Electronic absorption spectra and geometry of anion radicals generated from (E)-stilbene and ‘stiff’ stilbenes

Abstract

The electronic absorption spectra of anion radicals produced by γ-ray irradiation of (E)-stilbene (1), indeno[2,1-a]indene (2), 5,6,11,12-tetrahydrochrysene (3), (E)-1,1′-bi-indanylidene (4), and (E)-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-binaphthylidene (5) in glassy 2-methyltetrahydrofuran solution at 77 K have been measured. Examination of the spectra leads to the following conclusions. (a) The (E)-stilbene skeleton in the anion radical of (1) as well as of (2), (3), and (4) is planar or nearly planar; (b) in the anion radical of (5) immediately after its production, the ethylene bond and the C–Ph bonds are substantially twisted, and on controlled warming or on illumination, the twisting of the ethylene bond is increased.