Synthesis and electrochemical properties of tetrasubstituted tetraphenylethenes

Tetrakis(4-acetoxyphenyl and 4-benzoyloxyphenyt)ethenes If and 1g were obtained by acylation of tetrakis(4-hydroxyphenyl)ethene 1b. Ullmann etherification of 4,4'-dihydroxybenzophenone 2b and subsequent McMurry coupling yielded tetrakis(phenoxyphenyl)ethene 1i. The tetrakis(acetamidophenyl)ethene 1h was prepared in three steps from tetraphenylethene 1c by nitration, Raney-Ni reduction and subsequent acetylation. Alternatively, trifluoroacetamide 1j, 2-methylhexanamide 1k and 2,4-dimethylbenzamide 11, with less tendency to form 2D hydrogen bonding networks and thus increased solubility as compared to 1h, were prepared by acylation of 4,4'-diaminobenzophenone 2a and subsequent McMurry coupling. Compounds 1f-1 were investigated by cyclic voltammetry. While the phenyl ether derivative If displays single-electron processes during oxidation, a two-electron process was discovered for trifluoroacetamide 1j as was also supposed for the esters 1f and 1g. In addition, comproportionation constants were shown to be dependent on the solvent. In situ IR spectroelectrochernistry provided evidence for quinoidal type substructures in the dioxidized forms of tetraphenylethenes 1. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)