Subscriber access provided by SLUB Dresden Article On-Surface Annulation Reaction Cascade for the Selective Synthesis of Diindenopyrene Frank Eisenhut, Thomas Lehmann, Andreas Viertel, Dmitry Skidin, Justus Krüger, Seddigheh Nikipar, Dmitry A Ryndyk, Christian Joachim, Stefan Hecht, Francesca Moresco, and Gianaurelio Cuniberti ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b06459 • Publication Date (Web): 14 Nov 2017 Downloaded from http://pubs.acs.org on November 15, 2017

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1 2 3 4 OnSurface Annulation Reaction Cascade 5 6 7 8 9 for the Selective Synthesis of Diindenopyrene 10 11 12 1 1 2 1 1 13 Frank Eisenhut, Thomas Lehmann, Andreas Viertel, Dmitry Skidin, Justus Krüger, 14 15 Seddigheh Nikipar, 1 Dmitry A. Ryndyk, 1,3 Christian Joachim, 4 Stefan Hecht, 2 Francesca 16 17 ,1 1,5 18 Moresco,* and Gianaurelio Cuniberti 19 20 21 22 23 24 1Institute for Materials Science, Max Bergmann Center of Biomaterials, and Center for 25 26 27 Advancing Electronics Dresden, TU Dresden, 01069 Dresden, Germany 28 29 2 30 Department of Chemistry & IRIS Adlershof, HumboldtUniversität zu Berlin, BrookTaylor 31 32 Str. 2, 12489 Berlin, Germany 33 34 35 3Bremen Center for Computational Materials Science, Universität Bremen, Germany 36 37 38 39 4GNS & MANA Satellite, CEMES, CNRS, 29 rue J. Marvig, 31055 Toulouse Cedex, France 40 41 42 43 5Dresden Center for Computational Materials Science (DCMS), TU Dresden, 01069 Dresden, 44 45 46 Germany 47 48 49 50 51 52 53 54 55 56 57 *Corresponding author: francesca.moresco@tudresden.de 58 59 60 ACS Paragon Plus Environment 1 ACS Nano Page 2 of 19

1 2 3 ABSTRACT 4 5 6 7 We investigated the thermally induced onsurface cyclization of 4,10bis(2’bromo4’ 8 9 methylphenyl)1,3dimethylpyrene to form the previously unknown, nonalternant polyaromatic 10 11 hydrocarbon diindeno[1,2,3cd:1´,2´,3´mn]pyrene on Au(111) using scanning tunneling 12 13 14 microscopy and spectroscopy. The observed unimolecular reaction involves thermally induced 15 16 debromination followed by selective ringclosure to fuse the neighboring benzene moieties via a 17 18 fivemembered ring. The structure of the product has been verified experimentally as well as 19 20 21 theoretically. Our results demonstrate that onsurface reactions give rise to unusual chemical 22 23 reactivities and selectivities and provide access to nonalternant polyaromatic molecules. 24 25 26 27 28 29 30 31 Keywords: onsurface reaction, singlemolecule chemistry, scanning tunneling microscopy 32 33 (STM), nonalternant polyaromatic hydrocarbon, density functional theory, reaction mechanism 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 ACS Paragon Plus Environment 2 Page 3 of 19 ACS Nano

1 2 3 Onsurface synthesis represents one possible strategy to tailormake and precisely construct 4 5 6 nanostructures in which molecules form large covalent networks with atomic precision or to 7 8 synthesize molecules that are not achievable in solution.14 The most investigated reaction in this 9 10 57 11 field is the Ullmanncoupling. In the course of this reaction, one or several halogen atoms are 12 13 cleaved from the molecule thereby creating onsurface radicals which can form covalent bonds 14 15 either intramolecularly or intermolecularly leading to cyclization or polymerization. Exploiting 16 17 89 6 18 the latter pathway, molecular wires, 2D networks, as well as graphene nanoribbons have been 19 20 obtained. 1011 Despite the continuous drive to prepare large covalent structures from small 21 22 molecular precursors on metal surfaces, the selective formation of specific nonpolymeric, i.e. 23 24 25 discrete, molecules via surfaceinduced intramolecular reactions is of interest. Recent examples 26 27 include the reversible Bergmann cyclization, the generation of arynes, or the generation of anti 28 29 aromatic molecules.1215 30 31 32 Furthermore, suitable molecular precursors are used to generate polyaromatic 33 34 hydrocarbons (PAHs) on surfaces, allowing for their convenient characterization by scanning 35 36 1620 37 probe microscopy. Of particular interest are nonalternant PAHs since the presence of odd 38 39 numbered, such as fivemembered, rings can be seen as a topological defect and have been 40 41 shown to reduce the overall aromaticity. 21 Recently, fivemembered rings have been achieved by 42 43 11, 2223 44 surfaceassisted cyclodehydrogenation or elimination of hydrofluoric acid. In addition, 45 46 other ways to synthesize nonalternant PAHs on surfaces have been presented. 2426 47 48 Here, we report the onsurface synthesis of diindenopyrene on Au(111) starting from 49 50 51 4,10bis(2’bromo4’methylphenyl)1,3dimethylpyrene (Br2Me4Ph2Py). After thermally 52 53 induced debromination, regioselective cyclization to yield two fivemembered rings occurs 54 55 predominantly. Although, oligoindenopyrenes have been synthesized in solution, 27 56 57 58 59 60 ACS Paragon Plus Environment 3 ACS Nano Page 4 of 19

