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Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s
Author(s) -
Edelmann Michael J.,
Raimundo JeanManuel,
Utesch Nils F.,
Diederich François,
Boudon Corinne,
Gisselbrecht JeanPaul,
Gross Maurice
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200207)85:7<2195::aid-hlca2195>3.0.co;2-g
Subject(s) - chemistry , trimer , chromophore , dimer , cyclic voltammetry , crystallography , fluorene , fluorescence , photochemistry , supramolecular chemistry , delocalized electron , stereochemistry , electrochemistry , polymer , electrode , organic chemistry , physics , quantum mechanics , crystal structure
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 ( 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‐9 H ‐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 hetero‐trimers featuring extended π ‐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 π ‐electron conjugation along the oligomeric backbone, as had previously been observed for DEE‐substituted porphyrins.