Formation, spectral, electrochemical, and photochemical behavior of zinc N-confused porphyrin coordinated to imidazole functionalized fullerene dyads

Donor-acceptor dyads were constructed using zinc N-confused porphyrin (ZnNCP), a structural isomer of zinc tetraphenylporphyrin, as a donor, and fullerene as an electron acceptor. Two derivatives, pyridine-coordinated zinc N-confused porphyrin (Py:ZnNCP) and the zinc N-confused porphyrin dimer (ZnNCP-dimer) were utilized to form the dyads with an imidazole-appended fulleropyrrolidine (C₆₀lm). These porphyrin isomers formed well-defined 1:1 supramolecular dyads (C₆₀lm:ZnNCP) via axial coordination. The dyads were characterized by optical absorption and emission, ESI-mass, ¹H NMR, and electrochemical methods. The binding constant, K, was found to be 2.8 × 10⁴ M^-1 for C ₆₀lm:ZnNCP. The geometric and electronic structure of C ₆₀lm:ZnNCP were probed by using DFT B3LYP/3-21G(*) methods. The HOMO was found to be on the ZnNCP entity, while the LUMO was primarily on the fullerene entity. The electrochemical properties of C₆₀lm:ZnNCP was probed using cyclic voltammetry in o-dichlorobenzene, 0.1 n-Bu ₄NClO₄. The Py:ZnNCP was found to be easier to oxidize by over 340 mV compared to Py:ZnTPP. Upon dyad formation via axial coordination, the first oxidation revealed an anodic shift of nearly 90 mV. Evidence of photoinduced charge separation from the singlet excited ZnNCP to the appended fullerene was established from time-resolved emission and nanosecond transient absorption studies.