Synthesis of Graphene Nanosheets Containing Ultra-Narrow Nonplanar Nanopores on Surfaces

Synthesis of Graphene Nanosheets Containing Ultra-Narrow Nonplanar Nanopores on Surfaces | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Synthesis of Graphene Nanosheets Containing Ultra-Narrow Nonplanar Nanopores on Surfaces Junfa Zhu, Tianchen Qin, Fei Gao, Yulun Wu, Baiyao Liang, Lei Hu, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5454577/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Introduction of twisted structures into low-dimensional graphene-based nanostructures has important ramifications on their inherent physical behavior. The fabrication of graphene derivatives with nonplanar characteristics remains challenging, especially for extended two-dimensional (2D) structures. Herein, we report the synthesis of a novel nonplanar porous [32]annulene graphene nanosheet that contains narrowest periodic nanopores and exhibits the highest negative curvature among one-dimensional (1D) and 2D graphene-based nanostructures synthesized up to date. The success is driven by the dissymmetrical debromination and regioselective coupling reactions of precursor molecules on a Au(111) surface, as corroborated by scanning tunneling microscopy (STM) and synchrotron radiation photoemission spectroscopy (SRPES). We characterize electronic properties of the porous [32]annulene graphene nanosheets with the aid of scanning tunneling spectroscopy (STS), and demonstrate the generation of a low-energy state resulting from the hole doping at the interface. Physical sciences/Chemistry/Surface chemistry/Scanning probe microscopy Physical sciences/Chemistry/Physical chemistry/Reaction kinetics and dynamics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Polycyclic aromatic hydrocarbons (PAHs) have traditionally been regarded as a family of planar organic structures composed of fused benzene rings with alternating single and double bonds. With the development of synthetic chemistry, an unfavorable steric interaction or strain has been introduced into PAHs, the release of this strain forces structures to adopt nonplanar configurations 1 – 3 . Introduction of nonplanar characteristics to PAHs changes the dimensionality and electronic properties owing to local strain and π-electron redistribution, resulting in unprecedented electronic, magnetic, and quantum-coherent properties 4 – 7 . For instance, theoretical and experimental investigations have demonstrated the significance of nonplanar characteristics in enhancing spin–orbit coupling in graphene derivatives 8 – 10 . Moreover, the dihedral angle originated from the twisted configuration between structural units can tune the balance between the kinetic and potential exchange, leading to either enhanced antiferromagnetic coupling or the emergence of ferromagnetic coupling 11 , 12 . Nonplanar characteristics can be classified into three categories based on their Gaussian curvatures: 1) neutral curvature (cylindrical curvature), such as cycloparaphenylenes 13 ; 2) positive curvature (spherical curvature), such as bowl-shaped aromatics; 14 3) negative curvature (hyperbolical curvature), such as saddle-shaped and helical structures 15 , 16 . Neutral curvature generally exists in the derivatives of carbon nanotubes 17 . Positive curvature can be introduced by replacing hexagon with pentagon rings 18 . Negative curvature can be created by the integration of sterically constrained helicene-like segments 19 , distinguishing it from the other two types of curvature. 9,9′-bifluorenylidene (9,9′-BF), as a species of benzoannulated pentafulvalene (Fig. 1 a) 20 – 22 , is a well-known highly distorted alkene, being a promising structural unit for the construction of extended PAHs with a negative curvature. The repulsive interaction originating from the steric hinderance of hydrogen atoms twists the structure of 9,9′-BF (Fig. 1 b) 23 , 24 . Interestingly, the twisting effect elongates the bridged C = C double bond due to the non-coplanarity of p electrons, possibly making it bear C − C single bond feature and resulting in biradical character 21 , 25 . The 9,9′-BF-based derivatives with different configurations display distinct ground states (closed or open-shell), depending on the degree of tension 20 , 21 . In addition, the expansion of benzoannulated pentafulvalene from zero to two dimension (Fig. 1 c) may increase its twisting degree and potentially induce open-shell character, offering a promising strategy for developing organic quantum spin lattices. On-surface synthesis offers unparalleled advantages in the construction of two-dimensional (2D) graphene-based nanostructures with atomic precision 26 – 28 . The use of multi-halogenated precursors is a common approach for the synthesis of 2D porous graphene 29 , 30 . However, the associated Ullmann coupling reactions generally lack regioselectivity (Supplementary Fig. 1), limiting the quality of the target 2D network 31 . Herein, we report the synthesis of a novel nonplanar porous [32]annulene graphene network containing ultra-narrow nonplanar pores, through hierarchical coupling reactions of 9,9′-BF building blocks on Au(111) (Fig. 1 d). High-quality chiral polymers are formed by an unprecedented dissymmetric debromination and regioselective Ullmann coupling at the first step and they fuse laterally into 2D porous [32]annulene graphene nanosheet upon further annealing. Porous [32]annulene graphene contains the narrowest nanopores and exhibits the highest negative curvature among all the reported one-dimensional (1D) and 2D graphene-based nanostructures. We demonstrate that the nonplanar porous [32]annulene graphene networks exhibit closed-shell character because the tension-induced nonplanarity does not sufficiently elongate C = C double bonds to the extent generating open-shell character. However, owing to the nonplanarity, the significant interfacial charge transfer between the porous [32]annulene graphene and the Au(111) substrate results in the generation of a zero-energy state, associated with the depopulated valence band (VB). This work opens a new door for the selective synthesis of nonplanar porous graphene on surfaces. Results and discussion The self-assembled structure of intact