Step-by-step fabrication of porphyrin-fullerene supramolecular assemblies and their photoelectrochemical properties

Porphyrin-fullerene C-60 multilayered films have been successfully fabricated on an indium-tin-oxide (ITO) substrate by step-by-step, self-assembling, and surface sol-gel processes. First, cysteamine was self-assembled on the ITO surface, and then a C-60 layer was formed via N-H addition reaction. The layered C-60 further underwent another N-H addition with 1,2-diaminoethane to enable formation of the subsequent C-60 layer, giving a double-layered C-60 film. Meanwhile, the layered C-60 was treated with 2-aminoethanol to implant hydroxy groups on the C-60 layer, which was essential to promote the surface sol-gel reaction with titanium(IV) butoxide for implanting the titanium oxide layer. Then tetracarboxyphenylporphyrin was superimposed on the titanium oxide layer by the subsequent surface sol-gel reaction. By repeating these surface sol-gel reactions, the porphyrin layer was further assembled on the outermost layer. Accordingly, the porphyrin and C-60 multilayered films could be fabricated by the series of above-described step-by-step reactions. Absorption, fluorescence, quartz crystal microbalance, and photoelectrochemical investigations were carried out. Considerable photoinduced electron transfer between photoexcited porphyrin to C-60 was verified, even in the presence of the titanium oxide linking layer. Appreciable photocurrent generation from the multilayered films was observed, and its mechanism is described.