Article pubs.acs.org/Macromolecules
Multicomponent Click Polymerization: A Facile Strategy toward Fused Heterocyclic Polymers Haiqin Deng,†,‡ Ting Han,†,‡ Engui Zhao,†,‡ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,*,†,‡ and Ben Zhong Tang*,†,‡,§ †
Department of Chemistry, Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong ‡ HKUST-Shenzhen Research Institute, No. 9 Yuexing first RD, South Area, Hi-tech Park, Nanshan, Shenzhen 518057, China § Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology (SCUT), Guangzhou 510640, China S Supporting Information *
ABSTRACT: We herein report a facile and efficient multicomponent click polymerization route to construct fused heterocyclic polymers with advanced functionalities. Mediated by CuI and trimethylamine at room temperature, diynes, disulfonyl azide, and salicylaldehyde, or o-hydroxylacetophenone undergo polymerizations efficiently and smoothly, affording high-molecular-weight poly(iminocoumarin)s (Mw up to 64 600) in satisfactory yields (up to 99%). This multicomponent click polymerization approach enjoys remarkable merits of both multicomponent reactions and click reactions, such as simple operation, high reaction efficiency and isolation yield, mild reaction conditions, and common substrates. The resulting polymers possess outstanding film-forming ability, high thermal stability, and good morphological stability. With tetraphenylethene luminogens embedded in the polymer chains, their solutions fluoresce weakly, whereas their aggregates emit intensely, demonstrative of a typical feature of aggregation-enhanced emission. Furthermore, the obtained polymers with bright film emission and high photosensitivity can be facilely fabricated into well-resolved 2D and 3D patterns by treatment of their films with UV light. Additionally, thanks to the highly polarized conjugated structures, the polymer films possess outstanding refractive indices (1.9284−1.7734) in the visible and near-IR regions (400−893 nm), which can be further adjusted by UV light.
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INTRODUCTION
painful isolations, etc. Transition-metal-catalyzed coupling reactions are usually employed to prepare such polymers but are limited to fused heterocyclic substrates. To date, efficient synthetic methodologies to access functional polymers with insitu formation of fused heterocyclic moieties are scarce. Thus, the development of facile and efficient polymerization routes to afford functional polymers with fused heterocyclic units is highly desirable. “Click” reactions, as coined by Sharpless and co-workers, represent a class of chemical reactions, which proceed in high regio- and stereoselective manner with excellent yields under mild reaction conditions.9 In the past decade, these reactions have found widespread applications in the construction of various polymeric materials. For example, copper(I)-catalyzed
Recently, polymeric materials with novel molecular skeletons and advanced applications have gained a worldwide popularity among polymer chemists.1 In particular, fused heterocyclic polymers have received considerable attention, as witnessed by the great efforts devoted to the preparation of diverse fused heterocyclic polymers, such as poly(naphthopyran)s,2 poly(benzofuran)s,3 poly(isocoumarin)s,4 poly(benzylcarbazole)s,5 poly(benzothiophene)s,6 etc. The unique electronic structures of such conjugated fused heterocyclic building blocks endow the polymers with outstanding functionalities, e.g., lightemission and electron-transporting properties, which enable them to be applicable in polymer electronics, including polymer light-emitting diodes,5 organic photovoltaics,7 organic fieldeffect transistors,8 etc. Along with the technological implications of the fused heterocyclic polymers are their synthetic difficulties. These polymers with complicated structures often suffer from tedious synthetic routes, harsh reaction conditions, © XXXX American Chemical Society
Received: June 7, 2016 Revised: July 23, 2016
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DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules azide−alkyne “click” reaction has been widely utilized in the polymer field and has become one of the most reliable polymerization methods,10 through which a series of linear and hyperbranched poly(triazole)s with the formation of heterocyclic structures are synthesized.11 On the other hand, multicomponent reactions, in which three or more reactants are involved to afford a highly selective product in a one-pot manner,12 are also introduced into the field of polymer synthesis recently, which show remarkable merits of simple synthetic procedure, high efficiency, good atom economy, satisfactory functional group tolerance, diminished waste production, etc. The derived multicomponent polymerizations have produced a variety of well-defined polymers with fancy functionalities from simple precursors.13 Both click reactions and multicomponent reactions enjoy advantageous properties; thus, the combination of these two types of reactions is anticipated to inherit the remarkable merits from both of them, such as simple operation, high efficiency and isolation yield, mild reaction condition, and handy substrates. If such reactions can be developed as a tool into polymerization approach, it will be a great pathway to access desired polymeric materials with unique functionalities. Chang et al. recently devised a series of Cu-mediated multicomponent reactions. Alkynes and sulfonyl azides were reacted with amines, alcohols, or water to construct varied molecular skeletons.14 Following the frontier work, Wang et al. further developed CuI-catalyzed reactions of alkynes A, sulfonyl azides B, and salicylaldehydes C, which proceeded in a one-pot manner and in situ generated D with fused heterocyclic unit of iminocoumarins. (Scheme 1)15 Combining with previous
Scheme 2. Constructions of P1/2/3 by Copper-Catalyzed Multicomponent Click Polymerizations
characteristics. They emit more intensely as aggregates than in solutions. With these attributes, these polymers are promising to find real-world applications.
