Subscriber access provided by CHIBA UNIV C: Surfaces, Interfaces, Porous Materials, and Catalysis Adsorption-Induced Kondo Effect in Metal-Free Phthalocyanine on Ag(111) Julien Granet, Muriel Sicot, Iann C. Gerber, Geoffroy Kremer, Thomas Pierron, Bertrand Kierren, Luc Moreau, Yannick Fagot-Revurat, Simon Lamare, Frederic Cherioux, and Daniel Malterre J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b11141 • Publication Date (Web): 13 Apr 2020 Downloaded from pubs.acs.org on April 15, 2020

Just Accepted

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1 2 3 4 5 6 7 8 Adsorption-Induced Kondo Effect in Metal-Free 9 10 11 Phthalocyanine on Ag(111) 12 13 14 † ∗,† ‡ †,¶ † † 15 J. Granet, M. Sicot, I. C. Gerber, G. Kremer, T. Pierron, B. Kierren, 16 17 L. Moreau,† Y. Fagot-Revurat,† S. Lamare,§ F. Cherioux,´ § and D. Malterre† 18 19 20 †Universite´ de Lorraine, CNRS, IJL, F-54000 Nancy, France 21 22 ‡Universite´ de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue de Rangueil, 31077 Toulouse, 23 24 France 25 26 ¶Departement´ de Physique and Fribourg Center for Nanomaterials, Universite´ de Fribourg, 27 28 CH-1700 Fribourg, Switzerland 29 30 §Univ. Bourgogne Franche-Comte,´ FEMTO-ST, CNRS, UFC, 15B avenue des Montboucons, 31 32 F-25030 Besanc¸on cedex, France 33 34 35 36 37 ABSTRACT 38 39 40 We report on the formation of a two-dimensional supramolecular Kondo lattice made of organic 41 42 molecules comprising only C, N and H atoms namely metal-free phthalocyanines 2HPc (C H N ) 43 32 18 8 44 adsorbed on a Ag(111) surface. Low-temperature scanning tunneling microscopy/spectroscopy 45 46 (LT-STM/STS), ultra-violet photoemission spectroscopy (UPS) and density functional theory (DFT) 47 48 are used to investigate the electronic structure of the system for low molecular density and com- 49 50 mensurate self-assemblies. Abrikosov-Suhl resonances that are characteristic of the arising of a 51 52 Kondo effect are observed using both STS and UPS at low temperature. Whereas freestanding 53 54 2HPc is a no-spin bearing molecule, it acquires an unpaired electron in its π-conjugated lowest 55 56 unoccupied molecular orbital (LUMO) upon adsorption on Ag. As a result, the Kondo effect can 57 58 59 1 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 2 of 44

1 2 3 be interpreted as originating from the interaction between this unpaired π-spin and the Ag Fermi 4 5 sea. Extra side resonances are observed in STS spectra that are a manifestation of the coupling 6 7 between the π electron and molecular vibrational excitations, qualifying the effect as molecular 8 9 vibrational Kondo effect. The variation of the Kondo temperature TK of single molecules and upon 10 11 two-dimensional self-assembly is discussed. This study brings new insights in the Kondo-related 12 13 physics in correlation with molecular spins and low-dimensionality. Moreover, it may open new 14 15 routes to the synthesis of organic molecular spintronic devices. 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 2 60 ACS Paragon Plus Environment Page 3 of 44 The Journal of Physical Chemistry

1 2 3 INTRODUCTION 4 5 6 Molecular magnetism have attracted rising attention since molecular based magnetic materials 7 8 can have many technological applications in areas such as quantum computation,1,2 high-density 9 10 data storage and spintronics.3–7 Very early in the development of the field, metallophthalocyanines 11 12 (MPc) have proven to be a priviledged class of molecules to study magnetism at the nanometer 13 14 scale.8–11 Indeed, many MPc possess unpaired electrons in the gas phase and thus have non-zero 15 16 magnetic moments. Besides, bis-phthalocyanines sandwiching rare-earth ions have been shown 17 18 to behave as single-molecular magnets.12,13 Their applicative potential has already been demon- 19 20 strated, for example by fabricating functional supramolecular spin valves.14 21 22 The attractiveness of these molecules also lies in their easy synthesis, low cost and industrial 23 24 avaibility. Particularly, they can be evaporated under ultra-high vacuum (UHV) allowing the syn- 25 26 thesis of thin films.15 In addition, the planar geometry of their π-conjugated ligand that can lie 27 28 parallel to the surface on which they are adsorbed is an asset: the flatness of MPcs allows direct 29 30 hybridization with the orbitals of the underlying substrate leading to the modification of surface 31 32 properties and new exotic phenomena when in contact with various substrates such as ferromag- 33 34 netic (FM) materials,4 topological insulators, supraconductors or 2D materials.16–18 For instance, 35 36 in the case of the MPc/FM molecular spinterfaces, it has been shown that the addition of MPc 37 38 increases or invert the FM spin-polarization which is a key property regarding performance of spin 39 40 19–22 devices. In the case of CoPc/Bi2Se3, Caputo;et al. have evidenced by angular-resolved photo- 41 42 electron spectroscopy (ARPES), the modification of the topological surface states and the energy 43 44 shift of the Dirac cone due to charge transfer from the molecule to the surface23. When in contact 45 46 with superconductors, magnetic nano-objects can be envisaged as qubits for quantum computing 47 48 devices. In such cases, the governing factor is the strength of spin-superconductor interactions. 49 50 MPc/Pb(111) interfaces have been shown to be ideal platforms to tune locally this magnetic inter- 51 52 action strength by adsorbing the molecules on different sites or by continuously varying it using 53 54 24,25 the interaction with an STM tip. Finally, optical measurements of MPc/MoS2 heterojunctions 55 56 evidenced charge transfer that is sensitive to the transition metal core. This property allows for 57 58 59 3 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 4 of 44

