Dimerization Reaction of Regioisomeric Bis(phenylethynyl)benzene Radical Anions during Pulse Radiolysis

Abstract

Dimerization of a series of regioisomeric 1,4-, 1,3-, and 1,2-bis(phenylethynyl)benzene radical anions (bPEBs^.−) substituted by various electron-donor and/or electron-acceptor groups was studied during the pulse radiolysis in N,N-dimethylformamide (DMF). The transient absorption of bPEB^.− decayed with the formation of new bands attributed to the dimer radical anion of bPEB^.− and bPEB (bPEB₂^.−). From the dependence of decay and formation rates on the concentration of bPEB, the bimolecular rate constants of k_b=(1.2±0.1)×10⁷ to (3.2±0.2)×10⁸ M⁻¹ s⁻¹ were estimated. It is suggested that bPEB^.− dimerizes with bPEB through the formation of a CC bond between two sp carbon atoms, to give σ-type dimer radical anion (σ-(bPEB)₂^.−) with a diene-type structure. The k_b values of bPEB^.− with bPEB changed with the substitution pattern of the phenylacetylene group on the central benzene ring and the various kinds of donor and/or acceptor group.