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 1a and zinc and copper complexes 1b and 1c, 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 •- .