AN ELECTRON-SPIN-RESONANCE STUDY OF THE 2,5-DIPHENYLCHALCOPHENE RADICAL IONS

The 2,5-diphenylchalcophene radical ions (chalcogen = O, S, Se, Te) have been prepared by the action of alkali metal in 1,2-dimethoxyethane (anions), or by the action of sulphuric acid or thallium(III) trifluoroacetate in trifluoroacetic acid (TFAH) (cations), on the parent compounds. The ESR spectra of these radical ions have been interpreted as belonging to systems which are conformationally rigid on the ESR timescale, as is evident from the non-equivalence of the ortho- and meta-proton hyperfine coupling constants. The furan, thiophene and selenophene radical ions exhibit ESR spectra which are consistent with the expectation that the LUMO of the parent is symmetric and the HOMO, antisymmetric. The tellurophene radical anion shows a coupling to 125Te of 13.5 G in its ESR spectrum, while the spectrum of the tellurophene radical cation suggests that a change in the nature of the HOMO might have occurred in progressing down the series. When the tellurophene was photolysed in H2SO4/TFAH, the ESR spectrum of the furan radical cation was observed. The implication of this is discussed. © 1990.