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Azulene-Substituted Aromatic Amines. Synthesis and Amphoteric Redox Behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N‘,N‘-Tetra(6-azulenyl)-p-phenylenediamine and Their Derivatives
journal contribution
posted on 2005-03-18, 00:00 authored by Shunji Ito, Takahiro Kubo, Noboru Morita, Tadaaki Ikoma, Shozo Tero-Kubota, Jun Kawakami, Akio TajiriN,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N‘,N‘-tetra(6-azulenyl)-p-phenylenediamine (2a) and
their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b)
were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic
amines for multistage amphoteric redox materials. The redox behavior of each compound was
characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion
radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups
and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of
anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and
diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene
ring including the central nitrogen atoms. UV−vis spectral analysis of amines 1a,b and diamines
2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption
bands of the neutral species along with an increase of the new absorption maxima at 625, 605,
640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562,
478, and 545 nm, respectively. As indicated by a combined ESR and UV−vis spectral study, the
species giving rise to the new absorption maxima are concluded to be the generation of anion radicals
and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.