In Situ Generation of N -Heteroaromatic Polymers: Metal-Free Multicomponent Polymerization for Photopatterning, Morphological Imaging, and Cr(VI) Sensing
2021; Chinese Chemical Society; Volume: 4; Issue: 7 Linguagem: Inglês
10.31635/ccschem.021.202101137
ISSN2096-5745
AutoresYubing Hu, Neng Yan, Xiaolin Liu, Lingyu Pei, Canbin Ye, Wen‐Xiong Wang, Jacky W. Y. Lam, Ben Zhong Tang,
Tópico(s)Advanced Polymer Synthesis and Characterization
ResumoOpen AccessCCS ChemistryRESEARCH ARTICLE14 Jul 2022In Situ Generation of N-Heteroaromatic Polymers: Metal-Free Multicomponent Polymerization for Photopatterning, Morphological Imaging, and Cr(VI) Sensing Yubing Hu, Neng Yan, Xiaolin Liu, Lingyu Pei, Canbin Ye, Wen-Xiong Wang, Jacky W. Y. Lam and Ben Zhong Tang Yubing Hu Department of Chemistry, The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Institute for Advanced Study, The Hong Kong University of Science and Technology, Guangdong-Hong Kong-Macro Joint Laboratory of Optoelectronic and Magnetic Functional Materials, Clear Water Bay, Kowloon, Hong Kong 999077 HKUST-Shenzhen Research Institute, Nanshan, Shenzhen 518057 , Neng Yan School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong 999077 , Xiaolin Liu Department of Chemistry, The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Institute for Advanced Study, The Hong Kong University of Science and Technology, Guangdong-Hong Kong-Macro Joint Laboratory of Optoelectronic and Magnetic Functional Materials, Clear Water Bay, Kowloon, Hong Kong 999077 HKUST-Shenzhen Research Institute, Nanshan, Shenzhen 518057 , Lingyu Pei Department of Chemistry, The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Institute for Advanced Study, The Hong Kong University of Science and Technology, Guangdong-Hong Kong-Macro Joint Laboratory of Optoelectronic and Magnetic Functional Materials, Clear Water Bay, Kowloon, Hong Kong 999077 , Canbin Ye Center for Aggregation-Induced Emission, From Molecular Aggregates, SCUT-HKUST Joint Research Institute, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 , Wen-Xiong Wang School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong 999077 , Jacky W. Y. Lam *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Institute for Advanced Study, The Hong Kong University of Science and Technology, Guangdong-Hong Kong-Macro Joint Laboratory of Optoelectronic and Magnetic Functional Materials, Clear Water Bay, Kowloon, Hong Kong 999077 HKUST-Shenzhen Research Institute, Nanshan, Shenzhen 518057 and Ben Zhong Tang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Institute for Advanced Study, The Hong Kong University of Science and Technology, Guangdong-Hong Kong-Macro Joint Laboratory of Optoelectronic and Magnetic Functional Materials, Clear Water Bay, Kowloon, Hong Kong 999077 HKUST-Shenzhen Research Institute, Nanshan, Shenzhen 518057 Center for Aggregation-Induced Emission, From Molecular Aggregates, SCUT-HKUST Joint Research Institute, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 Shenzhen Institute of Molecular Aggregate Science and Engineering, School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172 AIE Institute, Guangzhou Development Distinct, Huangpu, Guangzhou 510530 https://doi.org/10.31635/ccschem.021.202101137 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Electron-deficient N-heteroaromatic polymers are crucial for the high-tech applications of organic materials, especially in the electronic and optoelectronic fields. Thus, the development of new polymerizations to afford adaptable electron-donating–accepting scaffolds in N-heteroaromatic polymers is in high demand. Herein, we have developed metal-free multicomponent polymerizations of diynes, diamines, and glyoxylates successfully for in situ generation of poly(quinoline)s with high molecular weights (Mw up to 16,900) in nearly quantitative yields. By tuning the electron distributions of the polymer backbones, the resulting poly(quinoline)s showed various aggregation-induced