Theoretical Insights into Unexpected Molecular Core Level Shifts

Letter Cite This: J. Phys. Chem. Lett. 2017, 8, 5718-5724

pubs.acs.org/JPCL

Theoretical Insights into Unexpected Molecular Core Level Shifts: Chemical and Surface Effects A. Sarasola,†,‡ M. Abadía,¶ C. Rogero,¶,‡ and A. Garcia-Lekue*,‡,§ †

Departamento de Física Aplicada I, UPV/EHU, Plaza Europa 1, E-20018, San Sebastián, Spain Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, E-20018 San Sebastián, Spain ¶ Centro de Física de Materiales (CSIC-UPV/EHU), Materials Physics Center MPC, Paseo Manuel de Lardizabal 5, E-20018 San Sebastián, Spain § IKERBASQUE, Basque Foundation for Science, E-48011, Bilbao, Spain ‡

S Supporting Information *

ABSTRACT: A set of density-functional theory based tools is employed to elucidate the influence of chemical and surface-induced changes on the core level shifts of X-ray photoelectron spectroscopy experiments. The capabilities of our tools are demonstrated by analyzing the origin of an unpredicted component in the N 1s core level spectra of metal phthalocyanine molecules (in particular ZnPc) adsorbed on Cu(110). We address surface induced effects, such as splitting of the lowest unoccupied molecular orbital or local electrostatic effects, demonstrating that these cannot account for the huge core level shift measured experimentally. Our calculations also show that, when adsorbed at low temperatures, these molecules might capture hydrogen atoms from the surface, giving rise to hydrogenated molecular species and, consequently, to an extra component in the molecular core level spectra. Only upon annealing, and subsequent hydrogen release, would the molecules recover their nominal structural and electronic properties.

M

involve chemical information. Core levels are also very sensitive to changes in the local electrostatic environment induced by the presence of the substrate and/or other surrounding molecules. Thus, disentangling the collective electrostatic effects from the chemical shifts is crucial for a correct interpretation of experimental XPS spectra. For the aforementioned tetrapyrrole molecules, several works have addressed the presence of unexpected components in the molecular core level spectra, specially in the N 1s signal, when the molecules are deposited on different surfaces.18−29 Such unpredicted features have been attributed to contaminants, to changes in the local environment induced by the presence of the substrate,18−22 or to chemical changes in the molecular composition.25−29 The purpose of the present paper is to obtain a deeper understanding of the role of the last two effects in the position of the core levels, i.e., in the core level shifts (CLSs). To achieve this, we have performed density functional theory (DFT)-based simulations of the N 1s XPS spectra and compared them with experimental measurements. Our theoretical results allow us to propose a possible scenario for the emergence of unexpected molecular core level features. Phthalocyanines, and their derivatives, have been widely studied and characterized by XPS (ref 25 and references therein). For this reason, we have chosen metal-phthalocya-

imicking natural processes has been a recurrent strategy for the development of human societies. More importantly, thanks to the advances in scientific knowledge and technological tools achieved over the last decades, biologically inspired research has evolved from the macroscale to the nanoscale. This poses an interdisciplinary challenge, involving fields such as molecular biology and surface science, aimed at the development of bioinspired nanodevices. Covering (partially or totally) an inorganic substrate with organic matter is an appropriate and viable architecture for such devices. Particularly promising nanoarchitectures can be formed via onmetal chemisorption of tetrapyrrole molecules (phthalocyanine and porphyrin molecules among others), which have often been proposed as ideal candidates for molecular electronics,1−3 spintronics,2,4,5 light harvesting and conversion,6,7 catalysis8,9 or even hydrogen storage.10−12 Additionally, the binding of small molecules or atoms, such as NO, CO, NH3 or H, to these molecules leads to modifications of molecular magnetic and/or electronic properties.13−17 Organic−inorganic interfaces are usually characterized by Xray photoelectron spectroscopy (XPS) technique, also known as ESCA (electron spectroscopy for chemical analysis). XPS is one of the most widely used surface analysis technique, as it provides valuable quantitative chemical state information about the surface of a material. Measuring the shift in the binding energy of different core levels, it is possible to verify the chemical integrity of a molecule, and to identify changes in its composition. However, the measured XPS spectra do not only © XXXX American Chemical Society

