Phenyl-substituted cibalackrot derivatives: Redox behavior, structure-properties relationships and in situ UV-vis/EPR-spectroelectrochemistry of radical ions

Abstract

Redox properties and UV–vis and EPR spectroelectrochemical behavior of cibalackrot (7,14-diphenyldiindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13‑dione, 1) and its six derivatives 2 - 7 carrying two substituted phenyl rings have been examined. The dyes are of potential interest for organic electronics and singlet fission for solar energy conversion. The compounds are reduced in two reversible one-electron steps under formation of a stable primary radical anion. Oxidation yields the radical cation in a first reversible step and the second step is quasireversible. The presence of radical ions was confirmed by in situ UV–vis/EPR spectroelectrochemistry. The substituents have different influence on oxidation and on reduction, as revealed using the LFER approach and interpreted with the help of calculated energies of frontier orbitals. The observed first reduction (Ered1) and first oxidation (Eox1) potentials correlate well with the calculated values and their difference (ΔE1) has photophysical relevance because it reflects the energy of HOMO-LUMO gap.