Bis-semiquinone (bi-radical) formation by photoinduced proton coupled electron transfer in covalently linked catechol-quinone systems: Aviram's hemiquinones revisited

The structure and reactivity of a covalently linked catechol-ortho-benzoquinone (hemiquinone) is studied by UV-Vis and IR absorption spectroscopy. Nanosecond transient absorption spectroscopy of the hemiquinone reveals the formation of bi-radical state consisting of two semiquinone units. It is a long-lived state resulting from proton coupled electron transfer (PCET).