precursor molecules TBBFY on Au(111) exhibits petaloid nodes with sixfold symmetric spokes, as shown in Figs. 2 a-b. According to DFT calculations, each spoke corresponds to an intact TBBFY precursor adsorbing perpendicularly on the Au(111) surface (Fig. 2 c and Supplementary Fig. 2). Such arrangement is attributed to the twisted geometry of two cross-conjugated π-planes of the 9,9′-BF building blocks. Two adjacent TBBFY molecules should be stabilized by Br···Br halogen bonds and C − Br···π interaction 32 . Interestingly, annealing at 390 K results in the dissymmetric debromination of TBBFY molecules at the diagonal sites. The subsequent Ullmann coupling leads to the formation of high-quality chiral covalent polymer chains. As illustrated in STM images and structural models in Figs. 2 d-f and Supplementary Fig. 3, the H-type motifs are assigned to the partially debrominated molecules, in which the two surviving Br terminals appear as small bright spots (cyan circles). Note that a brighter and larger spot is inlayed between the two adjacent Br terminals, which is attributed to the Au adatom (red arrows) interacting with Br through C − Br···Au···Br − C Coulomb attraction 33 . According to Br 3d synchrotron radiation photoemission spectroscopy (SRPES) in Fig. 3 a, the ratio of Br − C to Br − Au signal is near to 1:1 (1:0.89), indicating the high efficiency of dissymmetric debromination. The detailed reaction pathway and experimentally observed intermediates are shown in Supplementary Fig. 4. DFT calculations further support the dissymmetric debromination pathway of TBBFY on Au(111) as a kinetically favored reaction pathway. As displayed in Fig. 2 g, the energy barrier of debromination at diagonal positions is significantly lower than the case occurring at same-side positions. To our knowledge, regioselective C − C couplings on surfaces between precursors holding multiple equivalent active sites have not been reported 34 – 36 . In our case the high regioselectivity originates from the molecular asymmetric adsorption on the surface. Although the four C − Br sites of TBBFY are equivalent in gas phase, their different adsorption heights make them bearing distinct reactivity on surfaces, leading to dissymmetric debromination reactions. Since debromination is the rate-determining step of Ullmann coupling reaction of TBBFY on Au(111), chiral covalent polymers are formed with a high selectivity and quality. In contrast to the conventional random C − C coupling between equivalent active sites forming disordered 2D structures 31 (Supplementary Fig. 1), the high-quality chiral polymers act as effective templates for their subsequent lateral fusion into ordered porous [32]annulene graphene networks, upon further activation of remaining C − Br bonds. Porous [32]annulene graphene network was obtained by annealing the above sample to 480 K (Fig. 4 a). As illustrated in the magnified STM image in Fig. 4 b, periodic protrusions associated with the nonplanar characteristics within the building blocks are observed. This arises from the substantial internal strain induced by the steric hindrance of twelve hydrogen atoms between two adjacent fluorenylidene motifs (Figs. 4 c-d). One of the fluorenylidenes points away from the surface and manifests two bright dots. The significant reduction of both Br − C and Br − Au signal in Br 3d SRPE spectra (Fig. 3 a) suggests the complete cleavage of C − Br bonds and desorption of Br adatoms from the Au(111) surface. Meanwhile, the increase in the ratio of C[C 3 ] signal to C[C 2 H] (from 1:0.99 to 1:0.85) in the C 1s spectra (Fig. 3 b) indicates the formation of additional C − C bonds, corresponding to the formation of porous [32]annulene graphene networks. To investigate the electronic structure of porous [32]annulene graphene network, we conducted dI/dV spectroscopy and mapping. Four decent resonances are observed (Fig. 5 a and Supplementary Fig. 5) at energies of − 1726, −1107, + 35, and + 1655 mV, respectively, and the corresponding dI/dV maps obtained at these biases are shown in Figs. 5 b-e (more bias-dependent dI/dV maps are seen in Supplementary Fig. 6). Interestingly, the appearance of a low-energy state at + 35 mV might be a hint for the open-shell character, as expected in 9,9′-BF derivatives and their networks with a strong strain. However, unrestricted DFT calculations indicate that the energy profile of projected density of states (PDOS) of α (spin-up) and β (spin-down) electrons completely overlap, suggesting that the low-energy state is likely not derived from the open-shell character. In fact, for a graphene-based nanostructure on metal surfaces, the origin of a low-energy state could be from interfacial hole or particle doping apart from its inherent properties like open-shell or topological character. This is attributed to the VB or conduction band (CB) depopulation because of charge transfer between the structure and substrate. Therefore, we performed Bader charge calculation to unravel the charge transfer behavior at the interface of porous [32]annulene graphene and Au(111). According to the analysis on charge density difference, an interfacial charge transfer of approx. 2 e − per unit cell from porous [32]annulene graphene network to the Au(111) surface is obtained (Fig. 5 f). Figure 5 g shows the PDOS of the freestanding neutral porous [32]annulene graphene networks (top panel) and those on the Au(111) surface (bottom panel). Upon the adsorption of porous [32]annulene graphene on Au(111), their bands shift significantly toward the positive voltage and a weak zero-bias peak appears, in excellent agreement with the experimental results. Consequently, we attribute the four characteristic resonances at − 1726, −1107, + 35 and + 1655 mV to VB-2, VB-1, VB, and CB of porous [32]annulene graphene on Au(111), respectively. VB goes across Fermi level because of a strong interfacial charge transfer 37 . It occurs due to the low adsorption height of segments in porous [32]annulene graphene pointing towards the surface (2.92 Å), which is notably lower than planar graphene-based structures adsorbing on metal surfaces (~ 3.3 Å) 38 , 39 . We note that the interfacial charge transfer, together with a strong hybridization between