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, 1 5.20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H2P-COOH), 5-[4-benzoic acid]- 10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H2P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H2P-4COOH). The porphyrin-modified TiO2, nanoparticles were deposited on nanostructured OTE/SnO2 electrode together with nanoclusters of fullerene (C-60) 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+C-60)(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 l(3)(-)/l(-) redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO2 nanoparticles with fullerene [OTE/SnO2/(Ar-H2P-COO-TiO2 + C-60)(m), OTE/SnO2/(H-H2P-COO-TiO2+C-60)(n), and OTE/SnO2/(H2P-4COO-TiO2 + C-60)](n) are much larger than those of the reference systems of porphyrin-modified TiO2 nanoparticles Without C-60 [OTE/SnO2/(Ar-H2P-COO-TiO2)(n), OTE/SnO2/(H-H2PCOO-TiO2)(n), and OTE/SnO2/(H2P-4COO-TiO2)(n)]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO2/(H-H2P-COO-TiO2+C-60)(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. (c) 2005 Elsevier Ltd. All rights reserved.