Large hydroazaacene diimides: synthesis, tautomerism, halochromism, and redox-switchable NIR optics

A series of dihydro- and tetrahydro-tetraazaacene diimides containing 6 or 7 laterally fused six-membered rings were synthesized. Halochromic and redox-switchable vis-NIR optical characteristics were exhibited. Quinonoid tautomers of dihydrotetraazaacene derivatives were obtained and characterized, which exhibited adequate stability and existed in equilibrium with the more commonly observed benzenoid tautomer.