Controlling the Reaction Steps of Bifunctional Molecules 1,5-Dibromo

Subscriber access provided by READING UNIV

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Controlling the Reaction Steps of Bi-Functional Molecules 1,5Dibromo-2,6-Dimethylnaphthalene on Different Substrates Jing Liu, Bowen Xia, Hu Xu, and Nian Lin J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b04651 • Publication Date (Web): 24 May 2018 Downloaded from http://pubs.acs.org on May 24, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Controlling the Reaction Steps of Bi-Functional Molecules 1,5-Dibromo-2,6-Dimethylnaphthalene on Different Substrates Jing Liu,a Bowen Xia,a, b Hu Xu,b Nian Lin *, a

a

Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China b

Nanostructure Institute for Energy and Environmental Research, Division of Physical Sciences, South University of Science and Technology of China, Shenzhen, China Corresponding author: [email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 21

Abstract Using

scanning

tunneling

microscopy,

we

reveal

that

the

methyl

groups

of

1,5-dibromo-2,6-dimethylnaphthalene (DBDMN) suppress Ullmann-type intermolecular coupling on Au(111), Ag(111) and Cu(111) and steer the reactions toward different final products on the three substrates. On Au(111), the molecules form ordered structures stabilized by intermolecular halogen bonds and desorb from the surface at above 420 K. On Ag(111), the molecules form halogen-bonded structures but are converted into organometallic structures at 360 K and desorb from the surface at above 600 K. On Cu(111) the molecules form organometallic structures at 300 K and undergo an intermolecular cyclodehydrogenation reaction at above 480 K. The reaction yields C-C bonds between debrominated carbons and methyl groups, resulting in dibenz[a,h]anthracene derivates and ultra-narrow chiral-edge graphene nanoribbon motifs. This comparative study demonstrates a novel concept of using side groups to control the reaction steps that lead to specific final products on different substrates.

2


Page 3 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction On-surface reactions of organic molecules have been extensively investigated in the past decade aiming at the bottom-up fabrication of molecular nanostructures, including graphene nanoribbons, molecular wires and two-dimensional polymers, to name a few.1-8 In such a process, all reaction steps are confined on a substrate. The substrate thus often plays key roles, such as introducing steric hindrance, suppressing reaction kinetics9, 10 and lowering activation barriers.11 These effects may drive the precursor molecules along specific reaction pathways that lead to different products. The profound influences of the substrate are thought to be an effective mean to control the on-surface reactions towards specific structural motifs. In fact, the use of different substrates has been proven to be efficient in achieving various products on different substrate.12-17 In this work, we demonstrate a new strategy of using side groups to control the on-surface reaction steps that lead to distinctive final products on different substrates. To this end, we chose a bi-functional precursor molecule, 1,5-dibromo-2,6-dimethylnaphthalene (DBDMN), and studied the reactions on three noble metal surfaces of Au(111), Ag(111) and Cu(111) using scanning tunneling microscopy (STM). We discovered that the on-surface processes of DBDMN are terminated at different reaction stages on the three substrates, yielding different final products. As illustrated in Scheme 1, on Au(111), DBDMN monomers form halogen-bonded assemblies below 420 K and start to desorb at above 420 K without undertaking any on-surface reactions; on Ag(111), the halogen-bonded assemblies of DBDMN are converted into one-dimensional (1D) organometallic structures at 360 K, while further annealing at elevated temperatures does not activate covalent reactions but desorbs the organometallic structures; on Cu(111), DBDMN molecules form organometallic structures at 300 K and undertake a novel interrmolecular cyclodehydrogenation (CDH) reaction forming C-C bonds between debrominated carbons and methyl groups at 480 K. The products are dibenz[a,h]anthracene derivates and ultra-narrow graphene nanoribbon (GNR) motifs with chiral edges. These results are attributed to multiple effects including steric hindrance associated with the side groups, chemical reactivity of the substrates, adsorption strength of the molecules on the substrates and stability of organometallic intermediates.

3



Page 4 of 21

Scheme 1. Schematic illustration of distinctive reaction steps of DBDMN on Au(111), Ag(111) and Cu(111)

Experimental and Theoretical Methods All experiments were performed with a commercial UHV-STM system (Omicron GmbH) with a base pressure at the level of 10-10 mbar in the system. The atomically flat crystalline Au(111), Ag(111), and Cu(111) surfaces were prepared by repeated cycles of Ar+ sputtering followed by annealing at about 800 K. DBDMN molecules with a purity of 97% (commercially purchased from Asta Tech) were evaporated at room temperature (RT) onto the clean substrates. The samples were subsequently annealed at different temperatures. The STM tip was made out of an etched W wire (Ø 0.25 mm). All STM images were acquired at 78 K in the constant current mode, and processed by the WSxM software.18 First-principles calculations are carried out for the zigzag conjugated dimer and (2,1)-GNR absorbed on Cu(111) within the framework of density-functional theory (DFT)19, 20 as implemented in the Vienna ab initio Simulation Package (VASP).21 The ion-electron interaction is described by the projector-augmented wave potential (PAW).22 As for electron-electron interaction, a generalized gradient approximation (GGA) in the framework of the Perdew-Burke-Emzerhof (PBE)23,

24

is

employed. All calculations are performed with a plane-wave cutoff of 500 eV and the k-point sampling are 2*2*1 in the Monkhorst-Pack grid.25 A vacuum layer of 15 Å is applied between neighboring layers to ensure the decoupling of them. The structures are relaxed until the forces are smaller than 10-2 eV/Å. The geometry optimizations of DBDMN monomer and organometallic dimers (both Ag and Cu) were performed with the Gaussain09 software26 using DFT19, 20 calculations and B3LYP functional.27, 4


Page 5 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


28

The 6-31g(d,p) basis set was used for C and H atoms in all the species, and LANL2DZ basis set

with the corresponding effective core potential (ECP)29-32 were employed for Br, Ag and Cu atoms. The optimized models of these molecular species are shown in Figure S5 (Supporting Information) with their dimensions marked.