molecular and surface states, make porous [32]annulene graphene having a smaller band gap (1.69 eV) than all other nonplanar nanoporous graphene reported to date 30 , 40 . We elucidate the reason behind the closed-shell character of porous [32]annulene graphene networks. For the previously reported 9,9′-BF derivatives with biradical character, the biradical nature arises from a substantial twist in which pentafulvalene segments rotate along the parallel direction of the bridged C = C double bond 21 , 41 . This significant steric hindrance between two fluorenylidene fragments twists and elongates the C = C double bond to a length similar to that of a C − C single bond, generating the biradical character. However, for porous [32]annulene graphene networks, this strain is primarily relieved through the distortion of the fluorenylidene segments rather than by the elongation of bridged C = C double bonds (Supplementary Fig. 7). The pentafulvalene segments in the 9,9′-BF building block twist in a direction approximately perpendicular to the bridged C = C double bond, instead of rotating along the parallel direction. The length of the C = C double bond in porous [32]annulene graphene nanosheet is measured to be 1.39 Å, which is only slightly longer than conventional alkenes (~ 1.35 Å) thus insufficient to reach the transformation point between the C = C double bond and the biradical C − C single bond. Because of the significant strain within the ultra-narrow nonplanar pores, porous [32]annulene graphene nanosheet transforms into planar nanopores graphene after further annealing at a slightly higher temperature of 510 K (Figs. 6 a-b and Supplementary Fig. 8). The bond-resolving (BR) STM image obtained using a CO-functionalized tip reveals the detailed structure of the porous [46]annulene graphene network (Fig. 6 c). Unlike the porous [32]annulene graphene networks directly formed from 9,9′-BF, the structural unit of the porous [46]annulene graphene networks corresponds to the fused dimer of two 9,9′-BF monomers. On the basis of this observation, we propose the following reaction mechanism. Initially, due to the significant strain within the ultra-narrow nonplanar pores, the C − C bonds in the porous [32]annulene graphene network at certain positions cleave (colored red in Fig. 6 d). Subsequently, a series of intramolecular and intermolecular cyclodehydrogenation reactions 42 are activated within/between the 9,9′-BF monomers, resulting in the formation of new C − C bonds (colored cyan and purple in Fig. 6 d). The increased ratio of C[C 3 ] to C[C 2 H] in C 1s SRPES, from 1:0.85 (at 480 K) to 1:0.54 (at 510 K), supports the occurrence of cyclodehydrogenation reactions (Fig. 3 b). This also indicates a high-quality formation of the porous [46]annulene graphene networks, as the experimental ratio (1:0.54) closely matches the theoretical ratio (1:0.53). The band gap of porous [46]annulene graphene is 3.08 eV (Supplementary Fig. 9), much larger than that of the nonplanar porous [32]annulene graphene. Owing to the higher adsorption height (3.15 Å), no significant charge transfer between porous [46]annulene graphene networks and the Au(111) surface occurs, resulting in the absence of low-energy state and widening of the band gap. Conclusion In this article, we present an on-surface synthesis of the nonplanar porous [32]annulene graphene nanosheet with the narrowest nanopores among all 1D and 2D graphene-based nanostructures synthesized up to date. The rational design of the precursor molecule facilitates the dissymmetric debrominated coupling, leading to the formation of chiral polymer chains with a high regioselectivity. The chiral polymer chains subsequently serve as templates for the synthesis of porous [32]annulene graphene nanosheets. We demonstrate that [32]annulene graphene nanosheet keeps as closed-shell structure because the twisting direction of building blocks disfavors the open-shell geometry. The low-energy band appearing at the interface between porous [32]annulene graphene and Au(111) is attributed to VB depopulation due to charge transfer. The substantial tension within the nonplanar porous [32]annulene graphene nanosheets leads to C − C bond cleavage and cyclodehydrogenation reactions upon further gentle annealing, forming planar porous [46]annulene graphene nanosheets. Our work breakthroughs the general knowledge that an 2D substrate usually disfavors the formation of three-dimensional (3D) structures. By employing an adsorption-induced dissymmetric coupling strategy on surfaces, we achieved a high reaction efficiency for synthesis of nonplanar graphene nanosheet, which is inaccessible in solution-phase chemistry. In addition, the rational design of synthetic strategy presented in this work offers insights into the construction of organic spin lattices generated from structural tension. Declarations Conflicts of Interest The authors declare no competing financial interests. Author contributions T.Q., T.W. and J.Z. conceived the project and designed the experiments. T.Q. carried out the STM/STS experiments. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5454577","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":391573888,"identity":"f7d10415-f273-423c-b2df-26c083d69e54","order_by":0,"name":"Junfa 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China","correspondingAuthor":false,"prefix":"","firstName":"Honghe","middleName":"","lastName":"Ding","suffix":""},{"id":391573896,"identity":"2b1e0518-4ace-449d-b784-cb43961002bf","order_by":8,"name":"Jun Hu","email":"","orcid":"","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Hu","suffix":""},{"id":391573897,"identity":"bbfb64d4-60eb-444f-8ffb-25db477076d0","order_by":9,"name":"Qian Xu","email":"","orcid":"","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Qian","middleName":"","lastName":"Xu","suffix":""},{"id":391573898,"identity":"3d41944e-8c51-4bce-886d-7e757222ab54","order_by":10,"name":"Dezhou Guo","email":"","orcid":"","institution":"Beijing Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Dezhou","middleName":"","lastName":"Guo","suffix":""},{"id":391573899,"identity":"72fdd61a-4ddf-46cf-8f67-66a48392ab58","order_by":11,"name":"Tao Wang","email":"","orcid":"https://orcid.org/0000-0002-6545-5028","institution":"Shanghai Institute of Organic Chemistry, CAS","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-11-14 14:16:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5454577/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5454577/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71856380,"identity":"93e13a91-f8c1-47ba-8b29-db36e06ac2e6","added_by":"auto","created_at":"2024-12-19 08:17:47","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":299351,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDesign and on-surface synthesis of 2D porous graphene containing ultra-narrow nonplanar pores. a. \u003c/strong\u003ePentafulvalene. \u003cstrong\u003eb.