1 2 3 diindenopyrene derivatives presented in this article have not been reported so far to our 4 5 6 knowledge. In this work, we use scanning tunneling microscopy (STM) and spectroscopy (STS) 7 8 to resolve the molecular structure and electronic resonances in detail. More insight into the on 9 10 11 surface reaction mechanism is obtained by density functional theory (DFT) and electron 12 13 scattering quantum chemistry (ESQC) calculations. 14 15 16 17 18 RESULTS AND DISCUSSION 19 20 On-surface synthesis 21 22 Onsurface experiments were performed starting by the deposition of a submonolayer of the 23 24 25 Br 2Me 4Ph 2Py precursor molecules (Figure 1(a)) on a clean Au(111) surface kept at room 26 27 temperature. STM images were recorded at low temperature (T = 5 K) and under ultrahigh 28 29 vacuum (UHV) conditions. Figure 1(b) presents a constantcurrent STM image of a single 30 31 32 precursor molecule. 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Figure 1. Precursor molecule adsorbed on Au(111). (a) Molecular structure of the precursor 49 molecule 4,10bis(2’bromo4’methylphenyl)1,3dimethylpyrene (Br 2Me 4Ph 2Py). (b) STM 50 51 image of a single isolated precursor molecule. The STM scan (V = + 1.0 V; I = 100 pA) shows 52 that Br 2Me 4Ph 2Py molecules appear asymmetric after adsorption on Au(111). (c) Ballandstick 53 model of the fully relaxed Br Me Ph Py molecule obtained by density functional theory (DFT) 54 2 4 2 55 (colors: Catoms: blue; Bratoms: purple; Hatoms: grey). 56 57 58 59 60 ACS Paragon Plus Environment 4 Page 5 of 19 ACS Nano

1 2 3 As one can see in the STM image of Figure 1(b), one side of the molecule shows a larger 4 5 6 conductance, i.e. appears higher than the other one, despite the symmetry of the molecular 7 8 structure. To understand the adsorption conformation of the molecule, we performed density 9 10 11 functional theory (DFT) calculations. These calculations show that the carboncarbon bond 12 13 between the pyrene core and the lateral phenyl rings is rather flexible. The Br 2Me 4Ph 2Py 14 15 precursor is mainly adsorbed in a nonplanar conformation on the Au(111) surface with one of 16 17 18 the bromine atoms pointing towards and the other bromine atom pointing away from the surface. 19 20 This adsorption geometry explains the missing mirror symmetry and the significant apparent 21 22 height difference within the molecule observed in the STM image. 23 24 25 At higher coverages, the Br 2Me 4Ph 2Py molecules form onedimensional chains along the 26 27 fcc domain and rowlike ordered monolayers (see Figure S1 in the Supporting Information). 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 Figure 2. Debromination and planarization of Br 2Me 4Ph 2Py molecules on Au(111). (a) STM 48 49 image of three single isolated molecules after annealing to 160 °C for 5 min. The STM image (V 50 = + 0.5 V; I = 100 pA) shows that isolated molecules with different shapes adsorb at the kink 51 sites of the surface reconstruction. In the linescans in (b), taken along the molecules (marked in 52 53 (a) with the same color), one can directly observe that precursor molecules, partially planar and 54 completely planar molecules are on the surface after annealing. (c) STM image of several 55 molecules after annealing to 200 °C. The STM image (V = + 0.5 V; I = 100 pA) shows that all 56 57 58 59 60 ACS Paragon Plus Environment 5 ACS Nano Page 6 of 19