Results Molecular Assemblies Formed on Au(111) Figure 1a shows a representative STM image of the Au(111) surface after depositing DBDMN molecules onto the substrate at about 200 K followed by annealing at 300 K for 1 hour. The Au(111) surface is covered by a full monolayer of DBDMN monomers. Inset of Figure 1a displays the high-resolution STM image of an ordered domain of the molecular adlayer. The unit cell of the assembled structure, denoted as Structure A, is highlighted by the white parallelogram in inset of Figure 1a, whose parameters are a = 1.90±0.05 nm, b = 1.90±0.05 nm, and ߠ = 75±1°. A single DBDMN molecule in the ordered assembly appeared as a parallelogram, in which the two brighter vortices of the diagonal are assigned as Br atoms and the other two vortices as the methyl groups, as shown by the chemical structures superimposed in inset of Figure 1a. The chemical models superimposed on the STM image show the approaching of Br atoms in one molecule to H atoms in the naphthalene core of another one, implying a weak Br…H interaction,33, 34 as marked by the blue dashed lines in inset of Figure 1a.

5



Figure 1. (a) STM image of Structure A formed by DBDMN monomers after deposition of the molecules followed by 300 K annealing. Inset: High-resolution STM image of Structure A with chemical structures of the monomers superimposed. The unit cell is highlighted by the white parallelogram. (b) STM image of the Au(111) surface with DBDMN molecules after 420 K annealing. Domains of Structures B and C are marked by “B” and “C”, respectively. High-resolution STM images of Structures (c) B and (d) C with chemical structures of the monomers superimposed. The unit cells of the two structures are marked by the white parallelograms in (c) and (d). Imaging condition: (a) 0.6 V, 0.16 nA; (b)-(d) 1.1 V, 0.1 nA. Further annealing of the Au(111) sample at about 420 K resulted in two other ordered molecular assemblies (Figure 1b), which are denoted as Structures B and C, respectively, as marked in Figure 1b. Domains of the two assembled structures are separated by fuzzy areas originated from the migrating molecules on the surface, indicating a reduction in molecular coverage in comparison with the sample shown in Figure 1a. Presumably, desorption of molecules took place upon the thermal annealing at 420 K. Figures 1c and d display high-resolution STM images of Structures B and C, respectively. For Structure B, the unit cell is marked by the white parallelogram in Figure 1c with the parameters a = 1.82±0.05 nm, b = 1.81±0.05 nm, and ߠ = 88±1°. The close distance between the Br atom in one molecule and the H atom in methyl group of the neighboring, as illustrated by the chemical models superimposed on the STM image, suggests a Br…H interaction33, 34 between the

6


Page 6 of 21

Page 7 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


molecules, as marked by the blue dashed lines in Figure 1c. As for Structure C, the dimensions of the unit cell, as highlighted by the white parallelogram in Figure 1d, are a = b = 1.79±0.05 nm, and ߠ = 60±1°. The chemical structures superimposed on the STM image reveal the close distance and the specific orientations of the three Br atoms, suggesting the typical circular Br…Br halogen bonds between them,33, 34 as highlighted by the blue dashed lines in Figure 1d. The molecular densities of the three structures are 1.15 nm-2, 1.21 nm-2, 1.08 nm-2 for A, B and C, respectively. The DBDMN molecules completely desorbed from the Au(111) substrate after heating the sample at 550 K, and no reaction product was observed.

Organometallic Structures Formed on Ag(111) Deposition of DBDMN molecules onto the Ag(111) surface held at 300 K gave rise to a molecular assembly as shown in Figure 2a. This assembly is composed of ordered arrangement of the fan-like clusters which consist of three molecules, as shown by the chemical structures superimposed in inset of Figure 2a. The unit cell of the structure is marked by a white parallelogram in Figure 2a, with the dimensions of a = b = 1.71±0.05 nm, and ߠ = 60±1°. The three molecules in the fan-like clusters have their Br atoms approached, as revealed by the chemical models superimposed on the STM image, indicating halogen bonds between the molecules composing the clusters,33, 34 as highlighted by the blue dashed lines in inset of Figure 2a. The different shape of the molecules absorbed on Ag(111) comparing with those on Au(111) suggests the detachment of one Br-substituent in DBDMN molecules. The resulted debrominated carbons in the molecules can be stabilized by their interactions with the metal substrate.35-37 In fact, the molecular models of this assembled structure on Ag(111) depicted according to the unit cell dimensions (Figure S1, Supporting Information) suggest that the locations of the debrominated carbons in the molecules relative to the substrate lattice would enable the molecule-substrate bonding.37 The highly-selective formation of molecules with only one Br atom detached might be attributed to lifting of the remained C-Br bond in the molecule due to the anchoring of the debrominated carbon to the substrate atoms after the detachment of one of the Br atoms of DBDMN. This variation in molecular conformation, that is, an increased distance between substrate and the remained C-Br bond of DBDMN, would cause a reduced catalytic effect of the metal substrate,38 which impedes the dissociation of the remained C-Br bond at 300 K. The dim spots embedded in the molecular assembly, as highlighted by the white dashed circles in inset of Figure 2a, 7



are likely the detached Br atoms.

