In homogeneous catalysis, the catalyst is in the same phase as the reactant. The number of collisions between reactants and catalyst is at a maximum.In a patent, 148231-12-3, name is 5,8-Dibromoquinoxaline, introducing its new discovery. COA of Formula: C8H4Br2N2
Dramatically enhanced fluorescence of heteroaromatic chromophores upon insertion as spacers into oligo(triacetylene)s
In continuation of a previous study on the modulation of pi-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 (Fig. 1), a new series of trimeric hybrid oligomers (14-18 and 22-24, Fig. 2) were prepared (Schemes 1-3). Spacers used were both electron-deficient (quinoxaline-based heterocycles, pyridazine) and electron-rich (2,2?-bithiophene, 9,9-dioctyl-9H-fluorene) chromophores. With 19-21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra (Fig. 3) revealed that the majority of spacers provided heterotrimers featuring extended pi-electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo-trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non-fluorescent, the corresponding hetero-trimer may show a strong emission (Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) (Table 3 and Fig. 5). In each case, the first one-electron reduction step in the hetero-trimers appeared anodically shifted compared with DEE dimer 13 and homo-trimer 12. With larger spacer chromophore extending into two dimensions (as in 14-18, Fig. 2), the anodic shift (by 240-490 mV, Table 3) seems to originate from inductive effects of the two strongly electron-accepting DEE substituents rather than from extended pi-electron conjugation along the oligomeric backbone, as had previously been observed for DEE-substituted porphyrins.
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Reference£º
Quinoxaline – Wikipedia,
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