peri-Diselenolo-substituted 1,8-naphthalimide derivatives as bipolar matrices for redox reactions in a non-aqueous electrolyte†

Abstract

In the search for bipolar organic materials as electrodes in rechargeable batteries, we report peri-diselenolo-substituted 1,8-naphthalimides (NIs). The molecular architecture consists of structural motifs comprising a naphthalimide core, the peri-diselenide bridge, hydrogen or halogens at positions 3 and 6, and an alkyl chain with a fixed length of 4 and 8. The resulting architecture is unprecedented in the naphthalimide chemistry and quantum chemical modelling was employed to rationalize the new design better. The NI-derivatives are prepared starting from tetra-halogenated naphthalic anhydride via nucleophilic substitution at both peri-positions in the respective imide. Non-covalent interactions facilitate the NIs self-organization into ordered nanostructures studied by SEM, PXRD, solid-state NMR spectroscopy and molecular modelling. The electrochemical properties of NI-derivatives are analysed in half lithium-ion cells with ionic liquid electrolytes. By comparing the experimentally determined potentials with the theoretically calculated ones, the mechanism of electrochemical oxidation and reduction is deduced. It is shown that below 2.0 V, NIs interact with a maximum of 6Li⁺ due to the sequential reduction of the diselenide bridge and the carbonyl groups, whereas above 4.0 V, the oxidation of NIs takes place with the participation of the electrolyte counterion TFSI⁻ as a result of the involvement of Se atoms and carbons in the naphthalene unit. The hydrogen and halogen substituents affect both the self-organization, reduction and oxidation of NIs. The structural, morphological and compositional changes of the NIs after prolonged cycling are discussed based on ex situ XRD, SEM/EDS and EPR analyses. The data demonstrate that a molecular architecture based on peri-diselenolo-1,8-naphthalimide derivatives could be used to design new classes of organic bipolar electrodes.