Unoccupied electronic states in phthalocyanine thin films studied by inverse photoemission spectroscopy

Inverse photoemission (IPE) spectra of thin films of metal-free phthalocyanine (H2Pc), 3d-metal phthalocyanines (MPcs: M=Mn, Fe, Co, Ni, Cu and Zn) and lithium phthalocyanine (LiPc) have been measured to directly observe the electronic structures of their unoccupied states. In particular, IPE spectra of MPcs obtained systematically for 3d metals have been studied with the contribution from the 3d-metal orbitals to the electronic structures of the lower unoccupied states focused on. The difference spectra between MPcs (M=Mn, Fe, Co, Ni and Cu) and ZnPc as the reference are compared with the reported results from X-ray absorption spectroscopy as well as extended Hückel and density functional calculations to show that they reflect the density of unoccupied states derived from the central metals with permitting tentative assignments of their features.