The solid-state thermal reaction of brilliant red 3,3′,5,5′-tetraphenyldiphenoquinone 1 was examined. Three reductive colorless products, the corresponding hydroquinone and two benzofuran derivatives, were formed at 289.5 °C. Theoretical studies indicated that thermally excited triplet species having radical-type oxygen atoms participated in the reaction. Single-crystal diffraction study revealed short atomic contacts between carbonyl oxygen and the ortho-positions of the phenyl group, and these short atomic contacts would promote the thermal solid-state reaction. The reductive reactions observed in cumene, a radical propagation solvent and/or a hydrogen radical donating solvent, supported our speculation.
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