Communication Cite This: J. Am. Chem. Soc. 2019, 141, 48−52
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Direct Synthesis of Crystalline Graphdiyne Analogue Based on Supramolecular Interactions Weixiang Zhou,†,‡ Han Shen,†,‡ Chenyu Wu,§ Zeyi Tu,†,‡ Feng He,† Yanan Gu,†,‡ Yurui Xue,† Yingjie Zhao,§ Yuanping Yi,†,‡ Yongjun Li,*,†,‡ and Yuliang Li†,‡
J. Am. Chem. Soc. 2019.141:48-52. Downloaded from pubs.acs.org by UNIV OF KANSAS on 01/22/19. For personal use only.
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Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Research/Education Center for Excellence in Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China § College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China S Supporting Information *
nanowalls,20 nanosheets,10,21−23 and three-dimensional (3D) foams24 etc. Though crystalline graphdiyne nanowalls9,20 and nanosheets22 have been successfully constructed and the crystal structure was determined by high-resolution TEM, it is still a challenge to fabricate high-quality graphdiyne films due to the fact that (1) some types of side reactions such as trimerization, hydroalkynylation, and oxidation would occur for the reactive monomer hexaethynylbenzene,25 (2) irregular cross-linking between two ethynyl groups due to the free rotation of the single bond, both bringing to the random polymeric systems. To overcome these problems, there are two aspects can be considered. First, the utilization of an appropriate flat substrate interacting with the precursors might enhance the ability to generate the desired 2D networks. Second, introduction of supramolecular interactions to control the orientation of the monomers and the growing oligmers, thus avoiding defects and providing high crystallinity in the target networks, which is the key feature of the strategy that would be investigated here. Herein we reported the design and synthesis of a highly crystalline graphdiyne analogue, benzene substituted graphdiyne (Ben-GDY). Ben-GDY is an extended π-conjugated carbon network with six 1,3,5-triphenylbenzene rings connected with butadiyne linkages as the repeating hexagonal unit. The optimized framework of Ben-GDY is plotted in Figure 1b. The length of the acetylenic bond (C2−C3) in the butadiyne linkage is around 1.214 Å. Because of the stabilization effect of the triple bonds, both of the lengths of the bonds between C1 and C2 (1.393 Å) and that of C3−C3 (1.332 Å) are shorter than the C1−C1 bond. The Ben-GDY framework is a flat plane without any buckling. The sheet of Ben-GDY can be described by the plane group P1 with a lattice constant of a = 16.145 Å, b = 16.147 Å, γ = 120.134°. The phenyl rings connected with the triethynylphenyl framework with dihedral angles of 40.0−40.2°. The vicinity of alkynes was attached with benzene rings to provide the increased stability of the monomer through the bulkyprotection of alkynes. The π−π/CH−π interactions between the nearby benzene rings in the oligmers can force the alkyne skeleton into near flat surface, as evidenced by the fact
ABSTRACT: The synthesis of graphdiyne with an ordered internal structure is highly attractive for its various scientific and application investigations. We reported herein a rational method to fabricate a graphdiyne analogue with the help of supramolecular chemistry. The introduction of π−π/CH−π interactions controlled the conformations of the precursors and afforded multilayer graphdiyne analogue Ben-GDY through the wet chemical method. The in-plane periodicity of the multilayer Ben-GDY was corroborated by transmission electron microscopy and selected area electron diffraction, which showed a pattern well matched with ABC-style stacking.
