Dedicated to Professor David N. Reinhoudt on the occasion of his 60th birthdayIn continuation of a previous study on the modulation of p-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 p-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 p-electron conjugation along the oligomeric backbone, as had previously been observed for DEE-substituted porphyrins.Introduction. ± In a previous study, we had explored how the properties of oligomers made from (E)-1,2-diethynylethene (DEE, (E)-hex-3-ene-1,5-diyne) repeating units can be tuned or changed by the insertion of spacer chromophores [1]. For this purpose, a series of eleven hybrid oligomers 1 ± 11 (Fig. 1) were prepared, in which mostly aromatic hetero-spacers with different electronic characteristics were introduced between two DEE moieties. UV/VIS Studies revealed that the majority of the hetero-spacers were less effective than the homo-spacer DEE in trimeric 12 in facilitating p-electron delocalization along the linear conjugated oligomeric backbone. Electrochemical investigations by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) confirmed these results.On the other hand, fluorescence studies clearly demonstrated that a desirable function can be created or strongly enhanced upon insertion of hetero-spacers into pure DEE oligomers [2 ± 4]. Thus, the heterocyclic derivatives 7 ± 9, containing pyridine, pyrazine, or thiophene spacers, respectively, feature a strong fluorescence emission, which is present to a signi...

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We describe the first polymer-supported synthesis of poly(triacetylene)-derived monodisperse oligomers, utilizing Pd 0 -catalyzed Sonogashira and CadiotÀChodkiewicz-type cross-couplings as the key steps in the construction of the acetylenic scaffolds. For our investigations, Merrifield resin functionalized with a 1-(4-iodoaryl)triazene linker was chosen as the polymeric support (R2; Figure and Scheme 3). The linker selection was made based on the results of several model studies in the liquid phase (Schemes 1 and 2). For the solidsupport synthesis of the oligo(phenylene triacetylene)s 7b ± 7d, a set of only three reactions was required: i) Pd 0 -catalyzed Sonogashira cross-coupling, ii) Me 3 SiÀalkyne deprotection by protodesilylation, and iii) cleavage of the linker with liberation of the generated oligomers (Scheme 5). The longest-wavelength absorption maxima of the oligo(phenylene triacetylene)s 7a ± 7d shift bathochromically with increasing oligomeric length, from l max 337 nm (monomer 7a) to 384 nm (tetramer 7d; Table 2). Based on the electronic absorption data, the effective conjugation length (ECL) of the oligo(phenylene triacetylene)s is estimated to involve at least four monomer units and 40 C-atoms. p-Electron conjugation in these oligomers is less efficient than in the known oligo(triacetylene)s 14a ± 14d (Table 2) due to poor transmittance of p-electron delocalization by the phenyl rings inserted into the oligomeric backbone. Similar conclusions were drawn from the electrochemical properties of the two oligomeric series as determined by cyclic (CV) and rotating-disk voltammetry (RDV ; Table 3). In sharp contrast to 14b ± 14d, the oligo(phenylene triacetylene)s 7b ± 7d are strongly fluorescent, with the highest quantum yield F F 0.69 measured for trimer 7c ( Table 2). Whereas the Sonogashira cross-coupling on solid support proceeded smoothly, optimal conditions for alkyneÀalkyne cross-coupling reactions employing Pd 0 -catalyzed CadiotÀChodkiewicz conditions still remain to be developed, despite extensive experimentation (Scheme 7 and Table 1).

We report the first synthesis of poly(triacetylene)-derived oligomers by Pd(0)-catalysed Sonogashira and Cadiot-Chodkiewicz-type cross-coupling reactions on solid support. Oligo(phenylene triacetylene)s, members of a new class of linearly pi-conjugated oligomers with all-carbon backbones, feature very high fluorescence intensities.

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