Synthesis of new porphyrin-fullerene dyads capable of forming charge-separated states on a microsecond lifetime scale.

A series of covalently linked axially symmetric porphyrin-fullerene dyads with a rigid pyrrolo[3,4-c]pyrrolic linker enabling a fixed and orthogonal arrangement of the chromophores has been synthesized and studied by means of transient absorption spectroscopy and cyclic voltammetry. The lifetime of the charge-separated state has been found to depend on the substituents on the porphyrin core, reaching up to 4 μs for a species with meso-(p-MeOC6H4) substituents. The ground and excited electronic states of model compounds have been calculated at the DFT and TD-DFT B3LYP(6-31G(d)) levels of theory and analyzed with regard to the effect of the substituent on the stabilization of the charge-separated state in the porphyrin-fullerene ensemble with a view to explaining the observed dependence.