Figure 2. (a) STM image of the molecular assembly of DBDMN on Ag(111). The unit cell is highlighted by the white parallelogram. Inset: Zoom-in STM image of a fan-like molecular cluster with chemical structures of the debrominated molecules superimposed. Detached Br atoms are marked by the white dashed circles. (b) STM image of the organometallic chains formed on Ag(111) after heating the sample at about 360 K. (c) High-resolution STM image of an organometallic chain on Ag(111)) with the chemical structure superimposed. The separation of two adjacent Ag atoms in the chain is marked by the black arrow. The molecule and the Ag atom connected with the migrated organometallic bond are highlighted by the blue dashed circle. Imaging condition: (a) and (b) -0.1 V, 0.3 nA; (c) -0.05 V, 0.3 nA. Upon annealing the sample at about 360 K, we observed chain structures (Figure 2b). High-resolution STM image (Figure 2c) reveals that the chains consist of an alternate arrangement of brighter and darker segments. The separation between two adjacent brighter segments, as marked by the black arrow in Figure 2c, is 0.73±0.05 nm. This value is in accordance with the distance between two neighboring molecules with a trans-configuration connected by a Ag atom bonding to their debrominated carbons, i.e., 0.76 nm (Figure S5b, Supporting Information). Therefore, the chain structures are organometallic complex formed by the chemical bonding between debrominated DBDMN molecules and Ag atoms. We assign the brighter segments as silver atoms and the darker ones as molecular moieties, as illustrated by the chemical structure superimposed in Figure 2c. Such organometallic structures were commonly observed as intermediate species of Ullmann coupling reactions on Ag(111).9, 37, 39-41 It is noticed that some of the molecules in the organometallic chains are linked to Ag atoms with the different carbons from their Br-substituted ones. For instance, the organometallic bond between 8


Page 8 of 21

Page 9 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the molecule and the Ag atom marked by the blue dashed circle in Figure 2c is supposed to form between the Ag atom and the carbon numbered “1”. However, it turns out that the carbon numbered “8” instead of “1” is involved in the formation of C-Ag bond, as shown by the chemical structure superimposed in Figure 2c. This “migration” of organometallic bonds was feasible on metal surfaces through thermal activation in other works.42, 43 We observed the coverage of organometallic chains was reduced after heating the sample at 600 K (Figure S2, Supporting Information), suggesting the decomposition of the organometallic species followed by the desorption of the achieved fragments at this temperature. We did not identify any covalent product on Ag(111).

Covalent Structures Formed on Cu(111) via Intermolecular CDH Reaction. Figure 3a presents the STM image of the Cu(111) surface after depositing DBDMN molecules onto the substrate held below 300 K followed by annealing of the sample at 300 K for 0.5 hour. The high-resolution STM image (Figure 3b) shows the formation of dimeric species with cis- (marked with the green dashed circle in Figure 3b) and trans- (marked with the red dashed circle in Figure 3b) configurations, respectively. The length of a trans-dimer is about 1.5 nm (marked by the white arrow in Figure 3b), which agrees with the dimension of an organometallic dimer formed by two debrominated DBDMN molecules linked via a copper atom with a trans-configuration, i.e., 1.41 nm (Figure S5c, Supporting Information). Therefore, we assign the dimeric structures as organometallic dimers formed by two DBDMN molecules and a copper adatom, as shown by the chemical structures superimposed in Figure 3b. By comparing the debromination of DBDMN on Au(111), Ag(111) and Cu(111) at 300 K, one argue copper is the most reactive substrate and gold is the least reactive one, which is consistent with the previous reports.9, 37, 41, 44

9



Figure 3. (a) STM image of the Cu(111) surface after the deposition of DBDMN molecules followed by 300 K annealing. (b) High-resolution STM image of the organometallic dimers formed by DBDMN on Cu(111) with chemical structures superimposed. The organometallic dimers with cisand tran-configurations are marked by the green and red dashed circles, respectively. The length of the trans-dimer is marked by the white arrow. (c) STM image of the Cu(111) sample with DBDMN molecules after being annealed at about 480 K. The zigzag conjugated dimeric structures are highlighted by the white arrows. (d) High-resolution STM image of an organometallic wire formed on Cu(111) with the chemical structure superimposed. The separation of two adjacent Cu atoms in the wire is marked by the white arrow. The molecules and the Cu atom connected with the migrated organometallic bonds are highlighted by the blue dashed circle. Imaging condition: (a) and (b) 0.1V, 0.1 nA; (c) -0.2 V, 0.3 nA; (d) 0.01 V, 0.2 nA. Depositing DBDMN on the Cu(111) substrate held at 300 K and subsequent annealing at about 480 K resulted in extended molecular wires (Figure 3c). High-resolution STM image (Figure 3d) reveals a similar appearance of the organometallic chains with those formed on Ag(111). We assign the wires formed on Cu(111) as organometallic species, as illustrated by the chemical structure in Figure 3d. The distance between two adjacent brighter protrusions in the wires, as marked by the white arrow in Figure 3d, is 0.69±0.05 nm, which is consistent with the dimension of the proposed organometallic model (0.73 nm for the intermolecular separation, Figure S5c, Supporting Information). The blue dashed circle in Figure 3d highlights migration of organometallic bonds. In addition to the organometallic wires, we observed some dumbbell-shaped structures, as marked by the white arrows in Figure 3c. An STM image of an island assembled out of such dumbbell-shaped structures is shown in Figure 4a. The tip-to-tip distance of this structure is about 1.5 nm, as marked by the white arrow in Figure 4a. This value is larger than the methyl-to-methyl distance of a DBDMN monomer (0.81 nm, Figure S5a, Supporting Information) but shorter than twice the monomer length, implying the structures consisting of two covalently-linked monomers. The tip-manipulation experiment (Figure S3, Supporting Information) removed a dumbbell-shaped structure as a whole, confirming the formation of strong chemical bonds within this structure. The smooth connection between the molecular units in the dumbbell-shaped structures also hints a planar covalently-linked backbone. A model of a covalently-linked DBDMN dimer featuring a 3,1010


