Tuning of Interface Properties of Transition Metal Phthalocyanines on Metal Surfaces by Graphene: Ionization Potential and Graphene-Substrate Coupling

The recently increasing research efforts devoted to transition metal phthalocyanines (TMPcs) derive from their unique optical, electronic and magnetic properties. Interactions at metal interfaces can result in a drastic change of electronic and magnetic properties of these molecules.[1] We will focus on the discussion of the charge transfer via the transition metal for different TMPcs (TM=Co, Fe, Mn), although the charge transfer is expected to be complex and bidirectional in many cases. Alternatively to the exchange of the TM of the Pc, the interface energetics can be varied by the fluorination of the molecule changing the ionization potential. Intermediate layers like graphene can tune interactions at TMPc-metal interfaces. In this context, the graphene-substrate coupling plays an important role. At the example CoPc/CoPcF₁₆ we show that the fluorination may distinctly affect the electronic structure of the central metal atom of the TMPc at the interface.[2]
In particular, the analysis of L-edge X-ray absorption and photoemission spectra of the transition metal of the TMPc sheds light on local changes of the interfacial electronic structure.
[1] H. Peisert, et al., J Electron Spectrosc, 204 (2015) 49-60
[2] D. Balle, et al., J Phys Chem C, 121 (2017) 18564-18574