Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
Phys Chem Chem Phys. 2019 Jan 2;21(2):789-799. doi: 10.1039/c8cp03341b.
To identify reliable molecular design principles for energy level tuning in donor/acceptor conjugated polymers (CPs), we studied the governing factors by means of ab initio calculations based on density-functional theory (DFT). We investigated a series of CPs in which we independently and systematically varied the electron withdrawing power of the acceptor unit and the electron donating power of the donor unit, while maintaining the same conjugated chain conformation. We observed that the introduction of a stronger acceptor unit, while keeping the same donor unit in the CP, lowers the LUMO level, but leaves the HOMO level almost unchanged. Conversely, enhancing the strength of the donor unit for the same acceptor unit raises the HOMO level, while maintaining the LUMO level. We identified strong correlations between the frontier orbital energy levels and the degree of orbital localization, which depends on the electron donating or withdrawing power of the molecular groups carrying the orbitals. Moreover, the HOMO/LUMO gap of the CP is directly proportional to the charge transfer between donating and accepting units, which provides a robust design criterion for CPs.
为了确定供体/受体共轭聚合物（CPs）能级调谐的可靠分子设计原则，我们通过基于密度泛函理论（DFT）的从头算计算研究了控制因素。我们研究了一系列 CPs，其中我们独立且系统地改变了受体单元的吸电子能力和供体单元的给电子能力，同时保持相同的共轭链构象。我们观察到，在 CP 中引入更强的受体单元，同时保持相同的供体单元，会降低 LUMO 能级，但 HOMO 能级几乎保持不变。相反，对于相同的受体单元，增强供体单元的强度会提高 HOMO 能级，同时保持 LUMO 能级。我们确定了前沿轨道能级与轨道定域程度之间的强相关性，这取决于承载轨道的分子基团的给电子或吸电子能力。此外，CP 的 HOMO/LUMO 能隙与供体和受体单元之间的电荷转移直接成正比，这为 CPs 提供了一个稳健的设计标准。