1 2 3 molecules have been planarized after the complete debromination of the molecules and no 4 5 Ullmanncoupled structures have been observed. 6 7 8 9 10 To explore intramolecular onsurface chemical reactions using the Br 2Me 4Ph 2Py 11 12 precursor, the sample was annealed to 160 °C for 5 minutes. At this temperature, and as known 13 14 from the literature, 2832 a partial debromination is induced on Au(111). Figure 2(a) shows a STM 15 16 17 image after this annealing. Three main molecular species are visible at the kink sites of the 18 19 Au(111) herringbone reconstruction. At these defect points, the molecules are isolated on the 20 21 surface. These three, approximately triangular, molecular species show large differences in their 22 23 24 relative apparent height in the STM images. They have either two maxima, one maximum, or are 25 26 completely planar, as shown by the line scan in Figure 2(b). We attribute the molecule with two 27 28 maxima to the unreacted precursor Br Me Ph Py. Molecules having one maximum are partially 29 2 4 2 30 31 planarized and are thus assigned to a reaction intermediate, while the fully planar molecule 32 33 appears to correspond to a complete debrominated molecule. Beside the molecules at the kink 34 35 36 sites, we also found larger structures on the surface. By STM lateral manipulation, we prove that 37 38 these molecular structures are not covalently connected (see Figure S2 in the Supporting 39 40 Information) and correspond to weakly bound supramolecular assemblies, similar to the ones 41 42 43 observed after the precursor deposition but before heating. In addition and after annealing, we 44 45 propose that these noncovalently bound dimer and tetramer molecular structures are formed 46 47 from the partially planar intermediates by a halogen bond (see Figure S3 in the Supporting 48 49 50 Information). Further byproducts were never observed on the surface. 51 52 After a further annealing step to 200 °C, all molecules appear planar on the surface 53 54 (Figure 2(c)). At this temperature, the debromination is normally completed on Au(111). 2832 55 56 57 58 59 60 ACS Paragon Plus Environment 6 Page 7 of 19 ACS Nano

1 2 3 From our observations, we can conclude that debromination causes the planarization of the 4 5 6 molecules induced by an efficient unimolecular reaction (Figure 3). 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Figure 3. Imaging and spectroscopic measurement of single diindeno[1,2,3cd:1´,2´,3´ 30 31 mn]pyrene (DIP) molecules adsorbed on Au(111). (a) Closeup STM image (V = + 0.1 V; I = 32 100 pA) of DIP measured with a metallic tip. (b) DIP imaged with a COtip at constant height 33 34 and V = + 10 mV. The inset shows the same molecule superimposed with the relaxed molecular 35 structure of DIP. (c) Red and blue marks the position of point spectroscopy in (a) and the dI/dV 36 spectra have been taken at constant height; the color of the curves matches with the color with 37 38 the indicated tip position in (a). We observed resonances at 1.8 V, 1.3 V, +1.5 V and +2.45 V. 39 The surface state of Au(111) is observed at 0.5 V. Tip heights were stabilized at V = + 0.5 V 40 and I = 100 pA and the spectra range is from 2.5 V to + 2.5 V. 41 42 43 44 To assign the molecular structure of the final product of the described onsurface 45 46 reaction, we performed highresolution STM imaging. Figure 3(a) presents a molecule measured 47 48 49 with a metallic tip in constant current mode. By scanning this molecule with a COfunctionalized 50 51 STMtip in constant height mode,33 we obtained the highly resolved image presented in Figure 52 53 54 3(b). We observe that two fivemembered rings have been formed at the upper two bay regions 55 56 of the pyrene core, giving rise to an indene formation. Since the planarity of the structure is 57 58 59 60 ACS Paragon Plus Environment 7 ACS Nano Page 8 of 19

