Self-Metalation of Porphyrins by Cobalt Oxide: Photoemission Spectroscopic Investigation

Understanding the electronic structure between porphyrins and ultrathin metal-oxide film interfaces is vital for the rational design of functional molecular architectures. Here, we have studied the interfacial electronic properties of porphyrin molecular thin films on well-ordered thin layers of CoO(111) and metallic Co(100) surfaces by means of X-ray and ultraviolet photoemission spectroscopies. In this work, we observed the direct self-metalation of free-base porphyrin molecules at the interface to CoO(111) at room temperature by monitoring the N is core-level evolution. On metallic Co(100) films, no metalation occurs, but it can be induced by exposure to oxygen. The oxygen-induced metalation has, to the best of our knowledge, not been reported until now and might play an important role in processes where porphyrins are exposed to metals in a reactive environment.