\u003c/strong\u003e 9,9′-BF and its open-shell resonance structure induced by the elongation of the bridged C=C bond. \u003cstrong\u003ec.\u003c/strong\u003e Rational design of organic quantum spin lattice based on 9,9′-BF segments. \u003cstrong\u003ed.\u003c/strong\u003e Reaction scheme of TBBFY (2,7-dibromo-9-(2,7-dibromo-9H-fluoren-9-ylidene)-9H-fluorene) on Au(111) upon annealing at different temperatures, in which the golden balls represent Au adatoms.\u003c/p\u003e","description":"","filename":"Picture1.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/cdc9b0653c0b5191d4f70cd0.png"},{"id":71856382,"identity":"70c1992d-bc2f-4274-a0e9-d1b0d75e51f0","added_by":"auto","created_at":"2024-12-19 08:17:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":935957,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSelf-assembly structure of intact TBBFY molecules and chiral polymer chains formed by dissymmetric dehalogenation. a-c. \u003c/strong\u003eOverview (a), zoom-in (b) scanning tunneling microscopy(STM) images and density functional theory (DFT)-optimized top view of the adsorption model (c) of the self-assembly structure obtained by depositing TBBFY molecules on Au(111) held at room temperature. Tunneling parameters: (a,b) U= −856.9 mV, I= 0.120 nA. \u003cstrong\u003ed-f.\u003c/strong\u003e Overview (d), zoom-in (e) STM images and corresponding structural model (f) of the chiral polymer chains obtained by annealing the sample of (a) to 390 K. Tunneling parameters: (d,e) U= −420.1 mV, I= 0.180 nA. Atoms highlighted in grey, pink, green and golden correspond to C, H, Br and Au atoms, respectively. \u003cstrong\u003eg.\u003c/strong\u003e Energy diagram of debromination reactions of TBBFY on Au(111). The initial state, transition state, and final state are denoted as IS, TS, and FS, respectively. Atoms highlighted in black, white, brown and yellow correspond to C, H, Br and Au atoms, respectively.\u003c/p\u003e","description":"","filename":"Picture2.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/a7f3107ffb1795cb6ca3e34a.png"},{"id":71856384,"identity":"936fc3f6-9d1d-4861-ad95-1dcab23d2a63","added_by":"auto","created_at":"2024-12-19 08:17:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":312700,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSRPES of reaction products taken with increased temperature. a, b \u003c/strong\u003eBr 3d (a) and C 1s (b) core level spectra recorded by depositing TBBFY molecules onto Au(111) held at room temperature followed by stepwise annealing to 510 K. The photon energies used for the Br 3d and C 1s spectra are 180 and 380 eV, respectively. (c) Structural models of the main products at each reaction stage. Different atoms are marked by different colors to illustrate their chemical environments. The theoretical ratios of these C atoms are shown below the structural models.\u003c/p\u003e","description":"","filename":"Picture3.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/ad365bf30aea711a02899de8.png"},{"id":71856391,"identity":"cc1db484-c30d-4d75-9bbb-45b1bdc3e866","added_by":"auto","created_at":"2024-12-19 08:17:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":503919,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOn-surface synthesis of porous [32]annulene graphene network. a, b\u003c/strong\u003eOverview (a) and zoom-in (b) STM images of porous [32]annulene graphene networks obtained by annealing the sample of Fig. 2d to 480 K. Tunneling parameters: (a) U= −374.1 mV, I= 0.200 nA; (b) U= −1126.0 mV, I= 3.000 nA. \u003cstrong\u003ec.\u003c/strong\u003e Chemical structure of porous [32]annulene graphene networks covered on (b). \u003cstrong\u003ed.\u003c/strong\u003e DFT-optimized side and front views of the adsorption model of porous [32]annulene graphene network on Au(111). Color code: C, grey; H, pink; Au, golden.\u003c/p\u003e","description":"","filename":"Picture4.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/688939946401dc596a6cbbb2.png"},{"id":71857783,"identity":"6abfc098-1acf-42b5-a197-8d3bd016b14c","added_by":"auto","created_at":"2024-12-19 08:25:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":563718,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectronic structure of porous [32]annulene graphene network. a.\u003c/strong\u003e Point dI/dV spectra of porous [32]annulene graphene networks taken at the positions marked with corresponding colored dots in the inset STM image (scanned at −1126.0 mV, 3.000 nA). \u003cstrong\u003eb-e.\u003c/strong\u003e Constant-current dI/dV maps taken at −1726 (b), −1107 (c), +35 (d), and +1655 mV (e) using a metallic tip. All scale bars, 5 Å. \u003cstrong\u003ef.\u003c/strong\u003e The side and front views of the charge density difference with the isosurface value of ±0.004 eꞏÅ\u003csup\u003e–3\u003c/sup\u003e, where blue and yellow colors indicate charge depletion and accumulation, respectively. \u003cstrong\u003eg.\u003c/strong\u003e Density of states (DOS) projected onto the \u003cem\u003ep\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e orbitals of C atoms in porous [32]annulene graphene network calculated in gas phase (blue curve) and on the Au(111) surface (purple curve).\u003c/p\u003e","description":"","filename":"Picture5.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/878b4edb66e4191aded3805b.png"},{"id":71858237,"identity":"edb73278-153a-4908-a2b6-683f72c76832","added_by":"auto","created_at":"2024-12-19 08:33:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":549567,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOn-surface synthesis of porous [46]annulene graphene network. a, b \u003c/strong\u003eOverview (a) and zoom-in (b) STM images of porous [46]annulene graphene networks obtained by annealing the sample of Fig. 4a to 510 K. Tunneling parameters: (a,b) U= −749.8 mV, I= 0.140 nA. \u003cstrong\u003ec.