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RESULTS AND DISCUSSION Polymerizations. Prior to the development of the one-pot reaction of alkyne, sulfonyl azide, and salicylaldehyde or ohydroxylacetophenone into an efficient approach for preparing high-molecular-weight poly(iminocoumarin)s, we first prepared aryl alkyne 1a, alkyl alkyne 1b, and 4,4′-disulfonylazidophenyl ether 2 by following previously reported synthetic procedures.16 Salicylaldehyde 3a and o-hydroxylacetophenone 3b were commercially available and used as received. Their typical polymerizations proceeded efficiently in the presence of CuI and triethylamine (Et3N) under nitrogen environment at room temperature, earning desired polymeric products (P1/2/3) (Scheme 2). To determine the optimal condition for conducting the polymerization, solvent effect of polymerizing 1a, 2, and 3a was first investigated. We tested different common organic solvents, including tetrahydrofuran (THF), chloroform (CHCl3), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAc). On the basis of the polymerization results (Table 1), DMAc was the most suitable solvent among the tested
Scheme 1. CuI-Catalyzed One-Pot Reaction for the Synthesis of Iminocoumarins
analysis by Chang and co-workers, they proposed the following mechanism for this domino process. Catalyzed by CuI, A and B undergo a typical click reaction, namely azide−alkyne cycloaddition, and generate a key ketenimine intermediate, which is then coupled by the nucleophile transferred from C to form an anionic species. Afterward, the anionic species experience protonation and dehydration processes to yield the desired structure D. This reaction is featured by general applicability, mild reaction conditions, and versatile synthetic route and can produce substituted iminocoumarin derivatives efficiently. It is nice if such reaction can be utilized in the polymer field for the preparation of fused heterocyclic polymers. With this regard, we have successfully developed the abovementioned reaction into a three-component click polymerization approach to access fused heterocyclic polymers with advanced functionalities. As shown in Scheme 2, highmolecular-weight poly(iminocoumarin)s are obtained through polymerizing handy alkynes, sulfonyl azide, and salicylaldehyde or o-hydroxylacetophenone at room temperature. These polymers enjoy good processability, excellent thermal stability and morphological stability, remarkable photosensitivity and photopatternability, high and adjustable light refractivity, etc. With the luminescent tetraphenylethene (TPE) moieties, the polymers exhibit typical aggregation-enhanced emission (AEE)
Table 1. Influences of Different Solvents on the Polymerizationsa entry
solvent
yield (%)
Mw
Mw/Mn
1 2 3 4
THF CHCl3 DMSO DMAc
gel gel trace 91
42400
1.3
a
Proceeded under N2 at room temperature for 1 h, [CuI] = 20 mol %, [Et3N] = 0.88 M, [1a] = [2] = 0.20 M, [3a] = 0.44 M.
mediums, which gave the highest Mw and yield (Table 1, entry 4). Gels were formed rapidly in THF and CHCl3, as the polymeric products with high molecular weights were hardly soluble. On the other hand, polymeric product was obtained in a trace amount from DMSO. These results indicated that solvent exerted a pronounced effect on the polymerization. DMAc was employed for further studies. Next, we investigated the parameter of monomer concentration. We kept the ratio of [1a]:[2]:[3a] as 1:1:2.2 and performed polymerizations at different monomer concentrations. The yields, Mw and Mw/Mn values are summarized in Table 2. Indeed, the best polymerization result with Mw of B
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 2. Monomer Concentration Impact on the Polymerizationsa
Table 4. Polymerizations of Different Monomer Combinationsa
entry
[1a] (M)
yield (%)
Mw
Mw/Mn
entry
monomer
[1] (M)
yield (%)
Mw
Mw/Mn
1 2b 3 4
0.40 0.20 0.15 0.10
91 91 91 92
64600 42400 30300 30100
1.4 1.3 1.2 1.3
1b 2c 3 4
1a/2/3a 1a/2/3b 1a/2/3b 1b/2/3a
0.4 0.4 0.05 0.4
91 gel 82 99
64600
1.4
50200 25100
1.4 1.3
a
a
Proceeded at room temperature under N2 in DMAc for 1 h, [CuI] = 20 mol %, [Et3N] = 4.4 [1a], [1a] = [2], [3a] = 2.2 [1a]. bData taken from Table 1, entry 4.
Proceeded at room temperature under nitrogen in DMAc for 1 h, [1] = [2], [3] = 2.2 [1], [CuI] = 20 mol %, [Et3N] = 4.4 [1]. bData taken from Table 2, entry 1. cGellation within 1 min.
