Influence of the alkyl-chains length on the electronic structure and interface properties of 1,4-octasubstituted Zinc Phthalocyanines thin films on gold

We compare the interface properties of various 1,4,8,11,15,18,22,25 octa-alkyl-substituted zinc phthalocyanines fsButd8PcZn, sHepd8PcZn, sDecd8PcZng with those of unsubstituted zinc phthalocyanine sPcZnd on gold using x-ray photoemission spectroscopy and valence band ultraviolet photoemission spectroscopy. Although the separation between the aromatic cores in the evaporated thin films depends clearly on the alkyl-chain length, it is found that the nature of the substituents causes only minor changes of electronic properties, such as optical gap and ionization potential. It is shown that the observed small energetic shifts for film thicknesses larger than the molecule size cannot be understood in terms of a band bending like mechanism