Dramatically enhanced fluorescence of heteroaromatic chromophores upon insertion as spacers into oligo(triacetylene)s was written by Edelmann, Michael J.;Raimundo, Jean-Manuel;Utesch, Nils F.;Diederich, Francois. And the article was included in Helvetica Chimica Acta in 2002.SDS of cas: 148231-12-3 This article mentions the following:
In continuation of a previous study on the modulation of π-electron conjugation of oligo(triacetylene)s by insertion of central hetero-spacer fragments between two (E)-hex-3-ene-1,5-diyne ((E)-1,2-diethynylethene, DEE) moieties, trimeric hybrid oligomers (I; A = spacer, R = SiEt3, SiMe3) were prepared Spacers used were both electron-deficient (quinoxaline-based heterocycles, pyridazine) and electron-rich (2,2′-bithiophene, 9,9-dioctyl-9H-fluorene)chromophores. With a dipyridophenazine spacer, transition metal complexes were synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramol. assembly. The UV/visible spectra revealed that the majority of spacers provided heterotrimers featuring extended π-electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer and homo-trimer. This increase in emission intensity appears as a general feature of these systems: even if the spacer mol. is nonfluorescent, the corresponding hetero-trimer may show a strong emission. The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating disk voltammetry (RDV). In each case, the first 1-electron reduction step in the hetero-trimers appeared anodically shifted compared with DEE dimer and homo-trimer. With larger spacer chromophore extending into two dimensions, the anodic shift (by 240-490 mV) seems to originate from inductive effects of the two strongly electron-accepting DEE substituents rather than from extended π-electron conjugation along the oligomeric backbone, as had previously been observed for DEE substituted porphyrins. In the experiment, the researchers used many compounds, for example, 5,8-Dibromoquinoxaline (cas: 148231-12-3SDS of cas: 148231-12-3).
5,8-Dibromoquinoxaline (cas: 148231-12-3) belongs to pyrazine derivatives. Pyrazine has the elements of symmetry for the point group D2h. It has three mutually perpendicular two-fold axes. It also has three mutually perpendicular planes of symmetry. As a result, pyrazine also has a centre of symmetry. Pyrazines undergo nearly all of the same reactions as pyrimidines, from nucleophilic substitution (SNAr) to palladium-catalyzed cross coupling reactions.SDS of cas: 148231-12-3