Page 10 of 21

Page 11 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dimethyl-dibenz[a,h]anthracene structure with a zigzag conjugated backbone (demoted as “zigzag conjugated dimer” hereafter) is drawn in Figure 4a. In this model, covalent bonds form between the dehydrogenated methyl carbon in one molecule and the debrominated carbon in another molecule, forming a conjugated six-membered ring (highlighted in red) between two precursor molecules. The optimized tip-to-tip length of the zigzag conjugated dimer (1.45 nm, Figure 4c bottom) is in good accordance with the measured value. The simulated STM image (Figure 4c top) of a 3,10dimethyl-dibenz[a,h]anthracene molecule also agrees well with the experimental data (Figure 4b), which further confirms the proposed structure. The yield of these covalent products in the sample as shown in Figure 3c is about 20%.

Figure 4. (a) STM image of an island assembled out of the zigzag conjugated dimers formed by DBDMN on Cu(111) with the chemical structure superimposed. The tip-to-tip length of the structure is marked by the white arrow. (b) High-resolution STM image of a zigzag conjugated dimer. (c) Simulated STM image of a 3,10-dimethyl-dibenz[a,h]anthracene molecule on Cu(111) at bias = -0.05 V (top) and the optimized molecular model (bottom). The optimized dimensions of the structure are marked by numbers. (d) Schematic illustration of the reaction pathway of DBDMN molecules from organometallic intermediates to zigzag conjugated dimers on Cu(111). Imaging condition: (a) -0.1 V, 0.3 nA; (b): -0.01V, 0.4 nA. Figure 4d illustrates a conversion process from the organometallic oligomers (Figures 3a and b) to the zigzag conjugated dimers. Presumably, when annealed to about 480 K, the C-Cu bonds in the organometallic species dissociate, resulting in debromintaed DBDMN moieties diffusing on the 11



Page 12 of 21

surface. When the methyl group in one DBDMN approaches the debrominted carbon of another DBDMN, an intermolecular CDH (denoted as “inter-CDH” hereafter) reaction, which involves the C-H bond activation of the methyl groups and the bond formation between the activated methyl carbons and the debrominated carbons, takes place to form the covalent dimers. Each methyl group has two protons detached so that the final conjugated structure is achieved. As the last step, the unreacted debrominated carbons in the dimeric structures are passivated with H atoms,16,

45, 46

yielding the zigzag conjugated dimers. It has been reported that various precursor molecules undertake intermolecular or intramolecular CDH reactions on metal substrates,47-63 among which copper substrates were reported to show especially high catalytic activity.48, 49, 54 The inter-CDH reaction reported here is featured by the involvement of methyl carbons rather than the carbons in naphthalene core , which can be explained by a lower C-H bond dissociation energy for methyl groups substituting on naphthalene (~ 3.8 eV)64 than that for naphthalene core (~ 4.9 eV).64 Moreover, participation of the methyl group in one molecule in C-C bond formation is facilitated by the high reactivity of the Br-substituted carbons in other DBDMN molecules after their debromination. The debrominated carbons serve as locating sites, promoting the controllable and selective intermolecular C-C bonding. Further annealing the sample at 700 K yielded ribbon-like structures as shown in Figure 5a, while the organometallic species did not exist on the surface. The zoom-in STM image of the area highlighted by the white rectangle in Figure 5a (Figure 5b) shows that most segments in the ribbons possess kinked edges, as marked by the white lines in Figure 5b. The separation between two adjacent kinks, as marked by the white arrow in Figure 5b, is 0.63±0.05 nm. This value is very close to the intermolecular distance of the zigzag conjugated dimer (0.66 nm, Figure 4c bottom). A chemical structure of the ribbons is drawn in Figure 5b, showing the adjacent DBDMN moieties are connected with conjugated six-membered rings formed via the inter-CDH reactions. According to the naming convention derived by Han et al.,49 the proposed structure can be named as (2,1)-GNR. The optimized periodicity of (2,1)-GNR is 0.66 nm, which agrees well with the measured value. The DFT simulated STM image of (2,1)-GNR (Figure 5c) is in good agreement with the experimentally obtained images of the nanoribbons. This structure is the narrowest chiral GNR motifs that had ever been reported to be prepared by on-surface synthesis.17,

49, 54, 65, 66

The two opposite adsorption

chiralities of the ribbons were observed by STM (Figure S4, Supporting Information). Furthermore, 12


Page 13 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the DFT calculations of the electronic properties of (2,1)-GRN (Figure S6, Supporting Information) predict a 1.33 eV gap between valence band and conduction band. Apart from the (2,1)-GNR segments, we also observed some defect structures, as marked by the yellow arrows in Figure 5b. The formation of these defects was likely caused by uncontrollable side reactions triggered by the active copper substrate, or the covalent bonding between the molecules with migrated organometallic bonds.