1 2 3 tuneable optical absorption making those systems interesting for optoelectronic applications.16 4 5 Moreover, this flat-lying molecular adsorption configuration offers an open area to the vacuum 6 7 side. This gives the opportunity to manipulate the spin-state using on-top adsorption of alkali 8 9 atoms or molecules to induce electron doping. Such studies have led to the emerging research field 10 11 of on surface-magnetochemistry.26,27 12 13 In many cases, interfacial properties result from the hybridization of the highly directional dz2 - 14 15 orbital of the core metal atom with those of the substrate. Yet, for other MPc/inorganic interfaces, 16 17 coupling can arise from hybridization with the π (pz) orbital of the Pc ligand, as well. The filling of 18 19 the π-orbital by charge transfer modifies the spin state of the molecule in comparison with the free 20 21 one. As an example, it was shown that the no-spin bearing NiPc molecule acquires a 1/2-spin of 22 23 π-origin due to charge transfer upon adsorption on a Ag(100) single-crystalline surface.28,29 This 24 25 has been demonstrated by revealing the spectral signature which is typical of a 1/2-spin object in 26 27 interaction with an electron bath namely an Abrikosov-Suhl resonance of the differential conduc- 28 29 30–35 tance in the vicinity of the Fermi level EF using LT-STM/STS resulting from Kondo effect. 30 31 On the same Ag(100) surface, CuPc which possesses a 1/2-spin state in its ground state, acquires 32 33 an extra π-electron. In this last case, the molecule behaves as a two-spin system in contact with 34 35 conduction electrons leading to an interesting many-body phenomenon: a triplet-singlet Kondo 36 37 effect.28 Alternatively, STM and UPS measurements recorded on the CoPc/Ag(111) interface have 38 39 unravelled another more complex donation/backdonation scenario: electron injection occurs from 40 41 the Ag substrate to the Co-3d orbitals that is accompagnied with a back donation of electrons from 42 43 the π-orbitals to the substrate.36 44 45 Recently, it was shown by UPS that the metal-free phthalocyanine 2HPc which is a no-spin 46 47 bearing molecule in the gas phase can also become charged upon adsorption on Ag(111).37–39 We 48 49 can therefore wonder if this system could also exhibit a Kondo effect as in the case of NiPc or 50 51 CuPc on Ag(100). The implication of such a result would be that a purely organic phthalocyanine 52 53 adsorbed on a silver surface could give rise to interesting magnetic properties without the involve- 54 55 ment of 3d transition metal nor 4f rare-earth central ions as in previous studies. Indeed, only very 56 57 58 59 4 60 ACS Paragon Plus Environment Page 5 of 44 The Journal of Physical Chemistry

1 2 3 few examples of pure organic systems presenting Kondo effect have been reported so far.40–45 4 5 Despite the increasing attention devoted to the abovementioned hybrid MPc/inorganic inter- 6 7 faces, however the spin-polarized electronic properties of the 2HPc/Ag(111) interface had been 8 9 underlooked.37–39,46 Yet, this particular system could provide a means of investigating many-body 10 11 phenomena such as Kondo effect in many aspects,e.g. its intensity, spatial extension,47 quantum 12 13 44 criticality when a 1/2 spin in π orbital is involved rather than a 3d or 4f-orbital. It would therefore 14 15 broaden our knowledge on magnetism as well as on many-body physics at the nanometer scale and 16 17 at low dimensionality.40–43,47–62 Moreover, as illustrated above, a full description of the hybrid in- 18 19 terfaces must necessarily consider both interfacial sides. On the metal side, sizeable modifications 20 21 can also be expected as already observed with other π-conjugated molecules at the interface with 22 23 copper or silver surfaces.39,63–67 In the case of 2HPc/Ag(111), it has been shown that upon molec- 24 25 ular adsorption, an interfacial state forms originating from the well-known bare metal Shockley 26 27 state.39,68,69 Those hybrid interfacial states (HIS) are of particular importance for the understand- 28 29 ing of contact in organic semiconductor devices and their origin are not yet fully understood63,67. 30 31 Therefore, such a study might also unravel insights on the Ag hybrid interface state. 32 33 In this framework, we have investigated by LT-STM/STS, UPS and DFT, the electronic struc- 34 35 ture of adsorbed 2HPc on Ag(111) for single molecules as well as for two-dimensional self- 36 37 assembled molecular networks. We demonstrate the emergence of a Kondo effect regardless of the 38 39 coverage in the submonolayer regime. We think that this kind of hybrid interface with molecules 40 41 comprising only C, H and N-atoms may thus be envisaged to design metamaterials composed of 42 43 abundant and environmental-friendly compounds. 44 45 46 47 48 METHODS 49 50 51 The experiments were carried out in two ultra-high vacuum systems with a base pressure of 1 × 52 −10 53 10 mbar. One was equipped with a low-temperature Omicron STM operating at 5 K. The other 54 55 one was equipped with a ScientaOmicron DA30-L hemispherical analyzer and a monochromatized 56 57 58 59 5 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 6 of 44

1 2 3 He (hν = 21.2 eV) UV source for ARPES. As beam damage of the molecular layers was observed 4 I 5 on a timescale of about 20 min, duration of the measurements and sample position were adjusted 6 7 accordingly. Due to angular distribution of the photoemission intensity, ultra-violet photoemission 8 9 spectra were recorded at an emission angle of 45◦.54,70,71 Note that, in this geometry, the Shockley 10 11 surface state of Ag(111) lying in the L-gap around the Γ point of the surface Brillouin zone is not 12 13 detected69. All spectra were normalized to the count rate at the binding energy of 0.4 eV.LEED was 14 15 available on both UHV set-ups to characterize structural properties at a sample temperature of 80 K. 16 17 The Ag(111) single crystal was cleaned by repeated cycles of Ar+ sputtering at an energy of 1 keV 18 19 followed by an annealing to 800 K. 2HPc molecules were purchased from Aldrich and purified by 20 21 column chromatography (silica gel, dichloromethane) prior to use. They were evaporated from a 22 23 Knudsen cell at 565 K onto the sample held at room temperature. The STM images were recorded 24 25 at a tunneling current It and a bias voltage Vb where the sign corresponds to the voltage applied to 26 27 the sample. STS was acquired with a PtIr scissors-cut tip and a lock-in detection in open feedback 28 29 loop conditions at a frequency of 1100 Hz and a peak-to-peak bias voltage modulation for high- 30 31 resolution STS of 5 mV. 32 33 The electronic structures were obtained from DFT calculations with the VASP package72–75 34 35 which uses the plane-augmented wave scheme76,77 to treat core electrons. Perdew-Burke-Ernzerhof 36 37 (PBE) functional78 was used as an approximation of the exchange-correlation electronic term, 38 39 but PBE-D3 scheme79,80 was used firstly to optimize the geometry since Huang;et al. have ad- 40 41 dressed the importance of van der Waals corrections when dealing with Pc-metallic surfaces in- 42 43 teractions.81 The kinetic energy cutoff was set to 400 eV, with a gaussian smearing of 0.05 eV 44 45 and using a 2×2×1 k-points grid to optimize the structures with a convergence force criterium of 46 47 0.01 eV/A˚ for all allowed atoms to relax. For density of states (DOS) determinations, a 3×3×1 k- 48 49 points grid was used in conjunction with the tetrahedron method with Blochl¨ corrections scheme.82 50 51 We have confirmed that a 12 layers-slab with a vacuum height of more than 20 A˚ was necessary 52 53 to describe accurately the intrinsic Shockley surface state of the Ag (111) surface,83 see Fig. S3 54 55 for a band structure representation in the Supporting Information. As expected, two surface states 56 57 58 59 6 60 ACS Paragon Plus Environment Page 7 of 44 The Journal of Physical Chemistry

