Redox‐induced Modulation of Exchange Interaction in a High‐spin‐ground‐state Diradical/Triradical System

A triplet ground-state diradical molecule, bis(nitronyl nitroxide)-substituted diphenyldihydrophenazine (1(..) ), that can be converted into a one-electron oxidized species, 1(...+) , in the quartet ground state has been developed. Surprisingly, these species, 1(..) and 1(...+) , can be used under ambient conditions because they are reasonably stable under aerobic conditions, even in solution. The temperature-dependent magnetic susceptibilities reveal that 1(..) and 1(...+) are in the triplet state, with a weak exchange interaction (J1 /kB = +3.1 K) and quartet ground state with a strong exchange interaction (J2 /kB = +160 K), respectively. The interconversion between the neutral and one-electron oxidized species can be realized through electrochemical reactions. Significantly different absorption bands in the near-IR region newly appeared in the electronic spectra acquired during electrochemical oxidation/reduction.