Figure 5. (a) STM image of molecular ribbons formed on Cu(111) after heating the sample at 700 K. (b) Zoom-in STM image of the area marked by the white rectangle in (a) with the chemical structure superimposed. The kinked edges of the molecular ribbons are highlighted with the white lines. The separation of the adjacent kinks is marked by the white arrow. The defect structures are marked by the yellow arrows. (c) Simulated STM image of a (2,1)-GNR on Cu(111) at bias = -0.1 V with the STM image (top) and optimized molecular model (bottom) superimposed. The optimized periodicity of (2,1)-GNR is marked by number. Imaging condition: (a) 0.1 V, 0.3 nA; (b) and (c) 0.03 V, 0.3 nA. The comparison of the inter-CDH reaction of DBDMN on Cu(111) with those on Au(111) and Ag(111), where no covalent product was achieved, reveals the significant role of the copper substrate. On the one hand, a relatively strong adsorption strength of DBDMN on Cu(111) prevents molecular desorption before the activation of chemical conversions, which is the prerequisite for the on-surface reactions. In contrast, the weak adsorption strength of DBDMN on Au(111) leads to molecular desorption prior to any reaction. On the other hand, the high catalytic activity of the copper substrate48, 49, 54 enables the inter-CDH reaction at a relatively low temperature (~ 480 K). As a comparison, on the Ag(111) substrate, though molecules were held on the surface to form the organometallic species, no conversion of the organometallic intermediates was triggered even at a

13



Page 14 of 21

high annealing temperature (600 K).

Discussion Brominated precursors were demonstrated to undergo Ullmann coupling reaction on Au, Ag and Cu substrates in numerous studies.9, 37, 39, 41, 44, 60, 67, 68 Presumably, DBDMN is expected to undergo Ullmann coupling reaction and form covalent products (marked as “Ullmann products”) as schematically illustrated in Figure 6. However, such a reaction does not take place on Au(111), Ag(111) or Cu(111). This phenomenon is attributed to the huge steric hindrance between the adjacent molecular units in the proposed Ullmann products. Had an intermolecular C-C bonds been formed via Ullmann coupling, steric hindrance between the methyl groups and the naphthalene cores, as highlighted by the red ellipses in Figure 6, would lead to opposite tilts of adjacent molecular units through the rotation of the molecular moieties around the C-C bonds between them.47,

60

Such

variations in molecular conformations would take place at a temperature higher than other systems in which the steric hindrance is not an issue. However, at such a high temperature, other processes may occur, including desorption or other on-surface reactions.

Figure 6. Schematic illustration of the Ullmann coupling reactions of DBDMN on Au(111), Ag(111) and Cu(111). To be specific, on Au(111), the methyl side groups render a weak DBDMN-substrate interaction, as implied by the presence of Au(111) herringbones on the molecule-covered surface (Figures 1a and b). As a result, most DBDMN molecules desorb prior to debromination. It is worthwhile to mention that the Ullmann-type coupling with large steric hindrance had been achieved on Au(111) when large molecular precursors were employed,47, 53, 60 where the strong molecule-substrate adsorption strength enabled the on-surface reactions taking place prior to molecular desorption. On Ag(111), debromination occurs at a low temperature and leads to the formation of the organometallic structures. However, conversion of the organometallic structures to the Ullmann products is blocked 14


Page 15 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


by the steric hindrance. The molecules desorb prior to covalent reaction. On Cu(111), Ullmann-type coupling is hampered by the huge steric hindrance. Instead, inter-CDH reaction takes place because of (1) the strong molecule-substrate adsorption strength, and (2) the high reactivity of the copper substrate,48, 49, 54 which activates the dehydrogenation and intermolecular cyclization of DBDMN.

Conclusions In summary, we investigate the on-surface reactions of DBDMN molecules on Au(111), Ag(111) and Cu(111). We demonstrate that the on-surface processes of the precursor on the three noble metal substrates form distinctive final products. On Au(111), the molecules assemble into ordered structures, but desorb at relative low temperature due to a weak molecule-substrate interaction. On Ag(111), the reaction terminates at the organometallic chains. On Cu(111), the organometallic species are converted into covalent products via a novel inter-CDH reaction. These results demonstrate that the reaction steps can be controlled by selecting different substrates, which represents a new strategy of utilizing substrate effect to design molecular structures. Moreover, discovery of the on-surface inter-CDH reaction involving the bonding between methyl carbons and debrominated carbons enriches the toolbox of on-surface reactions for the preparation of molecular nanostructures.

Supporting Information Description Molecular models of the assembled structure on Ag(111). Thermal treatment of the Ag(111) sample with organometallic chains at 600 K. Tip-manipulation of the zigzag conjugated dimer formed by DBDMN on Cu(111). (2,1)-GNR motifs with opposite adsorption chiralities. Optimized models of the relevant molecular species. DFT calculated PDOS of (2,1)-GNR on Cu(111). This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgement This work was supported by Hong Kong RGC N_HKUST601/15.

15



References 1. 2. 3. 4. 5. 6.

7. 8. 9.

10.

11.

12. 13. 14.

15.

16.

17.