\u003c/strong\u003e BR-STM image of porous [46]annulene graphene network. Tunneling parameters: U= 5 mV. \u003cstrong\u003ed.\u003c/strong\u003e Proposed reaction mechanism toward the formation of porous [46]annulene graphene network from porous [32]annulene graphene network.\u003c/p\u003e","description":"","filename":"Picture6.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/0a38d9ff41a8b6e92c3d883d.png"},{"id":74380645,"identity":"fe733ef4-31b5-412c-aa3b-dbbab3a419e4","added_by":"auto","created_at":"2025-01-21 18:28:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3786837,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/c62147b9-bc89-4fc2-9e75-2cbf108132a3.pdf"},{"id":71856383,"identity":"dfb3fcbc-344a-41ea-accd-d2e2a8ad4130","added_by":"auto","created_at":"2024-12-19 08:17:47","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":7318599,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"QinSINat.Commun.docx","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/3fc6bc919de67adf55c28d4b.docx"},{"id":71857780,"identity":"13a54240-0631-4cde-a859-b91e731b036b","added_by":"auto","created_at":"2024-12-19 08:25:47","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":305001,"visible":true,"origin":"","legend":"\u003cp\u003eTOC\u003c/p\u003e","description":"","filename":"TOC.png","url":"https://assets-eu.researchsquare.com/files/rs-5454577/v1/153e3b56c3ed4a14aba757f4.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Synthesis of Graphene Nanosheets Containing Ultra-Narrow Nonplanar Nanopores on Surfaces","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePolycyclic aromatic hydrocarbons (PAHs) have traditionally been regarded as a family of planar organic structures composed of fused benzene rings with alternating single and double bonds. With the development of synthetic chemistry, an unfavorable steric interaction or strain has been introduced into PAHs, the release of this strain forces structures to adopt nonplanar configurations\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Introduction of nonplanar characteristics to PAHs changes the dimensionality and electronic properties owing to local strain and π-electron redistribution, resulting in unprecedented electronic, magnetic, and quantum-coherent properties\u003csup\u003e\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. For instance, theoretical and experimental investigations have demonstrated the significance of nonplanar characteristics in enhancing spin\u0026ndash;orbit coupling in graphene derivatives\u003csup\u003e\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Moreover, the dihedral angle originated from the twisted configuration between structural units can tune the balance between the kinetic and potential exchange, leading to either enhanced antiferromagnetic coupling or the emergence of ferromagnetic coupling\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eNonplanar characteristics can be classified into three categories based on their Gaussian curvatures: 1) neutral curvature (cylindrical curvature), such as cycloparaphenylenes\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e; 2) positive curvature (spherical curvature), such as bowl-shaped aromatics;\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e 3) negative curvature (hyperbolical curvature), such as saddle-shaped and helical structures\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Neutral curvature generally exists in the derivatives of carbon nanotubes\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Positive curvature can be introduced by replacing hexagon with pentagon rings\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Negative curvature can be created by the integration of sterically constrained helicene-like segments\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, distinguishing it from the other two types of curvature.\u003c/p\u003e \u003cp\u003e9,9\u0026prime;-bifluorenylidene (9,9\u0026prime;-BF), as a species of benzoannulated pentafulvalene (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea)\u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, is a well-known highly distorted alkene, being a promising structural unit for the construction of extended PAHs with a negative curvature. The repulsive interaction originating from the steric hinderance of hydrogen atoms twists the structure of 9,9\u0026prime;-BF (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb)\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Interestingly, the twisting effect elongates the bridged C\u0026thinsp;=\u0026thinsp;C double bond due to the non-coplanarity of \u003cem\u003ep\u003c/em\u003e electrons, possibly making it bear C\u0026thinsp;\u0026minus;\u0026thinsp;C single bond feature and resulting in biradical character\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The 9,9\u0026prime;-BF-based derivatives with different configurations display distinct ground states (closed or open-shell), depending on the degree of tension\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. In addition, the expansion of benzoannulated pentafulvalene from zero to two dimension (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) may increase its twisting degree and potentially induce open-shell character, offering a promising strategy for developing organic quantum spin lattices.\u003c/p\u003e \u003cp\u003eOn-surface synthesis offers unparalleled advantages in the construction of two-dimensional (2D) graphene-based nanostructures with atomic precision\u003csup\u003e\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. The use of multi-halogenated precursors is a common approach for the synthesis of 2D porous graphene\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. However, the associated Ullmann coupling reactions generally lack regioselectivity (Supplementary Fig.