An EPR and theoretical investigation of azoalkane and azobenzene radical cations

Abstract

Results for azoethane, 1,1′-azopropane, 2,2′-azopropane, 1,1′-azoadamantane, 2,3-diazabicyclo-[2.2.2]oct-2-ene (DBO), 1,4-dimethyl-2,3-diazabicyclo[2.2.2]oct-2-ene (Me₂DBO) and cis and trans-azobenzene radical cations are presented, as formed in solid freon matrices at low temperatures. The azoalkane radical cations are all formed in σ-states, corresponding to ionisation of the a_g orbital (out-of-phase lone-pair combination), while for the trans-azobenzene radical cation the assignment to the π-state cannot be definitely excluded, although experimental evidence would appear to suggest the σ-state: the cis-azobenzene radical cation isomerises to the trans-isomer. Semi-empirical calculations were also performed on selected examples of the above species, the conclusions from which are discussed.