Electronic absorption spectra and geometry of radical ions of tetraphenylethylene.

概要

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The geometry of the radical ions of tetraphenylethylene was studied by means of electronic absorption spectroscopy. The spectrum of the anion radical produced by γ-ray irradiation in frozen 2-methyltetrahydrofuran changes markedly on controlled warming. The resultant spectrum resembles the spectra of the anion radical in fluid solutions produced by potassium reduction and by pulse radiolysis. These spectra are distinctly different from the spectra of diphenylmethanide ion and of diphenylmethyl radical. From these facts it is inferred that the relaxed anion radical has a geometry in which the central ethylenic bond is twisted by an angle considerably smaller than 90°, in contrast with the near 90° twist in the dianion, and in which each bond connecting a phenyl group with an ethylenic carbon atom is twisted by a smaller angle than in the molecule. The spectrum of the cation radical produced by γ-ray irradiation in frozen matrices is similar to that of the cation radical produced by pulse radiolysis in fluid solutions and changes only slightly on controlled warming. The geometry of the relaxed cation radical is suggested to be similar to that of the molecule, in contrast with that of the anion radical.
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