We studied the thickness dependence of electronic structure and molecular orientation of neutral, square planar, diamagnetic diradical metal complex, bis(o-diiminobenzosemiquinonate) nickel(II) complexes (Ni(DIBSQ)(2)), thin films grown on a SiO2 substrate by using ultraviolet photoelectron spectroscopy in combination with metastable atom electron spectroscopy. We observed that the small hole-injection barrier of 0.46 eV for the monolayer film, and the barrier increases continuously with the film thickness and becomes larger than the electron-injection barrier. We further found that molecules are oriented with their long-axes nearly perpendicular to the surface both in the monolayer and multilayer films independent of the film thickness. (C) 2010 Elsevier B.V. All rights reserved.