Emergent Molecular Function Research Group, Center for Emergent Matter Science, RIKEN , Wako, Saitama 351-0198, Japan.
J Am Chem Soc. 2016 Jun 22;138(24):7725-32. doi: 10.1021/jacs.6b03688. Epub 2016 Jun 7.
The introduction of quinoidal character to π-conjugated polymers is one of the effective approaches to reducing the bandgap. Here we synthesized new π-conjugated polymers (PBTD4T and PBDTD4T) incorporating thienoquinoids 2,2'-bithiophene-5,5'-dione (BTD) and benzo[1,2-b:4,5-b']dithiophene-2,6-dione (BDTD) as strong electron-deficient (acceptor) units. PBTD4T showed a deep LUMO energy level of -3.77 eV and a small bandgap of 1.28 eV, which are similar to those of the analog using thieno[3,2-b]thiophene-2,5-dione (TTD) (PTTD4T). PBDTD4T had a much deeper LUMO energy level of -4.04 eV and a significantly smaller bandgap of 0.88 eV compared to those of the other two polymers. Interestingly, PBDTD4T showed high transparency in the visible region. The very small bandgap of PBDTD4T can be rationalized by the enhanced contribution of the resonance backbone structure in which the p-benzoquinodimethane skeleton in the BDTD unit plays a crucial role. PBTD4T and PBDTD4T exhibited ambipolar charge transport with more balanced mobilities between the hole and the electron than PTTD4T. We believe that the very small bandgap, i.e., the high near-infrared activity, as well as the well-balanced ambipolar property of the π-conjugated polymers based on these units would be of particular interest in the fabrication of next-generation organic devices.
将醌型结构引入到π共轭聚合物中是降低带隙的有效方法之一。在这里，我们合成了新的π共轭聚合物（PBTD4T 和 PBDTD4T），其中包含噻吩并[3,2-b]噻吩-2,5-二酮（TTD）（PTTD4T）作为强电子缺（受）单元。PBTD4T 具有深的 LUMO 能级（-3.77 eV）和小的能带隙（1.28 eV），与使用噻吩并[2,3-b]噻吩-2,5-二酮（TTD）的类似物（PTTD4T）相似。与其他两种聚合物相比，PBDTD4T 具有更深的 LUMO 能级（-4.04 eV）和明显更小的能带隙（0.88 eV）。有趣的是，PBDTD4T 在可见光区具有很高的透明度。PBDTD4T 的非常小的能带隙可以通过增强共振骨架结构的贡献来合理化，其中 BDTD 单元中的 p-苯醌二亚甲基骨架起着关键作用。PBTD4T 和 PBDTD4T 表现出双极性电荷输运特性，与 PTTD4T 相比，空穴和电子之间的迁移率更平衡。我们相信，基于这些单元的π共轭聚合物具有非常小的带隙，即高近红外活性以及良好的双极性特性，在下一代有机器件的制造中具有特别的兴趣。
