Thermal Conversion of Precursor Polymer to Low Bandgap Conjugated Polymer Containing Isothianaphthene Dimer Subunits

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• 作者：Tomokazu Umeyama ; Kohei Hirose ; Kei Noda ; Kazumi Matsushige ; Tetsuya Shishido ; Hironobu Hayashi ; Yoshihiro Matano ; Noboru Ono ; Hiroshi Imahori
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：1256-1264
• 全文大小：509K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1932-7455

文摘

Thermal conversion strategy has been utilized in the synthesis of a novel low bandgap polymer containing isothianaphthene (ITN) dimer structure and benzodithiophene (BDT) unit in the backbone (PBIBDT). First, a highly soluble precursor polymer with an alternating main chain structure of bicyclo[2.2.2]octadiene-fused thiophene dimer and BDT (PPBIBDT) was synthesized by a palladium(0)-catalyzed Stille coupling reaction. Then, heating of the yellow PPBIBDT film spin-coated on a glass plate yielded a dark blue film of PBIBDT that was insoluble in any organic solvents. Thermogravimetric analysis of PPBIBDT showed 14% weight loss with an onset at 230 掳C, corroborating the occurrence of the thermally induced retro-Diels鈥揂lder reaction. The PBIBDT film showed red-shifted, broad absorption in the visible and near-infrared regions with a maximum at 706 nm compared to the precursor polymer PPBIBDT with an absorption peak at 445 nm. The introduction of an ITN dimer unit in the backbone lowered the bandgap owing to the stabilized quinoid resonance structure. The field-effect hole mobility of PBIBDT was determined to be 1.1 脳 10^鈥? cm² V^鈥? s^鈥? with an on鈥搊ff ratio of 2.5 脳 10², while the PPBIBDT-based device revealed no p- and n-type responses. Organic photovoltaic devices were fabricated based on the planar heterojunction structure of PBIBDT and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and showed a power conversion efficiency of 0.07% under standard AM1.5 sunlight (100 mW cm^鈥?). These results obtained here will provide fundamental information on the design of thermally induced low bandgap polymers for device applications.