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.