Champness, N. R. Building with Molecules. Nat. Nanotechnol. 2007, 2, 671-672. Grill, L.; Dyer, M.; Lafferentz, L.; Persson, M.; Peters, M. V.; Hecht, S. Nano-Architectures by Covalent Assembly of Molecular Building Blocks. Nat. Nanotechnol. 2007, 2, 687-691. Gourdon, A. On-Surface Covalent Coupling in Ultrahigh Vacuum. Angew. Chem., Int. Ed. 2008, 47, 6950-6953. Palma, C.-A.; Samorì, P. Blueprinting Macromolecular Electronics. Nat. Chem. 2011, 3, 431-436. Champness, N. R. Surface Chemistry: Making the Right Connections. Nat. Chem. 2012, 4, 149-150. Lafferentz, L.; Eberhardt, V.; Dri, C.; Africh, C.; Comelli, G.; Esch, F.; Hecht, S.; Grill, L. Controlling On-Surface Polymerization by Hierarchical and Substrate-Directed Growth. Nat. Chem. 2012, 4, 215-220. Colson, J. W.; Dichtel, W. R. Rationally Synthesized Two-Dimensional Polymers. Nat. Chem. 2013, 5, 453-465. Dong, L.; Liu, P. N.; Lin, N. Surface-Activated Coupling Reactions Confined on a Surface. Acc. Chem. Res. 2015, 48, 2765-2774. Bieri, M.; Nguyen, M.-T.; Gröning, O.; Cai, J.; Treier, M.; Aït-Mansour, K.; Ruffieux, P.; Pignedoli, C. A.; Passerone, D.; Kastler, M.; et al. Two-Dimensional Polymer Formation on Surfaces Insight into the Roles of Precursor Mobility and Reactivity. J. Am. Chem. Soc. 2010, 132, 16669-16676. Pinardi, A. L.; Otero-Irurueta, G.; Palacio, I.; Martinez, J. I.; Sanchez-Sanchez, C.; Tello, M.; Rogero, C.; Cossaro, A.; Preobrajenski, A.; Gómez-Lor, B.; et al. Tailored Formation of N Doped Nanoarchitectures by Diffusion-Controlled On-Surface (Cyclo)-Dehydrogenation of Heteroaromatics. ACS Nano 2013, 7, 3676-3684. Dong, L.; Wang, S.; Wang, W.; Chen, C.; Lin, T.; Adisoejoso, J.; Lin, N. Transition Metals Trigger On-Surface Ullmann Coupling Reaction: Intermediate, Catalyst and Template. In On-Surface Synthesis. Advances in Atom and Single Molecule Machines; Gourdon, A., Eds.; Springer: Cham, 1996; pp 23-42. Gao, H. Y.; Wagner, H.; Zhong, D.; Franke, J. H.; Studer, A.; Fuchs, H. Glaser Coupling at Metal Surfaces. Angew. Chem., Int. Ed. 2013, 52, 4024-4028. Gao, H.-Y.; Franke, J.-H.; Wagner, H.; Zhong, D.; Held, P.-A.; Studer, A.; Fuchs, H. Effect of Metal Surfaces in On-Surface Glaser Coupling. J. Phys. Chem. C 2013, 117, 18595-18602. Dinca, L. E.; MacLeod, J. M.; Lipton-Duffin, J.; Fu, C.; Ma, D.; Perepichka, D. F.; Rosei, F. Tailoring the Reaction Path in the On-Surface Chemistry of Thienoacenes. J. Phys. Chem. C 2015, 119, 22432-22438. Li, Q.; Yang, B.; Lin, H.; Aghdassi, N.; Miao, K.; Zhang, J.; Zhang, H.; Li, Y.; Duhm, S.; Fan, J.; et al. Surface-Controlled Mono/Diselective ortho C-H Bond Activation. J. Am. Chem. Soc. 2016, 138, 2809-2814. Kong, H.; Yang, S.; Gao, H.; Timmer, A.; Hill, J. P.; Diaz Arado, O.; Monig, H.; Huang, X.; Tang, Q.; Ji, Q.; et al. Substrate-Mediated C-C and C-H Coupling after Dehalogenation. J. Am. Chem. Soc. 2017, 139, 3669-3675. Schulz, F.; Jacobse, P. H.; Canova, F. F.; van der Lit, J.; Gao, D. Z.; van den Hoogenband, A.; Han, P.; Klein Gebbink, R. J. M.; Moret, M.-E.; Joensuu, P. M.; et al. Precursor Geometry 16


Page 16 of 21

Page 17 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


18.

19. 20. 21. 22. 23. 24. 25. 26.

27. 28.

29. 30. 31. 32. 33.

34. 35.

36.

Determines the Growth Mechanism in Graphene Nanoribbons. J. Phys. Chem. C 2017, 121, 2896-2904. Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M. WSXM: A Software for Scanning Probe Microscopy and a Tool for Nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705. Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864. Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133. Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169. Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, 1758. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 865. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1997, 78, 1396. Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford CT, 2009. Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648-5652. Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 1994, 98, 11623-11627. Dunning Jr., T. H.; Hay, P. J. In Methods of Electronic Structrue Theory; Schaefer, H. F., Eds.; Plemun Press, 1977. Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Sc to Hg. J. Chem. Phys. 1985, 82, 270. Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82, 284. Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299. Desiraju, G. R.; Parthasarathy, R. The Nature of Halogen-Halogen Interactions: Are Short Halogen Contacts Due to Specific Attractive Forces or Due to Close Packing of Nonspherical Atoms? J. Am. Chem. Soc. 1989, 111, 8725–8726. Yoon, J. K.; Son, W.-j.; Chung, K.-H.; Kim, H.; Han, S.; Kahng, S.-J. Visualizing Halogen Bonds in Planar Supramolecular Systems. J. Phys. Chem. C 2011, 115, 2297-2301. Hla, S.-W.; Bartels, L.; Meyer, G.; Rieder, K.-H. Inducing All Steps of a Chemical Reaction with the Scanning Tunneling Microscope Tip: Towards Single Molecule Engineering. Phys. Rev. Lett. 2000, 85, 2777-0780. Cirera, B.; Björk, J.; Otero, R.; Gallego, J. M.; Miranda, R.; Ecija, D. Efficient Lanthanide Catalyzed Debromination and Oligomeric Length-controlled Ullmann Coupling of Aryl Halides. 17



37.

38.

39.

40.

