Highly Twisted 1,2:8,9-Dibenzozethrenes: Synthesis, Ground State, and Physical Properties

Two soluble and stable 1,2:8,9-dibenzozethrene derivatives (3,a,b) are synthesized through a palladium-catalyzed cyclodimerization reaction. X-ray crystallographic analysis shows that these molecules are highly twisted owing to congestion at the cove region. Broken-symmetry DFT calculations predict that they have a singlet biradical ground state with a smaller biradical character and a large singlettriplet energy gap; these predictions are supported by NMR and electronic absorption measurements. They have small energy gaps and exhibit far-red/near-infrared absorption/emission and amphoteric redox behaviors.