Photochemically induced dynamic nuclear polarization of 9,10- diphenylanthracene endoperoxide

Abstract

Abstract 1 H and 13 C nuclear spin polarizations are observed during light irradiation of 9,10-diphenylanthracene endoperoxide. It is shown that phenol and 10-hydroxy-10-phenyl-9-anthrone (HPA) are formed via a radical pair mechanism depending on the irradiation wavelength. The first step of the reaction consists in the formation of biradicals: through a CO bond cleavage in the far UV (γ ⩽ 290 nm) or through an OO bond cleavage when γ ⩾ 350 nm. The first biradical undergoes a fragmentation to a phenoxy/9-anthrone-10-phenyl-10-yl radical pair. Electron transfer in the latter produces a phenoxide anion and the related cation. Scavenging of these species by water leads to polarized phenol and HPA. The second biradical rearranges in a diepoxide. Its lifetime should be longer than 100 ps as it produced chemically induced dynamic nuclear polarization effects in the diepoxide. Phenol and HPA are then formed by subsequent reactions of this transient diepoxide. Singlet photoexcited states are involved in all these reactions.