Combining Zinc Phthalocyanines, Oligo( p ‐Phenylenevinylenes), and Fullerenes to Impact Reorganization Energies and Attenuation Factors

A study on electron transfer in three electron donor‐acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as the excited‐state electron donor and a fullerene (C 60 ) as the 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. The 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 ⋅  + ‐C 60  ⋅  − charge‐separated state formation comes at the expense of excited‐state interactions following ZnPc photoexcitation. At a first glance, the ZnPc ⋅  + ‐C 60  ⋅  − 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 .