1 2 3 maintained, the formed pentagons lead to a bending between the two upper arms of the molecule. 4 5 6 Note that the methyl groups, initially present in the Br 2Me 4Ph 2Py precursor, disappeared in the 7 8 final reaction product. We assign this onsurface synthesized, completely planar product 9 10 11 molecule to a diindeno[1,2,3cd:1´,2´,3´mn]pyrene (DIP) molecule, which to the best of our 12 13 knowledge has not been reported so far. 14 15 To investigate the electronic structure of the obtained DIP molecule, we have performed 16 17 18 scanning tunneling spectroscopy (STS) with a metallic tip. Figure 3(c) shows the differential 19 20 conductance spectra on single DIP molecules at the position marked by a red and a blue cross in 21 22 Figure 3(a). We associate the conductance peaks at +1.5 V and 1.3 V to two tunneling electronic 23 24 25 resonances that for simplicity we refer to as the lowest unoccupied molecular orbital (LUMO) 26 27 and the highest occupied molecular orbital (HOMO), respectively (see discussion below). Within 28 29 the bias voltage measurement range allowed by STM, we furthermore have access to two further 30 31 32 welldefined electronic resonances at 1.8 V and +2.45 V that for simplicity again we refer to as 33 34 HOMO1 and LUMO+1, respectively. On other positions of the DIP molecule, no strong 35 36 37 conductance peaks are observed. 38 39 40 41 Reaction mechanism 42 43 44 The proposed reaction path starting from the Br 2Me 4Ph 2Py precursor and ending in DIP on 45 46 Au(111) is summarized in Figure 4(a). The calculations show that after debromination, which is 47 48 favored on the Au(111) surface in comparison to this reaction in gas phase, 34 the molecule 49 50 51 cyclizes to form a fivemembered instead of a sixmembered ring (step 1). Comparing both 52 53 processes, we see that although the reaction intermediate with only hexagonal rings in step 2 is 54 55 about 0.3 eV lower in total energy, its formation energy barrier is 2.9 eV, i.e. , more than 1 eV 56 57 58 59 60 ACS Paragon Plus Environment 8 Page 9 of 19 ACS Nano

1 2 3 higher than for the fivemembered ring. The key for this selectivity is the preferred reactivity of 4 5 6 the debrominated radical species towards attack at the substituted phenyl position rather than the 7 8 benzylic site of the nearby internal methyl group. 35 From the formed internal pentadienyl radical 9 10 3 11 2, the methyl group at the sp carbon can migrate to the other, external methyl group, yielding 12 13 the sterically less congested pentadienyl radical 3 (step 2). Subsequently, both methyl groups are 14 15 combined and cleaved from the molecule, leaving one hydrogen atom at the initial site of the 16 17 18 external methyl substitution (step 3). Since the observed, final product is symmetrical, this 19 20 reaction sequence of cyclization, methyl migration and cleavage occurs subsequently within the 21 22 other half of the molecule (steps 46), resulting in the final planar structure. The overall reaction 23 24 25 appears to be driven by intramolecular strain release and an increase of the planarity of the π 26 27 system and hence stabilizing hybridization on the Au(111) surface. 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 ACS Paragon Plus Environment 9 ACS Nano Page 10 of 19

1 2 3 Figure 4. Reaction mechanism for the onsurface planarization of Br Me Ph Py to form the 4 2 4 2 5 planar DIP on Au(111). (a) Proposed reaction scheme and (b) Computed reaction energy 6 diagram for all relevant species and transitions, based on ab initio climbing imagenudged elastic 7 8 band (CINEB) calculations. The calculated effective barrier height is given in grey for each 9 individual barrier in units of eV. 10 11 12 13 As indicated by the rather small chemical reaction barriers, the intermediates 2 and 5 14 15 have short lifetimes and consequently have not been observed in our experiments. In contrast and 16 17 according to the relatively high barriers for the geminaldimethyl cleavage, we suppose that 18 19 20 some of the nonsymmetrical molecules imaged by STM (as for example in Figure 2(c)) are in 21 22 fact intermediates 3 and 6. Solely from the images a decisive differentiation is not possible. 23 24 However, all calculated reaction barriers show values lower than 2 eV, i.e. , all steps should be 25 26 27 accessible by heating the surface above 150 °C. 28 29 30 31 32 Mapping the electronic structure of the diindenopyrene molecule 33 34 35 For a detailed investigation of the electronic structure, we recorded dI/dV maps at bias 36 37 38 voltages corresponding to the resonances attributed to HOMO1, HOMO, LUMO and LUMO+1 39 40 (Figure 5(a)). The two fivemembered rings are expected to reduce the aromaticity of the DIP 41 42 21 43 molecule. Therefore, in the dI/dV maps, regions of higher differential conductance are located 44 45 close to the DIP benzene moieties, while regions of lower differential conductance are located on 46 47 the pentagonal rings. To further investigate the electronic structure of the DIP molecule, we have 48 49 36 50 calculated constantcurrent dI/dV maps for a DIP molecule physisorbed on Au(111) by ESQC 51 52 at the corresponding tunneling electronic resonance energies, as presented in Figure 5(b). As one 53 54 can see, the experimental differential conductance maps recorded at 1.3 V and +1.5 V are well 55 56 36 57 reproduced by the ESQC monoelectronic approximation indicating that the main molecular 58 59 60 ACS Paragon Plus Environment 10 Page 11 of 19 ACS Nano