1 2 3 are provided by the slab approach and the average energy of the two surface states (−86 meV) is 4 5 relatively close to the experimental energy value (−63 meV).69 To mimic the individual molecule 6 7 case, as well as to describe the C-phase, see definition below, a (7×7) and commensurate ([5 0; 3 8 9 6]) cell was used respectively. 10 11 12 13 14 RESULTS AND DISCUSSION 15 16 17 Structural Properties 18 19 20 The growth of 2HPc on Ag(111) in the submonolayer regime has been studied in previous works. 21 22 Three distinct phases form as a function of the coverage.38 For self-assemblies, the unit cells have 23 24 been determined.38 Yet, the adsorption geometry and especially the azimuthal orientation of the 25 26 molecules has only succinctly been addressed and remains elusive, particularly in self-assemblies. 27 28 Nevertheless, this information is of paramount importance to elucidate the electronic properties of 29 30 the metal-organic interface. Thanks to STM images with intramolecular resolution, we were able 31 32 to tackle this key point as will be explained below. 33 34 According to Kroger;et¨ al., at low molecular densities, 2HPc form disordered gas-like phases, 35 36 referred as G-phases where the intermolecular distance changes with coverage due to substrate- 37 38 mediated intermolecular repulsive interaction.38 Upon increasing coverages to 0.5-0.89 monolay- 39 40 ers at low temperature, they form a commensurate phase with the substrate referred as C-phase, 41 42 characterized by a nearly-square unit cell which epitaxy matrix is [5 0;3 6].38 Our LEED patterns 43 44 displayed in Fig.1(a) and Fig.2(a) exhibiting a diffuse ring around the [00] specular beam and sharp 45 46 spots, respectively are in line with those previous results. Sperl;et al. showed that 2HPc adsorb flat 47 48 onto the Ag(111) substrate i.e. the Pc ligand plane adsorbs parallell to the surface plane.46 The line 49 50 formed by the two pyrrolic hydrogen atoms inside the porphyrazine core which will be referred 51 52 to ”the 2H-axis” hereafter, was shown to be azimuthally oriented perpendicular to h011¯i cristallo- 53 54 graphic directions of the substrate. This was later confirmed by Kugel¨ et al.84 In C-phase, Bai;et 55 56 al. measured by STM an azimuthal angle between one vector of the unit cell and the molecular 57 58 59 7 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 8 of 44

1 2 3 axis of about 60◦ ± 3◦ without specifying the orientation of the 2H-axis.85 In the present work, 4 5 we determine the orientation of single molecules by comparing their STM appearance in Fig.1(b) 6 7 with the HOMO of the singly charged 2HPc anion calculated in ref.86 for which the splitted lobes 8 9 are perpendicular to the 2H-axis. The specific choice of comparison with the anion is justified by 10 11 the fact that the molecule gets negatively charged when adsorbed as we will discuss below. The 12 13 direction of the 2H-axis of the molecules is highlighted by blue lines in Fig.1(b). Our STM images 14 15 reveal that 2HPc not only adsorb with 2H-axis perpendicular to h011¯i directions (i.e. along h21¯1¯i 16 17 directions) as observed in literature46,84 but also parallell (within an angle error of ±2◦). Molecules 18 19 marked as C and C’ in Fig. 1(b) are representative of the two configurations. Likewise in Fig. 1(c), 20 21 molecules A and B adsorb in the same configuration as molecule C. In their recent work, Kugel¨ and 22 23 coworkers demonstrate that the only way to obtain a 2H-axis along one of the h011¯i direction is to 24 25 start with a molecule which 2H-axis is perpendicular to one h011¯i direction and induce tautomer- 26 27 ization by applying a bias voltage pulse U such that |U| > 0.45 V when the tip is located above the 28 29 molecule. It is claimed that the absence of 2H-axis along h011¯i directions can be explained by a 30 31 high difference in energy with the configuration where the 2H-axis lies perpendicular to h011¯i. 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 8 60 ACS Paragon Plus Environment Page 9 of 44 The Journal of Physical Chemistry

1 2 3 4 5 a b 6 C 7 8 9 10 11 12 13 14 C' 15 16 17 18 19 20 21 22 c d 23 2 1 nm 24 α 25 26 27 28 A 29 B 30 31 e 32 β 33 C' 34 1 35 [112] 36 3 37 38 [110] 39 40 41 Figure 1: The Structure of 2HPc/Ag(111) in G-phase. (a) LEED pattern recorded at an electron 42 43 energy of 15 eV. (b,c) High-resolution STM topographic images of 2HPc molecules on Ag(111). 44 45 Tunneling bias conditions: Vb = 1 mV, It = 200 pA. The close-packed h011¯i directions of the 46 47 Ag(111) are indicated by white lines in (b). The numbered crosses in (c) indicates the location 48 49 where the STS spectra displayed in Fig.3(a) and Fig.5(a) were recorded. Cyan lines in (b) indicate 50 51 the direction of the 2H-axis (see text) of the molecules. (d,e) Top views of the DFT calculated 52 53 relaxed most stable adsorption geometries. 54 55 56 57 58 59 9 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 10 of 44

1 2 3 On the contrary, in our work, we find two adsorption orientations that can simply be explained 4 5 by molecules that could rotate in the ligand plane. Fig.1(d,e) displays the two simulated most 6 7 stable adsorption configurations α and β corresponding to 2H perpendicular and parallell to h011¯i 8 9 directions, respectively in good agreement with our observations. The difference of adsorption 10 11 energy between these two geometries of minimum energy is only of about 0.2 eV. Molecules A, B 12 13 and C would therefore correspond to the α-case (Fig.1(d)), whereas molecule C’ would correspond 14 15 to the β-case (Fig.1(e)). From these models, one can see that the transition from one geometry to 16 17 the other can occur simply via a rotation of the molecule by 30◦. In our work, we found compelling 18 19 evidences that such rotation can happen. In Fig. S4 in the Supporting Information, two time 20 21 sequences issued from pairs of STM images recorded successively show molecules that rotate 22 23 without external stimuli other than the scanning tip governed by the tunneling parameters Vb,It 24 25 with Vb much smaller than the bias voltage threshold necessary to induce tautomerization. For the 26 27 particular coverage shown in Fig.1(b), the ratio of parallell to perpendicular configurations is 1/3 28 29 leading to the conclusion that the perpendicular geometry is the most stable one. 30 31 In the STM image of the C-phase displayed in Fig. 2(b), each molecule exhibits a pair of 32 33 splitted lobes. Assuming that they are perpendicular to the 2H-axis as in the case of molecules in 34 35 G-phase, the azimuthal angle δ with respect to the close-packed directions of Ag(111) as sketched 36 37 in Fig. 2(b) can be determined. The measured value of δ is 65◦ ± 3◦ similar within the angle 38 39 error to the azimuthal orientation of the experimentally most stable adsorption configuration α. 40 41 The structural model of the molecules self-organized as a C-phase obtained by DFT calculations 42 43 is shown in Fig.2(c). The angle δ = 62◦ is in excellent agreement with the experimental value 44 45 validitating this model to further extract the projected density of states (PDOS). The extra insight 46 47 we get from this STM analysis is that molecules in the less stable configuration such as molecule 48 49 C’ in Fig.1 (b) undergo an azimuthal rotation of about 30◦ upon self-assembling. Therefore, one 50 51 expects the ratio between the two configurations to increase when increasing the coverage in favor 52 53 of α configuration. However, this analysis is out of the range of this paper. 54 55 56 57 58 59 10 60 ACS Paragon Plus Environment Page 11 of 44 The Journal of Physical Chemistry

