Spectroscopic and electrochemical properties of 4-[(4′-hydroxy-3′,5′-dimethylphenyl)(aryl)-methylene]-2,6-dimethylcyclohexa-2,5-dienones

Diaryl quinone methides, 4-[(4′-hydroxy-3′,5′-dimethylphenyl)(aryl)-methylene]-2,6-dimethylcyclohexa-2,5-dienone (where aryl = 4-hydroxyphenyl, 1a; 4-methoxyphenyl, 1b; 3,4,5-trimethoxyphenyl, 1c) are synthesised by oxidation of the corresponding bis-phenols. These molecules are solvatochromic and have interesting acid–base properties. The neutral cationic and anionic states of 1 have characteristic visible absorptions, thus they can be used as indicators. Isomeric cations generated from 1b can be clearly distinguished by visible spectroscopy. The electrochemical properties of these diaryl quinone methides, 1a–1c are studied by cyclic voltammetry and coupled ESR. In the case of 1a, a quasi-reversible redox process is observed. In the case of either 1b or 1c two quasi-reversible redox couples are observed. The electrochemical processes are explained in terms of radical intermediates which are resonance stabilised. Stabilisation of this radical intermediate by methoxy group is inferred.