behaviors and photoresponsive abilities: The thin films of the poly(quinoline)s could be fabricated readily into well-resolved photopatterns by photolithography techniques. They could be utilized as fluorescent probes to visualize the morphologies of polymer materials directly; these include spherulites and microphase separation of polymer blends. Their nanoparticles demonstrated sensitive and highly selective fluorescence quenching to hexavalent chromium ion Cr(VI), thereby providing access for biological imaging of Cr(VI) in unicellular algae. Download figure Download PowerPoint Introduction Organic materials are recognized as an important branch of functional materials and have aroused intense academic and technological interest, especially in the electronic and optoelectronic fields.1,2 Polymer materials show superiority over their small molecule counterparts in terms of low cost, flexibility, high processability, and ease for large-scale production.3 On the other hand, the development of polymer materials with rational design in their electronic structure4 and intermolecular interactions5 is an essential topic in polymer science. Generally, the adjustment of electronic structures in polymer materials is achieved by tuning their conjugation length and electron donor–acceptor (D–A) strength.6 While high-molecular-weight conjugated polymers suffer from the problems of synthetic difficulty and low solubility,7 polymers with D–A building blocks display various advantages such as simple synthesis, ease of regulation, structure variation, and multiple functionalizations. To construct a D–A scaffold in polymer frameworks, an effective strategy is to introduce heteroatoms (e.g., O, N, S, etc.) to perturb the electronic distribution along the polymer backbones.8 Particularly, the introduction of N atoms in the form of diverse electron-deficient azaaromatics is widely applied owing to the high stability, good solubility, diverse intermolecular interactions, and unique physicochemical properties of these heterocyclics.9,10 To explore new horizons of N-heteroaromatic polymers, the development of concise and adjustable synthetic strategies is needed. To date, heteroaromatic polymers are mainly constructed by the covalent connection of heteroaromatic monomers through cross-coupling reactions (e.g., Suzuki–Miyaura, Stille, Heck, etc.) and direct C–H bond activation.11,12 These polymerizations are usually catalyzed by organometallic reagents or conducted under harsh reaction conditions. Not to mention the cost-consuming reagents and process; the tedious synthesis and narrow monomer scope of the above-mentioned polymerizations greatly confine the type of polymeric products. On the contrary, natural polymers such as DNA, RNA, and proteins are composed of various structural units and show considerable structural variations to perform broad biological functions.13,14 To mimic the versatility of nature, multicomponent polymerizations (MCPs) stand out as the straightforward methods to achieve structural diversity and multiple functionalities.15 From the viewpoint of synthetic chemistry, MCPs are derived from multicomponent reactions and thus, show many attractive inherited advantages, such as high efficiency, high atom economy, and operational simplicity.16,17 Although some achievements have been made in this area,18,19 the development of metal-free MCPs to construct multifunctional N-heteroaromatic polymers from readily available reagents is still charming. As an essential class of N-heteroaromatic, quinolines and their derivatives not only serve as structural motifs of alkaloids but also have found extensive applications in optoelectronics,20 pharmaceuticals, and agrochemicals.21 To embed quinolines in polymer frameworks, different synthetic strategies have evolved from polycoupling of quinoline monomers22 to in situ formation of poly(quinoline)s through direct polycyclization, involving Friedländer reaction,23 aza-Diels–Alder reaction,24,25 and alkyne-aldehyde/aniline