Organization of supramolecular assembly of 9-mesityl-10-carboxymethylacridinium ion and fullerene clusters on TiO2 nanoparticles for light energy conversion

TiO2 nanoparticles modified with composite nanoclusters of 9-mesityl-10-carboxymethylacridinium ion (Mes-Acr(+)-COOH) and fullerene (C-60) in acetonitrile-toluene (3 : 1, v/v) were deposited as thin films on nanostructured SnO2 electrode using an electrophoretic technique. The composite TiO2 films have broad as well as high absorbance properties, exhibiting a photoactive response under visible light excitation using I-3(-)/I- redox couple, in contrast with the reference multilayer films composed of the single component. This indicates that the composite cluster TiO2 film based on 9-mesityl-10-carboxymethylacridinium ion and fullerene harvests light widely in the visible region due to organization of the supramolecular assembly. In the case of a monolayer system of TiO2 nanocrystallites modified with Mes-Acr(+)-COOH, however, no net photocurrent is observed in the photocurrent action spectrum. This indicates that TiO2 nanoparticles act as materials to organize composite molecules rather than as those to accept electrons. An incident photon-to-photocurrent generation efficiency (IPCE) of 37% has been achieved at an applied bias potential of 0.2 V vs. SCE in the Mes-Acr(+)-COOH/C-60 composite system using TiO2 nanoparticles.