41.

42.

43.

44.

45.

46. 47.

48.

49.

50.

51.

J. Phys. Chem. C 2017, 121, 8033-8041. Zhou, X.; Wang, C.; Zhang, Y.; Cheng, F.; He, Y.; Shen, Q.; Shang, J.; Shao, X.; Ji, W.; Chen, W.; et al. Steering Surface Reaction Dynamics with Self-Assembly Strategy. Angew. Chem. Int. Ed. 2017, 56, 12852-12856. Zhang, Y. Q.; Kepcija, N.; Kleinschrodt, M.; Diller, K.; Fischer, S.; Papageorgiou, A. C.; Allegretti, F.; Bjork, J.; Klyatskaya, S.; Klappenberger, F.; et al. Homo-Coupling of Terminal Alkynes on a Noble Metal Surface. Nat. Commun. 2012, 3, 1286. Bieri, M.; Treier, M.; Cai, J.; Ait-Mansour, K.; Ruffieux, P.; Groning, O.; Groning, P.; Kastler, M.; Rieger, R.; Feng, X.; et al. Porous Graphenes: Two-Dimensional Polymer Synthesis with Atomic Precision. Chem. Commun. 2009, 0, 6919-6921. Eichhorn, J.; Strunskus, T.; Rastgoo-Lahrood, A.; Samanta, D.; Schmittel, M.; Lackinger, M. On-Surface Ullmann Polymerization via Intermediate Organometallic Networks on Ag(111). Chem. Commun. 2014, 50, 7680-7682. Zhou, X.; Bebensee, F.; Yang, M.; Bebensee, R.; Cheng, F.; He, Y.; Shen, Q.; Shang, J.; Liu, Z.; Besenbacher, F.; et al. Steering Surface Reaction at Specific Sites with Self-Assembly Strategy. ACS Nano 2017, 11, 9397-9404. Ferrighi, L.; Pis, I.; Nguyen, T. H.; Cattelan, M.; Nappini, S.; Basagni, A.; Parravicini, M.; Papagni, A.; Sedona, F.; Magnano, E.; et al. Control of the Intermolecular Coupling of Dibromotetracene on Cu(110) by the Sequential Activation of C-Br and C-H Bonds. Chem.-Eur. J. 2015, 21, 5826-5835. Píš, I.; Ferrighi, L.; Nguyen, T. H.; Nappini, S.; Vaghi, L.; Basagni, A.; Magnano, E.; Papagni, A.; Sedona, F.; Valentin, C. D.; et al. Surface-Confined Polymerization of Halogenated Polyacenes: The Case of Dibromotetracene on Ag(110). J. Phys. Chem. C 2016, 120, 4909-4918. Wang, W.; Shi, X.; Wang, S.; Van Hove, M. A.; Lin, N. Single-Molecule Resolution of an Organometallic Intermediate in a Surface-Supported Ullmann Coupling Reaction. J. Am. Chem. Soc. 2011, 133, 13264-13267. Talirz, L.; Sode, H.; Cai, J.; Ruffieux, P.; Blankenburg, S.; Jafaar, R.; Berger, R.; Feng, X.; Mullen, K.; Passerone, D.; et al. Termini of Bottom-Up Fabricated Graphene Nanoribbons. J. Am. Chem. Soc. 2013, 135, 2060-2063. Wang, T.; Lv, H.; Fan, Q.; Feng, L.; Wu, X.; Zhu, J. Highly Selective Synthesis of cis-Enediynes on a Ag(111) Surface. Angew. Chem. 2017, 56, 4762-4766. Cai, J.; Ruffieux, P.; Jaafar, R.; Bieri, M.; Braun, T.; Blankenburg, S.; Muoth, M.; Seitsonen, A. P.; Saleh, M.; Feng, X.; et al. Atomically Precise Bottom-Up Fabrication of Graphene Nanoribbons. Nature 2010, 466, 470-473. Treier, M.; Passerone, D.; Laino, T.; Rieger, R.; KlausMu¨llen; Passerone, D.; Fasel, R. Surface-Assisted Cyclodehydrogenation Provides a Synthetic Toute towards Easily Processable and Chemically Tailored Nanographenes. Nat. Chem. 2011, 3, 61-67. Han, P.; Akagi, K.; Federici Canova, F.; Mutoh, H.; Shiraki, S.; Iwaya, K.; Weiss, P. S.; Asao, N.; Hitosugi, T. Bottom-Up Graphene-Nanoribbon Fabrication Reveals Chiral Edges and Enantioselectivity. ACS Nano 2014, 8, 9181-9187. Wiengarten, A.; Seufert, K.; Auwärter, W.; Ecija, D.; Diller, K.; Allegretti, F.; Bischoff, F.; Fischer, S.; Duncan, D. A.; Papageorgiou, A. C.; et al. Surface-Assisted Dehydrogenative Homocoupling of Porphine Molecules. J. Am. Chem. Soc. 2014, 136, 9346–9354. Basagni, A.; Sedona, F.; Pignedoli, C. A.; Cattelan, M.; Nicolas, L.; Casarin, M.; Sambi, M. 18


Page 18 of 21

Page 19 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


52.

53.

54.

55. 56.

57.

58.

59.

60. 61.

62.

63.

64. 65.

