Preparation, Structure, and Amphoteric Redox Properties of p-Phenylenediamine-Type Dyes Fused with a Chalcogenadiazole Unit

4,7-Bis(dialkylamino)benzo[c][1,2,5]chalcogenadiazoles are a novel class of organic dyes that undergo reversible two-stage one-electron oxidation as well as one-electron reduction. They exhibit absorption maxima in the long-wavelength region, which are assigned as intramolecular charge transfer bands from the phenylenediamine moiety to the electron-accepting heterocycle. Their redox properties as well as molecular and crystal structures are affected by the alkyl substituents on the amino nitrogen and/or by the chalcogen atom (O, S, Se) in the heterocycle.