title: Synthesis and optical properties of acidochromic amine-substituted benzo[a]phenazines.
abstract: A new series of alkylamine- or arylamine-substituted benzo[a]phenazines have been synthesized from 1,2-naphthoquinones by employing simple sequential Michael-type addition with a variety of primary and secondary amines and the condensation reaction of the resulting amine-substituted 1,2-naphthoquinones with o-phenylenediamine. They exhibited absorption peaks originating from the charge transfer transition between the amine and pyrazine segments and benzo[a]phenazine localized π-π* transitions. Although the absorption spectra of the dyes were not significantly influenced by the nature of the solvents, addition of TFA led to a prominent red-shift in the absorption spectra owing to the protonation at the quinoxaline segment which enhanced the electron-accepting ability. The qualitative trends observed in the optical properties and acidochromism were supported by density functional theoretical computations. The dyes displayed positive solvatochromism in the emission spectra suggestive of a more polar excited state. The dyes were also characterized by a quasi-reversible reduction couple originating from the pyrazine segment which underwent shifts corresponding to electron-donating strength of the amine segment.
authors.affiliation: Organic Materials Lab, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247 667, India.
authors.forename: Prachi
authors.initials: P
authors.lastname: Singh
authors.forename: Abhishek
authors.initials: A
authors.lastname: Baheti
authors.forename: K R Justin
authors.initials: KR
authors.lastname: Thomas