Received: September 29, 2017 Accepted: November 6, 2017

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DOI: 10.1021/acs.jpclett.7b02583 J. Phys. Chem. Lett. 2017, 8, 5718−5724

Letter

The Journal of Physical Chemistry Letters

One of the surface-mediated mechanisms that might play a role in the photoemission spectra is the final state splitting induced by the symmetry reduction of the molecule upon adsorption on the surface. When C4v-symmetrical ZnPc molecules are deposited onto Cu(110), their preferential adsorption configuration on the terraces is almost flat with their molecular axes azimuthally rotated by about 27° with respect to the main crystallographic axes of the C2v-symmetrical Cu(110) surface (Figure 1b). As a result, the symmetry of the entire adsorbate complex (molecule and surface) is reduced, which in turn induces the splitting of the degenerated lowest unoccupied molecular orbital (LUMO) (see inset in Figure 2).

nines (MPc) as test systems for our work. MPc-s are planar organometallic molecules containing eight N atoms: four aza nitrogens (N−, marked in blue in Figure 1a), and four iminic

Figure 2. DOS of the adsorbate complex projected onto the MOs of an isolated gas-phase ZnPc molecule. Inset: degenerated LUMO orbitals of ZnPc. Figure 1. (a) Optimized geometry of ZnPc (a) in gas phase and (b) adsorbed on Cu(110). (c) Experimental N 1s XPS spectra for 1 ML of ZnPc (left) and FePc (right) deposited on Cu(110) with the substrate at RT and at 210 K (LT).

To quantify this splitting, we have calculated the density of states (DOS) of the adsorbate complex projected onto the molecular orbitals (MOs) of the isolated (gas-phase) molecule. As observed in Figure 2, the DOS peaks associated with the two degenerated LUMO states of the gas phase molecule are well separated in energy. This means that the degeneracy of the LUMO states has indeed been broken, and that the N 1s core level electrons can then be excited to final states separated by ∼100 meV. This energy difference, though, is much smaller than the measured CLS of the new component of N 1s for ZnPc/Cu(110) at submonolayer coverage, which indicates that the final state effect is not the major responsible for the observation of additional features in the XPS spectra. In addition to the splitting of the MOs, the presence of the metallic surface can also alter the core level positions of the N atoms via a complex interplay of charge transfer, local surface screening and environmental charge density effects. Notably, it is well-known that the existence of multiple final states might give rise to additional peaks (shake up satellites) in the XPS spectra of molecules adsorbed on surfaces, when significant charge transfer processes occur.33 However, based on the experimental observations, this possibility can be ruled out for the extra peak observed in the N 1s XPS spectra of ZnPc on Cu(110) at low temperature. Namely, as shown in Figure 1, the extra peak irreversibly disappears upon increasing the temperature from 210 to 298 K, which strongly indicates that it is related to some thermally activated process and not to the existence of charge-transfer induced multiple final states, as such an effect should be detectable at any temperature.

nitrogens coordinated to the metal core (metal−N, in red in Figure 1a). Despite their nonequivalence, it is well-known that the 1s core levels of the two types of N atoms lie very close in energy (e.g., ∼ 0.3 eV for CuPc30), which normally leads to the observation of an unresolved single N 1s core level peak in photoemission experiments.31,32 However, unexpected features are frequently found in the N 1s energy region. This is the case, for example, of some MPc molecules deposited on Cu(110). When the ZnPc or FePc molecules are deposited on Cu(110) held at 210 K, the corresponding N 1s spectra reveal unpredicted double peak structures, as shown in the top spectra of Figure 1c (blue). The features at higher binding energies are not observed when the molecules are deposited on the substrate at RT (bottom spectra, red), neither for multilayer evaporations. This second peak appears shifted by ∼1.8 eV as compared to the main peak at 398.3 eV. Although extra XPS components could be associated with molecular fragments and/ or rests of reactants or solvents due to a poor degassing of the evaporation cell, the detection of similar features for different porphyrin and phthalocyanine molecules on different surfaces justifies a systematic study of other possible scenarios involving either surface-induced local electronic variations and/or chemical changes.18−29 In the following, such chemical and surface effects will be analyzed in detail for ZnPc molecules on Cu(110). 5719


