Synthesis, crystal structure, and physical properties of 7,14-disubstituted pentacene-5,12-diones containing a methylenequinoid structure.

Title 7,14-disubsituted pentacene-5,12-diones were prepared for the first time by a nucleophilic substitution reaction of a pentacene-5,7,12,14-tetraone with aryl- or ethynyllithiums followed by a dehydroxylation reaction. The methylenequinoid structures with two conjugated carbonyl groups were clearly observed in their crystal structures. They showed intense absorptions in the visible region and amphoteric redox properties with high reduction potentials.