Oligothiophenes precursors

The heteroaromatic stannanes undergo the normal electrophilic substitution reactions of their protic precursors, and often to an enhanced degree. They are often prepared with the aim of a subsequent Stille cross-coupling reaction, and oligothiophenes with potentially useful optical and electron properties have been prepared by coupling between stannyl- and bromo-thiophenes, for example, Equation (63).204... 

The spiro-oligothiophenes shown in Fig. 33 are similar to 68. These com-poimds were reported by Pei and coworkers, who utihzed the Suzuki cross-coupUng reaction to connect the precursor thiophene chains and the halo-genated spiro cores [28,121). 

The first dyad molecule in which a fullerene was covalently linked to an oligothiophene 2.102 (Chart 1.20) was realized by Zotti elal. as a precursor for a corresponding polythiophene [202]. An azo... 

Soluble polythiophenes, 317 Soluble precursor route, 295 Solvatochromism, 329, 593 Solvent and solution pH, 431 Spectroelectrochemistry, 834 Spectroscopic methods, 535 Spin density, 837 Spiro oligothiophenes, 635 Structural analysis, 3 Structural nature, 2 Structure of polytoluidines, 575 Substituted polyanilines, 532, 619 Substituted pyrroles, 442 Sulfonates, 833... 

Thienyllitium and 4-hexyl-2-thienyllithium reacted with hexafluorobenzene to give the triaryl derivatives 201 (65 %) and 202 (66 %), respectively. The procedure is noteworthy since the lithiation of 3-hexylthiophene was regiospecific and resulted in the isolation of a single isomer. The compounds 201, 202 have been used as precursors for oligothiophene 203 synthesis and preparation of polymeric materials [105]. 

The main interest of unsubstituted oligothiophenes lies in their solid-state properties and in their application as organic semiconductors in electronic devices. Oligothiophenes may be synthesized via two dilferent routes, either by C—C-linkage reactions between thiophenes and/or oligothiophenes or by ring closure reactions from acychc precursor molecules. 

Ring closure reactions of acyclic precursor molecules Uke e.g. diacetylenes, 1,4-diketones, or 1,4-dithiins to form thiophene rings are also widely used to synthesize various types of oligothiophenes. These reactions are described in section 3.2.I.3. 

Aside from the arene-coupling methods, oligothiophenes can also be synthesized by ring closure reactions from aQ clic precursor molecules. Since there have been many reports using ring closure methods for the synthesis of mainly bi- and terthiophene derivatives [37], in the following only those examples which are related to conjugated materials are described. 

The cyclization of thienyl-substituted diacetylenes with hydrogen sulfide or sodium sulfide is also a very successful method for the synthesis of oligothiophenes. The key point here is the synthesis of the precursor diynes. Symmetrical diacetylenes can be obtained by the oxidative coupling of acetylenes with copper(I) or copper(II) salts ( Glaser, Hay, or Eglington coupling ). The synthesis of unsymmetric diynes proceeds best via the Cadiot-Chodkiewicz procedure in which an acetylene is reacted with an acetylic halide in the presence of copper(I) salts [117]. Therefore, thienyl-substituted acetylenes and bromoacetylenes are important starting materials. 

The second motivation of the recent development of oligothiophenes is related to their use as materials for electronic device applications. As early as 1974, a precursor article by H. Kuhn et al. [13] describes photocurrent measurements on Langmuir-Blodgett films of a-quinquethiophene (a-5T). In the mid-1980s, oligothiophenes... 

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