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nor the magnitude of the shift predicted theoretically agrees with the experimental observation of a second peak blue-shifted by ∼1.8 eV. These results indicate that the underlying substrate is not responsible for the measured double-peak structure. Having excluded surface-induced effects as the origin of the unpredicted CLSs, in the following we turn our attention to the role of different chemical processes that are likely to occur in the adsorbate complex. Strong shifts in the core levels of an atom are expected to occur if its chemical environment changes, e.g., if new bonds are formed.26−28 In comparison with previous studies, the energy position of the unpredicted N 1s component (∼1.8 eV) suggests the formation of new N−H bonds in the ZnPc molecule. In fact, several works have recently demonstrated the high affinity of tetrapyrrole molecules to hydrogen,34,35 and the possibility of having an excess of hydrogen atoms bonded to these molecules.10,26−28,36,37 Moreover it has also been demonstrated that the presence of these extra H atoms has an important influence on properties such as the energy band gap, the charge and spin state, or the molecular switching.38−44 Two distinct mechanisms involving the formation of N−H bonds have been reported: (1) demetalation of the core prior to the H capture26 and (2) direct hydrogenation of the aza-N atoms as well as of the central metal atom.36,37 With respect to the first mechanism, Rienzo et al. proposed that Zn-protoporphyrins deposited at low coverage on rutile TiO2(110) undergo a multiple-step process involving the loss of the central Zn atom (demetalation), followed by the capture of two hydrogen atoms by the inner N atoms.26 However, demetalation can be disregarded for ZnPc on Cu(110) based on previous experiments on the self-metalation of phthalocyanines on Cu(110), where it was demonstrated that nonmetalated phthalocyanines (H2Pc) remain intact on Cu(110) for temperatures below 480 K, after which they self-metalate.45 Accordingly, if the double-peak structure observed for MPc (top spectra in Figure 1c) was attributed to the demetalation and subsequent capture of hydrogen atoms, the resulting hydrogenated molecules (H2Pc) should remain unchanged when the temperature is increased from 210 K to RT, and this is not the case. All in all, the hydrogenation of intact ZnPc molecules seems to be a very plausible chemical mechanism to explain the extra peak in XPS. Gas-phase ZnPc molecules are known to have a strong affinity for hydrogen.34 Indeed, our energy calculations for free-standing molecules confirm that atomic hydrogen is stable at various molecular sites (see Figure S3 of the Supporting Information). The energetically most favorable attachment position is the aza-N site, and the molecule can then uptake up to 4 H atoms at equivalent aza positions. In addition to that, H atoms can also be stabilized at adsorption sites out of the plane of the molecule, e.g., on top of the Zn atom. Importantly, the calculated N 1s XPS spectra for gasphase hydrogenated ZnPc molecules show that the H adsorption at aza-N sites induces the appearance of a second peak at around 1.5−1.8 eV higher binding energies as compared to the non hydrogenated gas-phase molecule (values summarized in the Supporting Information).46 Motivated by this, we have extensively investigated the occurrence of a similar H uptake mechanism in the case of ZnPc adsorbed on Cu(110). At ultra high vacuum (UHV) conditions the hydrogenation of supported metal-phthalocyanines has been hitherto observed only upon either extremely high H2 dosing37 or by nanomanipulation at liquid He substrate

On the basis of the aforementioned observations, a DFT final-state approach, which does not take into account the possibility of having multiple final states, is employed to explore the surface-mediated changes (see details in Methods). In particular, we have calculated the N 1s CLSs for ZnPc either in gas phase or adsorbed on Cu(110). It should be noted that the final-state calculation method only provides accurate values of the CLSs between different atoms of a given species, but not the relative intensity of the corresponding XPS peaks. Thus, based on calculated values of the CLSs, we simulate the XPS spectra by just taking into account the relative number of N atoms of each type. For the gas phase molecule, we find two components of equal intensity and separated by 120 meV, as shown in Figure 3a. The components at lower BE are assigned

