CH direct arylation reactions of thieno [3,2-b]thiophenes (TT) with dibromo-substituted aromatic compounds afforded five different kinds of TT-based conjugated polymers, including donoracceptor and dye-containing polymers. Although various thiophene-based polymers have been synthesized previously via polycondensation using direct arylation reactions, our research demonstrates the first direct arylation polycondensation procedure using a TT monomer. The physical properties of the obtained polymers were evaluated by using UVvis absorption spectroscopy and cyclic voltammetry. The dye-containing polymer showed photovoltaic responses in a bulk heterojunction solar cells with a fullerene derivative.Recently, polycondensation via direct CH arylation 14 has become widely recognized as an effective method for the synthesis of π-conjugated polymers as it does not require the preparation of organometallic monomers and hence, does not generate metal-containing by-products. 59 The development of direct arylation polycondensation has allowed use of various monomers such as alkylated thiophenes, 22,23 Expansion of the range of applications of direct arylation polycondensation is important for it to be a reliable method for preparing materials for use in organic optoelectronic devices such as organic photovoltaics (OPV), organic light-emitting diodes (OLED), and organic field-effect transistors (OFET). In this research, we focused on the use of thieno-[3,2-b]thiophenes (TT) as a monomer in direct arylation polycondensation because TT-based polymers have shown excellent performance in OPV and OFET. 24,25 To our best knowledge, there has been no report of direct arylation polycondensation of TT. Direct arylation polycondensation of TT leads to preparation of high-performance polymer in a practical way. Herein, we report synthesis of five different kinds of TT-based polymers including donoracceptor and dye-containing conjugated polymers, via direct arylation polycondensation. The obtained polymers were evaluated in terms of their absorption, electrochemical, and photovoltaic properties. Results and DiscussionThree kinds of TT monomers were tested in direct arylation polycondensation with 2,7-dibromo-9,9-dioctylfluorene which is known to provide high solubility to conjugated polymers (Scheme 1).9,2628 The reaction with 3,6-dinonylthieno[3,2-b]-thiophene afforded a corresponding polymer (Polymer 1) with a molecular weight of 17800 in 83% yield under the previously reported conditions (Table 1, Entry 1). 16 Since precipitation of the polymer occurred during the reaction, the reaction was subsequently performed under diluted conditions (Entry 2). A relatively high molecular weight and yield were obtained at the concentration of 0.15 M. It should be noted that the highmolecular-weight polymer was obtained in 3h with only 2 mol % of a Pd precatalyst without a phosphine ligand which
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