Aerial oxidation of protonated aromatic amines. Isolation, X-ray structure, and redox and spectral characteristics of N-containing dyes.

This work reports the results of our investigation on the aerial oxidation of aromatic amines that are promoted by protic acid. While primary aromatic amines produce substituted phenazines as major products, N-phenyl-o-phenylenediamine produces polycyclic aromatic heterocycles like azaacene and secondary and tertiary amines give exclusively the dyes containing a triphenylmethane moiety. Isolation of the compounds and the effects of substitutions on the aromatic rings have been investigated. In this context, plausible reaction steps that are involved have been discussed. Single-crystal X-ray structure analyses of the representative compounds are solved to authenticate their formation. In almost every case, a high degree of delocalization of electron was noted. The compounds have been characterized thoroughly and show rich spectral properties. For example, the phenazine molecules exhibited absorption peaks between 475 and 605 nm because of the charge-transfer transition from the amine and tricyclopyrazine moiety. Their acidochromic and solvatochromic behaviors, which are supported by theoretical calculations, are investigated. The polycyclic azacene molecule exhibits strong absorption in the visible region and fluoresces with high quantum yield. The phenazine dyes undergo a quasi-reversible reduction at a low cathodic potential that varies linearly as a function of Hammett's constant.

One-pot synthesis of linearly fused N-heterocyles from their angular analogues and studies of their redox and electrochromic properties.

In an unusual chemical transformation, the angular heterocyclic compound [1]ClO(4), upon reaction with a primary aromatic amine, is transformed to a linear heterocyclic compound 3 via the angular intermediate [2]ClO(4) in one pot. Characterization of the compounds was primarily achieved by (1)H and (13)C NMR and mass spectral data. Analyses of single-crystal X-ray structures of the representative compounds confirmed their identities. These compounds exhibit notable spectral and redox properties. Their redox behavior is followed by spectral characterization of the electro-generated radicals. Electrochromic properties of the reference compounds are also explored.

Synthesis of azoaromatic dyes via redox driven C-N bond fusion.

Two novel organic azo-dyes (2(+)) that feature an intense intramolecular charge transfer transition with end absorption reaching into the NIR region are introduced. Syntheses of these compounds were achieved by an unusual redox-driven C-N bond fusion of the tricyclo azo-aromatic compounds (1(+)). The compounds show reversible electro- as well as proton chromism. The results have generated further scope of research in the area of designed syntheses of functional azoaromatics.