Figure 3. Calculated N 1s core level spectra for ZnPc in gas phase (a) and absorbed on Cu(110) (b). The position of the core levels for the eight different N atoms are indicated with red (metal-N) and blue (aza-N) lines (exact values are summarized in the Supporting Information). The N 1s shape was simulated using Gaussian/ Lorentzian curves with widths of 0.8 eV.

to the 4 aza nitrogens (indicated with blue lines in Figure 3a) and those at higher BE to the 4 nitrogen atoms coordinated with the Zn (red lines). Upon adsorption on Cu(110), the shape of the N 1s spectrum is notably modified (Figure 3b). Interestingly, the observed changes can be ascribed to the fact that surface induced effects depend sensibly on the exact position of the N atoms on the surface. All metal N atoms are located in equivalent positions over the substrate and, thus, only small relative differences in the corresponding core levels are observed (98%). Molecules were outgassed in vacuum before evaporation. The evaporation temperatures are around 670−700 K.

Figure 5. (a) Dehydrogenation path of HZnPc on Cu(110). (b) Corresponding energy profile.

dehydrogenation rate. Assuming an Arrhenius-type mechanism in which the thermally activated bond dissociation is mediated by the N−H streching mode,51 an exponential prefactor of ∼1014s−1 can be considered. Hence, changing the temperature from ∼210 K to RT, the NH dissociation rate is increased by approximately 6 orders of magnitude. This indicates that, at RT, most of the hydrogenated molecules have presumably lost the extra H atoms and have recovered their original chemical composition (ZnPc). Of course, this is accompanied by the quenching of the high BE peak associated with the pyrrolic N atoms (see Figure S6). In conclusion, our results shed light into the understanding of chemical and surface processes involved in the core-level shifts of organic molecules on surfaces. In particular, for ZnPc molecules on Cu(110), we have been able to rule out LUMO splitting, surface effects, and molecular demetalation as possible origins of the double peak detected in the low coverage and low temperature N 1s core level spectra. Moreover, although contaminated evaporation can not be completely excluded, we have demonstrated that molecular hydrogenation is an

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.7b02583. Complementary details of the theoretical calculations (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

