Organization of supra molecular 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 (C₆₀) 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 I₃^-/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/C₆₀ composite system using TiO₂ nanoparticles.