reactions26 (Figure 1a). However, the structural complexity of monomers, the use of metalloid catalysts, and harsh reaction conditions (high-temperature, time-consuming, inert gas protection, etc.) in these two-component polymerizations are issues that limit a wide range of polymer exploration. Therefore, we were motivated to develop facile and efficient metal-free MCPs for in situ formation of poly(quinoline)s from readily accessible starting materials. Among MCPs, the A3-coupling of alkynes, aldehydes, and amines has been widely explored as straightforward polymerization methodologies to obtain N-containing skeletons,27 including poly(oxazine)s,28 poly(dihydropyrrolone)s,29 poly(tetrahydropyrimidine)s,29 poly(dipropargylamine)s,30,31 and so on. Furthermore, in 2014, Bharate et al.32 reported a formic acid-catalyzed A3-coupling reaction of phenylacetylenes, arylamines, and glyoxylates to synthesize quinoline carboxylate esters at room temperature. Based on this reaction, metal-free MCPs of diynes, diamines, and glyoxylates have been developed successfully for the facile and efficient synthesis of functionalized poly(quinoline)s under mild reaction conditions (Figure 1b). Since the quinoline ring is electron-deficient, diynes with various electron-donating moieties were then applied to give D–A poly(quinoline)s with different optical properties and aggregation behaviors.33,34 Based on the different photoresponsive capabilities, photopatterns could be fabricated readily from their spin-coated polymer films in three kinds of response modes: on–off, dual–off, and weak–off. Incorporating fluorescent moieties with aggregation-induced emission (AIE) characteristics into the polymer backbones has endowed the resulting poly(quinoline)s with sensitivity to varying structural rigidity. Such property enables them to serve as agents for direct visualization of phase-separation and spherulite morphologies in polymer materials. The AIE-active poly(quinoline)s demonstrated the specific fluorescence response to hexavalent chromium ion Cr(VI) and have been applied for fluorescent detection of Cr(VI) in unicellular algae. Figure 1 | (a) The previous polymerization routes for in situ formation of poly(quinoline)s. (b) The developed polymerization route towards functionalized poly(quinoline)s P1a–1f/2a–2d/3 in this work. Download figure Download PowerPoint Experimental Section Materials All the chemicals utilized in this study were reagent grade and used as received without further purification. 1,2-Bis(4-ethynylphenyl)-1,2-diphenylethene ( 1a) and 1-(4-ethynylphenyl)-1,2,2-triphenylethene ( 4) were purchased from AIEgen Biotech Co., Limited (Hong Kong). Diynes 1b– 1f were synthesized employing previously reported procedures.28,35–38 4,4′-Oxydianiline ( 2a), 4,4′-diaminodiphenylmethane ( 2b), benzidine ( 2c), 4,4′-diaminobenzophenone ( 2d), ethyl glyoxylate ( 3), formic acid, and p-anisidine ( 5) were purchased from Sigma-Aldrich (Hong Kong) and J&K Scientific (Hong Kong). Polybutadiene (PB) (Mw = 200,000 g/mol), polystyrene (PS) (Mw = 280,000 g/mol), poly(methyl methacrylate) (PMMA) (Mw = 120,000 g/mol), and poly(ethylene glycol) (PEG) (Mw = 350,000 g/mol) were purchased from Sigma-Aldrich and Meryer (Shanghai, China). All organic solvents, including acetonitrile (CH3CN), dichloromethane (DCM), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF) at a super dry level, were obtained from J&K Seal (Hong Kong) and utilized as received. The stock solutions of metal ions were prepared from KF, KCl, KBr, KI, NaOAc, NaHCO3, Na2SO4, Na3PO4, NaCl, MgCl2·6H2O, CaCl2, AlCl3, FeCl3, CoCl2·6H2O, NiCl2·6H2O, CuCl2, Zn(NO3)2·7H2O, Pb(NO3)2, AgNO3, CdCl2·2.5H2O, HgCl2, CrCl3, K2Cr2O7, and K2CrO4 with double distilled water (ddH2O). Buffer solutions with varying pH values were purchased from Sigma-Aldrich and Riedel-de Haen (Honeywell, Hong Kong). Instrumentation Proton and carbon-13 nuclear magnetic resonance (1H and 13C NMR) spectra were obtained on a Bruker