Pyridinium-Functionalized Pyromellitic Diimides with Stabilized Radical Anion States

In this work, we report the stabilization of the reduced states of pyromellitic diimide by charge-balancing the imide radical anions with cationic pyridinium groups attached to the aromatic core. This structural modification is confirmed by single-crystal X-ray diffraction analysis. Characterization by (spectro)­electrochemical experiments and computations reveal that the addition of cationic groups to an already electron-deficient ring system results in up to +0.57 V shifts in reduction potentials, largely as a consequence of charge screening and lowest unoccupied molecular orbital-lowering effects. This formal charge-balancing approach to stabilizing the reduced states of electron-deficient pyromellitic diimides will facilitate their incorporation into spin-based optoelectronic materials and devices.