64 600 in 91% yield (Table 2, entry 1) was achieved when monomer concentration was the highest ([1a] = 0.40 M). Decreasing monomer concentration lowered down the molecular weights. It was reasonable since higher monomer concentration could promote intermolecular monomer collisions and thus give better polymerization results. Noteworthy, the polymerization still proceeded smoothly with satisfactory molecular weight even when only 0.10 M of monomers was employed (Table 2, entry 4). Based on both the polymerization results and economical considerations, 0.40 M was chosen as the suitable monomer concentration. Using the above optimized conditions, we examined the effect of reaction time (Table 3). The isolation yields remained
successfully obtained with the Mw of 25 100 in 99% yield (Table 4, entry 4). It demonstrates that both aryl and alkyl alkynes are suitable for the polymerization. Structural Characterizations. To verify the occurrence of the three-component polymerization and confirm the structures of resulting polymers, model compound was synthesized by the three-component coupling reaction shown in Scheme 3. TPEcontaining monoyne 5 and 4-methylbenzenesulfonyl azide 6 were synthesized according to our previous publications.17 Similar to polymer synthesis, 5, 6, and 3a were reacted in THF solution with the participation of CuI and Et3N at room temperature, furnishing model compound 4 with 85.7% isolation yield. The characterization data of 4 were consistent with its designed molecular structure. Afterward, the chemical structures of the polymers and model compound were fully confirmed by MS, IR, 1H NMR, and 13C NMR characterizations. The spectra of 4 and P1a/2/ 3a are compared with 1a, 2, and 3a and discussed here as examples. Their IR spectra are given in Figure 1. In alkyne 1a, two absorption peaks at 3275 and 2106 cm−1 are assignable to the stretching vibrations of C−H and CC groups, respectively. The N3 stretching vibration in monomer 2 is observed as a sharp and strong band peaked at 2159 and 2127 cm−1. Meanwhile, the stretching vibrations of aldehyde and hydroxyl groups in monomer 3a are located at 1666 and 3187 cm−1, respectively. However, in the spectral profile of 4 as well as P1a/2/3a, these characteristic peaks all disappeared, which suggests that the CC groups in 1a and the azido groups in 2 together with the aldehyde and hydroxyl groups in 3a are all consumed during the polymerization reaction. Two new bands at 1628 and 1560 cm−1, on the other hand, emerge in these spectral profiles, suggestive of the generation of Ar−CC and CN functionalities after the three-component click reaction. Their 1H NMR spectra were measured in chloroform-d in order to obtain further insight into the molecular skeletons. Figure 2 provides the detailed information. The acetylene proton of 1a, aldehyde proton, and hydroxyl proton of 2 resonate at δ 3.03, δ 11.01, and δ 9.90, respectively, which are absent in 4 and P1a/2/3a. Such a result further substantiates the conclusion drawn from IR analysis. In addition, the peak at δ 8.02, which is associated with the aromatic proton of 2, is shifted to high field after reaction. A new peak at δ 7.67 is found in 4 as well as P1a/2/3a, proving the generation of CC bond. These results prove that the triple bonds (CC) are fully transformed into the double bonds (CC) of the iminocoumarin structures. The 13C NMR spectra of P1a/2/3a, 1a, 2, 3a, and 4 are given in Figure 3. Two sets of peaks associated with the acetylene carbons of 1a resonate at δ 84.0 and δ 77.7, respectively. Two resonance peaks located at δ 196.80 and δ 161.76 are assigned to the aldehyde carbon and aromatic
Table 3. Effect of Reaction Time on the Polymerizationsa entry
t (h)
yield (%)
Mw
Mw/Mn
1 2b 3 4
0.5 1.0 2.0 4.0
92 91 89 90
49400 64600 48400 39300
1.3 1.4 1.3 1.3
a
Proceeded at room temperature under N2 in DMAc, [CuI] = 20 mol %, [Et3N] = 1.76 M, [1a] = 0.40 M, [2] = 0.40 M, [3a] = 0.88 M. b Data taken from Table 2, entry 1.
