Pulse radiolyses of anthraquinone and anthraquinone–triethylamine in acetonitrile and toluene at room temperature

Abstract

Nanosecond pulse radiolysis of anthraquinone (AQ) in several solvents has been performed at room temperature, and the following results are obtained: (1) In acetonitrile (CH₃CN), the formation of triplet AQ and a free-radical anion (AQ^˙–) of AQ is observed. The former is produced by energy transfer from an excited neutral of CH₃CN which may be produced via the geminate recombination of a radical cation and a radical anion of CH₃CN in a spur, while the latter is produced by electron transfer from anionic species such as a solvated electron, a monomeric and/or a dimeric radical anion of CH₃CN. In CH₃CN–triethylamine (TEA), both free AQ^˙– and triplet AQ mentioned above are also produced; however, the latter reacts with TEA, giving rise to the formation of free AQ^˙–(from the second triplet state of AQ) and an exciplex of the lowest triplet state of AQ with ground-state TEA. This exciplex decomposes to free AQ^˙– and the radical cation of TEA. (2) In toluene, only triplet AQ is produced by energy transfer from triplet toluene to AQ, and, in the presence of TEA, the formation of the triplet exciplex of AQ–TEA is observed. On a microsecond timescale, however, this exciplex changes to a contact ion pair followed by proton transfer, generating anthrasemiquinone radical and triethylamine radical in accordance with the result of photolysis.