含3-hexylthiophene與2,3-diethylthieno[3,4-b]pyrazine之低能隙共聚高分子開發與研究

Abstract

In this research, we employed GRIM, Universal GRIM and Suzuki coupling to synthesize low band conjugated copolymers consisting of electron-donating units (3-hexylthiophene, 3HT) and electron-accepting units (2,3-diethylthieno[3,4-b] pyrazine, ETP) in different ratios in order to adjust the electronic structure and photophysical properties of the copolymers. Each unit was decorated with long alkyl chains as side substitutions to enhance the solubility. GRIM and universal GRIM only successfully synthesized poly(3-hexylthiophene) (P3HT) but failed to synthesize any copolymers consisting of ETP owing to the failure in activating di-brominated monomers containing ETP. Copolymers containing 3HT and ETP in 1:1 to 4:1 molar ratio (P3HTETP-1-1 ~ -4-1) as well as fluorene and ETP (PBF) were successfully obtained via Suzuki coupling. These copolymers showed reasonable solubility in TCB while the solubility increased with increasing 3HT to ETP ratio. Decomposition temperatures ranges from 271oC to 446oC and the thermal stability enhanced with increasing 3HT content. Absorption maxima of these copolymers in TCB solution were extended to longer wavelengths (565~690nm) compared to P3HT (440nm) due to strong intramolecular donor-acceptor interaction. Optical band gaps were 1.27eV~1.77eV, decreasing with increasing ETP ratio in the copolymers. The absorptions in solid state showed red shifts in different magnitudes in comparison with the absorptions in solution, depending on the composition of the copolymers. HOMO levels (-4.64eV ~ -4.90eV) and LUMO levels(-2.69eV ~ -3.11eV), obtained from cyclic voltametry, were raised and lowered respectively with increasing ETP ratio in the copolymer. The change in LUMO was more significant than that in HOMO. These ETP containing low band gap copolymers are potential candidates for polymer solar cells to enhance the light harvesting.