Investigation of the Photoreduction of Anthraquinonedisulfonic Acid by Triethylamine with Fourier Transform Electron Spin Resonance

Abstract

The photoreduction of 9,10-anthraquinone-1,5-disulfonate and 9,10-anthraquinone-2,6-disulfonate with triethylamine in aqueous solution has been studied by laser photolysis using time-resolved Fourier transform electron spin resonance and optical detection in the nanosecond and microsecond time scale. With FT-ESR the semiquinone radical anions and the triethylamine radical cations could be detected at pH = 11 in Coulomb-coupled radical pairs in addition to the separated semiquinone radical anions. At pH = 14, the α-aminoalkyl radical could be detected as the decay product of the triethylamine radical cation. From the time dependence of the spin-polarized ESR intensities of the various components the lifetime of the Coulomb-coupled radical ion pair was determined. The radical ion pair decay exhibits a two-component behavior with a fast and a slow decay time. These lifetimes depend on the pH of the solution and are on the order of 10 ns to 2 μs.