\u0026nbsp;1), limiting the quality of the target 2D network\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Herein, we report the synthesis of a novel nonplanar porous [32]annulene graphene network containing ultra-narrow nonplanar pores, through hierarchical coupling reactions of 9,9\u0026prime;-BF building blocks on Au(111) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). High-quality chiral polymers are formed by an unprecedented dissymmetric debromination and regioselective Ullmann coupling at the first step and they fuse laterally into 2D porous [32]annulene graphene nanosheet upon further annealing. Porous [32]annulene graphene contains the narrowest nanopores and exhibits the highest negative curvature among all the reported one-dimensional (1D) and 2D graphene-based nanostructures. We demonstrate that the nonplanar porous [32]annulene graphene networks exhibit closed-shell character because the tension-induced nonplanarity does not sufficiently elongate C\u0026thinsp;=\u0026thinsp;C double bonds to the extent generating open-shell character. However, owing to the nonplanarity, the significant interfacial charge transfer between the porous [32]annulene graphene and the Au(111) substrate results in the generation of a zero-energy state, associated with the depopulated valence band (VB). This work opens a new door for the selective synthesis of nonplanar porous graphene on surfaces.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eThe self-assembled structure of intact precursor molecules TBBFY on Au(111) exhibits petaloid nodes with sixfold symmetric spokes, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b. According to DFT calculations, each spoke corresponds to an intact TBBFY precursor adsorbing perpendicularly on the Au(111) surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;2). Such arrangement is attributed to the twisted geometry of two cross-conjugated π-planes of the 9,9\u0026prime;-BF building blocks. Two adjacent TBBFY molecules should be stabilized by Br\u0026middot;\u0026middot;\u0026middot;Br halogen bonds and C\u0026thinsp;\u0026minus;\u0026thinsp;Br\u0026middot;\u0026middot;\u0026middot;π interaction\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eInterestingly, annealing at 390 K results in the dissymmetric debromination of TBBFY molecules at the diagonal sites. The subsequent Ullmann coupling leads to the formation of high-quality chiral covalent polymer chains. As illustrated in STM images and structural models in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-f and Supplementary Fig.\u0026nbsp;3, the H-type motifs are assigned to the partially debrominated molecules, in which the two surviving Br terminals appear as small bright spots (cyan circles). Note that a brighter and larger spot is inlayed between the two adjacent Br terminals, which is attributed to the Au adatom (red arrows) interacting with Br through C\u0026thinsp;\u0026minus;\u0026thinsp;Br\u0026middot;\u0026middot;\u0026middot;Au\u0026middot;\u0026middot;\u0026middot;Br\u0026thinsp;\u0026minus;\u0026thinsp;C Coulomb attraction\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. According to Br 3d synchrotron radiation photoemission spectroscopy (SRPES) in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the ratio of Br\u0026thinsp;\u0026minus;\u0026thinsp;C to Br\u0026thinsp;\u0026minus;\u0026thinsp;Au signal is near to 1:1 (1:0.89), indicating the high efficiency of dissymmetric debromination. The detailed reaction pathway and experimentally observed intermediates are shown in Supplementary Fig.\u0026nbsp;4. DFT calculations further support the dissymmetric debromination pathway of TBBFY on Au(111) as a kinetically favored reaction pathway. As displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg, the energy barrier of debromination at diagonal positions is significantly lower than the case occurring at same-side positions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo our knowledge, regioselective C\u0026thinsp;\u0026minus;\u0026thinsp;C couplings on surfaces between precursors holding multiple equivalent active sites have not been reported\u003csup\u003e\u003cspan additionalcitationids=\"CR35\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. In our case the high regioselectivity originates from the molecular asymmetric adsorption on the surface. Although the four C\u0026thinsp;\u0026minus;\u0026thinsp;Br sites of TBBFY are equivalent in gas phase, their different adsorption heights make them bearing distinct reactivity on surfaces, leading to dissymmetric debromination reactions. Since debromination is the rate-determining step of Ullmann coupling reaction of TBBFY on Au(111), chiral covalent polymers are formed with a high selectivity and quality. In contrast to the conventional random C\u0026thinsp;\u0026minus;\u0026thinsp;C coupling between equivalent active sites forming disordered 2D structures\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;1), the high-quality chiral polymers act as effective templates for their subsequent lateral fusion into ordered porous [32]annulene graphene networks, upon further activation of remaining C\u0026thinsp;\u0026minus;\u0026thinsp;Br bonds.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePorous [32]annulene graphene network was obtained by annealing the above sample to 480 K (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). As illustrated in the magnified STM image in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, periodic protrusions associated with the nonplanar characteristics within the building blocks are observed. This arises from the substantial internal strain induced by the steric hindrance of twelve hydrogen atoms between two adjacent fluorenylidene motifs (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-d). One of the fluorenylidenes points away from the surface and manifests two bright dots. The significant reduction of both Br\u0026thinsp;\u0026minus;\u0026thinsp;C and Br\u0026thinsp;\u0026minus;\u0026thinsp;Au signal in Br 3d SRPE spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) suggests the complete cleavage of C\u0026thinsp;\u0026minus;\u0026thinsp;Br bonds and desorption of Br adatoms from the Au(111) surface. Meanwhile, the increase in the ratio of C[C\u003csub\u003e3\u003c/sub\u003e] signal to C[C\u003csub\u003e2\u003c/sub\u003eH] (from 1:0.99 to 1:0.85) in the C 1s spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) indicates the formation of additional C\u0026thinsp;\u0026minus;\u0026thinsp;C bonds, corresponding to the formation of porous [32]annulene graphene networks.