almost unchanged throughout the tested time course. Remarkably, polymeric product with Mw of 49 400 was yielded within 0.5 h (Table 3, entry 1), demonstrative of the high efficiency of this three-component polymerization. Prolonging the reaction time to 1 h raised the Mw value to 64 600. Further extending the reaction time to more than 1 h could improve neither the Mw nor isolation yield. The reason behind this phenomenon is under investigation in our group. In later studies, we preferred 1 h as the reaction time. On the basis of the optimized reaction conditions, we explored the monomer scope in order to enrich molecular structures and introduce functionalities to the polymers. We tested the feasibility of o-hydroxylacetophenone 3b for polymerization. When 3a was replaced by 3b while keeping other conditions unchanged, gels were formed immediately and could hardly be dissolved. Such a rapid gel formation might be ascribed to the faster formation of conjugated molecular skeleton with high molecular weight and poorer solubility promoted by 3b. To settle the gelation issue, we reduced the concentration of 1a to 0.05 M, while keeping monomer ratio unchanged. The polymerization proceeded smoothly and yielded soluble polymeric product with Mw of 50 200, manifesting the general applicability of this powerful and efficient polymerization. Furthermore, alkyl alkyne 1b was polymerized with 2 and 3a under the same conditions (Table 4, entry 1). Then P1b/2/3a with desired structure was C
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 3. Synthesis of Model Compound 4
Figure 1. IR spectra of 1a (A), 2 (B), 3a (C), 4 (D), and P1a/2/3a (E). Figure 2. 1H NMR spectra of 1a (A), 2 (B), 3a (C), 4 (D), and P1a/ 2/3a (E) in chloroform-d with marked solvent peaks (∗).
carbon adjacent to the hydroxyl group of 2, respectively, while in the 13C spectrum of P1a/2/3a, they are all disappeared. Moreover, two new peaks related to the CN carbon and aromatic carbon adjacent to heterocyclic oxygen atom appear at δ 157.49 and δ 152.38, respectively, in the spectral profiles of 4 and P1a/2/3a. All the characterizations clearly reveal the precise structure of P1a/2/3a shown in Scheme 2. Thermal Stability. Generally, polymers with conjugated or cross-linked structures tend to be thermally stable and are thus good candidates for heat-resistant materials. We estimated the thermal stability of the resulting polymers via thermogravimetric analysis (TGA) at a heating rate of 10 °C/min. Figure 4 depicts their thermal degradation process when gradually heated from 50 to 800 °C. The degradation temperatures (Td) at the point of 5% weight loss are located in the region of 286− 341 °C. Noteworthy, P1a/2/3a and P1a/2/3b retain more than 50% of their weights at a temperature of up to 800 °C. These results clearly illustrated the good thermal stability of the polymeric products, which are much better than many commercial polymeric materials.18 We further examined their thermal properties by differential scanning calorimetry (DSC)
measurement (Figure 5). As revealed by the high glasstransition temperatures (135−230 °C), all the polymers show high morphological stability. Photophysical Properties. Most conventional fluorophores encounter the problem of aggregation-caused fluorescence quenching, which sets the hurdle for their utilizations in varied fields. We discovered that some propeller-shaped molecules (e.g., hexaphenylsilole and TPE) display an opposite characteristic of aggregation-induced emission (AIE).19 These molecules faintly emit in solutions, but intensely fluoresce upon forming aggregates. Based on lots of experimental results, it is proposed that the AIE phenomenon is mainly due to the restriction of intramolecular motions.20 Bearing the AIE-active TPE moieties, all the polymers and model compound are thus anticipated to stem the feature from TPE units.21 Then, 4 and P1a/2/3a were taken as examples, and their photophysical properties were systematically investigated. Keeping a constant fluorophore concentration of 10 μM, absorption spectra of 4 in D
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules
Figure 5. DSC curves of P1/2/3 recorded under a N2 atmosphere during the second heating scan.
THF solution (Figure S1) and P1a/2/3a in DMSO solution (Figure S2) were first measured. The absorption maximum of P1a/2/3a was located at 360 nm, whereas that of 4 was peaked at 350 nm. The larger absorption wavelength of P1a/2/3a can be ascribed to its more extended conjugation. By means of a spectrofluorometer, we then investigated the emission behaviors of 4 in THF/water mixtures and P1a/2/3a in DMSO/water mixtures with different water fractions ( f w). Figure 6A shows the emission spectra of 4. The photoluminescence (PL) curves are almost flat lines at low f w (≤40%), indicating no obvious fluorescence. Intense emission is observed when f w is increased to 50%. Further raising f w significantly enhances its light emission. At the f w of 70%, the fluorescence intensity reaches the highest point, which is 178fold higher than that of its pure THF solution (Figure 6B). P1a/2/3a exhibits similar fluorescence properties (Figure 7A). Its DMSO solution is faintly emissive with spectral maximum at ∼585 nm. Then, the emission intensity increases steadily upon the gradual addition of water with blue-shifted emission peak. The emission intensity reaches the highest point at the f w of 50%, and the value is 17-fold of its DMSO solution (Figure 7B). At f w of higher than 50%, the emission intensity gradually drops. This is presumably due to the decrease in effective concentration caused by its poor solubility in such aqueous mixtures with high water content. Furthermore, its emission behavior can be directly visualized by naked eyes as shown in Figure 7A, which clearly demonstrates the AEE characteristic. Light Refractivity. Continuing advances in optoelectronic devices have drawn an increasing attention to high refractive index (n) materials,22 which possess a wide variety of applications, such as lenses, prisms, antireflective coatings, organic light-emitting diodes, and image sensors.23 High-n polymers are advantageous over other high-n materials, owing to their low density, high processability, impact resistance, etc. However, typical n values of conventional polymers, including polystyrene, polycarbonate, polyacrylate, poly(methyl methacrylate), etc., often lie in the range of 1.49−1.58.24 In practical applications, polymers with high n values (≥1.70) are often required. Theoretically, aromatic rings, heteroatoms, and highly polarizable π-conjugated functionalities are beneficial to increasing the n value. Considering plenty of TPE moieties and heteroatoms lying in the polymer skeleton as well as a polarized conjugated backbone, we expected high n values for
Figure 3. 13C NMR spectra of 1a (A), 2 (B), 3a (C), 4 (D), and P1a/ 2/3a (E) in chloroform-d with marked solvent peaks (∗).