1 2 3 orbital contribution to those resonances are coming from the HOMO and the LUMO molecular 4 5 6 orbitals, respectively. Notice a little discrepancy between the experimental and calculated 7 8 LUMO maps, certainly originated from a slightly different adsorption conformation of the DIP 9 10 11 molecule used in the calculations. The separation of one lobe (experimental) to two lobes 12 13 (calculated) on both sides of DIP in the LUMO maps was already observed on a Cu 14 15 phthalocyanine molecule. This difference comes probably from a slight deformation of the 16 17 37 18 molecular skeleton at the hexagonal carbon ring. 19 20 21 22 To theoretically simulate the 1.8 V and +2.45 V dI/dV maps, it was necessary to 23 24 superpose several ESQC calculated DIP molecular orbital maps. This is an indication that those 25 26 two resonances cannot be described solely by a single molecular orbital contribution of the 27 28 38 29 corresponding manybody Slater determinants normally describing those resonances. In 30 31 particular, the 1.8 V dI/dV map can be fairly well reproduced by a weighted superposition of the 32 33 calculated HOMO2, HOMO1 and HOMO dI/dV maps with a negative contribution from the 34 35 36 HOMO, while the +2.45 V dI/dV map is a weighted superposition of the calculated LUMO+2 37 38 and LUMO+1 dI/dV maps (see Figure S4). 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment 11 ACS Nano Page 12 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Figure 5. Mapping of the molecular orbital contribution of the DIP tunneling electronic 25 resonances. (a) Experimental constant–current differential conductance maps recorded at the 26 27 identified resonant bias values (HOMO1: V = 1.8 V; HOMO: V = 1.3 V; LUMO: V = +1.5 V; 28 LUMO+1: V = +2.45 V). Image sizes are 3.00 nm x 2.75 nm. Current for all images was 100 pA. 29 30 (b) Calculated differential conductance maps at the corresponding energy resonances using 31 monoelectronic elastic scattering quantum chemistry (ESQC). The HOMO1* and LUMO+1* 32 resonance maps were obtained by mixing multiple monoelectronic states to match the 33 34 experimental observations (see Figure S4). 35 36 37 38 CONCLUSION 39 40 41 In summary, we report the onsurface synthesis of previously unknown diindeno[1,2,3 42 43 cd:1´,2´,3´mn]pyrene molecule on Au(111). This intramolecular reaction makes use of the 44 45 activation of the inner carbon scaffold by surfaceassisted dehalogenation. Indene units, fused to 46 47 48 the pyrene core, are formed via a regioselective cyclization pathway followed by methyl group 49 50 migration and elimination. DFT modeling supports our experimental observations while the 51 52 53 reaction mechanism is identified by NEB calculations. Moreover, the structure of the DIP 54 55 molecules can be resolved by highresolution STM images with a functionalized tip and the 56 57 electronic structure investigated by scanning tunneling spectroscopy. Frontier orbital resonances 58 59 60 ACS Paragon Plus Environment 12 Page 13 of 19 ACS Nano

1 2 3 as well as HOMO1 and LUMO+1, which resemble mixtures of several molecular resonances, 4 5 6 are accessible with this technique and the calculated differential conductance maps show a 7 8 striking agreement. Using such onsurface chemical approach in combination with proper design 9 10 11 of molecular precursors should prove useful to access further nonalternant polyaromatic 12 13 hydrocarbons. 14 15 16 17 18 19 20 21 22 23 24 25 METHODS 26 27 28 Experimental Details. Details on the synthesis of Br 2Me 4Ph 2Py can be found in the Supporting 29 30 Information. STM experiments were performed using a custombuilt instrument operating at a 31 32 −10 33 low temperature of T ≈ 5 K and ultrahigh vacuum (p ≈ 1 × 10 mbar) conditions. STM 34 35 measurements were acquired in constantcurrent mode with the bias voltage applied to the 36 37 sample. The highresolution STM measurements were acquired in constantheight mode, and the 38 39 39 40 tip apex was terminated with a CO molecule, which was picked up from the surface. 41 42 Differential conductance measurements were fulfilled with a metallic tip using lockin detection 43 44 with a modulation frequency of 833 Hz and a modulation amplitude of 20 mV. An Au(111) 45 46 + 47 single crystal was used as substrate and prepared by repeated cycles of sputtering (Ar ) and 48 49 annealing (730 K). After this cleaning procedure, Br 2Me 4Ph 2Py was evaporated from a Knudsen 50 51 cell at a deposition temperature of 420 K. Temperatureinduced experiments were carried out by 52 53 54 annealing the sample at the respective temperature for 5 min after transferring it out of the STM 55 56 57 58 59 60 ACS Paragon Plus Environment 13 ACS Nano Page 14 of 19