\u003c/p\u003e \u003cp\u003eTo investigate the electronic structure of porous [32]annulene graphene network, we conducted dI/dV spectroscopy and mapping. Four decent resonances are observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;5) at energies of \u0026minus;\u0026thinsp;1726, \u0026minus;1107, +\u0026thinsp;35, and +\u0026thinsp;1655 mV, respectively, and the corresponding dI/dV maps obtained at these biases are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb-e (more bias-dependent dI/dV maps are seen in Supplementary Fig.\u0026nbsp;6). Interestingly, the appearance of a low-energy state at +\u0026thinsp;35 mV might be a hint for the open-shell character, as expected in 9,9\u0026prime;-BF derivatives and their networks with a strong strain. However, unrestricted DFT calculations indicate that the energy profile of projected density of states (PDOS) of \u003cem\u003eα\u003c/em\u003e (spin-up) and \u003cem\u003eβ\u003c/em\u003e (spin-down) electrons completely overlap, suggesting that the low-energy state is likely not derived from the open-shell character. In fact, for a graphene-based nanostructure on metal surfaces, the origin of a low-energy state could be from interfacial hole or particle doping apart from its inherent properties like open-shell or topological character. This is attributed to the VB or conduction band (CB) depopulation because of charge transfer between the structure and substrate. Therefore, we performed Bader charge calculation to unravel the charge transfer behavior at the interface of porous [32]annulene graphene and Au(111). According to the analysis on charge density difference, an interfacial charge transfer of approx. 2 e\u003csup\u003e\u0026minus;\u003c/sup\u003e per unit cell from porous [32]annulene graphene network to the Au(111) surface is obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg shows the PDOS of the freestanding neutral porous [32]annulene graphene networks (top panel) and those on the Au(111) surface (bottom panel). Upon the adsorption of porous [32]annulene graphene on Au(111), their bands shift significantly toward the positive voltage and a weak zero-bias peak appears, in excellent agreement with the experimental results. Consequently, we attribute the four characteristic resonances at \u0026minus;\u0026thinsp;1726, \u0026minus;1107, +\u0026thinsp;35 and +\u0026thinsp;1655 mV to VB-2, VB-1, VB, and CB of porous [32]annulene graphene on Au(111), respectively. VB goes across Fermi level because of a strong interfacial charge transfer\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. It occurs due to the low adsorption height of segments in porous [32]annulene graphene pointing towards the surface (2.92 \u0026Aring;), which is notably lower than planar graphene-based structures adsorbing on metal surfaces (~\u0026thinsp;3.3 \u0026Aring;)\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. We note that the interfacial charge transfer, together with a strong hybridization between molecular and surface states, make porous [32]annulene graphene having a smaller band gap (1.69 eV) than all other nonplanar nanoporous graphene reported to date\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eWe elucidate the reason behind the closed-shell character of porous [32]annulene graphene networks. For the previously reported 9,9\u0026prime;-BF derivatives with biradical character, the biradical nature arises from a substantial twist in which pentafulvalene segments rotate along the parallel direction of the bridged C\u0026thinsp;=\u0026thinsp;C double bond\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. This significant steric hindrance between two fluorenylidene fragments twists and elongates the C\u0026thinsp;=\u0026thinsp;C double bond to a length similar to that of a C\u0026thinsp;\u0026minus;\u0026thinsp;C single bond, generating the biradical character. However, for porous [32]annulene graphene networks, this strain is primarily relieved through the distortion of the fluorenylidene segments rather than by the elongation of bridged C\u0026thinsp;=\u0026thinsp;C double bonds (Supplementary Fig.\u0026nbsp;7). The pentafulvalene segments in the 9,9\u0026prime;-BF building block twist in a direction approximately perpendicular to the bridged C\u0026thinsp;=\u0026thinsp;C double bond, instead of rotating along the parallel direction. The length of the C\u0026thinsp;=\u0026thinsp;C double bond in porous [32]annulene graphene nanosheet is measured to be 1.39 \u0026Aring;, which is only slightly longer than conventional alkenes (~\u0026thinsp;1.35 \u0026Aring;) thus insufficient to reach the transformation point between the C\u0026thinsp;=\u0026thinsp;C double bond and the biradical C\u0026thinsp;\u0026minus;\u0026thinsp;C single bond.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBecause of the significant strain within the ultra-narrow nonplanar pores, porous [32]annulene graphene nanosheet transforms into planar nanopores graphene after further annealing at a slightly higher temperature of 510 K (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea-b and Supplementary Fig.\u0026nbsp;8). The bond-resolving (BR) STM image obtained using a CO-functionalized tip reveals the detailed structure of the porous [46]annulene graphene network (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). Unlike the porous [32]annulene graphene networks directly formed from 9,9\u0026prime;-BF, the structural unit of the porous [46]annulene graphene networks corresponds to the fused dimer of two 9,9\u0026prime;-BF monomers. On the basis of this observation, we propose the following reaction mechanism. Initially, due to the significant strain within the ultra-narrow nonplanar pores, the C\u0026thinsp;\u0026minus;\u0026thinsp;C bonds in the porous [32]annulene graphene network at certain positions cleave (colored red in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). Subsequently, a series of intramolecular and intermolecular cyclodehydrogenation reactions\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e are activated within/between the 9,9\u0026prime;-BF monomers, resulting in the formation of new C\u0026thinsp;\u0026minus;\u0026thinsp;C bonds (colored cyan and purple in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). The increased ratio of C[C\u003csub\u003e3\u003c/sub\u003e] to C[C\u003csub\u003e2\u003c/sub\u003eH] in C 1s SRPES, from 1:0.85 (at 480 K) to 1:0.54 (at 510 K), supports the occurrence of cyclodehydrogenation reactions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). This also indicates a high-quality formation of the porous [46]annulene graphene networks, as the experimental ratio (1:0.54) closely matches the theoretical ratio (1:0.53).