and Stereoselective Polymerizations towards Functional Chalcogen

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Three-Component Regio- and Stereoselective Polymerizations towards Functional Chalcogen-Rich Polymers with AIE-Activities Qingqing Gao, Ling-Hong Xiong, Ting Han, Zijie Qiu, Xuewen He, Herman H.Y. Sung, Ryan T. K. Kwok, Ian D. Williams, Jacky W. Y. Lam, and Ben Zhong Tang J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b06493 • Publication Date (Web): 28 Aug 2019 Downloaded from pubs.acs.org on August 28, 2019

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Journal of the American Chemical Society

Three-Component Regio- and Stereoselective Polymerizations towards Functional Chalcogen-Rich Polymers with AIE-Activities Qingqing Gao,†,‡ Ling-Hong Xiong,⊥Ting Han,†,‡ Zijie Qiu,†,‡ Xuewen He,†,‡ Herman H. Y. Sung,‡ Ryan T. K. Kwok,†,‡,§ Ian D. Williams,‡ Jacky W. Y Lam,†,‡,§,* and Ben Zhong Tang†,‡,§ †HKUST-Shenzhen

Research Institute, No. 9 Yuexing 1st RD, South Area, Hi-tech Park, Nanshan, Shenzhen 518057, China; of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Division of Life Science, Institute of Advanced Study and Department of Chemical and Biological Engineering; §Center for Aggregation-Induced Emission, SCUT-HKUST Joint Research Institute, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China. ⊥Shenzhen Center for Disease Control and Prevention, Shenzhen 518055, P. R. China ‡Department

Supporting Information ABSTRACT: Polymers containing rich chalcogen elements are rarely reported due to the lack of facile synthesis methods. Herein, a novel multicomponent polymerization route towards chalcogen-rich polymers was introduced. A series of poly(vinyl sulfones) (PVSs) were synthesized at room temperature using readily prepared monomers. PVSs were generated with high regio– and stereo–selectivity in high yields (up to 92.3 %). Rich chalcogen elements endowed PVSs with distingctive multi-functionalities. The PVSs possessed good solubility and film-forming ability. Their thin films exhibited outstanding refractive indices up to 1.8062 at 550.0 nm together with good optical transparency in the visible region. Thin films of some polymers can also be fabricated into well-resolved fluorescent photopatterns by photolithography. Thanks to the unique redox properties of selenium, post-modification by oxidation reaction of P1a/2/3a successfully eliminate the caused heavy atom effect and endow resulting polymers with novel functionality as fluorescent bio-probes for cellular imaging.

INTRODUCTION Chalcogen calls also the oxygen family and belongs to Group 16 element in the periodic table. This family consists of nonmetal elements including oxygen (O) and sulfur (S), metalloid elements including selenium (Se) and tellurium (Te), and the radioactive metal element including polonium (Po).1 As we know, oxygen and sulfur are ubiquitous and essential elements to sustain functions of all the lifeforms.2,3 Besides, sulfurcontaining materials were also applied in therapeutic field,4-9 electronic and photonic industry10-14 and as high-refractiveindex materials.15-19 As for selenium or tellurium materials, they were reported to possess unique photovoltaic properties20-23 and exhibit responses to redox, coordination or radiation and then were used as drug-delivery vehicles.24-29 It’s foreseeable that materials combining rich and different chalcogen elements are supposed to enjoy multi-functionalities and shows potentials as advanced materials in various fields. Nevertheless, there is little use of selenium and tellurium in polymer chemistry because of the lack of good approaches towards processable materials. Polyselenophenes or polytellurophenes are representative Se/Te-containing polymers but the preparation methods suffered from low yield and long polymerization time.30,31 Most selenium/tellurium-containing polymers only have single elements in their structures.24-29,32-34 Few structures with larger than two kinds of chalcogen elements embedded in their structures were published.13,31,35,36 Overall, polymers containing rich and different chalcogen elements are rarely reported. Thus, even fewer polymers with different chalcogen elements in different combinations can be found. However, the attractive potentials of processable chalcogen-rich polymers still encourage people to explore feasible

