Abstract

Abstract In toluene and ethanol containing triethylamine (TEA), a reaction of the lowest excited triplet state [3AQ(T1)] of anthraquinone (AQ) with ground-state TEA gave rise to the formation of an exciplex [3(AQ–TEA)*] which converted into a contact ion pair between the AQ radical anion (AQ−·) and the TEA radical cation (TEA+·). By an intramolecular proton transfer, this contact ion pair yielded anthrasemiquinone radical followed by the formation of 9,10-anthracenediol (AQH2); in ethanol, the monoanion (AQH−) of AQH2 was also produced. In ethanol/TEA, moreover, not only the decay rate constant of 3(AQ–TEA)* but also the quantum yield for the photoreduction of AQ were affected by the change of TEA concentration. This was interpreted in terms of the existence of a rapid interconversion between 3(AQ–TEA)* and atriplex [3(AQ–TEA2)*] of 3AQ(T1) with ground-state TEA. In contrast to the exciplex formation in ethanol and toluene, free AQ−· (and TEA+·) and 3(AQ–TEA)* [or a contact (or solvent-separated) ion pair between AQ−· and TEA+·] were produced in acetonitrile via the second and lowest excited triplet states of AQ, respectively: In the submicrosecond time regime, 3(AQ–TEA)* or the contact (or solvent-separated) ion pair dissociated into the radical ions (AQ−· and TEA+·) followed by their second-order reaction yielding finally AQH2 and AQH−.

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