Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO 2 nanoparticles for light energy conversion

Abstract

TiO 2 nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di- tert-butylphenyl]-21 H,23 H-porphyrin ( Ar– H 2P – COOH ), 5-[4-benzoic acid]-10,20-tris[3,5-di- tert-butylphenyl]-21 H,23 H-porphyrin ( H– H 2P – COOH ), and 5,10,15,20-tetra[4-benzoic acid]-21 H,23 H-porphyrin ( H 2P – 4COOH ). The porphyrin-modified TiO 2 nanoparticles were deposited on nanostructured OTE/SnO 2 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 TiO 2 composite electrode denoted as OTE/SnO 2/(porphyrin-modified TiO 2 nanoparticle+C 60) n . The porphyrin-modified TiO 2 composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using I 3 − / I − redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO 2 nanoparticles with fullerene [OTE/SnO 2/( Ar– H 2P – COO– TiO 2 +C 60) n , OTE/SnO 2/( H– H 2P – COO– TiO 2 +C 60) n , and OTE/SnO 2/( H 2P – 4COO– TiO 2 +C 60) n ] are much larger than those of the reference systems of porphyrin-modified TiO 2 nanoparticles without C 60 [OTE/SnO 2/( Ar– H 2P – COO– TiO 2 ) n , OTE/SnO 2/( H– H 2P – COO– TiO 2 ) n , and OTE/SnO 2/( H 2P – 4COO– TiO 2 ) n ]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO 2/( H– H 2P – COO– TiO 2 +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 TiO 2 nanoparticles plays an important role in improvement of the light energy conversion properties.