Pulse radiolysis of monohalogenated biphenyls. Correlation of absorption spectra of the radical cations with photoelectron spectroscopic data

Abstract

Radical cations from monohalogenated biphenyls have been investigated by means of pulse radiolysis, and their optical and kinetic properties are compared with corresponding data for the biphenyl radical cation itself. While fluoro substitution does not exert a strong effect on the optical absorption characteristics and decay kinetics of the radical cations, para-substitution by chlorine, bromine, or iodine leads to a substantial red shift in the absorption maxima and an increase in the half-life. The maxima of the transient near i.r. absorption bands can be linearly correlated to ionization potentials from photoelectron spectroscopy. The data suggest that the investigated monohalogenated biphenyls undergo at least partial planarization upon radical-cation formation.