Poly(triacetylene) Oligomers: Synthesis, Characterization, and Estimation of the Effective Conjugation Length by Electrochemical, UV/Vis, and Nonlinear Optical Methods

Martin, Rainer E.; Günter, Peter; Bosshard, Christian; Gubler, U.; Gramlich, Völker; Gross, Maurice; Boudon, Corinne; Gisselbrecht, Jean‐Paul; Diederich, François

doi:10.1002/chem.19970030919

Cited by 84 publications

(103 citation statements)

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“…3,a) [6], in agreement with a significant increase in p-electron delocalization along the elongated backbone. In contrast, the insertion of a hetero-spacer between two DEE moieties, in most cases, did not produce a similar extension of p-electron conjugation ( Table 2).…”

supporting

confidence: 74%

“…While DEE oligomers such as those in the series 1a and 1b display increasing third-order optical nonlinearities with increasing chain-length [6], they exhibit only little fluorescence emission. The introduction of aromatic spacers between two DEE moieties may alter both linear and nonlinear optical as well as fluorescence properties, thus opening the way to new and interesting classes of oligomers and polymers.…”

mentioning

confidence: 98%

“…Also, the trans-Pt II (PEt 3 ) 2 center in 14 was expected to partially interrupt p-electron conjugation along the linear backbone [16]. For further comparison, the trimeric PTA oligomer 3 [6], with a DEE homo-spacer, was also considered in this study.…”

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confidence: 99%

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Modulation ofπ-Electron Conjugation in Oligo(triacetylene) Chromophores by Incorporation of a Central Spacer

Martin

Wytko

Diederich

et al. 1999

HCA

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A comprehensive series of trimeric hybrid oligomers 4 – 14 (Fig. 2) was prepared by insertion of different hetero‐spacers between two (E)‐hex‐3‐ene‐1,5‐diyne (=(E)‐1,2‐diethynylethene, DEE) moieties, and the optical and electrochemical properties of the resulting π‐conjugated materials compared to those of the DEE dimer 2 and trimer 3, which formally contains a DEE moiety as homo‐spacer. The hetero‐spacers varied from benzenoid (phenylene, naphthalene, biphenylene, anthracene), to π‐electron‐deficient (pyrazine, pyridine) and π‐electron‐rich (thiophene, furan) aromatic rings, and to an organometallic trans‐Pt(PEt3)2 fragment. The hybrid oligomers were synthesized following a general strategy which relied on the Sonogashira cross‐coupling between mono‐deprotected DEE 15 and the appropriately bis‐functionalized spacer (Scheme and Table 1). UV/VIS Studies revealed that the majority of the hetero‐spacers were less effective than the homo‐spacer DEE in facilitating π‐electron delocalization along the linearly conjugated oligomeric backbone (Table 2 and Fig. 3). With increasing degree of benzenoid aromaticity in the hetero‐spacer, the electronic communication between the terminal DEE moieties in the hybrid oligomers was reduced. As a remarkable exception, a large bathochromic shift of the longest‐wavelength absorption maximum, which is indicative of enhanced π‐electron delocalization, was obtained upon introducing an anthracene‐9,10‐diyl moiety as hetero‐spacer into oligomer 7 (Figs. 3 and 6). Electrochemical investigations by cyclic and steady‐state voltammetry confirmed the limited extent of π‐electron delocalization in the majority of the hybrid oligomers (Table 3). The fluorescence properties of many of the DEE hybrid materials were dramatically enhanced upon incorporation of the hetero‐spacers (Table 2). The heterocyclic derivatives 10 – 12, containing pyridine, pyrazine, or thiophene spacers, respectively, displayed a strong fluorescence emission, which is present to a significant extent neither in DEE homo‐oligomers nor in the individual heteroaromatic spacer components, demonstrating the value of combining different repeat units to modulate oligomeric and polymeric properties. The pyridine derivative 10 provided an interesting example of a molecular system, in which both the electronic absorption (Fig. 4) and emission characteristics (Table 2) can be reversibly switched as a function of pH (Fig. 5).

