Photoreduction of 9,10-anthraquinone by triethylamine: a Fourier-transform EPR study

Abstract

Abstract Using time resolved Fourier-transform EPR spectroscopy the photoreduction of anthraquinone by triethylamine in 2-propanol solution was investigated. The spin-polarized anthraquinone triplet deactivates by hydrogen transfer from the solvent and electron transfer from triethylamine generating 10-hydroxy-anthroxyl-9 radicals, ketylradicals and semiquinone anion radicals and amine radical cations, respectively. All radicals are spin-polarized by triplet mechanism and partially by radical pair mechanism. Competitive chemical kinetics of triplet deactivation, lifetimes of two different primary radical ion pairs and secondary reduction reactions of ground state anthraquinone have to be included in the kinetic depending on the lifetimes on the Coulomb-coupled radical ion pairs follow unimolecular decay or are amine catalysed depending on the number of amine molecules in the first solvation shell. Furthermore, the absolute amount of spin polarization and spin lattice relaxation rates of the radicals could be determined.