UV–vis and ECD spectroelectrochemistry of atropisomeric naphthalenediimide derivative

The UV–vis and ECD spectroelectrochemistry (SEC) of a chiral binaphthalenylamine derivative of the N-butyl naphthalenediimide (NDIB-NH₂) enantiomers were applied to measure UV–vis and ECD spectra of NDIB-NH₂ radicals and dianion formed in the reduction and oxidation processes observed in cyclic voltammetry (CV). The CV curves and EPR spectroelectrochemistry enabled us to establish conditions at which a radical-anion [NDIB-NH₂]̇.⁻, a dianion [NDIB-NH₂]²⁻, and a radical-cation [NDIB-NH₂]̇.⁺ are formed. The DFT restricted open-shell CAM-B3LYP-D3/def2TZVP/PCM calculations demonstrated that in the radical-anion [NDIB-NH₂]̇.⁻, spin is spread over the NDI system while in the radical-cation [NDIB-NH₂]̇⁺ it is spread over the aminonaphthalene moiety. The UV–vis spectra of radical-anion and dianion show the most significant changes in the 400–800 nm range. In that range, the ECD spectra varied with the change of electrode potential more than the UV–vis did and enabled the identification of a new ECD band of [NDIB-NH₂]̇.⁻ at ca. 400 nm hidden in the background in the UV spectra at −1000 mV. A broad structured ECD pattern with a maximum at ca. 530 nm was observed for [NDIB-NH₂]̇.⁻ (−1000 mV), while a single smooth ECD band of [NDIB-NH₂]²⁻ was located at 520 nm (−1750 mV). For the first time, an isosbestic point (455 nm) was found in ECD spectroelectrochemical measurements for the radical-cation [NDIB-NH₂]̇.⁺ in equilibrium with the NDIB-NH₂ neutral form. The TD-DFT CAM-B3LYP-D3/6-31G** calculations combined with the hybrid (explicit combined with implicit) solvation model fairly well reproduced the UV–vis and ECD SEC of neutral and redox forms of NDIB-NH₂ but the ECD spectrum of [NDIB-NH₂]̇.⁺ above 390 nm.