Ionization-Induced Double Charge Transfer in Metallophthalocyanines Revealed by Ab Initio Simulation of 2p Photoelectron Spectra

We report on a joint experimental and theoretical investigation of the metal 2p X-ray photoelectron spectra of transition-metal phthalocyanines MnPc, FePc, and CoPc. Using a multiconfigurational approach including spin-orbit coupling, we obtain nearly quantitative agreement with experiment. In all investigated systems, we found an unexpected and robust physical effect induced by core ionization, namely a drastic reorganization of the valence electronic structure. This reorganization is characterized by a pronounced stabilization of doubly excited ligand-to-metal charge-transfer configurations, which become energetically favored in the final states. This ionization-induced double charge transfer is found to be common to all metallophthalocyanines studied. Furthermore, we identify a nearly linear correlation between the stabilization energies obtained from restricted active space configuration interaction (RAS-CI) calculations and a simple hydrogenic/Slater screening estimate, providing an intuitive and practical descriptor to assess when such charge-transfer states are expected to dominate after core ionization.