1 2 3 4 a b c 5 6 δ 7 8 9 10 11 12

13 [112] 14 1 nm 15 [110] 16 17 18 Figure 2: The Structure of 2HPc/Ag(111) in C-phase. (a) LEED pattern recorded at an electron 19 20 energy of 14 eV. (b) Corresponding STM topographic image. Tunneling bias conditions: Vb = 21 22 −1.8 V, It = 200 pA. The close-packed h011¯i directions of the Ag(111) are indicated by a black 23 24 star. Cyan lines indicate the direction of the 2H-axis of the molecules (see text). (c) Top view of 25 26 the simulated relaxed adsorption geometry. Rectangles in dashed line represent the unit cells in (a) 27 28 reciprocal and (b,c) direct space. 29 30 31 32 Kondo effect in single molecules 33 34 35 In previous works, it was demonstrated from UPS and two-photon photoemission (TPPE) mea- 36 37 surements that charge transfer occurs from the Ag(111) substrate to the Pc ligand of 2HPc.38,39 In 38 39 the C-phase, this was evidenced by the occupancy of the LUMO orbital upon adsorption resulting 40 41 in a state located at an energy of −0.15 eV and which has been called former-LUMO (F-LUMO) in 42 43 reference to the LUMO state of the free molecule. In addition, an unoccupied HIS develops from 44 45 the former Shockley-type electronic state of the bare Ag(111) surface. It originates from the steep- 46 47 ening of the surface potential upon molecular adsorption. This nearly-free electron state has been 48 39 49 characterized by a band onset located at an energy of +0.23 ± 0.03 eV above EF . Knowing the 50 51 abovementioned results, one can reasonably raise the following question: would self-assembled 52 53 2HPc behave like 1/2-spin in contact with a free electron bath possibly giving rise to Kondo ef- 54 55 fect? Would this effect persists for single molecules? To elucidate the arising of a Kondo effect for 56 57 58 59 11 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 12 of 44

1 2 3 a single molecule as well as for a self-assembly, we performed STS and UPS on G and C-phases. 4 5 First, we address the Kondo effect in single molecules using STS and UPS. STS spectra in the 6 7 enery range around E are reported in Fig.3(a). They were recorded with the STM tip located above 8 F 9 molecules A, B and C’ displayed in Fig.1(c). All tunneling spectra show two main characteristics: 10 11 (i) a sharp electronic resonance in the close vicinity of EF , labeled κ in Fig.3(a), (ii) a conductance 12 13 peak located at about +52 meV, labeled ν. As no molecular nor substrate’s state is expected in a 14 15 range of ±10 meV around EF, we can, as a first guess, reasonably attribute the resonance at EF to 16 17 Kondo effect. Yet, as other phenomena could lead to the formation of a peak in the differential 18 19 conductance spectrum next to EF, a magnetic field or temperature dependency of the full width at 20 21 half maximum (FWHM) of the resonance should be recorded and compared to laws governing the 22 23 effect in order to unambiguously attribute its origin to Kondo effect.87,88 Alternatively, UPS can 24 25 be used since a typical spectrum of a Kondo system exhibits a sharp resonance at EF at tempera- 26 27 87,89,90 tures below the Kondo temperature TK . Upon increasing temperature, this peak is expected 28 29 to broaden and decrease in intensity.91–93 Such a relationship with temperature is what is experi- 30 31 mentally observed as displayed in Fig. 3(b) showing UPS spectra recorded at temperatures of 9 K, 32 33 80 K and 285 K. At T= 9 K, a narrow and intense peak is observed at EF . At T= 80 K, the peak is 34 35 broader and its intensity is strongly reduced to finally almost vanish at T= 285 K. 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 12 60 ACS Paragon Plus Environment Page 13 of 44 The Journal of Physical Chemistry

1 2 3 4 a b 5 κ 6 7 ν 8 1 9 10 11 A 12 13 14 B 15 16 17 bare Ag(111) 18 C' 19 20 21 22 23 24 25 26 27 Figure 3: Electronic properties of 2HPc/Ag(111) in G-phase. (a) Dotted lines are dI/dV spectra 28 29 recorded with the tip on top of molecules labeled A,B and C’ in Fig.1(c). Set point is: Vb = 1 mV, 30 th 31 It = 200 pA. The dashed blue line is a dI/dV spectrum recorded on a 4 molecule (not in Fig.1(c)). 32 33 Set point : Vb = 25 mV, It = 200 pA. The full grey line was recorded further away from the 34 35 molecules on bare Ag surface at the position indicated by the grey cross in Fig. 1(c). The Fano fits 36 37 represented by the black lines yields: A: q = 1.73, K = −7.99 meV and Γ = 11.78;B: q = 7.22, 38 39 K = −6.25 meV and Γ = 12.39;C’: q = 54, K = −1.16 meV and Γ = 9.8. A vertical shift 40 41 was added for clarity. (b) UPS spectra recorded at T= 9 K, 80 K and 285 K and on bare Ag(111)

42 ◦ 43 substrate at T= 9 K (black line) and at an emission angle of 45 . 44 45 46 The resonance observed in UPS spectra can not be assigned to any state of the substrate since 47 48 the UPS spectrum recorded under the same experimental conditions on the bare Ag(111) surface 49 50 is flat next to E as shown as a black line in Fig.3(b). Thanks to the concomitance of a resonance at 51 F 52 E in the STS spectrum and the temperature behavior of the photoemission feature at E , one can 53 F F 54 now unambiguously attribute it to a Kondo resonance. 55 56 The next feature of the STS spectra to be discussed is the peak ν at E = 52 ± 5 meV. This side 57 ν 58 59 13 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 14 of 44