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe band gap of porous [46]annulene graphene is 3.08 eV (Supplementary Fig.\u0026nbsp;9), much larger than that of the nonplanar porous [32]annulene graphene. Owing to the higher adsorption height (3.15 \u0026Aring;), no significant charge transfer between porous [46]annulene graphene networks and the Au(111) surface occurs, resulting in the absence of low-energy state and widening of the band gap.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this article, we present an on-surface synthesis of the nonplanar porous [32]annulene graphene nanosheet with the narrowest nanopores among all 1D and 2D graphene-based nanostructures synthesized up to date. The rational design of the precursor molecule facilitates the dissymmetric debrominated coupling, leading to the formation of chiral polymer chains with a high regioselectivity. The chiral polymer chains subsequently serve as templates for the synthesis of porous [32]annulene graphene nanosheets. We demonstrate that [32]annulene graphene nanosheet keeps as closed-shell structure because the twisting direction of building blocks disfavors the open-shell geometry. The low-energy band appearing at the interface between porous [32]annulene graphene and Au(111) is attributed to VB depopulation due to charge transfer. The substantial tension within the nonplanar porous [32]annulene graphene nanosheets leads to C\u0026thinsp;\u0026minus;\u0026thinsp;C bond cleavage and cyclodehydrogenation reactions upon further gentle annealing, forming planar porous [46]annulene graphene nanosheets. Our work breakthroughs the general knowledge that an 2D substrate usually disfavors the formation of three-dimensional (3D) structures. By employing an adsorption-induced dissymmetric coupling strategy on surfaces, we achieved a high reaction efficiency for synthesis of nonplanar graphene nanosheet, which is inaccessible in solution-phase chemistry. In addition, the rational design of synthetic strategy presented in this work offers insights into the construction of organic spin lattices generated from structural tension.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eT.Q., T.W. and J.Z. conceived the project and designed the experiments. T.Q. carried out the STM/STS experiments. F.G. and D.G. performed the theoretical calculations. T.Q., Y.W., B.L., L.H., W.Y., Z.C., H.D., J.H. and Q.X. carried out the SRPES experiments. The experimental data and theoretical results were analysed and discussed by all the authors. T.Q., T.W. and J.Z. wrote the paper, with contributions from all the authors. J.Z. supervised the project.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (22272157, 21872131, and U1932214).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBall, M. et al. Contorted Polycyclic Aromatics. \u003cem\u003eAcc. Chem. Res.\u003c/em\u003e \u003cstrong\u003e48\u003c/strong\u003e, 267-276 (2014).\u003c/li\u003e\n\u003cli\u003eRickhaus, M., Mayor, M. \u0026amp; Jur\u0026iacute;ček, M. Strain-induced helical chirality in polyaromatic systems. \u003cem\u003eChem. Soc. 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Deceptive orbital confinement at edges and pores of carbon-based 1D and 2D nanoarchitectures. \u003cem\u003eNat Commun\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 1062 (2024).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5454577/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5454577/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntroduction of twisted structures into low-dimensional graphene-based nanostructures has important ramifications on their inherent physical behavior. The fabrication of graphene derivatives with nonplanar characteristics remains challenging, especially for extended two-dimensional (2D) structures. Herein, we report the synthesis of a novel nonplanar porous [32]annulene graphene nanosheet that contains narrowest periodic nanopores and exhibits the highest negative curvature among one-dimensional (1D) and 2D graphene-based nanostructures synthesized up to date. The success is driven by the dissymmetrical debromination and regioselective coupling reactions of precursor molecules on a Au(111) surface, as corroborated by scanning tunneling microscopy (STM) and synchrotron radiation photoemission spectroscopy (SRPES). We characterize electronic properties of the porous [32]annulene graphene nanosheets with the aid of scanning tunneling spectroscopy (STS), and demonstrate the generation of a low-energy state resulting from the hole doping at the interface.\u003c/p\u003e","manuscriptTitle":"Synthesis of Graphene Nanosheets Containing Ultra-Narrow Nonplanar Nanopores on Surfaces","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-19 08:17:42","doi":"10.21203/rs.3.rs-5454577/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"021f8de5-6819-4eee-9034-2dd0315ad0cd","owner":[],"postedDate":"December 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":41738369,"name":"Physical sciences/Chemistry/Surface chemistry/Scanning probe microscopy"},{"id":41738370,"name":"Physical sciences/Chemistry/Physical chemistry/Reaction kinetics and dynamics"}],"tags":[],"updatedAt":"2025-01-21T18:20:47+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-19 08:17:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5454577","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5454577","identity":"rs-5454577","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}