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.