1 2 3 feature appears as a resonance and its intensity with respect to the zero-bias one depends on the 4 5 tip location. Upon certain tip conditions (see supplementary information for further details), the 6 7 Kondo resonance is not observed. In those cases, the dI/dV spectrum has an upside down hat shape 8 9 as depicted in Fig.3(a). The two step-edges are located at about ±Eν which is the standard line- 10 11 shape observed when inelastic processes corresponding to vibrational excitation energies of Eν get 12 13 activated. However, the side feature appears more as a resonance than as a step. According to,94–98 14 15 it can be understood as originating from the splitting of the zero-bias resonance resulting from 16 17 the electron-vibron coupling. Other Kondo organic/inorganic systems exhibit as well, such peaks 18 19 of vibronic nature.28,29,40,99,100 In particular, conductance spectra recorded over CuPc and NiPc on 20 21 Ag(100) exhibit such fingerprints at comparable excitation energies28,29 and might correspond to 22 23 the activation of torsion modes.101 24 25 32,33 According to Refs., TK can be roughly determined by fitting the Kondo resonance with a 26 27 Fano function lineshape expressed as, disregarding the instrumental broadening:102,103 28 29 30 2 (q + ) eV − k 31 2 ;  = (1) 32 (1 +  ) Γ 33 34 35 36 37 where Γ is the 1/2 FWHM such that Γ =kBTK, q the Fano asymmetry parameter and k the energy 38 39 shift of the resonance from TK . 40 41 As an example, the fitting results of the dI/dV spectra recorded at the center of molecules A, 42 43 B and C’ are reported in Fig. 3(a) as black lines. Another set of 4 measurements is shown in 44 = 130 20 q 45 Fig.S1. The mean fitted TK is TK K with a standard deviation of K and ranges from 46 0.3 50 47 to more than . The high q values indicates that the tunneling process occurs preferentially 48 through the molecular orbital than to the conduction-electron continuum. Strong lineshape and 49 50 FWHM variations are observed between the molecules. The possible influence of the adsorption 51 52 configuration will be discussed below in relation to DFT calculations. 53 54 55 56 57 58 59 14 60 ACS Paragon Plus Environment Page 15 of 44 The Journal of Physical Chemistry

1 2 3 Kondo effect in self-assembly 4 5 6 To investigate the arising of a Kondo effect in the commensurate self-assembly, STS and UPS 7 8 were carried out. Results are displayed in Fig.4. To start with, STS was recorded over a large 9 10 bias voltage range to investigate the overall electronic properties of the interface. Whereas UPS 11 12 probe occupied states only, STS gives access to energy regions above and below Fermi level in 13 14 a single-shot experiment enabling a direct comparison with UPS and TPPE spectra of previous 15 16 studies.38,39 The differential conductance dI/dV spectrum in Fig.4(a) reveals distinct peaks that can 17 18 unambiguously be assigned. Peaks located at about −0.12 V and −1.2 V are attributed to F-LUMO 19 20 and HOMO, respectively according to ref.38,104 At positive bias, the step-like feature which is typ- 21 22 ical of a nearly-free electron two-dimensional gas is assigned to the HIS. Its edge is located at 23 24 +0.23 ± 0.01 V, in very good agreement with the band edge measured by TPPE.39 The F-LUMO 25 26 and HOMO states are also detected by UPS as indicated in Fig.S5 in the Supporting Information. 27 28 As already explained in ref.,38 the presence of an occupied F-LUMO state results from the charge 29 30 transfer from the Ag surface to the molecule. Hence, both our STS and UPS experiments show 31 32 that the molecule is negatively charged in agreement with these previous results. As well as for 33 34 single molecules, a resonance at EF was obtained using STS and UPS techniques. Bringing for- 35 36 ward the same arguments as for the case of single molecules, one can conclude that this resonance 37 38 is the experimental signature of the Kondo effect. A high-resolution STS spectrum in Fig.4(b) ex- 39 40 hibits, as in the case of single 2HPc, an extra peak at about 50 meV leading to the conclusion that 41 42 electron-vibron coupling is not hindered by intermolecular interactions inside the self-assembly 43 44 thus resulting in a vibrational Kondo effect. Once again, this is corroborated by the inelastic elec- 45 46 tron tunneling spectrum shown in blue line in Fig.4(b) recorded over the Pc ligand and exhibiting 47 48 the characteristic symmetric two-step like lineshape. The Kondo temperature TK obtained by fit- 49 50 ting the STS spectra recorded over 7 molecules inside the supramolecular network ranges from 51 52 57 to 69 K as displayed in Fig. S2. It is about twice smaller than for single molecules. Possible 53 54 explanations for the difference between the two phases will be discussed in section V. 55 56 57 58 59 15 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 16 of 44

1 2 3 Density of states calculated by DFT 4 5 6 In order to correlate spectroscopic peaks observed in STS and UPS spectra with the molecular 7 8 electronic structure, we have computed the DOS of 2HPc in C-phase and projected it onto atomic 9 10 orbitals. As shown in Fig.4(d), this PDOS is dominated by pz orbitals. One peak below −1 eV 11 12 corresponds to the HOMO state. Crossing EF, another prominent peak of pz character corresponds 13 14 to the F-LUMO state. Although the calculated energy position of this state is upshifted compared 15 16 to experiments due to a well-known drawback of standard DFT calculations that do not properly 17 18 account for HOMO-LUMO gap, it remains in good agreement with experimental data and supports 19 20 the identification of the electronic states of the dI/dV spectrum of Fig.4(a). 21 22 A net charge transfer of 0.32e− of sp-orbital character occurs from the substrate to the adsorbate 23 24 region. Again, this value is only qualitative since charge transfer estimated from DFT calculations 25 26 depends critically on the computational details.105 Spin density distributions have been calculated 27 28 as well and are shown in Fig.4(e). Obviously, the no spin bearing free 2HPc molecule does not 29 30 exhibit any spin density (Fig.4(e),left). However, upon adsorption on Ag(111), (Fig.4(e),right) 31 32 we observe a distribution of the spin electron density in the inner region of the molecule situated 33 34 mostly on the pyrrole parts. This is very similar to what is observed for the anionic species as 35 36 displayed in Fig.4(e) (center panel). The DFT results confirm the scenario that the origin of the 37 38 Kondo effect lies in the filling of the molecular π states occuring upon adsorption on the silver 39 40 surface. 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 16 60 ACS Paragon Plus Environment Page 17 of 44 The Journal of Physical Chemistry

