Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO2 nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (). The porphyrin-modified TiO2 nanoparticles were deposited on nanostructured OTE/SnO2 electrode together with nanoclusters of fullerene (C60) in acetonitrile–toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO2 composite electrode denoted as OTE/SnO2/(porphyrin-modified TiO2 nanoparticle+C60)n. The porphyrin-modified TiO2 composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using image redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO2 nanoparticles with fullerene [OTE/SnO2/(+C60)n, OTE/SnO2/(+C60)n, and OTE/SnO2/(+C60)n] are much larger than those of the reference systems of porphyrin-modified TiO2 nanoparticles without C60 [OTE/SnO2/()n, OTE/SnO2/()n, and OTE/SnO2/()n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO2/(+C60)n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO2 nanoparticles plays an important role in improvement of the light energy conversion properties.