Electronic States of 2,3-Diamino-1,4-naphthoquinone and Its N‑Alkylated Derivatives

Diaminoquinones with a captodatively stabilized biradicaloid structure are candidates for singlet fission, but few such compounds are known. We report the solution spectroscopy and photophysics of 1,2,2,3-tetramethyl-2,3-dihydro-1H-naphtho­[2,3-d]­imidazole-4,9-dione (1): its steady-state and transient UV–visible absorption, linear dichroism in stretched poly­(vinyl alcohol), and magnetic circular dichroism. We also describe the absorption spectra of the stable radical ions 1 •+ and 1 •– and of two parent structures, 2,3-diamino-1,4-naphthoquinone (2) and 2,3-bis­(methylamino)-1,4-naphthoquinone (3). The spectra are interpreted and electronic transitions are assigned by comparison with the results of density functional theory and MS-CASPT2 calculations.