ARX 400 NMR spectrometer (Bruker, USA) in deuterated DMSO with tetramethylsilane (TMS; δ = 0 ppm) as an internal reference. High-resolution mass spectra (HRMS) were recorded on a GCT premier CAB048 mass spectrometer (Waters Corporation, USA) operating in matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mode. Infrared (IR) spectra were recorded on a PerkinElmer 16 PC Fourier transform IR (FTIR) spectrophotometer (PerkinElmer, USA). Gel permeation chromatography (GPC) was performed in THF at an elution rate of 1.0 mL/min on a Waters Associates GPC system equipped with a Waters 1515 high-performance liquid chromatography (HPLC) pump and interferometric UV absorption detector (Waters Corporation, USA). Standard polystyrenes (PSs) were utilized for plotting calibration curves for number-average molecular weights (Mn) and weight-average molecular weight (Mw) determination. The polymer samples were dissolved in THF (2 mg/mL), filtered through a 0.45 μm polytetrafluoroethylene (PTFE) filter, and then injected into the GPC system. UV–vis and photoluminescence (PL) spectra were measured on a Milton Ray Spectronic 3000 Array spectrophotometer (Milton Roy Company, USA) and a PerkinElmer LS 55 spectrophotometer (PerkinElmer, USA), respectively. Thermogravimetric analysis (TGA) was performed on a TGA Q5000 (TA Instruments, USA) under nitrogen at a heating rate of 10 °C/min. The fluorescent images were taken under normal room light and 330−380 nm UV illumination using a Nikon Eclipse 80i fluorescent microscope (Nikon, Japan). Particle size analysis was determined by the dynamic light scattering (DLS) technique at room temperature using a Zetaplus potential analyzer (Brookhaven Instruments Corp., USA). Synthesis of model compound A mixture of ethyl glyoxylate ( 3, 2 mmol), 1-(4-ethynylphenyl)-1,2,2-triphenylethene ( 4, 2 mmol), and p-anisidine ( 5, 3 mmol) in DCM (3 mL) containing formic acid (1 mL) was stirred at room temperature for 5 h. After reaction completion, the resulting mixture was extracted three times with DCM/water, and the organic layer was concentrated using a vacuum rotary evaporator. The crude product was purified by silica-gel column chromatography using DCM/hexane mixture (1/3, v/v) as the eluent. A pale-yellow solid, M1, was obtained in a 72% yield. Polymer synthesis All the polymerizations proceeded smoothly under air atmosphere at room temperature. Glyoxylate ( 3) was purified through vacuum distillation and stored in anhydrous DCM, twice its volume, in a 4 °C refrigerator. A typical procedure for the polymerization of 1a, 2a, and 3 is shown below: diyne ( 1a) (0.2 mmol) and diamine ( 2a) (0.2 mmol) were added to 0.25 mL of DCM in a 15 mL Schlenk tube with a magnetic stirrer. Glyoxylate ( 3) (0.15 mL of DCM solution) and formic acid (0.3 mL) was injected into the system sequentially, and the resulting mixture was stirred for 3 h. After reaction completion, 5 mL of THF was added to the deep red intermediate, and the solution was added dropwise into 200 mL of hexane/methanol mixture (1/10, v/v). The precipitates were collected by filtration, followed by a drying process in a vacuum to a constant weight. Structural characterization is provided in the Supporting Information. Photopatterning Thin films of poly(quinoline)s were fabricated on silicon wafers through spin-coating polymer solutions in 1,2-dichloroethane (15 mg/mL). The thin polymer films were irradiated through a copper photomask with a grid pattern by UV light from an Oriel Mercury Arc Lamp (Oriel® Instruments, USA) with the incident light intensity of ∼15 mW/cm2 at 15 cm distance in the air at room temperature. The duration of the photoirradiation process was controlled for generating dual-mode photopatterns. Polymer morphological observation The stock solutions (0.05 g/mL) of the homopolymer and poly(quinoline)s were prepared by dissolving them in their corresponding suitable solvents (PS, PB, and PMMA in toluene; poly(quinoline)s, and PEG in chloroform). The dilute