1 2 3 4 a b 5 6 HOMO 7 8 HIS 9 10 F-LUMO 11 12 13 14 15 c 16 d 17 18 19 20 21 22 23 24 25 26 27 e 28 bare Ag(111) 29 30 31 32 33 34 35 36 37 38 Figure 4: Electronic properties of 2HPc/Ag(111) in C-phase. (a,b) dI/dV spectra recorded over 39 40 the center of one molecule in the self-assembly. Set point are (a) Vb = −1 V, It = 100 pA, (b) 41 42 Vb = 1 mV, It = 200 pA for top curve and Vb = 50 mV, It = 200 pA for bottom curve. A vertical 43 44 shift was added for clarity. The Fano fit represented by the black line superimposed to the top curve 45 46 in (b) yields: q = 21, K = −0.35 meV and Γ = 5.0. (c) UPS spectra recorded at T= 9 K, 80 K, 47 ◦ 48 285 K and on bare Ag(111) substrate at T= 9 K at an emission angle of 45 . (d) Computed density 49 50 of states projected (PDOS) onto atomic orbitals of 2HPc on Ag(111), (e) from left to right: spin 51 52 density distribution of neutral, anionic 2HPc species in the gas-phase and adsorbed on Ag(111). 53 54 The sign of the spin is indicated in yellow/cyan. The isovalue for the electronic spin density is 55 −7 ˚ 3 56 roughly 10 e/A in both cases. 57 58 59 17 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 18 of 44

1 2 3 Electronic surface properties of Ag(111) 4 5 6 To utterly describe the organometallic interface, the Ag properties must be investigated as well. 7 8 Moreover, their knowledge will help us better understand the Kondo effect. In the following, 9 10 we are interested in the modifications of the Ag surface properties when a very small amount of 11 12 molecules is adsorbed such as in Fig. 1(b). To begin with, we have recorded a dI/dV curve on 13 14 pristine Ag(111) prior to molecular adsorption. It is shown as a grey dashed curve in Fig.5(a). 15 16 Its lineshape and energy onset is typical of the well-known Ag Shockley surface state.68,106,107 Af- 17 18 ter molecular adsorption at low coverage, a dI/dV spectra have been recorded on the uncovered 19 20 Ag surface in between molecules. They are quite different compared to the one observed on the 21 22 pristine Ag surface and they depend strongly on the location where they were recorded. Spectra 23 24 2 to 4 are given in Fig.5(a) as examples. The spectra can be described as a step-like lineshape 25 26 with prominent peaks superimposed to it. As will be explained below, those extra peaks are eigen- 27 28 states resulting from electron confinement. STM and conductance maps are shown in Fig.5(c-f). 29 30 A strong spatially textured background between the molecules is observed for energies eVb above 31 32 the Ag Shockley state energy onset E0. This is illustrated by the STM image recorded at −40 meV 33 34 in Fig.5(b). The effect is even better evidenced on the three conductance maps shown in Fig.5(c-f). 35 36 Indeed, whereas the dI/dV map recorded at −0.1 V in (c) shows a constant and homogeneous back- 37 38 ground, strong variation of the conductance is observed on the flat areas of bare Ag between the 39 40 molecules for the map at eVb > E0 in Fig.5(d-f). Moreover, it depends strongly on the energy. Due 41 42 to these characteristics, we attribute these observations to the formation of standing wave patterns 43 44 resulting from the scattering of the 2D nearly free electron surface state of Ag. In other words, 45 46 2HPc molecules act as electron scatterers of nanometric size. 47 48 49 50 51 52 53 54 55 56 57 58 59 18 60 ACS Paragon Plus Environment Page 19 of 44 The Journal of Physical Chemistry

1 2 3 4 a b c 5 6 7 8 9 10 4 11 12 3 13 2 14 15 16 d e f 17 18 19 20 21 22 23 24 25 26 27 2 nm 28 29 30 Figure 5: Electronic properties of Ag in G-phase. (a) dI/dV spectra recorded on Ag(111) between 31 32 molecules in solid lines and on a pristine Ag(111) surface in dashed line. Numerical labels 2 to 4 33 34 correspond to the position of the tip marked by a matching colored cross in Fig.1(c) and Fig.S4(b). 35 36 Tunneling bias conditions: Vb = −1.8 V, It = 200 pA. (b) STM topographic image. Tunneling bias 37 38 conditions: Vb = −40 mV, It = 200 pA, (c-f) dI/dV maps recorded at −100 mV,−40 mV,+10 mV 39 40 and +30 mV, respectively. Tunneling current It = 200 pA. 41 42 43 44 On those maps, the most surprising feature is the one observed at the center of the image 45 46 as pointed by the green arrow in Fig.5(d-f) that is reminiscent of electron confinement in closed 47 48 2D artificial hexagonal Ag nanovacancies,108 nanoislands109–111 or even 2D porous molecular net- 49 50 works adsorbed on coinage (111) metal surfaces.112 What is remarkable is that, contrary to those 51 52 2D resonators that are closed structures delimited by hard walls, the pattern of this current work 53 54 have been obtained with only 4 or 5 molecules that are 2 to 5 nm apart and thus forming an open 55 56 structure. In the abovementioned examples of electron confinement, the potential barrier is con- 57 58 59 19 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 20 of 44

1 2 3 sidered as continuous whereas it is obviously discontinuous in the present work. Shchyrba;et al. 4 5 showed previously partial confinement insides molecular pores with missing borders.113 Pennec;et 6 7 al. showed confinement of the Ag surface state in a U-shaped cavity formed of linear molecular 8 9 walls. However, to the best of our knowledge, the formation of an open walls molecular confining 10 11 cavity has not been evidenced yet and therefore deserves a keen interest. 12 13 Scattering of the surface state of (111) surfaces of coinage metals by π- conjugated molecules 14 15 have been previously observed.114–118 When self-assembled in specific ways such as in Ref.117 or 16 17 organized in metal-organic frameworks, molecules can act as scattering walls for electrons of a 18 19 two-dimensional electron gas. Quantum well arrays can thus be formed with well-defined molec- 20 21 ular boundaries. Single π-conjugated molecular scatterer has been modeled114 as a collection of 22 23 atomic total absorbers at the position of the carbon atoms using multiple scattering expansion as de- 24 25 velopped for quantum corrals.119 In molecular porous networks, scattering molecules are described 26 27 in the framework of the boundary elements method where molecular boundaries correspond to con- 28 29 stant rectangular potential.116 The case of 2HPc on Ag(111) at low coverage is singular in the sense 30 31 that it represents an intermediate case between the two situations cited above. Therefore, to explain 32 33 the patterns observed in our work, a complementary theoretical approach might be necessary and 34 35 further experimental investigations are required. This demonstrates that the 2HPc/Ag(111) inter- 36 37 face offers the possibility to explore new fundamental aspects of quantum physics i.e. the electron 38 39 scattering by an object of nanometric size composed of a collection of atomic-like scatterers co- 40 41 valently bonded. Besides, it holds promise for the design of tunable low-dimensional electron 42 43 resonator. As will be discussed in section V, quantum confinement might have a non negligible 44 45 impact on the Kondo effect. 46 47 48 49 Discussion 50 51 52 In this section, we would like to address the mechanism behind the variation of TK within the G- 53 54 phase as well as with molecular density. In previous sections we have shown that TK for single 55 56 molecules can vary by about several tens of K. In addition, it is about twice smaller in the C-phase 57 58 59 20 60 ACS Paragon Plus Environment Page 21 of 44 The Journal of Physical Chemistry