polymerization methods with mild conditions and high yields. For the construction of chalcogen-rich polymers, several strict conditions are required to produce such polymeric materials. They are: (1) availability of commercially/synthetically starting materials; (2) existence of polymerization strategy with high efficiency, good yield and mild condition and (3) availability of polymerization that produce processable macromolecules with well-defined structures. To deal with these harsh conditions, multi-component polymerization (MCP) was chosen since different chalcogen elements can be introduced by different monomers, which considerably decreased the difficulties of monomer synthesis. MCPs also present advantages such as high efficiency, mild reaction condition, atom economy, and operational simplicity.37-41 Then We were attracted by the work published by Liu et. al, a copper-catalyzed regio- and stereospecific selenosulfonation of alkynes with arylsulfonyl hydrazides and diphenyl diselenide and successfully developed it into a facile multi-component polymerization.42 By this new technique, we obtained regio- and stereoselective poly(vinyl sulfone)s (PVSs) which meets all the above harsh requirements. In the presence of potassium persulfate, the copper-catalyzed sulfonation of diynes, 4,4'–oxybis(benzenesulfonyl hydrazide) and diphenyl dichalcogen was carried out at room temperature under the protection of nitrogen, affording chalcogen-rich PVSs with regio– and stereo–selectivity in high yields (Scheme 1). This novel MCP strategy introduced four different chalcogen elements by different combination of monomers, which endowed PVSs with distingctive multi-functionalities. PVSs showed pretty high refractive indices in the visible region and patterned fluorescent images were generated. New function as bio-probe for cellular imaging was realized after P1a/2/3a was

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post-modified by oxidation. This pioneer polymerization strategy introduced three chalcogen elements with different combinations into the prepared polymer. Scheme 1. Cu-Catalyzed MCP toward PVSs. X

1

3

2

O

S

R

Cu(MeCN)4PF6,K2S2O8

O O S H2NHN O

O

X

+

R

O NHNH2

O S O

O

DMF/MeCN, rt

S

O

n X

X P1/2/3

O X= Se, Te, S

(CH)8

R= O 1a

1b

O 1c

O

3a-c 1d

RESULTS AND DISCUSSION Polymerization To develop the copper-catalyzed one-pot reaction of diyne, 4,4'–oxybis(benzenesulfonyl hydrazide) and diphenyl dichalcogen into a facile strategy for preparing PVSs, monomers with multiple functional groups were designed and prepared. And we optimized the polymerization conditions using tetraphenyl ethylene (TPE)–containing diyne (1a), 4,4'– oxybis(benzenesulfonyl hydrazide) (2) and diphenyl diselenide (3a) as model monomers. The effects of different parameters including solvent, solvent ratio, catalyst, monomer concentration and time course were examined systematically

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(details were recorded in supporting information). In the presence of Cu(MeCN)4PF6 and K2S2O8, polymerizations of terminal diynes, arylsulfonul hydrazides and diphenyl dichalcogen were carried out in DMF/MeCN mixture (v/v =1:1) for 3h at room temperature (Scheme 1). With the optimized conditions in hand, we tried different monomer combinations to enrich the polymers’ structures. Monomers 1a and 1b are rigid and wholly conjugated with different conjugation lengths while 1c and 1d enjoyed soft alkyl chain and electron-donating groups in their structures. We also purchased monomer 3 with different chalcogen elements. The results showed that all the polymerization procceded smoothly under optimum conditions except for P1a/2/3c. Monomer 1a is a TPEcontaining diyne and its polymerizations gave P1a/2/3a and P1a/2/3b with good molecular weights (Mw = 12,600 and 20,800) in high yields (92.3 % and 87.1 %). However, P1a/2/3c was turned to be yellow gel probably due to the sulfur crosslinking. Then, we successfully increased its solubility by introducing 3a into the polymer, affording P1a/2/3ac with a moderate molecular weight. The rigid and linear structure of monomer 1b endowed P1b/2/3a and P1b/2/3b with moderate solubility. Monomer 1c and 1d possess alkyl chain, which imparted their polymeric products with good solubility and satisfactory molecular weight in good yields. In summary, above results demonstrated the versatility and wide monomer scope of this polymerization.

