Facile fabrication and photolectrochemical properties of porphyrin-fullerene assemblies by self-assembly and surface sol-gel processes

Ultrathin photoelectric conversion films consisting of a porphyrin-fullerene photoredox pair were fabricated by the combined use of room-temperature covalent-bonding and surface sol-gel processes. First, cysteamine was self-assembled on an indium-tin-oxide (ITO) electrode. The cysteamine-modified electrode was then immersed in C₆₀ solution, giving immobilization of C₆₀ via bond formation between the amino group of cysteamine and C₆₀. Next, the C₆₀-modified electrode was dipped in 2-ethanolamine solution to implant the hydroxy group to the immobilized C₆₀ via the bond formation between C₆₀ and the amino group; thus, the hydroxy group was exposed as the outermost layer. Then, Ti(OBu)₄ and tetracarboxyporphyrin (TCPP) were alternately assembled on the C₆₀ layer by the surface sol-gel process, to give an assembly of TCPP, titanium oxide species [Ti(O)], and C₆₀ on the ITO electrode. The double layering of TCPP-Ti(O) was possible. The spectral characterization of the films was carried out. In the presence of sacrificial reagents, anodic photocurrents were generated from these modified electrodes. The incorporation of the C₆₀ layer resulted in the substantial enhancement of the photocurrents as compared with that of the TCPP layer alone, suggesting effective electron-transfer reactions between TCPP and C₆₀ that contribute to the photocurrent increase. The photocurrents increased by the double layering of the TCPP and Ti(O) layers.