The electronic structure modi. cations of copper phthalocyanine (CuPc) induced by interactions with Na are investigated with X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). The initial Na doping induces energy level shift, which has a linear dependence in the semi-log plot. For high doping ratios, the shifts of the energy levels diverge from each other. A detailed analysis of the core levels indicates that the doped Na ions tend to interact first with the Pc orbital around the N atoms. However, as the doping ratio increases, strong chemical reactions take place, involving transitions from Cu-II to Cu-I. (c) 2008 Elsevier B. V. All rights reserved.