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wo-dimensional (2D) carbon materials have captured great attention due to their potential technological applications in nanoelectronics, energy storage, and batteries.1,2 The prerequisite for the success of 2D polymerizations is the precise control of monomer assembly before or in the process of covalent bond generation; if not, aperiodic, cross-linked networks are preferred. Shape-persistent monomers and directional interactions; that is, an interface or layered crystal was used to control specific bonding geometries for templating the formation of the target 2D structure. The sp- and sp2-hybridized graphdiyne (GDY)2−5 exhibits highly conjugated π system, conformably distributed pores, and controllable electronic properties,6 which perform in various applications comparable to conventional sp2-hybridized carbon systems. The reliable fabrication of GDY extend its study from theoretical predictions into practical studies, where it has exhibited many applications such as catalysts,7−9 rechargeable batteries,10−12 solar cells,13 electronic devices,14 detectors,15 biomedicine and therapy,16 and water purification.17 The synthesis of GDY was first achieved through a Glaser coupling reaction on copper foil,4 in which the copper foil functioned as the reservoir of coupling catalysts and the planar template for the controlled conformal growth of 2D GDY sheets. Following this ground-breaking work, GDY has been fabricated in the morphologies of nanowires,18 nanotube arrays,19 © 2018 American Chemical Society
Received: September 13, 2018 Published: December 20, 2018 48
DOI: 10.1021/jacs.8b09945 J. Am. Chem. Soc. 2019, 141, 48−52
Communication
Journal of the American Chemical Society
Figure 2. Supramolecular interactions for controlling the molecular geometry and preorganization. (a) The molecular structures of the model dimmer ditriethynyl-benzene (DiTEB) and dihexaethynylbenzene (DiHEB); (b) torsion barriers of DiTEB and DiHEB along the torsion angle as indicated in panel a. Crystal structures of the monomer 3 (c), and 6 (d), in which the CH−π interactions critical for stacking of layers were indicated: a, 3.068 Å; b, 2.844 Å; c, 2.884 Å; d, 2.861 Å. CH−π interactions critical for assembling alkyne units toward following coupling reactions were emphasized: e, 2.798 Å; f, 2.810 Å; g, 2.772 Å.
Figure 1. Supramolecular approach for ordered 2D graphdiyne. (a) 1,3,5-Triethynylbenzene without directional interactions formed 3D porous film.11 (b) The introduction of π−π/CH−π interactions for controlling the flat bonding geometries: C1, C2, C3, and C4 are denoted (black red), the torsion angles of the attached benzene rings (purple), the bond lengths (blue), C−H···C short contacts (red) and the cavity (d = 5.1 Å) surrounded by attached benzenes are shown, and the unit cell of Ben-GDY is denoted by the black line.
the C 1 s core level spectra displays the major fractions of CC (sp2, 284.7 eV), CC (sp, 285.4 eV), CO (286.5 eV), and CO (288.8 eV) (Figure 3a). The existence of CO and C O groups is ascribed to the oxygenization of the terminal alkyne on the edge of the 2D molecular framework. The appearance of the Raman signal at 2192 cm−1 (the CC stretching) in the Ben-GDY films (Figure 3b) is a strong proof for the generation of conjugated butadiyne bridges from the coupling reaction of the terminal alkyne (which shows a CC vibration at 2115 cm−1; Figure S3). G-band at 1593 cm−1 indicates that the Ben-GDY films contain abundant aromatic rings, and a D-band at 1374 cm−1 is assigned to the vibration of the bonds connecting two carbon triple bonds and the stretching of the CC bonds connecting triply coordinated carbon atoms and its doubly coordinated carbon neighbors, also the stretching of CC bonds connecting doubly coordinated phenyl rings carbon atoms.27 The observed signals agree well with the simulated Raman spectra calculated at HSE06/def2-SVP level (also combined with DFT-D3 dispersion correction) of theory, which supports the proposed assignments (Figure S9). C K-edge NEXAFS spectrum of Ben-GDY (Figure S11) showed the π* orbitals of the ethynyl group, which further confirmed the formation of butadiyne bridge.28 The ultraviolet−visible (UV−vis) absorption analysis was employed to investigate the optical properties of Ben-GDY film. An obvious bathochromic shift was observed in the UV−vis spectra of the Ben-GDY film as compared with that of the monomer 3, which is ascribed to the enhanced electron delocalization through the highly π-conjugation. The optical bandgap (Ebg) estimated from the absorption onset is 2.47 eV (Figure 3c). The energy level of valence band (i.e., Evb) of Ben-
