Effect of solvent on spectra produced by pulse radiolysis of solutions of organic electron scavengers

Abstract

Pulse radiolysis of some organic electron scavengers in solvents covering a range of polarity indicates the type of product found spectroscopically to be a function of the polarity and the reactivity of the solvent. In solvents of low polarity large yields of the triplet state of the solute are produced except in cases where the excited solute can abstract a hydrogen atom from the solvent. In solvents of intermediate polarity (tetrahydrofuran and triethylamine) much lower yields of triplet states are formed and increased yields of anions and neutral radicals are obtained. However, anion yields are still much less than those recorded for glassy solutions at 77 °K. Naphthalene is unable to reduce G ( ɸ 2 ĊOH) when solutions of benzophenone in either an ether or an aliphatic amine are pulsed and it is concluded that for these solvents triplet benzophenone is not a major precursor of ɸ 2 ĊOH, although it plays a significant role in cyclo hexane. Aqueous solutions of molecules known to have highly characteristic triplet-triplet absorption spectra give very low or undetectable yields of triplet states. The yield of the naphthalene-hydrogen atom adduct increases through the series; benzene, cyclo hexane, tetrahydrofuran, diethyl ether, triethylamine, methanol, water, i.e. it follows the yield of separated ion pairs. Evidence as to the nature of the precursors of this species and those of the triplet states of the solutes is presented.