Metallophthalocyanines: Versatile electron-donating building blocks for fullerene dyads

A thorough investigation on the physicochemical properties, including electrochemisty and photophysics, of a new class of donor-acceptor hybrids, namely, phthalocyanine-fullerene dyads, consisting of free base la and zinc and copper complexes Ib and le, respectively, brings new insights into the stabilization of charge-separated radical ion pairs and the impact of redoxactive transition-metal centers on the photoperformance of macrocyclic phthalocyanines. In these dyads, the role of the phthalocyanines is twofold: First, it functions as an antenna (i.e., absorbing very efficiently light in the visible region of the solar spectrum) and, second, as a donor molecule-once photoexcited. The initial photoexcitation is succeeded by an ultrafast electron transfer largely due to the strong electronic coupling between electron donor (Pc) and electron acceptor (C ₆₀) generating surprisingly long-lived radical ion pairs Pc ^•+-C ₆₀ ^•- with lifetimes of several nanoseconds. Large driving forces for the charge recombination and small reorganization energies of the Pc-C ₆₀ ensembles corroborate slow charge recombination dynamics, which, in turn, helps to rationalize the long lifetimes of Pc ^•+-C ₆₀ ^•+.