that the model dimer with parallel conformation showed ∼4.5 kcal mol−1 lower energy than the vertical one (Figure 2b), which could gather a large stabilization energy in the target network. These π−π/CH−π interactions were also evidenced in the optimized structure as the short C−H···C contacts of 2.26−2.49 Å between the attached benzene C−H and the butadiyne carbon, and the short C−H···C contacts of 2.79−2.82 Å between attached benzene rings (Figure 1b). At the same conditions, the hexethynyl dimmer showed only ∼0.1 kcal mol−1 rotation barriers (Figure 2b), which decreased the probability to form crystalline films. The modeling of the key step in Bohlmann’s coupling mechanism26 (Figure S1) indicated that the introduction of nearby benzene rings would increase the homocoupling reaction barrier due to repulsion between benzene rings. Therefore, higher reaction temperature would be expected. The single-crystal X-ray diffraction (XRD) analysis of the monomer 3 (Figure 2c) and 6 (Figure 2d) revealed some key π−π/CH−π interactions needed for the assembly of monomers to the intermediates or the bottom layer grown previously. These supramolecular interactions ensured the lateral growth of the layers on the copper surface and prevented the cross-linking across the layers. The synthesis of monomer 3 is shown in Supporting Information. Ben-GDY was prepared via the Glaser−Hay coupling reaction of 3 in pyridine with copper foil as the substrate and catalyst at higher temperature (110 °C) as expected. XPS (Figure S2) shows that the Ben-GDY film consists of elemental carbon. Deconvolution and curve fitting of 49
DOI: 10.1021/jacs.8b09945 J. Am. Chem. Soc. 2019, 141, 48−52
Communication
Journal of the American Chemical Society
semiconducting due to these highly localized π HO and σ* LU orbitals, which are different from the delocalized π and π* orbitals of metallic graphene sheet. Optical microscopy of the Ben-GDY film transferred to a quartz substrate revealed sheet morphology (inset of Figure 4a).
Figure 3. Spectral characterization and electronic band structure of Ben-GDY. (a) XPS spectra of Ben-GDY. (b) Experimental and simulated Raman spectra of Ben-GDY. (c) UV−vis spectra of Ben-GDY film exfoliated from the copper foil, the bandgap was given by the onset of the absorption. (d) Conductivity measurement of Ben-GDY film on the copper substrate. (e) Calculated electronic band structure and corresponding partial density of states (PDOS) of Ben-GDY. The black, red, blue, and cyan lines present the total density of states, PDOS of CC (sp C, C2, C3), CC (sp2 C, C1), CC (sp2 C, C4), respectively. The first Brillouin zone high symmetry points are labeled as follows: Γ (0, 0, 0), B (1/2, 0, 0), F (0, 1/2, 0). (f) Wave function of highest occupied crystal orbital (HOCO) and lowest unoccupied crystal orbital (LUCO) at Γ point in unit cell of Ben-GDY.
GDY was measured by ultraviolet photoelectron spectroscopy (UPS). Subtracting the UPS width (Figure S4) from excitation energy (HeI, 21.22 eV gave the Evb of 6.61 eV. Furthermore, the conduction band energy Ecb (4.14 eV) was obtained from Evb − Ebg. The electronic band gap of Ben-GDY agrees with the that of 1,3,5-graphdiyne reported by Barth et al.29 The current−voltage (I−V) curve was also measured at a bias voltage from −1 to +1 V (Figure 3d). The conductivity of Ben-GDY film is determined to be 6.77 × 10−3 S m−1. The electronic band structure and corresponding PDOS of Ben-GDY are calculated under HSE06 functional in the Brillouin zone, and the results are shown in Figure 3e. Both valence-band maximum (VBM) and conduction-band minimum (CBM) are found to be located at the first Brillouin zone Γ point. The calculated band gap energy of Ben-GDY is 2.66 eV, which is consistent well with the measured optical band gap (2.47 eV). HOCO and LUCO at Γ point in unit cell of BenGDY are plotted in Figure 3f (Figure S8). Both CBM and VBM are 2-fold degenerated at Γ point. The HOCO is mainly localized at the π orbital of hexagonal benzene rings and CC bonds. However, the LUCO is located at the σ* bond connecting the attached benzene rings and that connecting the CC chains with the framework benzene. Ben-GDY is
Figure 4. (a) AFM images of exfoliated sheets, inset, height analysis along the green lines (across the slit generated by stress-cracking) shows a uniform thickness of ∼30 nm; digital photograph of the BenGDY film transferred to a quartz substrate, a hole generated by the solvent evaporation induced stress-cracking. (b) SEM images of BenGDY film. (c) TEM image of Ben-GDY film. (d) HRTEM of Ben-GDY. (e) Scanning TEM image, (f) elemental mapping of the C in the BenGDY nanosheets, and (g) an overlay of these two images. (h) SAED of Ben-GDY film. Simulated ABC stacking model of Ben-GDY: (i) top view, (j) side view.
