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−.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
In solvents with an oxygen atom such as EPA (ether-isopentane-ethanol5:5:2 in volume ratio), ethanol, ethanolwater, and 2-methyltetrahydrofuran at 77 K, o-benzoylbenzoic acid (BBA) and methyl o-benzoylbenzoate (MBB) exhibit dual phosphorescences, and their decay curves can well be analyzed by biexponential functions with lifetimes almost equal to those of the triplet-triplet absorptions. Since phosphorescence excitation spectra in solvents stated above indicate the existence of two types of ground-state BBA (and MBB), we have proposed that the short-lived (Ta) and long-lived (Tb) triplet states are produced independently by excitation of the corresponding ground-state conformers. In solvents with no oxygen atom such as cyclohexane and 3-methylpentane, however, no dual phosphorescences can be seen. This may be due to the existence of a rapid interconversion between the T, and Tb states.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.