An ordered copper-phthalocyanine (CuPc) single layer deposited on the Au(110) surface has been electron-doped by exposition to potassium. Progressive occupation of the former lowest unoccupied molecular orbitals (LUMOs) up to the filling of the twofold degenerate LUMO and LUMO+1 and LUMO+2 levels, has been detected by near-edge x-ray absorption spectroscopy spectra. The electronic states filled by electron transfer from the alkali atoms are localized at the interface, and the process induces a redistribution of the density of states with a conspicuous decrease in spectral density at the Fermi level. Localization of the final states, sudden decrease in density of states at the Fermi level, minor screening of the electron-hole excitations, and enhanced excitonic effects of doped CuPc with respect to the pristine CuPc single-layer concur to suggest that the electron injection produces a Mott insulator where correlation effects dominate the electronic properties. © 2009 The American Physical Society

Metal phthalocyanine (MPc, with M = Fe, Co, Ni, Cu, Zn) thin-films grown on Au(110) have been electron-doped by exposition to alkali metal (potassium). Progressive occupation of the former lowest unoccupied molecular orbital (LUMO) up to the filling of the 2-fold degenerate LUMO with 2e(g) symmetry has been observed in photoemission spectra for the NiPc, CuPc, and ZnPc films. The evolution of the electron filling induces a different process for FePc and CoPc, whose empty electronic states localized on the central metal atoms are involved in the electron donation process by the alkali metal. Electron filling is accompanied by a sudden decrease of the work function mainly due to a variation of the surface dipole. The molecular films remain semiconducting, with the hole injection barrier strongly reduced at saturation of the electron filling. The selective influence of the electron donation process on the molecular states (ligands, metal-related) is discussed