Table 1. Multicomponent Polymerizations of Different Monomersa entry

monomers

c1

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

2 3 4 5 6 7 8 9

yield (%) 92.3 64.1 81.4 87.1 44.3 79.7 70.0 gel 79.1

Mwb

Mw/Mnb

Sd

1.8 1.4 1.4 2.7 1.2 2.0 1.5

√ ▲ √ √ ▲ √ √ ▲

12,600 8,200 10,800 20,800 e6,500 13,800 14,800 8,200

1.8

aCarried

out in DMF/MeCN mixture (v/v =1:1) under nitrogen at room temperature in the presence of Cu(MeCN)4PF6 and K2S2O8 for 3h. [1] = [2] = [3] = 0.2 M, [Cu(MeCN)4PF6] = 0.02 M, [K2S2O8] = 0.8 M. bDetermined by GPC in THF on the basis of a linear polystyrene calibration. cData taken from Table S1, entry 8. dSolubility (S) tested in common organic solvents, such as dichloromethane, chloroform and tetrahydrofuran: √ = completely soluble; ▲ = partially soluble; × = insoluble. eSoluble fraction. f[3a]:[3c] = 4:1.

Model Reaction Model compound 6 was synthesized by selenosulfonation of TPE–yne 4, benzenesulfonyl hydrazide 5 and diphenyl diselenide 3a to verify the polymer structure (Scheme 2A). Besides, in order to prove the regio– and stereo-selectivity of the reaction, model compound 8 was also synthesized (Scheme 2B). Single crystals of 8 (CCDC 1842945) were obtained by slow evaporation of chloroform solution of 8. As only E isomer of 8 was obtained by single crystal X–ray diffraction analysis, the regio– and stereo–selectivity of the reaction was confirmed and corresponding reaction mechanism was provided in Figure S33.42 Scheme 2. Synthetic Route to (A) Model Compound 6 and (B) 8.

Structural Characterization All the obtained polymers were fully characterized by standard NMR and IR spectroscopic techniques (Figure S5– S25). We chose the spectra of monomer 1a, 2 and 3a, model compound 6 and 8, and polymer P1a/2/3a as example for the

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discussion. Firstly, their 1H NMR spectra were compared in Figure 1. Both of the resonance of the acetylene protons of monomer 1a at δ 3.03 (a) and amine protons of monomer 2 at δ 4.15 and δ 8.39 (b and c) disappeared in the spectra of the model compound 6 and 8, and P1a/2/3a. On the other hand, new peaks associated with vinyl proton absorption emerged at δ 6.20 in the spectra of 6 (d), 8 (d’) and P1a/2/3a (d’’). Besides, compared with the spectra of 6 and 8, the resonance peaks of P1a/2/3a were much

broader which revealed its polymeric nature. Similarly, their 13C NMR spectra were recorded in Figure 1 (right row). The peaks related to the alkyne carbons of 1a resonated at δ 83.66 (e) and δ 77.68 (f) and were absent in spectrum (J), (K) and (L). On the other hand, the vinyl carbon near the selenium atom resonated at δ 157.81 (g) and was found in 6, 8 and P1a/2/3a. Overall, the characterization data of 6 and P1a/2/3a showed high similarity, which indicated the precise structure of the polymer.

Figure 1. (Left) 1H NMR spectra of (A) 1a, (C) 3a, (E) 6 and (F) P1a/2/3a in dichloromethane-d2, (B) 2 in dimethyl sulfoxide-d6 and dichloromethane-d2, and (D) 8 in chloroform-d. (Right) (G)–(L) corresponding 13C NMR spectra. The solvent peaks were marked with asterisks. Solubility, Light Refraction and Photopatterns High-refractive-index polymers (HRIP) serve as advanced optoelectronic materials and they have attracted much attention for their broad optical engineering applications including waveguides, organic light-emitting diodes (OLEDs), lens, prisms and antireflective coatings.43-49 The refractive index (RI) of conventional polymers mostly lies in 1.30 – 1.70 and polymers with RI over 1.70 usually possess п-conjugated structures with aromatic heterocyclic rings or thiophene units.50,51 However, these HRIPs usually show poor solubility and low optical transmittance in the visible region, which hinder them for use in the optical field. Therefore, processable HRIPs are still in high demand.52-54 Incorporating atoms or substituents with large atomic polarizabilities, high molar refractions or small molar values is a general strategy to increase materials’ refractive indices.15-19 A variety of atoms such as sulfur,

phosphorus and heavy halogens (bromine and iodine) were reported for fabricating HRIPs.55-57 Since PVSs possessing rich