solutions of poly(quinoline)s were prepared by dissolving 0.005 g of polymers in 2 mL chloroform. Solutions of polymer blends were prepared using two different polymers at a volume ratio of 1:1. The dilute solutions of poly(quinoline)s were added into solutions of homopolymers and polymer blends at a volume ratio of 1/5 to function as polymeric fluorescent indicators (1.0 wt %). Thin films of homopolymers and polymer blends were fabricated on quartz plates through spin-coating at 1000 rpm for 60 s and dried overnight, followed by observation under a PL microscope. Algal incubation and confocal imaging The freshwater green algae Chlamydomonas reinhardtIII (C. reinhardtIII) has been maintained in our laboratory for more than 10 years. They were cultured in the artificial WC (Woods Hole Chu-10) medium29 with bubbled air at 23.5 °C with a 16:8 light/dark cycle. To test the biocompatibility of poly(quinoline)s, the C. reinhardtIII (1 × 106 cells per mL) was exposed to poly(quinoline)s for 96 h at different concentrations (0, 2, 5, 10, 20, 30, 50, and 100 μM). After the test, the cell count was obtained under the microscope using a traditional hemocytometer-based method. Then the 96-h EC50 could be calculated based on the toxicity test results. The toxic effects of Cr(VI) were determined using a similar experimental protocol. The algal cells (C. reinhardtIII, 5.0 × 106 cells mL−1)were co-incubated with poly(quinoline)s (50 μM) in the artificial WC medium. Then algal cells were exposed to 200 μg/L of Cr(IIII) and Cr(VI) for 24 h. The samples were then washed with the artificial WC medium, followed by centrifugation (2000 rpm, 3 min) three times. Then algal samples were placed in 1% glutaraldehyde for 10 min and finally transferred to a confocal dish for the observation under fluorescent microscope. Besides, we also added 1 mM Ascorbate (vitamin C) into the Cr(VI) exposed group, and the algal samples were analyzed by confocal microscopy. Results and Discussion Polymerization methodology To develop this metal-free polymerization for the facile and efficient synthesis of poly(quinoline)s, we used commercially available tetraphenylethene (TPE)-containing diyne ( 1a), 4,4′-oxydianiline ( 2a), and ethyl glyoxylate ( 3) as model monomer combination to optimize the polymerization conditions. Based on the coupling reaction reported by Bharate et al.,32 the polymerizations were catalyzed by formic acid and carried out at room temperature in a one-pot manner. As listed in Table 1, the effects of various parameters, including the reaction atmosphere, solvent, catalyst, monomer ratio, and reactants concentration, were systematically studied to acquire the resulting poly(quinoline)s with high molecular weights in high yields. The effect of reaction atmosphere was first examined and showed that the polymerization carried out under air behaved better than under nitrogen due to the final oxidation step at the proposed mechanism (entries 1 and 2). The influence of good solvents for monomers including CH3CN, DCM, THF, DMSO, and DMF was then investigated (entries 2–6). The best polymerization result was obtained in DCM, which afforded poly(quinoline)s with the highest Mw of 12,200 in 84% yield. Next, the volume of formic acid in a 1 mL reaction mixture was increased gradually to obtain the most suitable amount of acid catalyst for polymerization. As shown in entries 7–9, the Mw of poly(quinoline)s was finally raised to 13,800 in an 89.3% yield. Tuning the molar ratio of [ 3]/[ 1a] had a negative effect on the polymerization results (entries 10 and 11). Further, the monomer concentration was optimized to obtain soluble poly(quinoline)s with the highest Mw of 16,900 in a nearly quantitative yield (entries 12 and 13). Table 1 | Optimization of the Polymerization Conditions toward Poly(quinoline)s a No. Solvent Acid (mL) [ 3]/[ 1a] [ 1a] (M) Yield (%) Mwb PDIb 1c CH3CN 0.1 2.5 0.2 65.8 9400 1.96 2 CH3CN 0.1 2.5 0.2 75.4 11,300 1.98 3 DCM 0.1 2.5 0.2 84.0 12,200 1.91 4 