Figure 4. TGA thermograms of P1/2/3 collected under a N2 atmosphere at a heating rate of 10 °C/min. E
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules
Figure 6. (A) Emission spectra of 4 in THF/H2O mixtures (10 μM) with different f w under 350 nm excitation light. (B) Plot of relative emission intensity (I/I0) at the wavelength of 526 nm versus f w of the aqueous mixtures.
Figure 8. Change in n values of thin film of P1a/2/3a before and after UV irradiation.
Figure 7. (A) Photographs of P1a/2/3a in DMSO/H2O mixtures (10 μM) with different f w captured under the irradiation from a hand-held UV lamp (365 nm). (B) Emission spectra of P1a/2/3a in DMSO/ H2O mixtures with different f w under 360 nm excitation light. (C) Plot of I/I0 at peak emission intensities versus the f w of the aqueous mixtures.
Fluorescent Pattern. Polymers with good photosensitivity have been utilized as photoresist materials in photolithography and photoengraving processes. If a polymer is processable and photosensitive as well as luminescent, it will be ideal for luminescent pattern fabrications, which have profound implications in constructing electronic and photonic devices as well as investigating biological sensing systems.25 Generally, there are two classes of photosensitive polymers in the fabrication of fluorescent patterns: (a) photo-oxidative polymers decompose after UV light irradiation, and then 2D positive fluorescent patterns are generated due to the quench of fluorescence in the exposed regions; (b) photo-cross-linkable polymers generate insoluble luminescent products upon exposure to UV light, and 3D negative fluorescent patterns can be formed after removal of soluble unexposed parts. Sometimes, these two processes can occur simultaneously, and thus both 2D and 3D fluorescent patterns can be produced. The photosensitivity and intense emission of the polymer thin film indicate its high potential as luminescent patterns at nanoscale via the photolithography technique. The polymer film was first formed by spin-coating the solution of P1a/2/3a on silicon wafer and a sequential drying process at room temperature. Afterward, the polymer film was covered by a copper photomask and exposed to UV light under ambient environment for 20 min. Then, a clear fluorescent 2D pattern
these polymers. Then uniform solid film of P1a/2/3a was fabricated on silica wafers via a spin-coating process, and its n values were recorded along with wavelength change as an example. Indeed, distinguished n values of 1.9284−1.7734 were achieved within the wavelength range of 400−893 nm, and the n value at the point of 632.8 nm is 1.7866 (Figure 8). With abundant photosensitive groups embedded in the polymer chain, the n values of polymer films can be easily modulated by UV treatment. UV light is thus used to irradiate the film of P1a/2/3a. As expected, the n values drop to 1.6604−1.5849 from initial 1.9284−1.7734 with a decrease of 0.1282 at 632.8 nm after 15 min, displaying good refractivity tunability. Such great decrease can be ascribed to the change of polymer structure caused by the UV-assisted reaction. The breakage of unsaturated bonds decreases the conjugation and hence leads to the dramatic decrease of the n values. With high and modulable n values, the prepared polymers are ideal candidates in the applications of optical communication devices and optical data storage. F
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules (Figure 9A) was produced, as examined by fluorescence microscope. Apparently, the unexposed regions (squares)
weights (Mn), relative weight-average molecular weights (Mw), and the polydispersity indices (Mw/Mn) of the obtained polymers were measured on a Waters 1515 GPC system with standard polystyrenes for Mw and Mn calibration by utilizing interferometric refractometer detector. In a typical measurement, polymer samples dissolved in DMF (∼3 mg mL−1) were passed through a 0.45 μm PTFE syringetype filter to remove insoluble matters, and then an autosampler was used to inject ∼20 μL of the sample solution into the GPC system. DMF doped with LiBr (0.05 M) was used as the eluent with a constant flowing rate of 1.0 mL min−1. UV−vis spectra and PL spectra were recorded on a Milton Roy Spectronic 3000 array spectrophotometer and a PerkinElmer LS 55 spectrofluorometer, respectively. TGA and DSC analyses were carried out on a PerkinElmer TGA 7 analyzer and a Setaram DSC 92 analyzer, respectively, both conducted under a N2 atmosphere at a heating rate of 10 °C min−1. Polymer thin films were fabricated on