<i>In Situ</i> Generation of <i>N</i> -Heteroaromatic Polymers: Metal-Free Multicomponent Polymerization for Photopatterning, Morphological Imaging, and Cr(VI) Sensing

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