Influence of topology on the long-range electron-transfer phenomenon.

Intramolecular electron-transfer phenomena in the radical anions derived from the partial reduction of diradicals (E,E)-p-divinylbenzene-beta,beta'-ylene bis(4-tetradecachlorotriphenylmethyl) diradical (1) and (E,E)-m-divinylbenzene-beta,beta'-ylene bis(4-tetradecachlorotriphenylmethyl) diradical (2) have been studied by optical and ESR spectroscopy. The synthetic methodology used allows for complete control of the geometry of diradicals 1 and 2, which have para and meta topologies, respectively, as well as of their E/Z isomerism. This fact is used to show the influence of the different topologies on the ease of electron transfer, which is larger for the para than for the meta isomer, in which a small or negligible electronic coupling is observed. A related monoradical compound (E)-bis(pentachlorophenyl)[4-(4-bromophenyl-beta-styryl)-2,3,5,6-tetrachlorophenyl]-methyl radical (3), which has only one such redox site, has also been obtained and studied for comparison purposes.