Electrochemical and structural investigation of the interactions between naphthalene diimides and metal cations

Abstract

The effects of Li⁺ and Mg²⁺ on the electrochemical behaviour and photoreduction of N,N′-bis(2,6-diisopropylphenyl)naphthalene diimide (Dipp₂NDI) have been investigated using cyclic voltammetry and UV-vis spectroscopy. Strong cation–anion interactions between Li⁺ or Mg²⁺ and [Dipp₂NDI]²⁻ result in solvent-dependent anodic shifts of the NDI˙^−/2− redox couple. In organic solvents of moderate dielectric constant and donor ability, the two, one-electron redox processes typically observed for Dipp₂NDI merge into a single, two-electron process. This strong metal cation effect has been leveraged for the photoreduction of Dipp₂NDI to [Dipp₂NDI]²⁻via a disproportionation process. Chemical reduction of Dipp₂NDI with iPrMgCl has allowed the isolation of Mg²⁺ complexes of [Dipp₂NDI]²⁻. Single crystal X-ray diffraction was used to determine the structure of a dimeric complex, [(Dipp₂NDI)Mg₂(THF)₃]₂, that features strong coordination of Mg²⁺ by the oxygen atoms of the reduced NDI.