Organization of supramolecular assemblies of fullerene, porphyrin and fluorescein dye derivatives on TiO2 nanoparticles for light energy conversion

TiO2 nanoparticles were modified with a porphyrin derivative, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H2P-COOH), and fluorescein derivatives, 9-[2-(3-carboxy-9,10-diphenyl)anthryl]-2,7-difluoro-6-hydroxy-3H-xanthen-3-one (DPAX-COOH) and 2′,7′-difluorofluorescein (FL-COOH). The dye-modified TiO2 nanoparticles were deposited on nanostructured OTE/SnO2 (OTE: optically transparent electrodes) together with nanoclusters of fullerene (C60) from acetonitrile/toluene (3:1, v/v) using an electrophoretic deposition technique. The dye-modified TiO2 composite electrodes [OTE/SnO2/(dye + C60)n] have broad as well as high absorbance properties in the visible region, exhibiting the photo response under visible light excitation using I3-/I- redox couple. The incident photon to photocurrent efficiency (IPCE) for these electrodes increases in order: OTE/SnO2/(H2P)n < OTE/SnO2/(H2P-COO-TiO2)n < OTE/SnO2/(H2P-COO-TiO2 + C60). The IPCE value can be further improved by replacing H2P-COOH with a fluorescein derivative containing an electron donor moiety: DPAX-COOH (DPA: diphenylanthracene). The maximum IPCE value (42%) is obtained for OTE/SnO2/(DPAX-COO-TiO2 + C60)n under the bias of 0.2 V vs. SCE.