Molecules-Oligomers-Nanowires-Graphene Nanoribbons: A Bottom-Up Stepwise On-Surface Covalent Synthesis Preserving Long-Range Order. J. Am. Chem. Soc. 2015, 137, 1802-1808. Sánchez-Sánchez, C.; Brüller, S. B.; Sachdev, H.; Müllen, K. M.; Krieg, M.; Bettinger, H. F.; Nicolaï, A.; Meunier, V.; Talirz, L.; Fasel, R.; et al. On-Surface Synthesis of BN-Substituted Heteroaromatic Networks. ACS Nano 2015, 9, 9228-9235. Ruffieux, P.; Wang, S.; Yang, B.; Sánchez-Sánchez, C.; Liu, J.; Dienel, T.; Talirz, L.; Shinde, P.; Pignedoli, C. A.; Passerone, D.; et al. On-Surface Synthesis of Graphene Nanoribbons with Zigzag Edge Topology. Nature 2016, 531, 489-492. Sanchez-Sanchez, C.; Dienel, T.; Deniz, O.; Ruffieux, P.; Berger, R.; Feng, X.; Müllen, K.; Fasel, R. Purely Armchair or Partially Chiral: Noncontact Atomic Force Microscopy Characterization of Dibromo-Bianthryl-Based Graphene Nanoribbons Grown on Cu(111). ACS Nano 2016, 10, 8006-8011. Ammon, M.; Sander, T.; Maier, S. On-Surface Synthesis of Porous Carbon Nanoribbons from Polymer Chains. J. Am. Chem. Soc. 2017, 139, 12976-12984. Liu, M.; Liu, M.; She, L.; Zha, Z.; Pan, J.; Li, S.; Li, T.; He, Y.; Cai, Z.; Wang, J.; et al. Graphene-Like Nanoribbons Periodically Embedded with Four- and Eight-Membered Rings. Nat. Commun. 2017, 8, 14924. Wang, X. Y.; Dienel, T.; Di Giovannantonio, M.; Barin, G. B.; Kharche, N.; Deniz, O.; Urgel, J. I.; Widmer, R.; Stolz, S.; De Lima, L. H.; et al. Heteroatom-Doped Perihexacene from a Double Helicene Precursor: On-Surface Synthesis and Properties. J. Am. Chem. Soc. 2017, 139, 4671-4674. Hieulle, J.; Carbonell-Sanroma, E.; Vilas-Varela, M.; Garcia-Lekue, A.; Guitian, E.; Pena, D.; Pascual, J. I. On-Surface Route for Producing Planar Nanographenes with Azulene Moieties. Nano Lett. 2018, 18, 418-423. Di Giovannantonio, M.; Urgel, J. I.; Beser, U.; Yakutovich, A. V.; Wilhelm, J.; Pignedoli, C. A.; Ruffieux, P.; Narita, A.; Mullen, K.; Fasel, R. On-Surface Synthesis of Indenofluorene Polymers by Oxidative Five-Membered Ring Formation. J. Am. Chem. Soc. 2018, 140, 3532-3536. Pham, T. A.; Tran, B. V.; Nguyen, M.-T.; Stöhr, M. Chiral-Selective Formation of 1D Polymers Based on Ullmann-Type Coupling: The Role of the Metallic Substrate. Small 2017, 13, 1603675. Eisenhut, F.; Lehmann, T.; Viertel, A.; Skidin, D.; Kruger, J.; Nikipar, S.; Ryndyk, D. A.; Joachim, C.; Hecht, S.; Moresco, F.; et al. On-Surface Annulation Reaction Cascade for the Selective Synthesis of Diindenopyrene. ACS Nano 2017, 11, 12419-12425. Cirera, B.; Gimenez-Agullo, N.; Bjork, J.; Martinez-Pena, F.; Martin-Jimenez, A.; Rodriguez-Fernandez, J.; Pizarro, A. M.; Otero, R.; Gallego, J. M.; Ballester, P.; et al. Thermal Selectivity of Intermolecular versus Intramolecular Reactions on Surfaces. Nat. Commun. 2016, 7, 11002. Williams, C. G.; Wang, M.; Skomski, D.; Tempas, C. D.; Kesmodel, L. L.; Tait, S. L. Dehydrocyclization of Peripheral Alkyl Groups in Porphyrins at Cu(100) and Ag(111) Surfaces. Surf. Sci. 2016, 653, 130-137. Luo, Y.-R. In Comprehensive Handbook of Chemical Bond Energies. CRC Press: Boca Raton, 2007; pp 50-51. Han, P.; Akagi, K.; Canova, F. F.; Shimizu, R.; Oguchi, H.; Shiraki, S.; S.Weiss, P.; Asao, N.; Hitosugi, T. Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons. ACS Nano 2015, 9, 12035-12044. 19



66. de Oteyza, D. G.; Garcia-Lekue, A.; Vilas-Varela, M.; Merino-Diez, N.; Carbonell-Sanroma, E.; Corso, M.; Vasseur, G.; Rogero, C.; Guitian, E.; Pascual, J. I.; et al. Substrate-Independent Growth of Atomically Precise Chiral Graphene Nanoribbons. ACS Nano 2016, 10, 9000-9008. 67. Koch, M.; Gille, M.; Viertel, A.; Hecht, S.; Grill, L. Substrate-Controlled Linking of Molecular Building Blocks: Au(111) vs. Cu(111). Surf. Sci. 2014, 627, 70-74. 68. Zhang, H.; Lin, H.; Sun, K.; Chen, L.; Zagranyarski, Y.; Aghdassi, N.; Duhm, S.; Li, Q.; Zhong, D.; Li, Y.; et al. On-Surface Synthesis of Rylene-Type Graphene Nanoribbons. J. Am. Chem. Soc. 2015, 137, 4022-4025.

20


Page 20 of 21

Page 21 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents Image

21


Controlling the Reaction Steps of Bifunctional Molecules 1,5-Dibromo

Recommend Documents