chalcogen elements (S, Se, Te) with large atomic polarizabilities and high molar refractions and high contents of aromatic rings, they are supposed to enjoy high refractive indices.35,58 Although the PVSs possess many aromatic rings, they still show good solubility in common organic solvents such as DCM, chloroform and THF, which endowed the polymers with good processability. The light refraction spectra of their transparent uniform thin films fabricated by spin–coating technique were shown in Figure 2. P1/2/3 displayed RI values of 1.8898–1.5845 in a wide wavelength range of 400–900 nm. PVSs exhibited high RI values of 1.6212–1.8062 at 550.0 nm, which is reasonable according to the above analysis. Among the PVSs, P1c/2/3a showed an RI value of 1.8062 at 550.0 nm and it also enjoyed good processability, which was outstanding in the reported HRIPs.50,51 Besides, TPE-containing polymers were found to be photosensitive under strong UV exposure.59 Refractive index of P1a/2/3a decreased gradually with prolongation of irradiation time and a Δn of 0.05 was observed at 550.0 nm (Figure 2B).



Sulfur-containing inorganic/organic polymeric hybrid materials have been well developed and few selenium-containing polymers were also reported.60-65 However, tellurium-containing HRIPs are rarely reported. This is the pioneer work combining different chalcogen elements (O, S, Se, Te) together to fabricate processable organic polymeric material and HRIPs were successfully produced with n values up to 1.8062 at 550.0 nm.

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dispersion, PVSs can be seen as promising candidate as functional coating materials for advanced optical devices.

Figure 3. Two-dimensional fluorescent photopatterns generated by photo-oxidation of (A) P1a/2/3a and (B) P1a/2/3b. The photographs were taken under UV illumination (330−385 nm).

Figure 2. (A) Refractive index and chromatic dispersion of polymer thin films. Wavelength dependence of refractive indices of thin films of P1/2/3. Abbreviation: n = refractive index, νD = Abbé number = (nD−1)/(nF−nC), where nD, nF, and nC are the RI values at wavelengths of 589.2, 486.1, and 656.3 nm, respectively, D = chromatic dispersion = 1/νD. (B) Wavelength dependence of refractive index of thin films of P1a/2/3a at different UV irradiation time.

Post-modification by oxidation Reaction Although the polymer world contains a variety of controlled polymerization methods towards functional polymers with welldefined structures. Resulting from the lack of catalytic systems and limited polymerization techniques, it is still challenging to synthesize polymers with complicated structures or functional groups directly by their corresponding monomers. Under such situation, post-modification of polymer is an attractive and effective way to endow synthetic polymers with more sophisticated structures.70-72 Nowadays, selenium–containing polymers are attracting researchers’ attention due to their unique redox properties.26-28 Herein, we utilized the response behavior of P1a/2/3a to hydrogen peroxide to post-modify its structure as OP1a/2/3a (Scheme 3C). To verify the oxidation reaction, we also oxidized model compound 6 and 8 (Scheme 3A, 3B) (experimental procedure can be found in supporting information). Scheme 3. Oxidation Reaction of (A) 8, (B) 6 and (C) P1a/2/3.

As previously mentioned, P1a/2/3a and P1a/2/3b possessed good film-forming ability and were emissive at solid state. Such characteristics make them promising materials for fabricating nanoscale fluorescent photopatterns. The patterned fluorescent images show potential applications in displays, optical memory devices as well as imaging industries.67-69 We spin–coated the toluene solutions ( ～10 mg/mL) of polymers on silica wafers and dried them in ambient atmosphere. Then the formed films were irradiated by UV light (power = 180 W) in air for 20 min through copper photomasks. The emission of the irradiated parts (dark line) was quenched due to the photo-oxidation reaction, whereas the unexposed parts remained emissive.59 Thus, two– dimensional photopatterns with high contrast and sharp edges were readily fabricated by the effective photolithography technique (Figure 3). What’ more, PVSs are stable under normal room light (Figure S36 and S37). Together with their good processability, high and tunable RI values and low chromatic