1 2 3 as compared with the G-phase. 4 5 Prior to that, the question arises whether the UPS spectra of the two phases corroborate STS 6 7 results. To answer it, a quantitative extraction of T would be necessary. However, such analysis 8 K 9 requires a temperature dependence of the linewidth of the Kondo peak together with theoretical 10 11 calculations of the spectral function.120 Solely based on (i) the width and intensity of the Kondo 12 13 resonance which are larger for the C-phase than for the G-phase, (ii) theoretical descriptions of 14 15 the variation of the spectral function87 and (iii) experimental photoemission intensity of heavy 16 17 87,89,90,120 fermions systems as a function of TK , we would conclude that the C-phase has a higher 18 19 TK than the G-phase. This would contradict our STS measurements. However, in the present case, 20 21 a direct parallel with those available works on strongly correlated materials is not totally valid since 22 23 the π-orbital is involved instead of 4f states. In addition, here, electron-vibron coupling related 24 25 to vibrational energies very close to EF is present. The presence of such a coupling might result 26 27 in satellite Kondo resonances at energies related to Eν and therefore might contribute to the width 28 29 98 of the UPS spectra in the close vicinity of EF . The intensity of the coupling is likely to vary 30 31 between the two phases thus affecting differently the intensity and the width of the corresponding 32 33 resonances. Further theoretical work is required to properly describe molecular vibrational Kondo 34 35 effect and to analyze experimental UPS lineshape when charge-vibron coupling is present in a 36 37 Kondo system. As a conclusion, the following discussion can only be based on TK extracted from 38 39 STS. 40 41 The Kondo temperature inside the G-phase can be assumed to depend on the adsorption config- 42 43 uration.53 Nevertheless, it is not supported by our DFT calculations: adsorption heights and PDOS 44 45 are very similar for both α and β configurations. Comparing G and C-phase, a possible explanation 46 47 could lie in the effect of intermolecular interactions. It has been shown in some Pc supramolecular 48 49 assemblies that ligand-ligand interaction could engender a lifting of the molecules, reducing the 50 51 28,56 molecule-substrate coupling and thus, TK . However, according to our DFT calculations, the 52 53 adsorption height varies only minutely between the two phases. In addition, as shown in Fig.S6 54 55 in the Supporting Information, the PDOS of the 2HPc molecule on Ag(111) at low concentration 56 57 58 59 21 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 22 of 44

1 2 3 is very similar to the one of molecules in the C-phase reported in Fig.4(d). The position of the 4 5 F-LUMO varies only a little and a charge transfer of 0.27 electrons has been extracted. This is 6 7 very close to the value of 0.32 electrons obtained for the self-assembly. This supposes that the 8 9 coupling strength with the substrate doesn’t vary much upon formation of the C-phase and can not 10 11 account for the strong variation of TK . 12 13 The Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is an alternative origin. It is an 14 15 indirect spin-spin interaction mediated by the conduction electrons of the metal. Depending on 16 17 distance, it favours ferromagnetic or antiferromagnetic (AFM) alignments of single magnetic mo- 18 19 ments. It has been shown that an interplay between the Kondo effect and the RKKY interaction 20 21 exists in supramolecular assemblies, as well.52,62 The width of the Abrikosov-Suhl resonance is 22 23 strongly affected or even suppressed due to the magnetic coupling between the spins. More specif- 24 25 ically, FM RKKY interaction sharpens the resonance and, on the other hand, the AFM RKKY 26 27 broadens it.121 Unfortunately, it is very challenging to test the assumption whether RKKY inter- 28 29 action is responsible for the reduction of TK in the self-assembly. Indeed, in order to demonstrate 30 31 it, a thought experiment would be to measure TK by STS as a function of the molecule-molecule 32 33 distance for a pair of molecules to mimic the conditions of the two-impurities Kondo problem.122 34 35 However, in such a case of a molecular pair, surface electrons would dominate the RKKY inter- 36 37 action due to their lower kF compared to bulk electrons and couldn’t be used to conclude on the 38 39 exchange coupling in the self-assembly for which the surface state has hybridized with a molecular 40 41 orbital to form the unoccupied HIS. Nevertheless, one can tentitatively apply the following formula 42 43 sin(2kF r) to predict the sign of the exchange coupling in the commensurate phase: J = J0 2 , where 44 (2kF r) 45 kF is the Fermi wave vector of the substrate and r, the distance between the spins. The latter pa- 46 47 rameter r can be estimated from the calculated lattice parameters of the rectangular unit cell (black 48 49 −1 123 dashed line in Fig. 2(c)) that are equal to 1.51 nm and 1.45 nm) and kF = 12.02 nm . Moreover, 50 51 we discard the influence of the second-nearest neighbors due to the fast decay of the exchange for 52 53 bulk electrons. The result gives an AFM coupling between nearest-neighbors molecules. This 54 55 would lead to an increase of TK compared with the single impurity case which contradicts our ex- 56 57 58 59 22 60 ACS Paragon Plus Environment Page 23 of 44 The Journal of Physical Chemistry

1 2 3 perimental findings. Therefore RKKY can not account for the decrease of T upon formation of 4 K 5 self-assembly. 6 7 The observed variation of T between the two phases could be alternatively explained consid- 8 K −1 9 ρ J ering that TK is directly proportional to exp F , where ρF is the substrate’s density of states at the 10 11 Fermi energy and J is the exchange coupling at the magnetic impurity.87 This relationship indicates 12 13 that when ρF is reduced, TK is reduced as a result. At low molecular concentration, the uncovered 14 15 substrate exhibits a Shockley surface state that participates to ρF . In the case of the C-phase, as 16 17 this state hybridizes with the LUMO state of the free molecule to form the HIS shifted above EF , 18 19 ρF is reduced in comparison with the isolated molecules and thus, would explain the decrease of 20 21 TK for the C-phase. 22 23 The influence of the surface state on the Kondo resonance width has been a topic of debate for 24 25 many years (see Ref.124 and references therein). Some works on Ag(111) have suggested a mi- 26 27 nor role for surface-state electrons in the Kondo effect.125 Only very recently, Li;et al. tackle this 28 29 controversy using LT-STM/STS on Co adsorbates on Ag(111).124 They unambiguously demon- 30 31 strate the influence of the surface state on the Kondo resonance by measuring the width of the 32 33 zero-bias peak as a function of the lateral distance to the impurity. The key point is that they ev- 34 35 idenced an oscillatory dependency as a function of the distance to the magnetic impurity which 36 37 periodicity matches the half Fermi wavelength of the Ag(111) surface state. Moro-Lagares;et al. 38 39 obtained experimentally and theoretically a nearly linear relationship between TK and the surface- 40 41 state contribution local density of states of the substrate.126 Besides, both works emphasize the 42 43 effect of quantum confinement of the surface state. In particular, it was evidenced that in a quan- 44 45 tum corral, the Kondo width can be significantly increased (more than three times).124 As at low 46 47 molecular density in the 2HPc/Ag(111) system, quantum confinement of the Ag surface state is 48 49 also observed, it probably also plays a significant role on the high value of TK and its variation in 50 51 the G-phase. The effect of the Shockley surface state on TK has also been observed on molecules 52 53 such as Co-tetraphenylporphirin on Cu(111).115 In this work, Iancu;et al. showed that molecules 54 55 exposed to Cu surface state electrons exhibit a higher TK than molecules inside a self-assembled 56 57 58 59 23 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 24 of 44