silicon wafers from their 1,2-dichloroethane solutions (∼10 mg mL−1) via spincoating process (1000 rpm; 1 min). Photoinduced reactions were conducted under a Spectroline ENF-280C/F UV lamp (∼18.5 mW cm−2). Fluorescent patterns were obtained from the above-mentioned polymer films, which were subjected to UV irradiation through copper photomask and then imaged under an optical microscope with UV light source (Olympus BX 41). The n values were estimated by a Woollam ellipsometer (model Alpha-SE) with wavelength ranging from 400 to 893 nm. Polymer Synthesis. Using a standard Schlenk technique, all the polymerizations proceeded smoothly under nitrogen. Herein, typical polymerization procedures are shown as below with the polymerization of Table 2, entry 1, as an example. First, 0.20 mmol of diyne 1a, 0.20 mmol of sulfonyl azide 2, and 0.04 mmol of CuI were added into a 10 mL Schlenk tube equipped with a magnetic stirrer. Afterward, DMAc (0.5 mL), salicylaldehde 3a (0.44 mmol), and Et3N (0.88 mmol) were sequentially added. After stirring at room temperature for 1 h, the reaction mixture was diluted by 5 mL of CHCl3 and then precipitated in 200 mL of CHCl3/hexane mixture (1/10) through a cotton-filled dropper. The precipitate was then collected by filtration, followed by a drying process in a vacuum. Structural characterization information for all polymers is as follows: P1a/2/3a (Table 4, Entry 1). Yellow powder; 91%; Mw: 64 600; Mw/Mn: 1.4. IR (KBr), ν (cm−1): 3056, 1627, 1562, 1486, 1451, 1309, 1243, 1152, 1088. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.99, 7.77, 7.68, 7.50, 7.34, 7.05, 7.01. 13C NMR (100 MHz, CDCl3), δ (ppm): 159.36, 157.73, 152.19, 144.53, 143.20, 141.06, 140.93, 139.96, 137.85, 132.66, 132.43, 132.17, 131.43, 131.25, 129.75, 129.54, 129.05, 128.71, 128.50, 127.98, 127.90, 126.96, 126.04, 124.63, 119.89, 119.77, 119.23, 118.96, 116.46, 116.17. P1a/2/3b (Table 4, Entry 3). Yellow powder; 82%; Mw: 50 200; Mw/Mn: 1.4. IR (KBr), ν (cm−1): 3059, 1622, 1576, 1554, 1486, 1448, 1301, 1245, 1156, 1087. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.89, 7.69, 7.56, 7.39, 7.06, 7.03, 2.23. 13C NMR (100 MHz, CDCl3), δ (ppm): 159.25, 158.64, 151.60, 143.97, 143.21, 141.28, 132.07, 131.43, 131.35, 129.53, 129.32, 127.98, 127.85, 126.98, 125.86, 125.84, 125.42, 120.81, 118.82, 117.18, 16.89. P1b/2/3a (Table 4, Entry 4). Yellowish-white powder; 99%; Mw: 25 100; Mw/Mn: 1.3. IR (KBr), ν (cm−1): 3066, 2965, 2929, 2868, 1633, 1566, 1488, 1454, 1300, 1244, 1154, 1086. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.11, 7.96, 7.86, 7.80, 7.78, 7.55, 7.45, 7.37, 7.13, 6.87, 6.74, 6.72, 4.91, 1.61. 13C NMR (100 MHz, CDCl3), δ (ppm): 159.64, 156.54, 155.88, 152.10, 144.22, 138.06, 137.37, 132.22, 131.23, 130.09, 128.94, 128.53, 128.05, 127.89, 126.16, 124.06, 119.76, 119.32, 119.09, 116.57, 114.94, 114.46, 64.44, 41.85, 31.11. Model Reaction. Into a stirred mixture of CuI (0.05 mmol), monoyne 5 (0.50 mmol) and p-toluenesulfonyl azide 6 (0.50 mmol) in 3 mL of DMAc were slowly added salicylaldehde 3a (0.55 mmol) and Et3N (1.10 mmol) via syringe under N2. The reaction mixture was stirred overnight at room temperature and then diluted with DCM (3 mL) and NH4Cl aqueous solution (3 mL). After extraction with DCM for three times, the organic layers were collected and concentrated, followed by purification of the crude residue through a silica gel column chromatograph (ethyl acetate/hexane: v/v; 1/2). 4: yellow
Figure 9. (A) 2D fluorescent pattern of P1a/2/3a taken under UV light and 3D fluorescent patterns of P1a/2/3a taken under (B) daylight and (C) UV light illuminations. Scale bar: 200 μm; excitation wavelength: 330−385 nm.
remain original greenish-yellow emission, while the exposed regions (dark lines) become dimly emissive presumably because of the structure change upon UV irradiation. Afterward, we further washed the 2D fluorescent pattern with 1,2-dichloroethane. The unexposed regions were dissolved and easily removed, and a 3D pattern was then clearly observed under daylight (Figure 9B). Furthermore, the remained regions emit blue light under UV illumination (Figure 9C). We believe that the photoinduced cross-linking reaction occurred upon the UV treatment, making the exposed regions hardly soluble; meanwhile, some of the fluorescent moieties were decomposed, resulting in dimer emission. As mentioned above, the unsaturated bonds were broken during UV illumination, which decreased the conjugation of the polymer chain. Thus, the pattern was observed with blue-shifted fluorescence.
