Radical and Redox Forms of Pyridyl Appended MB-DIPYs.

Abstract

We discuss the synthesis and properties of pyridine-appended nickel(II) complex of "Manitoba dipyrromethene" (Ni^II(MB-DIPY)), which is stable radical at ambient conditions. The Ni^II(MB-DIPY), 6^• shows absorption at ∼1300 nm and a g-value of ∼2.00 in EPR. The redox features of Ni^II(MB-DIPY) were studied by electro- and spectroelectrochemistry. The reduced form, 6^-, has an intense NIR absorption and a broad spectrum in the visible region, making this compound a prospective non-fullerene acceptor for light-harvesting. The axial coordination and photophysical properties of the supramolecular dyad formed between pyridine-appended Ni^II(MB-DIPY) with zinc 5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin (TPP^F20Zn) were also studied. Ni^II(MB-DIPY) 6^• failed to interact with TPP^F20Zn. However, reduced Ni^II(MB-DIPY) in its anionic form, 6^-, self-assembles and forms a donor-acceptor dyad with TPP^F20Zn with a binding constant of K_a = 1.13 × 10² M^-1 and fluorescence quenching constant of K_SV = 1.31 × 10³ M^-1. This work represents the first report on the potential of MB-DIPYs to self-assemble and form a donor-acceptor type supramolecular dyad with TPP^F20Zn. This study explored the potential of the MB-DIPYs to act as a non-fullerene acceptor in light-harvesting supramolecular donor-acceptor systems formed via non-covalent interactions.