THF 0.1 2.5 0.2 26.3 3700 1.61 5 DMSO 0.1 2.5 0.2 32.8 3900 1.34 6 DMF 0.1 2.5 0.2 41.2 4000 1.42 7 DCM 0.2 2.5 0.2 89.6 12,300 1.62 8 DCM 0.3 2.5 0.2 89.3 13,800 1.84 9 DCM 0.4 2.5 0.2 90.6 5800 1.71 10 DCM 0.3 2.2 0.2 82.8 6300 1.75 11 DCM 0.3 3.5 0.2 91.7 13,200 1.88 12 DCM 0.3 2.5 0.4 90.6 15,400 2.05 13 DCM 0.3 2.5 0.8 96.7 16,900 1.98 aCarried out in different solvents and catalyzed by formic acid with various volumes under air atmosphere for 3 h at room temperature. [ 1a] = [ 2a]. The molar concentration is obtained by dividing the mole of solute by the volume of solvent. bMw and the polydispersity index (PDI) are determined by GPC employing THF as eluent based on a linear polystyrene calibration. cCarried out in nitrogen atmosphere. Based on the optimized polymerization conditions, the versatility and scope of the polymerizations were investigated and enriched with different combinations of diynes and diamines (Table 2). The terminal diynes 1b– 1f were readily synthesized according to the literature methods, and the diamines 2b– 2d were commercially available. The polymerizations of 1a– 1f/ 2a– 2c/ 3 proceeded smoothly under mild reaction conditions, generating conjugated poly(quinoline)s with high Mw (up to 16,900) in high yields (up to 97.5%). Such a high efficiency was attributed to the high reactivity of the activated aldehyde groups of glyoxylates. Among these polymers, P 1b/ 2a/ 3, under the same optimized conditions, formed insoluble gels in 3 h, possibly due to the great entanglement and intermolecular forces of the flexible heteroatom-rich polymer chains. P 1c/ 2a/ 3a under the same optimized conditions gelled quickly, which may be related to an autoacceleration effect, considering the high reactivity of the electron-donating monomers 1c. Monomer 1d with a rigid and short-conjugated length gave a polymer with decreased Mw in moderate yield. The efficiency of polymerizations became lower when silicon-containing and electron-withdrawing monomers ( 1e and 1f) were used because of their weak nucleophilicity of alkyne groups. The polymerizations of different diamines also produced P 1b/ 2a/ 3a and P 1c/ 2a/ 3a with a high Mw in high yields. However, monomer 2d failed to polymerize, possibly due to its difficulty in forming imine intermediates with glyoxylates. Altogether, the successful synthesis of P 1a– 1f/ 2a– 2c/ 3 demonstrated that this convenient and highly efficient polymerization route provides a great structural diversity of poly(quinoline)s. Table 2 | Polymerizations of Different Monomersa No. Monomer Yield (%) Mwb PDIb 1 1a + 2a + 3 96.7 16,900 1.98 2c 1b + 2a + 3 93.2 9800 1.75 3d 1c + 2a + 3 90.1 12,000 1.94 4 1d + 2a + 3 83.1 7200 1.53 5 1e + 2a + 3 9.6 3300 1.10 6 1f + 2a + 3 13.7 2700 1.13 7 1a + 2b + 3 95.8 13,900 1.85 8 1a + 2c + 3 97.5 16,100 2.30 9 1a + 2d + 3 Trace aCarried out in 0.5 mL DCM and 0.3 mL HCOOH for 3 h under air at room temperature. [ 1] = 0.4 M, [ 2] = 0.4 M, [ 3] = 1.2 M, where the concentration of solute is based on the volume of DCM as solvent. bDetermined by GPC based on a linear polystyrene calibration. P 1b/ 2a/ 3 and P 1c/ 2a/ 3 formed gels under the optimization reaction conditions. cCarried out in 0.5 mL DCM for 1 h. dCarried out in 1 mL DCM for 3 h. The FTIR and NMR spectroscopies have been employed to determine the chemical structures of all the obtained P 1a– 1f/ 2a– 2c/ 3 ( Supporting Information Figures S1–S16). For better understanding, the characterization results of P 1a/ 2a/ 3 were taken for representative structural analysis with reference to the small molecular model compound M1, the corresponding monomers 1a, 2a, and 3 in Supporting Information. Collectively, all the FTIR spectra of the obtained poly(quinoline)s displayed no typical absorption peaks associated with the monomer structures and showed C=N stretching vibration at 1661–1689 cm−1. All the resonance peaks related to the reactive functional groups of monomers were absent in the NMR spectra of M1 and P 1a– 1f/ 2a– 