Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.
J Phys Chem B. 2013 Jan 17;117(2):690-6. doi: 10.1021/jp3090974. Epub 2013 Jan 2.
Varying composition of π-donor/acceptor moieties has been considered as an effective strategy for fine-tuning of the electronic properties of D-A conjugated copolymers. In this study, the change of optoelectronic properties with the change of donor/acceptor ratios is investigated on the basis of first-principles density functional calculations. Copolymers containing moieties of similar π-electron donating and/or accepting capabilities, e.g., thiophene (T)-methoxythiophene (OT), exhibit a linear dependence of electronic properties (especially, HOMO/LUMO, band gap, and bandwidth) on the D/A content. In contrast, for strong D/A contrast systems, e.g., thiophene (T)-thienopyrazine (TP), the electronic properties vary nonlinearly with D/A compositions. However, when the block size of one parent monomer in a strong D/A contrast system is fixed, the variation of electronic properties shows a remarkable linear correlation against D/A compositions. We found that the deviation of electronic properties from a linear composition dependence is dominated by the strength of orbital interactions between D and A. Weak orbital interactions between D and A moieties tend to lead to a nonlinear composition dependence. Our results provide useful insights for band gap tuning through the adjustment of D/A compositions in D-A conjugated copolymers.
π-供体/受体部分的组成变化被认为是精细调整 D-A 共轭共聚物电子性质的有效策略。在这项研究中，基于第一性原理密度泛函计算，研究了光电性质随供体/受体比例变化的变化。含有类似π-电子供体和/或受体能力部分的共聚物，例如噻吩（T）-甲氧基噻吩（OT），其电子性质（特别是 HOMO/LUMO、带隙和带宽）与 D/A 含量呈线性关系。相比之下，对于强 D/A 对比系统，例如噻吩（T）-噻吩并吡嗪（TP），电子性质随 D/A 组成呈非线性变化。然而，当强 D/A 对比系统中一种母体单体的块大小固定时，电子性质的变化对 D/A 组成表现出显著的线性相关性。我们发现，电子性质偏离线性组成依赖性主要由 D 和 A 之间轨道相互作用的强度决定。D 和 A 部分之间弱的轨道相互作用往往导致非线性组成依赖性。我们的结果为通过调整 D-A 共轭共聚物中的 D/A 组成来调谐带隙提供了有用的见解。
