Synthesis of novel amphiphilic zinc phthalocyanines and fabrication of zinc phthalocyanine¯titanium oxide multilayers

Two novel amphiphilic zinc phthalocyanines (TAZnPc and ASZnPc) have been synthesized. It has been shown that they form stable monolayers on a nanometer-sized colloidal TiO2 subphase and are suitable for the fabrication of alternating zinc phthalocyanine-titanium oxide multilayers via the Langmuir¯Blodgett method. Surface pressure-area isotherm and absorption spectroscopic studies show that uniform TAZnPc (ASZnPc)¯TiO2 alternating multilayers are formed. It has been found that the TAZnPc molecules lie almost flat on the substrate surface, while ASZnPc molecules are oriented nearly perpendicular to the substrate surface. Transparent SnO2 electrodes coated with alternating ASZnPc¯TiO2 multilayers were found to exhibit a higher photovoltage response than TAZnPc¯TiO2 coated electrodes. This demonstrates that the molecular arrangement of the zinc phthalocyanine moiety in the multilayers has an important influence on the photovoltaic properties of the sensitized SnO2 electrode.