Pulse radiolysis study of salt effects on reactions of aromatic radical cations with Cl–. Part 2.—Spectral shifts and decay kinetics of diphenylpolyene radical cations in the presence of tetrabutylammonium hexafluorophosphate

Abstract

Pulse radiolysis of all-transα,ω-diphenyl-substituted polyenes, such as 1,4-diphenylbuta-1,3-diene, 1,6-diphenylhexa-1,3,5-triene and 1,8-diphenyl-octa-1,3,5,7-tetraene, in 1,2-dichloroethane solution has been undertaken in the absence and presence of Bu₄NPF₆. The absorption maxima of the diphenylpolyene radical cations are shifted to shorter wavelengths in the presence of the salt. This is evidence for the formation of the contact ion pairs between the radical cations and PF^–₆. The decays of the radical cations, which are due to neutralization reactions with Cl^–, are retarded by the addition of the salt. The rate constants for the neutralization reactions have been determined for the free-ion and ion-paired states. The pulse radiolysis results are compared with those for other aromatic compounds such as triphenylethylene, tetraphenylethylene and perylene. The appreciable spectral shift is characteristic of the diphenylpolyene radical cations.