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Single crystal of 9 (CCDC 1842080) was obtained by slow evaporation of its THF solution and its structure was confirmed by crystal analysis (Table S5). The comparison among the NMR spectra of P1a/2/3a, 9, 10 and OP1a/2/3a gave more detailed structural information of oxidation products. As shown in Figure 4 (left), the resonance peak of vinyl protons of P1a/2/3 at δ 6.20 (a) was absent in the spectra of 9, 10 and OP1a/2/3a. Meanwhile, the hydrogen on the benzene ring (near sulfone groups) of 9 and 10 resonated at δ 8.08 (b and b’), which located at the same place with that of OP1a/2/3a (b’’). Similarly, in Figure 4 (right), the vinyl carbons near the selenium atom resonated at δ 158.70 (e), which were completely disappeared in the spectra 10 and OP1a/2/3a. Instead, two new peaks associated with the

acetylene carbons resonances emerged at δ 93.51 (d) and δ 85.21 (c) in the spectra of 9, 10, and OP1a/2/3a. Both of the above comparison and the high similarity between the two spectra indicated the occurrence and completion of post-modification by oxidation and gave information about the precise structure of OP1a/2/3a. Based on above discussion, this post-modification reached completion and selenium atoms dropped from the polymers. Thus, the caused heavy atom effect disappeared at the same time, which may benefit the luminous performance of PVSs considerably and endow prepared polymers with new functionalities.

Figure 4. (Left) 1H NMR spectra of (A) P1a/2/3a in dichloromethane–d2, (B) model compound 9, (C) 10 and (D) OP1a/2/3a in chloroform–d. (Right) (E)–(H) Corresponding 13C NMR spectra. The solvent peaks were marked with asterisks.

Photophysical Properties Recently, luminogens with aggregation–induced emission (AIE) characteristics catch scientists’ sight as novel fluorescent materials. Different from traditional aggregation–caused quenching (ACQ) materials, AIE luminogens (AIEgens) are strongly emissive in aggregate or solid state due to the restriction of intramolecular motion (RIM).73 Here, the introduction of TPE unit, a traditional AIEgen, into P1a/2/3a, P1a/2/3b, P1a/2/3ac, 6 and 8 endowed them with AIE properties (S28-S32). Such introduction gave TPE-containing polymers solid/aggregate-state emissive properties and possibly brought them new functionalities. Although P1a/2/3a is AIE– active, its powder showed weak emission (Φ= 2.7%) (Figure 5, inset picture). Post-modification by H2O2 tuned the structure of P1a/2/3a and completely eliminate the heavy atom effects of selenium element. Obviously, OP1a/2/3a enjoyed a nearly 5fold solid state QY value (Φ = 13.4%) as solid-state emissive polymeric material. OP1a/2/3a also turned out to be AIE-active and showed a large αAIE value of 37.5 than P1a/2/3a (αAIE = 3.6), where αAIE was defined as I/I0 and I0 was the emission intensity in pure THF solution. The post-modification by oxidation was turned to be feasible and effective to tune PVSs’ photophysical properties.

Figure 5. (A): Fluorescent photographs of (upper row) P1a/2/3a and (lower row) OP1a/2/3a in in THF/water mixtures with different water fractions (fw) taken under 365 nm UV irradiation from a hand–held UV lamp. (B) The emission spectra of model compound OP1a/2/3a in THF/water mixtures with different water fractions (fw). Solution concentration: 10 μM; excitation wavelength: 350 nm. (C) The plot of αAIE (I/I0) versus the water fraction of the THF/water mixtures of P1a/2/3a OP1a/2/3a. Inset: fluorescent photographs of



P1a/2/3a and OP1a/2/3a owder taken under 365 nm UV illumination from a hand–held UV lamp.

Cell imaging The solid-state luminescence of TPE-containing PVSs encouraged us to explore their application in cell imaging application. As solid-state emissive polymeric materials, PVSs enjoyed some advantages over small molecules: (1) the chromophore is chemically bonded to the polymer and is hard to detach; (2) good photo-stability; (3) the chromophore is evenly distributed; (4) PVSs are much easier to purify and separate from impurities. For small molecules, impurities would cause signal loss in bio-imaging application. Since biomolecules attached with impurities bind to the specific target sites, thus biomolecules that combine small molecules as signal outputs will have no target sites to bind and then lead to signal loss.74,75 The in vitro cytotoxicity of P1a/2/3a and OP1a/2/3a to HeLa cells was investigated using a MTT cell-viability assay (Figure S34). The cell viability of cells remained at above 80% at tested concentrations even up to 100 μM within 24 h, indicating that both P1a/2/3a and OP1a/2/3a possessed low cytotoxicity. The low cytotoxicity makes them promising bio-compatible materials for bio-imaging applications. The application of OP1a/2/3a and P1a/2/3a in in–vitro cellular imaging was studied using confocal laser scanning microscopy (CLSM). SYTO 59 is a red fluorescent dye (Figure 6C and 6G). After incubation with OP1a/2/3a and P1a/2/3a, the HeLa cells were fixed and the cells were stained with the polymer dyes. As shown in Figure 6B, intense yellow fluorescence was observed inside the cells. The overlay image 6D provided solid proof that OP1a/2/3a tended to stain HeLa cells. On the other hand, no fluorescent signals were observed in cells incubated with P1a/2/3a. These results manifested that the oxidized polymer OP1a/2/3a was a promising fluorescent bioprobe for cellular imaging with a high fluorescence contrast. Overall, after post-modification, solid-state emissive OP1a/2/3a presented new functionality as bio-imaging fluorescent probe.

