Published: October 23, 2011 r2011 American Chemical Society 23512 dx.doi.org/10.1021/jp208734f | J. Phys. Chem. C 2011, 115, 23512–23518 ARTICLE pubs.acs.org/JPCC Theoretical and Experimental Study of Bonding and Optical Properties of Self-Assembly Metallophthalocyanines Complexes on a Gold Surface. A Survey of the SubstrateÀSurface Interaction. Ingrid Ponce, ‡ J. Francisco Silva, ‡ Ruben O~ nate, ‡ Sebastian Miranda-Rojas, § Alvaro Mu~ noz-Castro, † Ramiro Arratia-P  erez,* ,† Fernando Mendizabal,* ,§ and Jos  e H. Zagal ‡ † Doctorado en Fisicoquimica Molecular, Relativistic Molecular Physics (ReMoPh) Group, Universidad Andres Bello, Av. Republica 275, Santiago, Chile ‡ Departamento de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile Casilla 40, Sucursal Matucana, Santiago 9170022 Chile § Departamento de Química, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile b S Supporting Information 1. INTRODUCTION Self-assembled monolayers (SAMs) 1,2 have attracted signifi- cant attention in the literature because of their applications in many areas such as, biology, physics, optics, and chemistry 3,4 because of their high selectivity and stability. 5 SAMs consist of molecules having a headgroup and a tail group with functionality, where the headgroup has special affinity for a substrate, and the tail exhibits a functional group whose terminal end provides the functionality of the SAMs. Usually, the functional group is a redox center or a molecule that can undergo fast electron-transfer (ET) processes. In general, the headgroup of the SAM film pro- motes the spontaneous adsorption of the appropriated mole- cules from the solution onto a metal substrate. In this respect, the chemisoption of thiolates on gold represents the most important class of SAMs in electrochemical studies, 6 leading to interesting modified electrodes, 7À9 which continues to be a focus for research interest because of their importance in supramolecular nano- technology, fundamentals studies of ET reactions, and so on. 10À12 Gold exhibits strong affinity for sulfur leading to the formation of AuÀS bonds, involving an energy of 35À45 kcal/mol, 13 where thiols can serve as effective “molecular anchors” to immobilize molecules that act as catalyst for ET reactions. Therefore, these assemblies can be used as electrochemical sensors for several target molecules, among other applications. In particular, the advantages of SAM-gold electrodes using different metallopha- locyanine complexes have been reported by Nyokong et al. for the electrochemical detection of several analytes. 14 To immobilize metallophthalocyanine molecules (MPc) on gold surfaces, we have employed 4-aminothiophenol (4-ATP) and 4-mercatopyridine (4-MP), denoted for simplicity as L, to form a SAM structure on a Au(111) support (Scheme 1), follo- wed by an axial coordination of the aromatic amino or pyridil group to the cobalt(II) phthalocyanine or iron(II) phthalocya- nine (CoPc and FePc, respectively). STM experiments have pro- vided direct evidence that a complete monolayer of 4-ATP or 4-MP can be formed. The complete self-assembly process pro- duces a stable and highly ordered conducting film where the phthalocyanines remain parallel to the gold surface forming “umbrella” like structures 15 due to the densely packed 4-ATP monolayer onto which CoPc or FePc molecules are coordinated. Received: September 9, 2011 Revised: October 12, 2011 ABSTRACT: The formation of self-assembly monolayers (SAMs) based on a gold substrate and a thiolate ligand as “anchor” fragment of metallophtalocya- nine has been employed as strategy toward the obtention of modified electrodes. In this Article, the formation of SAM’s involving iron and cobalt phtalocyanines anchored by 4-aminothiophenol (4-ATP) and 4-mercatopyr- idine (4-MP) to the Au(111) surface is explored by both experimental and theoretical studies for a better understanding of their bonding pattern and optical properties. The self-assembly metallophthalocyanines complexes on gold electrode exhibits an interesting charge donation from the 4-ATP or 4-MP toward both gold substrate and phtalocyanine, denoting an effective goldÀMPc interaction mediated by the titled anchor ligands. In addition, the optical properties of the self-assembled complexes supported on the gold electrode exhibit in conjuction with the well-described Q-band an interesting charge transfer from the Pc (π) toward the gold surface, as could be observed in the FePc-4MP-Au 26 assembly.