 2937, 1601, 1438, 1392, 1245, 1171, 1022, 797, 651. 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.84, 7.35, 7.21, 6.95, 6.78, 4.02, 1.85, 1.58.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b02192. Time course of polymerization of 1a, 2, and 3; the single crystal data of compound 7; HRMS spectra of 6 and 7; IR spectra of 6 and P2; time course study of MCTP of 1a, 2, and 4 and the corresponding 1H NMR spectra; refractive indices and chromatic dispersions of thin films of P1 and P3a−d; the photophysical properties of 6−7, P1−2, and P3a−d (PDF) Single crystal structure of 7 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*(R.H.) E-mail [email protected]; Tel +86-2223-7066. *(B.Z.T.) E-mail [email protected]; Tel +852-2358-7375. ORCID

Rongrong Hu: 0000-0002-7939-6962 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by the National Science Foundation of China (21404041, 21490573, and 21490574), the Guangdong Natural Science Funds for Distinguished Young Scholar (2016A030306045), the National Basic Research Program of China (973 Program; 2013CB834701), the Innovation and Technology Commission of Hong Kong (ITC-CNERC14SC01), the Fundamental Research Funds for the Central Universities (2015ZJ002 and 2015ZY013), and the G u a ng d o n g I nn o v a t i v e Re s e a r c h T e a m Pr og r a m (201101C0105067115).

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