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functional poly(vinyl sulfone)s. In the presence of potassium persulfate, the selenosulfonation of diynes, 4,4'– oxybis(benzenesulfonyl hydrazide) and diphenyl dichalcogen was catalyzed by copper(II), affording PVSs with high regio– and stereo–selectivity in high yields. This polymerization proceeded smoothly at room temperature under the protection of nitrogen. The resulting PVSs possessed good solubility and film-forming ability. Their thin films fabricated by spin–coating exhibited high refractive indices up to 1.8062 at 550.0 nm. Due to the presence of TPE unit in their structures, model compound 6, 10, P1a/2/3a, P1a/2/3b, P1a/2/3ac and OP1a/2/3a were AIE– active. Thanks to the solid-state emission and photosensitivity, well-resolved fluorescent photopatterns of P1a/2/3a and P1a/2/3b could be readily fabricated by the photolithography technique. The selenium atom endowed P1a/2/3a with redox property, and its oxidized form (OP1a/2/3a) could serve as an effective fluorescent bio-probe for cellular imaging.

ASSOCIATED CONTENT Supporting Information Materials and methods, synthesis and structural characterization data of P1/2/3, model reaction, post-functionalization reaction, biology experiments, optimization of polymerization conditions, effect of solvent, solvent ratio, catalyst, monomer concentration and time course on the polymerization, HRMS spectra of 6, 8, 9 and 10, structural characterization (IR, 1H NMR and 13C NMR spectra) of P1a/2/3b, P1b/2/3a, P1c/2/3a, P1b/2/3b, P1c/2/3b, P1d/2/3b, P1a/2/3ac, TGA and DSC thermograms of P1/2/3, absorption spectra of P1/2/3, OP1a/2/3a, 6 and 10, emission spectra of P1a/2/3b, P1a/2/3ac and 10 in THF/water mixtures with different water fractions (fw), mechanism of reaction, quantum yield of P1/2/3, 1H NMR and absorption spectra of P1a/2/3a before and after daylight irradiation, and single-crystal data of 8 (CCDC 1842945) and 9 (CCDC 1842080). Crystal data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

AUTHOR INFORMATION Corresponding Author *[email protected] *[email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

Figure 6. (A and E): bright field of live HeLa cells. Confocal images of live HeLa cells labeled with (B) OP1a/2/3a, (F) P1a/2/3a and (C) and (G) SYTO 59. (D) Overlay of (B) and (C). (H) Overlay of (F) and (G). The signal from OP1a/2/3a and SYTO 59 (for nuclei staining) was yellow and red, respectively. Conditions: OP1a/2/3a and P1a/2/3a: excitation: 405 nm, emission: 430-560 nm; SYTO 59: excitation: 568 nm, emission: 620-680 nm. Scale bar: 20 μm.

CONCLUSIONS In this work, we reported an efficient one-pot threecomponent polymerization toward chalcogen-rich multi-

This work has been partially supported by the National Science Foundation of China (21788102, 21490570 and 21490574), the Research Grant Council of Hong Kong (16308116, 16303815, C6009–17G and A-HKUST605/16), the Innovation and Technology Commission (ITC-CNERC149C01 and ITCPD/17-9) and the Science and Technology Plan of Shenzhen (JCYJ20160229205601482 and JCYJ20170818113602462). L. H. X is grateful for the support from the National Natural Science Foundation of China (21705111).

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