A. Sarasola: 0000-0001-9193-2185 5722


Letter


(15) Isvoranu, C.; Knudsen, J.; Ataman, E.; Schulte, K.; Wang, B.; Bocquet, M.-L.; Andersen, J. N.; Schnadt, J. Adsorption of ammonia on multilayer iron phthalocyanine. J. Chem. Phys. 2011, 134, 114711. (16) Strózė cka, A.; Soriano, M.; Pascual, J. I.; Palacios, J. J. Reversible Change of the Spin State in a Manganese Phthalocyanine by Coordination of CO Molecule. Phys. Rev. Lett. 2012, 109, 147202. (17) Wang, Y.; Li, X.; Zheng, X.; Yang, J. Spin switch in iron phthalocyanine on Au(111) surface by hydrogen adsorption. J. Chem. Phys. 2017, 147, 134701. (18) Yu, S.; Ahmadi, S.; Sun, C.; Adibi, P. T. Z.; Chow, W.; Pietzsch, A.; Göthelid, M. Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110). J. Chem. Phys. 2012, 136, 154703. (19) Di Santo, G.; Castellarin-Cudia, C.; Fanetti, M.; Taleatu, B.; Borghetti, P.; Sangaletti, L.; Floreano, L.; Magnano, E.; Bondino, F.; Goldoni, A. Conformational Adaptation and Electronic Structure of 2H-Tetraphenylporphyrin on Ag(111) during Fe Metalation. J. Phys. Chem. C 2011, 115, 4155−4162. (20) Diller, K.; Klappenberger, F.; Marschall, M.; Hermann, K.; Nefedov, A.; Wö ll, C.; Barth, J. V. Self-metalation of 2Htetraphenylporphyrin on Cu(111): An x-ray spectroscopy study. J. Chem. Phys. 2012, 136, 014705. (21) Katsonis, N.; Vicario, J.; Kudernac, T.; Visser, J.; Pollard, M. M.; Feringa, B. L. Self-Organized Monolayer of meso-Tetradodecylporphyrin Coordinated to Au(111). J. Am. Chem. Soc. 2006, 128, 15537− 15541. (22) Borghetti, P.; El-Sayed, A.; Goiri, E.; Rogero, C.; Lobo-Checa, J.; Floreano, L.; Ortega, J. E.; de Oteyza, D. G. Spectroscopic Fingerprints of Work-Function-Controlled Phthalocyanine Charging on Metal Surfaces. ACS Nano 2014, 8, 12786−12795. (23) Belogorokhov, A. I.; Bozhko, S. I.; Chaika, A. N.; Ionov, A. M.; Trophimov, S. A.; Rumiantseva, V. D.; Vyalikh, D. Electronic structure and self-assembling processes in platinum metalloporphyrins: photoemission and AFM studies. Appl. Phys. A: Mater. Sci. Process. 2009, 94, 473−476. (24) Bai, Y.; Sekita, M.; Schmid, M.; Bischof, T.; Steinruck, H.-P.; Gottfried, J. M. Interfacial coordination interactions studied on cobalt octaethylporphyrin and cobalt tetraphenylporphyrin monolayers on Au(111). Phys. Chem. Chem. Phys. 2010, 12, 4336−4344. (25) Palmgren, P.; Angot, T.; Nlebedim, C. I.; Layet, J. M.; Le Lay, G.; Göthelid, M. Ordered phthalocyanine superstructures on Ag(110). J. Chem. Phys. 2008, 128, 064702. (26) Rienzo, A.; Mayor, L. C.; Magnano, G.; Satterley, C. J.; Ataman, E.; Schnadt, J.; Schulte, K.; O’Shea, J. N. X-ray absorption and photoemission spectroscopy of zinc protoporphyrin adsorbed on rutile TiO2(110) prepared by in situ electrospray deposition. J. Chem. Phys. 2010, 132, 084703. (27) Lovat, G.; Forrer, D.; Abadia, M.; Dominguez, M.; Casarin, M.; Rogero, C.; Vittadini, A.; Floreano, L. Hydrogen Capture by Porphyrins at the TiO2(110) surface. Phys. Chem. Chem. Phys. 2015, 17, 30119−30124. (28) Garcia-Lekue, A.; González-Moreno, R.; Garcia-Gil, S.; Pickup, D. F.; Floreano, L.; Verdini, A.; Cossaro, A.; Martín-Gago, J. A.; Arnau, A.; Rogero, C. Coordinated H-Bonding between Porphyrins on Metal Surfaces. J. Phys. Chem. C 2012, 116, 15378−15384. (29) Zanoni, R.; Aurora, A.; Cattaruzza, F.; Decker, F.; Fastiggi, P.; Menichetti, V.; Tagliatesta, P.; Capodilupo, A.-L.; Lembo, A. Metalloporphyrins as molecular precursors of electroactive hybrids: A characterization of their actual electronic states on Si(100) and (111) by AFM and XPS. Mater. Sci. Eng., C 2007, 27, 1351−1354. EMRS 2006 Symposium A: Current Trends in Nanoscience - from Materials to Applications. (30) Ruocco, A.; Evangelista, F.; Gotter, R.; Attili, A.; Stefani, G. Evidence of Charge Transfer at the Cu-phthalocyanine/Al(100) Interface. J. Phys. Chem. C 2008, 112, 2016−2025. (31) Alfredsson, Y.; Brena, B.; Nilson, K.; Åhlund, J.; Kjeldgaard, L.; Nyberg, M.; Luo, Y.; Mårtensson, N.; Sandell, A.; Puglia, C. Electronic structure of a vapor-deposited metal-free phthalocyanine thin film. J. Chem. Phys. 2005, 122, 214723.