1 2 3 cluster. These results are in favor of our observation of a lower T upon self-assembly. 4 K 5 6 7 8 CONCLUSIONS 9 10 11 As a conclusion, we have studied the electronic properties of the metal-free phthalocyanine 2HPc 12 13 adsorbed on Ag(111) surfaces by means of scanning tunneling and photoelectron spectroscopies 14 15 and compared the experimental results with DFT calculations. We have evidenced a partial filling 16 17 of a molecular π state lying next to the Fermi level. The presence of this extra π-spin in the 18 19 molecule leads to the emergence of a Kondo effect at low temperature for single molecules as well 20 21 as for molecules arranged in a 2D self-assembly. 22 23 The fact that we deal with a metal-free phthalocyanine offer many future prospects. In other 24 25 words, the absence of a metal ion at the center of the molecule is the asset of this system. Indeed, 26 27 it has been shown that this metal free central cavity of 2HPc can be manipulated by STM in 28 29 many ways: tautomerization84, partial or total deshydrogenation or direct Ag metalation can be 30 31 induced.46 Therefore, one can envisage to investigate the influence of such modifications on the 32 33 Kondo physics. As an example, a 2HPc molecule can be transformed into an AgPc molecule in 34 46 35 the self-assembly and study the effect on TK . In that case, TK is likely to change through the 36 37 modification of the local coupling with the substrate via the up or down-lifting of the molecules or 38 39 the RKKY interaction between neighbouring molecules. 40 41 Besides the STM manipulation-based approach, local modification of the electronic and mag- 42 43 netic properties of 2HPc can be obtained by on- surface synthesis such as chemical doping or 44 26,85 45 metallation upon adsorption of alkali or metallic atoms under UHV. Using Li dopants, the 46 26 47 charge transfer could be locally modulated and the molecular spin could be tuned . In an- 48 49 other study, Bai;et al. showed that 2HPc react strongly with Fe atoms to form FePc molecules 50 85 51 on Ag(111). This on-surface metalation process was theoretically shown to be energetically fa- 52 127 53 vorable for M=Co, Ni, Mn on 2HPc/Ag(111). It would be particularly interesting to study the 54 55 Kondo physics in the MPc/2HPc hetero-molecular arrays as a function of MPc concentration. 56 57 58 59 24 60 ACS Paragon Plus Environment Page 25 of 44 The Journal of Physical Chemistry

1 2 3 Overall, any combination of the above cited manipulation strategies might be used. For these rea- 4 5 sons, this system offers an exceptionnaly rich playground for investigating the molecular Kondo 6 7 physics. 8 9 10 11 Supporting Information Available 12 13 STS spectra of G and C-phases and Fano fits. Calculated band structure of Ag. Sequence of 14 15 STM images showing in-plane molecular rotation. UPS spectra of G and C-phases. Computed 16 17 density of states projected onto atomic orbitals of 2HPc molecules on Ag(111) assembled in a 18 19 7 × 7 arrangement. Details on tip conditions for the observation of the Kondo resonance in STS 20 21 spectra. 22 23 This material is available free of charge via the Internet at http://pubs.acs.org. 24 25 26 27 28 References 29 30 31 1. Urtizberea, A.; Natividad, E.; Alonso, P. J.; Andres,´ M. A.; Gascon,´ I.; Goldmann, M.; 32 33 Roubeau, O. A Porphyrin Spin Qubit and Its 2D Framework Nanosheets, Adv. Funct. Mater 34 35 2018, 28,1801695–15. 36 37 38 2. Gaita-Arino,˜ A.; Luis, F.; Hill, S.; Coronado, E. Molecular Spins for Quantum Computation, 39 40 Nat. Chem. 2019, 11, 301–309. 41 42 43 3. Cavallini, M.; Gomez-Segura, J.; Ruiz-Molina, D.; Massi, M.; Albonetti, C.; Rovira, C.; 44 45 Veciana, J.; Biscarini, F. Magnetic Information Storage on Polymers by Using Patterned 46 Angew. Chem., Int. Ed. 2005 44 47 Single-Molecule Magnets, , ,888–892. 48 49 4. Cinchetti, M.; Dediu, V. A.; Hueso, L. E. Activating the Molecular Spinterface, Nat. Mater. 50 51 2017, 16, 507–515 52 53 54 5. Bogani, L.; Wernsdorfer, W. Molecular Spintronics Using Single-Molecule Magnets, Nat. 55 56 Mater. 2008, 7, 179–186 57 58 59 25 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 26 of 44

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1 2 3 TOC IMAGE 4 5 6 7 8 9 10 11 KONDO 12 STS UPS 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 - 32 e 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 39 60 ACS Paragon Plus Environment a The Journal of Physicalb Chemistry Page 40 of 44 κ 1 2 ν 3 1 4 5 6 7 8 9 A 10 11 12 B 13 14 15 16 bare Ag(111) 17 C' 18 19 20 21 22 23 ACS Paragon Plus Environment 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 41 of 44 The Journal of Physical Chemistry c a1 b 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 4 19 20 21 22 23 3 24 25 26 2 27 28 29 30 31 32 33 34 35 e 36d f 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 a b 2 3 4 C 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 C' 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 d 37 c 1 nm 38 2 39 α 40 41 42 43 44 45 46 47 A 48 49 B 50 51 52 53 54 e 55 56 β 57 58 C' 59 60 1 [112] 3 ACS Paragon Plus Environment [110] Pagea 43 of 44 The Journal of Physical Chemistry c 1 b 2 3 4 5 6 δ 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 [112] 26 27 28 29 ACS Paragon Plus Environment 1 nm 30 31 32 [110] 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 a The Journal of Physicalb Chemistry Page 44 of 44

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