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Modulation ofπ-Electron Conjugation in Oligo(triacetylene) Chromophores by Incorporation of a Central Spacer

Martin

Wytko

Diederich

et al. 1999

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“…The enhanced solubility of oligomers 19a-f allowed an estimation of the effective conjugation length [30] of PTA polymers [28]. The effective conjugation length indicates the number of repeat units in a conjugated polymer required to furnish size-independent redox, optical, and other properties.…”

Section: Methodsmentioning

confidence: 99%

“…A second interest in monodisperse -conjugated oligomers of defined length and constitution arises from their potential to act as molecular wires in molecular scale electronics and nanotechnological devices [25]. Therefore, we prepared two series of oligomers 18a-e, end-capped with phenylethynyl residues [26,27] and Me 3 Si-end-capped 19a-f [28] in order to estimate, by extrapolation, the properties of infinite-chain PTA polymers (Scheme 6). The series of monomer to hexamer 19a-f has recently been extended to a monodisperse hexadecamer with a length of 11.9 nm [29].…”

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Functional acetylenic molecular architecture

Diederich¹

1999

Pure and Applied Chemistry

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A diversity of perethynylated building blocks, in particular derivatives of tetraethynylethene (TEE, 3,4-diethynylhex-3-ene-1,5-diyne), were prepared for the construction of multinanometer-sized functional molecular objects. Macrocyclic acetylenic scaffolding yielded perethynylated antiaromatic octadehydro [12]annulenes and aromatic dodecadehydro [18]annulenes as well as highly stable expanded radialenes with extended all-carbon cores. An attempted new synthesis of perethynylated octadehydro [12]annulenes was unsuccessful and led to the isolation of a highly strained permethylenated cycloocta-1,5-diyne instead. Acyclic acetylenic scaffolding using both TEEs and 1,2-diethynylethenes (DEEs (E)-hex-3-ene-1,5-diynes) afforded the first oligomers and polymers with the poly(triacetylene) backbone [PTA, -(CϵC-CR¼CR-CϵC) n -]. The effective conjugation length for this third class of linearly conjugated polymers with a nonaromatic all-carbon backbone, besides polyacetylene and poly(diacetylene), was determined to be in the range of 7-10 monomeric units. By lateral attachment of dendrons along the conjugated backbone of PTA oligomers, cylindrically shaped dendrimers were obtained which can be viewed as insulated molecular wires. Donoracceptor substituted arylated TEEs and DEEs were prepared, and their unusual electrochemical properties and tendency to undergo photochemical trans → cis isomerization were investigated. Measurements of third-order nonlinear optical effects by third harmonic generation revealed useful structure-function relationships. The highest second hyperpolarizabilities ␥ were obtained for two-dimensionally fully conjugated systems with reduced molecular symmetry. PERETHYNYLATED BUILDING BLOCKS FOR MODULAR CHEMISTRYAcetylenic molecular scaffolding in one, two, and three dimensions aims at producing new nanoscale molecular and polymeric materials that exhibit unusual electronic and optical function and properties. These efforts have greatly benefited from the recent renaissance in preparative acetylene chemistry [1] and, in particular, from the discovery of novel metal-catalyzed cross-coupling reactions for C-C bond formation [2]. A rich variety of peralkynylated building blocks have been prepared as starting materials in this modular synthetic approach to new advanced materials [3][4][5][6] and, among these, derivatives of tetraethynylethene (1, TEE, 3,4-diethynylhex-3-ene-1,5-diyne) [7][8][9] are particularly useful. Today, TEEs of nearly any desired functionalization and silyl-protection are available. Additional perethynylated chromophores such as the [3]radialene 2 [10] and [3]cumulene 3 [11] have been prepared in our laboratory. On the other hand, all efforts to synthesize the perethynylated allene 4, a precursor to threedimensional networks and for formation of helical polymers, have failed in the past [12] (Scheme 1). MACROCYCLIC ACETYLENIC SCAFFOLDINGOxidative Glaser-Hay macrocyclization of cis-bis(trialkylsilyl)-protected TEEs yielded the per(silylethynyl)ated octadehydro [12]annulenes...

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PM3 geometry optimization and CNDO/S-CI computation of UV/Vis spectra of large organic structures: Program description and application to poly(triacetylene) hexamer and taxotere

1999

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Poly(triacetylene) Oligomers: Synthesis, Characterization, and Estimation of the Effective Conjugation Length by Electrochemical, UV/Vis, and Nonlinear Optical Methods

Cited by 84 publications

References 43 publications

Modulation ofπ-Electron Conjugation in Oligo(triacetylene) Chromophores by Incorporation of a Central Spacer

Modulation ofπ-Electron Conjugation in Oligo(triacetylene) Chromophores by Incorporation of a Central Spacer

Functional acetylenic molecular architecture

PM3 geometry optimization and CNDO/S-CI computation of UV/Vis spectra of large organic structures: Program description and application to poly(triacetylene) hexamer and taxotere

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