Electron‐Transfer Chemistry and Redox‐Switching of Stilbene‐Like Heteroaromatic Compounds — Syntheses, Optoelectrochemical and ESR/ENDOR Studies

Abstract

AbstractRedox‐active compounds, in which the electron donor and the acceptor subunits are covalently linked by a vinylene spacer group were synthesised and their properties were investigated by cyclovoltammetry, spectroelectrochemistry, and ESR/ENDOR spectroscopy. — 10‐Methylphenothiazinyl, 10‐methylphenoxazinyl, and phenoxathiinyl were used as electron‐donating groups whereas 9,10‐anthraquinon‐2‐yl and phenyl groups were employed as acceptors. The synthesis of the push‐pull‐substituted stilbenes 1a, 1b, 1c, 2a, 2b and 2c was achieved by Wittig coupling of the heterocyclic aldehydes with the anthraquinoyl or phenyl phosphonium salts. The diastereoisomers were separated either by chromatography or by crystallization. — The redox potentials of the (Z) and (E) isomers differ 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 hand, electron attachment leads to configurationally stable radical anions. This behaviour is rationalised in terms of the electron distribution reflected by the hyperfine data established by ESR/ENDOR spectroscopy.