C. Rogero: 0000-0002-2812-8853 A. Garcia-Lekue: 0000-0001-5556-0898 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank L. Floreano and M. Blanco-Rey for useful discussions, and acknowledge support from the Basque Departamento de Educación and UPV/EHU (Grants No. PI2016-1-0027, IT-756-13 and IT-621-13), the Spanish Ministry (Grants No. MAT2016-78293-C6-4-R, MAT2016-78293-C6-5R, and FIS2016-75862-P), and the European Union FP7-ICT Integrated Project PAMS under Contract No. 610446.

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REFERENCES

(1) Hamann, C.; Hietschold, M.; Mrwa, A.; Müller, M.; Starke, M.; Kilper, R. In Molecular Electronics; Lazarev, P., Ed.; Topics in Molecular Organization and Engineering; Springer: Netherlands, 1991; Vol. 7; pp 129−138. (2) Niu, T.; Li, A. Exploring single molecules by scanning probe microscopy: Porphyrin and phthalocyanine. J. Phys. Chem. Lett. 2013, 4, 4095−4102. (3) Auwärter, W.; É cija, D.; Klappenberger, F.; Barth, J. V. Porphyrins at interfaces. Nat. Chem. 2015, 7, 105−120. (4) Brede, J.; Atodiresei, N.; Kuck, S.; Lazić, P.; Caciuc, V.; Morikawa, Y.; Hoffmann, G.; Blügel, S.; Wiesendanger, R. Spin- and Energy-Dependent Tunneling through a Single Molecule with Intramolecular Spatial Resolution. Phys. Rev. Lett. 2010, 105, 047204. (5) Krull, C.; Robles, R.; Mugarza, A.; Gambardella, P. Site- and orbital-dependent charge donation and spin manipulation in electrondoped metal phthalocyanines. Nat. Mater. 2013, 12, 337−343. (6) Himpsel, F.; Cook, P.; de la Torre, G.; Garcia-Lastra, J.; Gonzalez-Moreno, R.; Guo, J.-H.; Hamers, R.; Kronawitter, C.; Johnson, P.; Ortega, J. Design of solar cell materials via soft X-ray spectroscopy. J. Electron Spectrosc. Relat. Phenom. 2013, 190, 2−11. (7) Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nat. Chem. 2014, 6, 242−247. (8) Sedona, F.; Di Marino, M.; Forrer, D.; Vittadini, A.; Casarin, M.; Cossaro, A.; Floreano, L.; Verdini, A.; Sambi, M. Tuning the catalytic activity of Ag(110)-supported Fe phthalocyanine in the oxygen reduction reaction. Nat. Mater. 2012, 11, 970−977. (9) Mohamed, E. A.; Zahran, Z. N.; Naruta, Y. Efficient electrocatalytic CO2 reduction with a molecular cofacial iron porphyrin dimer. Chem. Commun. 2015, 51, 16900−16903. (10) Yang, K.; Liu, L.; Zhang, L.; Xiao, W.; Fei, X.; Chen, H.; Du, S.; Ernst, K.-H.; Gao, H.-J. Reversible Achiral-to-Chiral Switching of Single Mn-Phthalocyanine Molecules by Thermal Hydrogenation and Inelastic Electron Tunneling Dehydrogenation. ACS Nano 2014, 8, 2246−2251. (11) Guo, J.-H.; Zhang, H.; Miyamoto, Y. New Li-doped fullereneintercalated phthalocyanine covalent organic frameworks designed for hydrogen storage. Phys. Chem. Chem. Phys. 2013, 15, 8199−8207. (12) Lü, K.; Zhou, J.; Zhou, L.; Wang, Q.; Sun, Q.; Jena, P. Scphthalocyanine sheet: Promising material for hydrogen storage. Appl. Phys. Lett. 2011, 99, 163104. (13) Wäckerlin, C.; Chylarecka, D.; Kleibert, A.; Müller, K.; Iacovita, C.; Nolting, F.; Jung, T. A.; Ballav, N. Controlling spins in adsorbed molecules by a chemical switch. Nat. Commun. 2010, 1, 61. (14) Hieringer, W.; Flechtner, K.; Kretschmann, A.; Seufert, K.; Auwärter, W.; Barth, J. V.; Görling, A.; Steinrück, H.-P.; Gottfried, J. M. The Surface Trans Effect: Influence of Axial Ligands on the Surface Chemical Bonds of Adsorbed Metalloporphyrins. J. Am. Chem. Soc. 2011, 133, 6206−6222. 5723


