ELECTRON-TRANSFER CHEMISTRY AND REDOX-SWITCHING OF STILBENE-LIKE HETEROAROMATIC-COMPOUNDS - SYNTHESES, OPTOELECTROCHEMICAL AND ESR ENDOR STUDIES/

Redox-active compounds, in which the electron donor and the acceptor s ubunits are covalently linked by a vinylene spacer group were synthesi sed and their properties were investigated by cyclovoltammetry, spectr oelectrochemistry, and ESR/ENDOR spectroscopy. - 10-Methylphenothiazin yl, 10-methylphenoxazinyl, and phenoxathiinyl were used as electron-do nating groups whereas 9,10-anthraquinon-2-yl and phenyl groups were em ployed as accepters. The synthesis of the push-pull-substituted stilbe nes 1a, 1b, 1c, 2a, 2b, and 2c was achieved by Wittig coupling of the heterocyclic aldehydes with the anthraquinoyl or phenyl phosphonium sa lts. The diastereoisomers were separated either by chromatography or b y crystallization. - The redox potentials of the (Z) and (E) isomers d iffer only slightly. Spectroelectrochemical measurements indicate that the radical cations of the phenothiazine and phenoxazine derivatives undergo rearrangement from the (Z) to the (E) isomers. On the other ha nd, electron attachment leads to configurationally stable radical anio ns. This behaviour is rationalised in terms of the electron distributi on reflected by the hyperfine data established by ESR/ENDOR spectrosco py.