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CONCLUSIONS In this contribution, a facile and efficient approach has been successfully developed to prepare poly(iminocoumarin)s by one-pot click polymerizations of diyne, disulfonyl azide, and salicylaldehyde or o-hydroxylacetophenone. These polymerizations take advantages of both multicomponent reactions and click reactions, such as outstanding efficiency, mild reaction, inexpensive catalyst, and good atom economy. The obtained polymers possess distinguished and tunable refractive indices as well as good thermal stability. With TPE moieties, the polymers display AEE characteristics and fluoresce intensely upon aggregation. Moreover, their strong aggregate/solid-state emission and photosensitive features enable them to be promising materials for fabricating 2D and 3D fluorescent patterns with high resolution. Further investigations are undergoing to explore the functionalities of the polymers by modifying their structures.
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EXPERIMENTAL SECTION
Materials and Instruments. DMAc, CHCl3, DMSO, Et3N, and all other chemicals were ordered from J&K Scientific, Sigma-Aldrich, or Merck and utilized as received. A distillation process from sodium benzophenone ketyl was performed for THF under nitrogen prior to usage. Preparations of diynes 1 and monoyne 5 were reported previously. 1 H/13C NMR spectra were obtained in chloroform-d by means of a Bruker ARX 400 NMR spectrometer by employing the internal reference tetramethylsilane (TMS; δ = 0 ppm). MALDI-TOF mass spectra together with IR spectra were collected from a GCT Premier CAB 048 mass spectrometer and a PerkinElmer 16 PC FT-IR spectrophotometer, respectively. Relative number-average molecular G
DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules solid; 85.7%. HRMS (MALDI-TOF): m/z 629.2038 [M+, calcd 629.2025]. IR (KBr), ν (cm−1): 3056, 1627, 1562, 1486, 1451, 1309, 1243, 1152, 1088. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.91 (d, J = 8.2 Hz, 2 H), 7.67 (s, 1 H), 7.60−7.44 (m, 3 H), 7.41−7.24 (m, 5 H), 7.19−7.08 (m, 9 H), 7.08−7.00 (m, 8 H), 2.42 (s, 3 H). 13C NMR (100 MHz, CDCl3), δ (ppm): 157.49, 152.38, 144.76, 143.77, 143.64, 143.05, 141.85, 140.40, 139.66, 139.39, 132.51, 132.00, 131.60, 131.52, 131.51, 131.34, 129.94, 129.39, 128.56, 128.22, 127.96, 127.95, 127.86, 127.25, 126.86, 126.77, 125.88, 120.00, 116.71, 21.77.
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(6) Gruber, J.; Li, R. W. C.; Silva, A. M. L.; Matos, J. R. Electrochemical Syntheses of Poly(4,7-benzofuran ethylene) and Poly(4,7-benzothiophene ethylene). Polym. J. 1997, 29, 718. (7) (a) Scharber, M. C.; Sariciftci, N. S. Efficiency of BulkHeterojunction Organic Solar Cells. Prog. Polym. Sci. 2013, 38, 1929. (b) Cao, W. R.; Xue, J. G. Recent Progress in Organic Photovoltaics: Device Architecture and Optical Design. Energy Environ. Sci. 2014, 7, 2123. (8) (a) Osaka, I.; Abe, T.; Shimawaki, M.; Koganezawa, T.; Takimiya, K. Naphthodithiophene-Based Donor-Acceptor Polymers: Versatile Semiconductors for OFETs and OPVs. ACS Macro Lett. 2012, 1, 437. (b) Knopfmacher, O.; Hammock, M. L.; Appleton, A. L.; Schwartz, G.; Mei, J. G.; Lei, T.; Pei, J.; Bao, Z. N. Highly Stable Organic Polymer Field-Effect Transistor Sensor for Selective Detection in the Marine Environment. Nat. Commun. 