Chemically induced dynamic electron polarization in the photoreduction of aromatic ketones with pi pi*-type triplet state

Chemically induced dynamic electron polarization (CIDEP) spectra of radical s produced in the photoreduction reaction of aromatic ketone/triethylamine systems were measured by time resolved ESR method. Anion radicals with net absorption (Abs) CIDEP were produced in ethanol with a base such as KOH, wh ile ketyl type radicals with net emissive (Em) CIDEP have been formed in cy clohexane and benzene. Laser power dependence measurement indicates that ne t Em CIDEP of ketyl radicals is generated by a two-photon process while the production of ketyl radical itself is by one-photon process. Therefore, it was concluded that net Em CIDEP is generated through radical-tripler pair mechanism (RTPM) between the triplet state aromatic ketone and the produced ketyl radical. While RTPM is reasonably considered as an origin of net Em CIDEP for ketyl radicals, it is difficult to determine the CIDEP mechanism of the net Abs polarization of anion radicals in the present systems. Possi ble mechanisms were tentatively proposed for the present net Abs CIDEP gene ration.