title: Diindolo[2,3-b:2',3'-f]pyrrolo[3,2-b]pyrroles as electron-rich, ladder-type fluorophores: synthesis and optical properties.
abstract: Previously unknown ladder-type heteroacenes were synthesized in just two steps from aromatic amines, 2-nitrobenzaldehydes, and biacetyl. A recently discovered multicomponent process affording 1,4-dihydropyrrolo[3,2-b]pyrroles was followed by the Cadogan reaction, which resulted in simultaneous closure of two additional pyrrole rings. Rod-like compounds synthesized in this way were stable in the absence of light, and they were transformed into bis(tert-butoxycarbonyl) derivatives. The rigid herringbone-like structure resulted in a strong absorption in the λ=350-410 nm region and very strong violet and blue emission, which was bathochromically shifted relative to the emission of the parent 1,4-dihydropyrrolo[3,2-b]pyrroles. The optical properties of these compounds strongly suggest that the conjugation spanned the entire π system. The HOMO energy level was located at -4.6 to -5.1 eV.
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw (Poland).
authors.forename: Anita
authors.initials: A
authors.lastname: Janiga
authors.forename: Maciej
authors.initials: M
authors.lastname: Krzeszewski
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Gryko
keywords: HOMO level; acenes; fluorescence; fused-ring systems; nitrogen heterocycles