Antimony halides as solvents. Part VIII. Spectral studies of polycyclic hydrocarbons in liquid antimony trichloride solution

Abstract

The u.v.–visible spectra of 16 aromatic hydrocarbons have been measured in liquid antimony trichloride at 80 °C. They all show at least one clearly defined absorption band which is not observed in the absorption spectrum of either component alone. For the weakly basic polycyclic hydrocarbons the single band is attributed to charge-transfer interaction. The more basic hydrocarbons show additional bands due to R,SbCl₂⁺ formed in the equilibrium reaction: R + 2SbCl₃⇌ R,SbCl₂⁺+ SbCl₄^–. Perylene which is oxidised quantitatively to the radical cation in liquid antimony trichloride in the presence of oxygen shows an identical spectrum to that in sulphuric acid. The spectrum of naphthacene and pentacene radical cations has also been measured.