Formation of Hybrid Electronic States in FePc Chains Mediated by the Au(110) Surface Maria Grazia Betti,* ,† Pierluigi Gargiani, ‡ Carlo Mariani, † Stefano Turchini, § Nicola Zema, § Sara Fortuna, ∥,⊥ Arrigo Calzolari, ¶ and Stefano Fabris ∥,⊥ † Dipartimento di Fisica, CNISM, CNIS, Universita ̀ di Roma La Sapienza, Piazzale Aldo Moro 2, I- 00185 Roma, Italy ‡ Dipartimento di Fisica, Universita ̀ di Roma La Sapienza, Piazzale Aldo Moro 2, I - 00185 Roma, Italy § ISM-CNR, Via delFosso del Cavaliere 100, 00133 Roma, Italy ∥ CNR-IOM DEMOCRITOS, Theory@Elettra group, S.S. 14, km 163.5, I-34149 Trieste, Italy ⊥ SISSA, Via Bonomea 265, I-34136, Trieste, Italy ¶ CNR-Nano Istituto di Nanoscienze, Centro S3, I-41125 Modena, Italy * S Supporting Information ABSTRACT: Iron−phthalocyanine (FePc) molecules depos- ited on the Au(110) surface self-organize in ordered chains driven by the reconstructed Au channels. The interaction process induces a rehybridization of the electronic states localized on the central metal atom, breaking the 4-fold symmetry of the molecular orbitals of the FePc molecules. The molecular adsorption is controlled by a symmetry-determined mixing between the electronic states of the Fe metal center and of the Au substrate, as deduced by photoemission and absorption spectroscopy exploiting light polarization. DFT calculations rationalize this mixing of the Fe and Au states on the basis of symmetry arguments. The calculated electronic structure reproduces the main experimental spectral features, which are associated to a distorted molecular structure displaying a trigonal bipyramidal geometry of the ligands around the metal center. ■ INTRODUCTION The design of 1D and 2D architectures based on the self- assembly of metallorganic molecules is nowadays a widely exploited path, with the final objective of tailoring their electronic, transport, and magnetic properties. 1−3 The elec- tronic, magnetic, and transport properties of simple metal- lorganic systems can be tuned by modifying the molecule− molecule interaction and the molecule−substrate coupling. 2,4−8 This goal requires a detailed knowledge of the evolution of the molecular orbitals when deposited on a suitable substrate and of the interaction strength at the interface. In this framework, metal−phthalocyanines (M−C 32 H 16 N 8 , MPcs) represent an interesting class of metallorganic systems, as they can coordinate most of the metals of the periodic table. MPcs are stable aromatic dyes composed by four pyrrolic and four benzene rings arranged around the central metal atom, with a 4- fold symmetry as isolated molecules. They may constitute exemplary molecular biomimetic prototypes 9 for studying electronic states in different conditions of solid aggregation, by self-assembling them on templating surfaces able to drive well ordered 1D and 2D architectures. 10−12 Their charge transport and delocalization are mainly due to the π- conjugation, 13 whereas the central metal atom can be exploited to control their magnetic properties. The interaction process can reduce the 4-fold symmetry of the planar molecule as observed in similar molecular 1D and 2D structures adsorbed on metal surfaces, 14−20 affecting the electronic level ordering and symmetry, hence producing peculiar new magnetic and transport properties. In this article, we study FePc molecular chains arranged along the Au(110) reconstructed nanorails, addressing the orbital symmetry and the electronic mixing between the organic molecular orbitals and the substrate states, by means of both experimental and theoretical approaches. FePc and CoPc deposited on Au(110) present considerable interaction of the central metal atom with the metal substrate while the benzene and pyrrole macrocycles are less involved in the process. 21,22 The purpose herewith is to follow the interaction process at the ordered FePc single-layer on Au(110), identifying the electronic states involved in the interaction, their localization, mixing, and symmetry. The electronic spectral density of states is measured by means of synchrotron-based photoelectron and absorption spectroscopy. The electronic structure and the density of states (DOS) are computed from first-principles in the framework of DFT for a model system that correctly predicts recent structural results. 23 The experimental and Received: January 19, 2012 Revised: March 22, 2012 Published: March 26, 2012 Article pubs.acs.org/JPCC © 2012 American Chemical Society 8657 dx.doi.org/10.1021/jp300663t | J. Phys. Chem. C 2012, 116, 8657−8663