Role of the Anchored Groups in the Bonding and Self-Organization of Macrocycles: Carboxylic versus Pyrrole Groups

A combination of variable temperature scanning tunneling microscopy, near edge X-ray adsorption fine structure and density functional theory has been used to investigate the chemisorption and self-assembly of metal-free protoporphyrin IX molecules on Cu(110) surface. The molecules in contact with the substrate suffer irreversible molecular transformations, mainly deprotonation of the carboxylic groups and metalation of the pyrroline subunits. The carboxylate group has been revealed as the anchored group versus the tetrapyrrole ring. We study the role played by the carboxylic acid groups in the surface-molecular bonding and how its presence affects the supramolecular structure.