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 indiumtin-oxide (ITO) electrode. The cysteamine-modified electrode was then immersed in C(60) solution, giving immobilization of C(60) via bond formation between the amino group of cystearnine and C(60). Next, the C(60)-tnodified electrode was dipped in 2-ethanolamine solution to implant the hydroxy group to the immobilized C(60) via the bond formation between C(60) 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 C(60) layer by the surface sol-gel process, to give an assembly of TCPP, titanium oxide species [Ti(O)], and C(60) 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 C(60) 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 C(60) that contribute to the photocurrent increase. The photocurrents increased by the double layering of the TCPP and Ti(O) layers.