Property tuning in unsymmetrical alkoxy zinc phthalocyanines by introduction of perfluoro-tert-butoxy end groups

Two peripherally octasubstituted zinc phthalocyanines (ZnPcs) bearing six alkoxy residues and two adjacent carboxylic acid anchoring groups were synthesized in order to assess the benefits deriving from the insertion of fluorocarbon domains at the periphery of ZnPc photosensitizers to be used in dye-sensitized solar cells (DSSCs). To this end the alkoxy substituents were terminated with tert-butoxy groups in one case and with perfluoro-tert-butoxy groups in the other. The two ZnPc analogs showed similar light absorption properties and both dyes were able to inject electrons into the conduction band of TiO2 upon photoexcitation. Interestingly, DSSCs based on the fluorous dye exhibited power conversion efficiency almost three times as high as that of its hydrocarbon analog (0.89% vs 0.34%), thus showing that the performance of devices based on ZnPcs can be significantly improved by coating the dye with an outer fluorous layer.