1 2 3 without breaking the ultrahigh vacuum. Subsequently, the sample was cooled and transferred 4 5 6 back again inside the STM. 7 8 Computational Details. Density functional theory (DFT) in a mixed Gaussian and plane wave 9 10 4042 11 scheme, as implemented in the Quickstep code of the CP2K package was used to study the 12 13 adsorption of individual molecules and understand the mechanism of the chemical reaction. We 14 15 applied PerdewBurkeErnzerhof exchangecorrelation functionals, 43 GoedeckerTeterHutter 16 17 44 18 pseudo potentials and a valence doubleζ basis set, together with the DFTD3 method of 19 20 Grimme 45 for van der Waals correction. The Au(111) substrate was modelled as a slab of three 21 22 atomic gold layers with periodic boundary conditions, representing an infinite Au(111) surface. 23 24 25 Full geometry optimizations were carried out for initial, intermediate and final reaction steps, 26 27 with the lowest gold layer fixed. The reaction path was obtained by climbing image nudged 28 29 elastic band (CINEB) calculations, 46 which account for correct transition states. The reported 30 31 32 barrier heights correspond to the system at 0 K, whereas finite temperature can lower the barriers 33 34 due to dynamic effects. To confirm the final reaction product, the monoelectronic elastic 35 36 36 37 scattering quantum chemistry (ESQC) approach has been adopted to calculate constantcurrent 38 39 dI/dV spectra and maps. 40 41 42 43 44 ASSOCIATED CONTENT 45 46 Supporting Information. Details on the synthesis of the precursor, additional STM data, as well 47 48 as details on calculated differential conductance maps. This material is available free of charge 49 50 51 on the ACS Publications website at http://pubs.acs.org. 52 53 54 55 The authors declare no competing financial interests. 56 57 58 59 60 ACS Paragon Plus Environment 14 Page 15 of 19 ACS Nano

1 2 3 4 5 AUTHOR INFORMATION 6 7 8 Corresponding Authors 9 10 Email: francesca.moresco@tudresden.de 11 12 13 14 15 ACKNOWLEDGEMENT 16 17 This work was funded by the ICTFET European Union Integrated Project ATMOL and PAMS. 18 19 20 Support by the German Excellence Initiative via the Cluster of Excellence EXC1056 ‘‘Center for 21 22 Advancing Electronics Dresden’’ (cfaed), the International Helmholtz Research School 23 24 ‘‘Nanonet’’, and the German Research Foundation ( via SFB 951) is gratefully acknowledged. 25 26 27 We further thank the Center for Information Services and High Performance Computing (ZIH) at 28 29 TU Dresden for computational resources. T.L. gratefully acknowledges the International 30 31 Excellence Graduate School on Emerging Materials and Processes Korea (iEGSEMP Korea) in 32 33 34 the context of TU Dresden’s Institutional Strategy The Synergetic University. 35 36 37 38 39 40 41 42 REFERENCES 43 44 1. Lindner, R.; Kühnle, A., OnSurface Reactions. ChemPhysChem 2015, 16 , 15821592. 45 46 2. Shen, Q.; Gao, H.Y.; Fuchs, H., Frontiers of OnSurface Synthesis: From Principles to 47 Applications. Nano Today 2017, 13 , 7796. 48 3. Mendez, J.; Lopez, M. F.; MartinGago, J. A., OnSurface Synthesis of Cyclic Organic 49 Molecules. Chem. Soc. Rev. 2011, 40 , 45784590. 50 4. Gourdon, A., OnSurface Covalent Coupling in Ultrahigh Vacuum. Angew. Chem. Int. 51 52 Ed. 2008, 47 , 69506953. 53 5. Hla, S.W.; Bartels, L.; Meyer, G.; Rieder, K.H., Inducing All Steps of a Chemical 54 Reaction with the Scanning Tunneling Microscope Tip: Towards Single Molecule Engineering. 55 Phys. Rev.Lett. 2000, 85 , 27772780. 56 57 58 59 60 ACS Paragon Plus Environment 15 ACS Nano Page 16 of 19

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