X-ray photoelectron spectroscopy of clean and gas-doped films of phthalocyanines

Films of a range of phthalocyanines which had been deposited by vacuum sublimation were analysed using X-ray photoelectron spectroscopy (XPS). Spectra of the major peaks were recorded before exposure to NOX (NO2+N2O4), after exposure to 9 vpm NOX in air, after exposure to undiluted NOX and finally after heating the exposed film to 150 degrees C. The phthalocyanines studied were: metal-free (H2Pc), magnesium (MgPc), vanadyl (VOPc), manganese (MnPc), iron (FePc), cobalt (CoPc), nickel (NiPc) and copper (CuPc). The presence of NOX (which would have given rise to new N 1s and O 1s peaks in the XPS spectra) was not detected in any of the films following the exposure to 9 vpm, although slight shifts in the positions of some peaks were observed. All XPS spectra exhibited changes following the exposure of the films to undiluted NOX. H2Pc clearly suffered severe chemical attack. The effect on the metal phthalocyanines was not so severe, but was different for each metal complex. None of the spectra was restored to the pre-NOX form by heating to 150 degrees C after exposure to the undiluted NOX. In order to explain the changes in the C 1s XPS spectra which were observed during these experiments, it was found necessary to modify a previous interpretation of the C 1s spectrum.