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The Journal of Physical Chemistry Letters (32) Ahmadi, S.; Agnarsson, B.; Bidermane, I.; Wojek, B. M.; Noël, Q.; Sun, C.; Göthelid, M. Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine. J. Chem. Phys. 2014, 140, 174702. (33) Bagus, P. S.; Ilton, E. S.; Nelin, C. J. The interpretation of XPS spectra: Insights into materials properties. Surf. Sci. Rep. 2013, 68, 273−304. (34) Tsetseris, L. Hydrogen- and oxygen-related effects in phthalocyanine crystals: formation of carrier traps and a change in the magnetic state. Phys. Chem. Chem. Phys. 2014, 16, 3317−3322. (35) Li, S.; Yuan, D.; Yu, A.; Czap, G.; Wu, R.; Ho, W. Rotational Spectromicroscopy: Imaging the Orbital Interaction between Molecular Hydrogen and an Adsorbed Molecule. Phys. Rev. Lett. 2015, 114, 206101. (36) Yang, K.; Xiao, W.; Liu, L.; Fei, X.; Chen, H.; Du, S.; Gao, H.-J. Construction of two-dimensional hydrogen clusters on Au(111) directed by phthalocyanine molecules. Nano Res. 2014, 7, 79−84. (37) Zhang, J.; Wang, Z.; Zhong, J.; Yuan, K.; Shen, Q.; Xu, L.; Niu, T.; Gu, C.; Wright, C.; Tadich, A. Single-Molecule Imaging of Activated Nitrogen Adsorption on Individual Manganese Phthalocyanine. Nano Lett. 2015, 15, 3181−3188. (38) Liu, L.; Yang, K.; Jiang, Y.; Song, B.; Xiao, W.; Li, L.; Zhou, H.; Wang, Y.; Du, S.; Ouyang, M. Reversible single spin control of individual magnetic molecule by hydrogen atom adsorption. Sci. Rep. 2013, 3, 1210. (39) Swart, I.; Sonnleitner, T.; Repp, J. Charge state control of molecules reveals modification of the tunneling barrier with intramolecular contrast. Nano Lett. 2011, 11, 1580−1584. (40) Uhlmann, C.; Swart, I.; Repp, J. Controlling the orbital sequence in individual Cu-phthalocyanine molecules. Nano Lett. 2013, 13, 777−780. (41) Kumagai, T.; Hanke, F.; Gawinkowski, S.; Sharp, J.; Kotsis, K.; Waluk, J.; Persson, M.; Grill, L. Thermally and vibrationally induced tautomerization of single porphycene molecules on a Cu(110) surface. Phys. Rev. Lett. 2013, 111, 246101. (42) Kumagai, T.; Hanke, F.; Gawinkowski, S.; Sharp, J.; Kotsis, K.; Waluk, J.; Persson, M.; Grill, L. Controlling intramolecular hydrogen transfer in a porphycene molecule with single atoms or molecules located nearby. Nat. Chem. 2014, 6, 41−46. (43) Bischoff, F.; Seufert, K.; Auwärter, W.; Joshi, S.; Vijayaraghavan, S.; Écija, D.; Diller, K.; Papageorgiou, A. C.; Fischer, S.; Allegretti, F. How surface bonding and repulsive interactions cause phase transformations: Ordering of a prototype macrocyclic compound on Ag(111). ACS Nano 2013, 7, 3139−3149. (44) Auwärter, W.; Seufert, K.; Bischoff, F.; Écija, D.; Vijayaraghavan, S.; Joshi, S.; Klappenberger, F.; Samudrala, N.; Barth, J. V. A surfaceanchored molecular four-level conductance switch based on single proton transfer. Nat. Nanotechnol. 2011, 7, 41−46. (45) Abadía, M.; González-Moreno, R.; Sarasola, A.; Otero-Irurueta, G.; Verdini, A.; Floreano, L.; Garcia-Lekue, A.; Rogero, C. Massive Surface Reshaping Mediated by Metal Organic Complexes. J. Phys. Chem. C 2014, 118, 29704−29712. (46) For gas-phase FePc, the capture of two H atoms at aza-N sites (i.e., the formation of H2FePc) gives rise to a CLS of about 1.9 eV with respect to the metal-N atoms. Moreover, a third XPS signal coming from the non-hydrogenated aza-N atoms is predicted at around −0.9 eV. Although these values might be modified by the interaction with the surface, they qualitatively explain the experimental data for FePc at LT, and further reinforce our interpretation of the extra XPS peaks resulting from molecular hydrogenation. (47) Yamashige, H.; Matsuo, S.; Kurisaki, T.; Perera, R. C. C.; Wakita, H. Local Structure of Nitrogen Atoms in a Porphine Ring of meso-Phenyl Substituted Porphyrin with an Electron-Withdrawing Group Using X-ray Photoelectron Spectroscopy and X-ray Absorption Spectroscopy. Anal. Sci. 2005, 21, 635−639. (48) Bae, C.; Freeman, D. L.; Doll, J. D.; Kresse, G.; Hafner, J. Energetics of hydrogen chemisorbed on Cu(110): A first principles calculations study. J. Chem. Phys. 2000, 113, 6926−6932.

