Electron acceptor surface states due to oxygen adsorption on metal phthalocyanine films

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Abstract
The dependence of the surface photovoltage of NiPc and CuPc films on oxygen ambient has been measured, and the observed effects can be quantitatively accounted for with a theoretical model which involves the transfer of charge from the Pc ring to the adsorbed O2 and the formation of a Pcδ+–Oδ−2 species at the surface of the Pc film. Symmetry arguments based on a simple bonding model are used to explain the nature of these O2 electron acceptor surface states. Charge transfer complexes such as this are important both to the doping of these organic semiconductors, and to a fundamental understanding of the oxidations photocatalyzed by these porphyrinlike materials which are closely related to some of the processes which occur during photosynthesis.