Dedicated to Prof. Atsuhiro Osuka on the occasion of his 55 th birthday uptake of selected dyes was demonstrated.

The synthesis and optical characterization of six novel heteroaromatic-based chromophores is described. The new dyes present mostly an A-D-A general framework, where A is an electron-deficient aromatic ring and D is an electron-rich pyrrolo[3,2-b]pyrrole moiety, linked via triple bonds. It was demonstrated that the increase in the molecular length of the chromophore effectively extends π-conjugation. The effect of structural variations on photophysical properties was studied in detail for these compounds and the relationship between the structure and photophysical properties was thoroughly elucidated by comparison with simpler tetraaryl-analogues. The strong charge-transfer characteristic of these functional dyes can be illustrated by large Stokes shifts (4100-7100 cm(-1)) for A-D-A architectures. The replacement of phenyl rings at positions 2 and 5 with the arylethynylaryl substituents bathochromically shifts both absorption and emission at ca. 50-150 nm. The clear dependence of fluorescence maxima on the electron-accepting property of the peripheral arylethynyl substituent emphasizes strong π-conjugation in these molecules. The donor-acceptor interactions were also found to influence the two-photon absorption properties.

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.