Radical and Redox Forms of Pyridyl Appended MB‐DIPYs

We present the properties of the first pyridyl-appended nickel(II) complex of Manitoba dipyrromethene. Axial coordination of Ni^II(MB-DIPY)s with TPP^F20Zn was studied using UV–vis and fluorescence spectroscopy. The electronic structures and spectroscopic properties of the chromophores were investigated theoretically by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.

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.

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