2014, 5, 2954. (c) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.; Spiess, H. W.; Mullen, K. Ultrahigh Mobility in Polymer Field-Effect Transistors by Design. J. Am. Chem. Soc. 2011, 133, 2605. (9) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004. (10) (a) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation” of Azides and Terminal Alkynes. Angew. Chem., Int. Ed. 2002, 41, 2596. (b) Meldal, M.; Tornoe, C. W. CuCatalyzed Azide-Alkyne Cycloaddition. Chem. Rev. 2008, 108, 2952. (11) (a) Qin, A. J.; Lam, J. W. Y.; Tang, B. Z. Click Polymerization. Chem. Soc. Rev. 2010, 39, 2522. (b) Qin, A. J.; Lam, J. W. Y.; Tang, B. Z. Click Polymerization: Progresses, Challenges, and Opportunities. Macromolecules 2010, 43, 8693. (12) (a) Cioc, R. C.; Ruijter, E.; Orru, R. V. A. Multicomponent Reactions: Advanced Tools for Sustainable Organic Synthesis. Green Chem. 2014, 16, 2958. (b) Domling, A.; Wang, W.; Wang, K. Chemistry and Biology Of Multicomponent Reactions. Chem. Rev. 2012, 112, 3083. (c) Ruijter, E.; Scheffelaar, R.; Orru, R. V. A. Multicomponent Reaction Design in the Quest for Molecular Complexity and Diversity. Angew. Chem., Int. Ed. 2011, 50, 6234. (13) (a) Kreye, O.; Toth, T.; Meier, M. A. R. Introducing Multicomponent Reactions to Polymer Science: Passerini Reactions of Renewable Monomers. J. Am. Chem. Soc. 2011, 133, 1790. (b) Ihara, E.; Hara, Y.; Itoh, T.; Inoue, K. Three-Component Polycondensation of Bis(diazoketone) with Dicarboxylic Acids and Cyclic Ethers: Synthesis of New Types of Poly(ester ether ketone)s. Macromolecules 2011, 44, 5955. (c) Deng, X. X.; Cui, Y.; Du, F. S.; Li, Z. C. Functional Highly Branched Polymers from Multicomponent Polymerization (MCP) Based on the ABC Type Passerini Reaction. Polym. Chem. 2014, 5, 3316. (d) Chan, C. Y. K.; Tseng, N. W.; Lam, J. W. Y.; Liu, J. Z.; Kwok, R. T. K.; Tang, B. Z. Construction of Functional Macromolecules with Well-Defined Structures by Indium-Catalyzed Three-Component Polycoupling of Alkynes, Aldehydes, and Amines. Macromolecules 2013, 46, 3246. (e) Liu, Y. J.; Roose, J.; Lam, J. W. Y.; Tang, B. Z. Multicomponent Polycoupling of Internal Diynes, Aryl Diiodides, and Boronic Acids to Functional Poly(tetraarylethene)s. Macromolecules 2015, 48, 8098. (14) (a) Bae, I.; Han, H.; Chang, S. Highly Efficient One-Pot Synthesis of N-sulfonylamidines by Cu-Catalyzed Three-Component Coupling of Sulfonyl Azide, Alkyne, and Amine. J. Am. Chem. Soc. 2005, 127, 2038. (b) Cho, S. H.; Yoo, E. J.; Bae, L.; Chang, S. CopperCatalyzed Hydrative Amide Synthesis with Terminal Alkyne, Sulfonyl Azide, and Water. J. Am. Chem. Soc. 2005, 127, 16046. (c) Yoo, E. J.; Bae, I.; Cho, S. H.; Han, H.; Chang, S. A Facile Access to Nsulfonylimidates and Their Synthetic Utility for the Transformation to Amidines and Amides. Org. Lett. 2006, 8, 1347. (15) Cui, S. L.; Lin, X. F.; Wang, Y. G. Novel and Efficient Synthesis of Iminocoumarins via Copper-Catalyzed Multicomponent Reaction. Org. Lett. 2006, 8, 4517. (16) (a) Hu, R. R.; Lam, J. W. Y.; Liu, J. Z.; Sung, H. H. Y.; Williams, I. D.; Yue, Z. N.; Wong, K. S.; Yuen, M. M. F.; Tang, B. Z. Hyperbranched Conjugated Poly(tetraphenylethene): Synthesis, Ag-
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b01217. Figures S1 and S2 (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*(B.Z.T.) E-mail
[email protected]; Tel +852-2358-7375; Fax +852-2358-1594. *(J.W.Y.L.) E-mail
[email protected]; Tel +852-2358-7375; Fax +852-2358-1594. Author Contributions
H.D. and T.H. contributed equally. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work has been partially supported by National Basic Research Program of China (973 Program; 2013CB834701 and 2013CB834702), the National Science Foundation of China (21490570 and 21490574), the Research Grants Council of Hong Kong (604913, 16303815, and 16305014), the I n n o v a t io n a n d T e c h n o l o g y C o m m i s s i o n ( I T C CNERC14SC01), and the University Grants Committee of Hong Kong (AoE/P-03/08). B. Z. Tang expresses thanks for the support of the Guangdong Innovative Research Team Program (201101C0105067115).
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DOI: 10.1021/acs.macromol.6b01217 Macromolecules XXXX, XXX, XXX−XXX
