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

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 (bPEB 2 .− ). From the dependence of decay and formation rates on the concentration of bPEB, the bimolecular rate constants of k b =(1.2±0.1)×10 7 to (3.2±0.2)×10 8  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.