Case Study for Artificial Photosynthesis: Noncovalent Interactions between C₆₀-Dipyridyl and Zinc Porphyrin Dimer

In this study, a new modified C₆₀ derivative with an oPE/oPPV conjugated bridge bearing two pyridyl groups has been used in combination with a flexible porphyrin dimer (<b>ZnP</b>_<b>2</b>) to construct an electron donor/acceptor hybrid (<b>C</b>_<b>60</b><b>-dipyr·ZnP</b>_<b>2</b>). This hybrid is based on metal to ligand coordination between the zinc centers of the porphyrin dimer and the two pyridyl groups that oPE/oPPV linker bears. In order to investigate the interactions between the electron donor and acceptor entities, both in the ground state and in the excited states, comprehensive photophysical assays have been carried out. In particular, both absorption and fluorescence titrations provided evidence for strong interactions between the electron donor and the electron acceptor within the hybrid. A binding constant (<i>K</i>_ass) in the order of 5.0 × 10⁵ M^–1 has been derived. Furthermore, transient absorption measurements revealed intramolecular electron-transfer from the photoexcited porphyrin dimer (<b>ZnP</b>_<b>2</b>) to the fullerene derivative (<b>C</b>_<b>60</b><b>-dipyr</b>), leading to a long-lived charge-separated state with a lifetime of up to 1525 ps