Taking Advantage of the Electronic Excited States of [60]-Fullerenes

The optical, electrochemical and excited state properties of C-60 fullerene and its derivatives, combined with their peculiar structural features, have made them ideal modules for the construction of complex architectures which feature light induced processes. Here are described three selected classes of such systems investigated in our group by taking advantage of some intrinsic excited state properties of C-60 fullerenes such as fluorescence, triplet lifetimes, or sensitized singlet oxygen luminescence. Fullerene hybrid assemblies with Cu(I), Ru(II), and Re(I) complexes undergo ultrafast photoinduced electron transfer (PET) upon excitation of the metal-to-ligand-charge-transfer (MLCT) excited;states of the metal-complexed moiety. In the case of the Cu(I) system, occurrence of PET by fullerene excitation depends on the specific functionalization of the carbon sphere. Fullerodendrimers equipped with oligophenylenevinylene moieties and showing enhanced or reduced PET as a function of dendrimer structure and size are presented along with simpler monochromophoric fullerodendrimers which illustrate the capability of fullerene triplets to probe dendritic shielding effects. The peculiar ground and excited-state properties of rigid and conformationally flexible fullerene-porphyrin systems arranged in a face-to-face fashion are described, both with meso,meso-linked or triply fused porphyrin oligomers. Control of the direction and nature of photoinduced processes is achieved in such systems, which additionally show charge transfer or porphyrin-centered near-infrared luminescence. The whole work is discussed in a historic perspective and further development for photoactive fullerodendrimers and face-to-face arrays, particularly in solar energy conversion devices, is envisaged.