Atomic force microscopy (AFM) showed the nanoscale morphology of Ben-GDY film (Figure 4a). The film was revealed to be a 30 nm thick flat sheet. SEM images again showed the smooth surface of the Ben-GDY film (Figure 4b), and EDS point analysis indicated the appearance of carbon, trace oxygen and without copper (Figure S5). Compared with the reported 3D porous film11 and nanofibers film30 grown from triethynylbenzene on copper foil in pyridine, our supramolecular strategy successfully controlled the conformation of the intermediate oligmers and ensured the lateral growth of the layers on the copper surface (the detailed growth mechanism is shown in Figure S12). The powder XRD pattern (Figure S13) 50
DOI: 10.1021/jacs.8b09945 J. Am. Chem. Soc. 2019, 141, 48−52
Communication
Journal of the American Chemical Society indicates the crystallinity of Ben-GDY film. The diffraction peak at 15.239° corresponds to the 0.58 nm interlayer spacing. The strong diffraction peak at 18.920° relates to the diffraction spacing of 0.47 nm. The internal structure of the Ben-GDY was evaluated by SAED performed in TEM. Figure 4c gives a typical lowmagnification TEM image of the Ben-GDY film. Elemental mapping of the selected region in Figure 4e shows the uniform carbon atoms distribution (Figure 4e−g). The hexagonal pattern 2D periodicity revealed by SAED (Figure 4h) confirms the high crystallinity of the Ben-GDY (Figure 1b). The experimental diffraction pattern almost exactly matched that expected for the proposed ABC stacking model (Figure 4i,j) (Figures S14−16). Hence, the trigonal crystal structure with ABC stacking (space group R32) was confirmed for the graphdiyne synthesized in this work. HRTEM of the synthesized Ben-GDY film (Figure 4d) revealed the 0.47 nm interval lattice fringes, which is related to (3 0 0) spacing of the primitive unit cell. In summary, we have synthesized a carbon-rich 2D graphdiyne analogue with the help of supramolecular chemistry. The introduction of π−π/CH−π interactions controlled the conformations of the precursors and afforded crystalline multilayer graphdiyne analogue. TEM and SAED corroborated the in-plane periodicity of the multilayer Ben-GDY, and the SAED pattern revealed the ABC-type stacking. This kind of synthetic 2D materials with an ordered internal structure are greatly beneficial for their various scientific and application investigations.
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Research Program of the Chinese Academy of Sciences (XDA09020302).
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.8b09945. Synthesis procedures and characterization data (PDF) Data for C30H18, C0.5HCl (CIF) Data for C28H18 (CIF) Data for P1 (CIF) Data for P1 (CIF) Data for R32 (CIF)
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*
[email protected] ORCID
Chenyu Wu: 0000-0002-6450-6268 Yingjie Zhao: 0000-0002-2668-3722 Yuanping Yi: 0000-0002-0052-9364 Yongjun Li: 0000-0003-1359-1260 Yuliang Li: 0000-0001-5279-0399 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Nature Science Foundation of China (21672222, 21790050, 21790051), NSFC-DFG joint fund (21661132006), the National key research and development project of China (2016YFA0200104), the key program of the Chinese Academy of Science (QYZDY-SSW-SLH015), and the Strategic Priority 51
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