2c/ 3, indicating a great extent of the coupling reaction. The NMR spectra of M1 and P 1a/ 2a/ 3 exhibited similar proton and carbon resonances of the ethyl groups with the spectrum of ethyl glyoxylate. FTIR and NMR analysis of P 1a– 1f/ 2a– 2c/ 3 confirmed a good correspondence with their chemical structures in Figure 1. The thermal properties of the obtained poly(quinoline)s were evaluated by TGA and differential scanning calorimetry (DSC) in Supporting Information Figure S17. The TGA results suggested that all the generated heteroatom-rich polymers showed high thermal stability, possibly due to their rigid quinoline structures. Their thermal degradation temperatures with 5% weight loss (Td) ranged from 268 to 301 °C. The glass transition temperature of the poly(quinoline)s varied from 73 to 141 °C due to their different conformational flexibility of polymer chains. All the poly(quinoline)s obtained displayed good solubility properties in commonly used organic solvents such as DCM, THF, CH3CN, DMSO, and so on. Their good film-forming capabilities were also verified through a simple spin-coating process. Their good performance in thermal stability, solubility, and processability provided easy access to explore their multiple functionalities and advanced applications. Photophysical properties The incorporation of various electron-donating moieties in the conjugated poly(quinoline)s encouraged us to study their photophysical properties. We investigated the absorption of M1 and P 1a– 1f/ 2a– 2c/ 3 in dilute THF solutions at first ( Supporting Information Figure S18). The UV spectra of the polymers exhibited a maximum, ranging from 322 to 375 nm. The emission of the polymer powders was screened by simple observation under UV irradiation ( Supporting Information Figure S19). By tuning the polymer backbone using alkyne monomers with different electron-donating abilities, the obtained P 1a– 1c/ 2a/ 3 with TPE, alkoxy-connected phenyl, and triphenylamine (TPA) groups were selected for PL investigations (Figures 2a–2c). Figure 2 | Chemical structures and PL spectra Chemical structures and PL spectra of (a and d) P1a/2a/3, (b and e) P1b/2a/3, and (c and f) P1c/2a/3 in THF/water mixtures (50 μM) with different water fractions (fw). Excitation wavelength: 350 nm for (d and e) and 380 nm for (f). Inset: Photos of poly(quinoline)s in pure THF, THF/water mixture, and solid-state taken under UV light. (g-i) Fluorescent photopatterns generated by the photomasked UV irradiation of polymer thin films on silicon wafers. (g) P1a/2a/3 irradiated for 5 and 40 min, (h) P1b/2a/3 irradiated for 40 and 90 min, and (i) P1c/2a/3 irradiated for 5 and 40 min. Download figure Download PowerPoint To gain insight into the structure–property relationships, the PL spectra of P 1a– 1c/ 2a/ 3 in THF solutions and THF/water mixtures were investigated systematically (Figure 2d–2f). The results showed that water addition and nonsolvent of polymers led to an emission improvement for TPE-containing P 1a/ 2a/ 3. Such aggregation-enhanced emission (AEE) phenomenon was attributable to the restricted molecular motions of TPE moieties in the aggregate state.39 In fact, TPE is frequently utilized as an AIE-active luminogen to embed the resulting polymers with AIE or AEE characters for multiple applications in the aggregate state.40 While the PL maximum wavelength of P 1a/ 2a/ 3 showed no apparent shift, the PL maximum of P 1b/ 2a/ 3 and P 1c/ 2a/ 3 exhibited varying degrees of bathochromic shift with increasing fw in THF/water mixtures. With the same electron-withdrawing carbonyl-functionalized quinolines, P 1b– 1c/ 2a/ 3 were introduced with stronger electron-donating groups than P 1a/ 2a/ 3. Hence, the intramolecular charge transfer (ICT) of the donor–π–acceptor structures in P 1b– 1c/ 2a/ 3 made their emission redshifted gradually with increasing polarity in THF/water mixtures. Such redshift variations in P 1b– 1c/ 2a/ 3 could a
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