(49) Ozawa, N.; Roman, T.; Nakanishi, H.; Diño, W. A.; Kasai, H. Quantum states of a hydrogen atom adsorbed on Cu(100) and (110) surfaces. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 115421. (50) Spencer, M. J.; Nyberg, G. L. DFT modelling of hydrogen on Cu(110)- and (111)-type clusters. Mol. Simul. 2002, 28, 807−825. (51) Murray, C.; Dozova, N.; McCaffrey, J. G.; FitzGerald, S.; Shafizadeh, N.; Crepin, C. Infra-red and Raman spectroscopy of freebase and zinc phthalocyanines isolated in matrices. Phys. Chem. Chem. Phys. 2010, 12, 10406−10422. (52) Soler, J. M.; Artacho, E.; Gale, J. D.; García, A.; Junquera, J.; Ordejón, P.; Sánchez-Portal, D. The SIESTA method for ab initio order- N materials simulation. J. Phys.: Condens. Matter 2002, 14, 2745. (53) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (54) Jónsson, H.; Mills, G.; Jacobsen, K. Classical and Quantum Dynamics in Condensed Phase Simulations; World Scientific: Singapore, 2011; Chapter 16, pp 385−404. (55) Henkelman, G.; Jónsson, H. Improved tangent estimate in the nudged elastic band method for finding minimum energy paths and saddle points. J. Chem. Phys. 2000, 113, 9978−9985. (56) Henkelman, G.; Uberuaga, B. P.; Jónsson, H. A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J. Chem. Phys. 2000, 113, 9901−9904. (57) Smidstrup, S.; Pedersen, A.; Stokbro, K.; Jónsson, H. Improved initial guess for minimum energy path calculations. J. Chem. Phys. 2014, 140, 214106. (58) Pehlke, E.; Scheffler, M. Evidence for site-sensitive screening of core holes at the Si and Ge (001) surface. Phys. Rev. Lett. 1993, 71, 2338. (59) Pasquarello, A.; Hybertsen, M. S.; Rignanese, G. M.; Car, R. Core-level shifts in Si(001)-SiO2 systems: The value of first-principle investigations. Fundamental Aspects of Ultrathin Dielectrics on Si-Based Devices 1998, 47, 89−102. (60) García-Gil, S.; García, A.; Ordejón, P. Calculation of core level shifts within DFT using pseudopotentials and localized basis sets. Eur. Phys. J. B 2012, 85, 239.

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Theoretical Insights into Unexpected Molecular Core Level Shifts

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