Redox‐Induced Modulation of Exchange Interaction in a High‐Spin Ground‐State Diradical/Triradical System

Abstract 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 ( J 1 / k B = +3.1 K) and quartet ground state with a strong exchange interaction ( J 2 / k B = +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.