Highly dimerizable radical cation of 3,3′,5,5′‐tetramethylbenzidine

Cation radical salts of 3,3′,5,5′‐tetramethylbenzidine (TMB) were studied in terms of dimerization of the radical cation, and compared with the salts of other aromatic diamines, including Wurster's blue perchlorate. ESR spectra of several TMB salts were measured in solid‐state, and analyzed by the singlet‐triplet model for a radical dimer. The singlet‐triplet energy separation has been obtained as 0.15 eV for (TMB)ClO4. The dimerization of the TMB radical cation in acetonitrile solution of (TMB)ClO4 was estimated from ESR and visible spectral results. In consequence, (TMB)+. is highly dimerizable in solution, compared with the systems of other diamines.