Novel trends of electrochemical oxidation of amino-substituted triphenylamine derivatives

A series of amino-substituted triphenylamine derivatives have been synthesized and the electrochemical and spectral characteristics has been investigated. Triphenylamine is also used as a reference. p-Amino-triphenylamine (1) showed two reversible redox couples at E1/2 = 0.59 and 1.09 V in CH2Cl2. The stable cation radical 1+ was generated electrochemically and exhibited strong bands in the visible region as determined in situ by UV/Vis/NIR spectroelectrochemical methods. The second oxidation product 12+ could be generated electrochemically, but was not very stable after long time electrolysis at applied potentials higher than 1.15 V. p,p′-Diamino-triphenylamine (2), p-methyl-p′,p″-diamino-triphenylamine (2a), p-methoxy-p′,p″-diamino-triphenylamine (2b) and p,p′,p″-triamino-triphenylamine (3) are more stable in CH3CN than in CH2Cl2 during cyclic scans at oxidation potentials. The oxidation potentials of the various amino-substituted TPA derivatives and the stability of the oxidized products are solvent-dependent and relate to the molecular structures.