Theoretical study of the near-edge CuLx-ray absorption spectrum of copper phthalocyanine

Copper tetraazaporphyrin is used as a model for copper phthalocyanine in theoretical simulations of the features observed at the Cu L2,3 near-edge x-ray absorption spectra. Theoretical results obtained by a density-functional theory approach provided interpretations of the different features observed experimentally, including the so-called white line and the satellite structures, leading to the conclusion that the solid phase arrangement exerts no significant influence on the shape of the Cu L2,3 copper molecular spectrum. The calculations show that the unoccupied $3d$ levels are essentially located in the plane (3d_x²-y²) of the molecule with a small contribution that has an out-of-plane 3d_z²-r² and 3dxz,yz character. The angular dependence of the copper unoccupied electronic levels could be used to confirm the orientation of the copper tetraazaporphyrin on the substrates.