Combining zinc phthalocyanines, oligo(p-phenylenevinylenes), and fullerenes to impact reorganization energies and attenuation factors.

In the present article the study of electron transfer in three electron donor-acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as excited state electron donor and a fullerene (C60) as ground state electron acceptor. These complexes are brought together by axial coordination at ZnPc. The key variable in our design is the length of the molecular spacer, namely oligo-p-phenylenevinylenes. Lack of appreciable ground state interactions is in accordance with strong excited state interactions as inferred from the quenching of ZnPc centered fluorescence and the presence of a short-lived fluorescence component. Full-fledged femtosecond and nanosecond transient absorption spectroscopy assays corroborated that the ZnPc•+-C60•- charge-separated state formation comes at the expense of excited state interactions following ZnPc photoexcitation. At first glance, the ZnPc•+-C60•- charge-separated state lifetime increased from 0.4 to 86.6 ns as the electron donor-acceptor separation increased from 8.8 to 29.1 Å. A closer look at the kinetics revealed that the changes in charge-separated state lifetime are tied to a decrease in the electronic coupling element from 132 to 1.2 cm-1, an increase in the reorganization energy of charge transfer from 0.43 to 0.63 eV, and a large attenuation factor of 0.27 Å-1.