Cao Zhiqiang, Li Zhaofan, Mooney Madison, Do Changwoo, Hong Kunlun, Rondeau-Gagné Simon, Xia Wenjie, Gu Xiaodan
School of Polymer Science and Engineering, Center for Optoelectronic Materials and Devices, The University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States.
Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011, United States.
Macromolecules. 2024 Oct 21;57(21):10379-10388. doi: 10.1021/acs.macromol.4c01496. eCollection 2024 Nov 12.
The conjugated polymer's backbone conformation dictates the delocalization of electrons, ultimately affecting its optoelectronic properties. Most conjugated polymers can be viewed as semirigid rods with their backbone embedded among long alkyl side chains. Thus, it is challenging to experimentally quantify the conformation of a conjugated backbone. Here, we performed contrast variation neutron scattering on rigid conjugated donor-acceptor (D-A) diketopyrrolopyrrole (DPP) polymers with selectively deuterated side chains to measure the conjugated backbone conformation. We first synthesized DPP-based polymers with deuterated side chains, confirmed by NMR and FTIR. Using contrast variation neutron scattering, we found that the DPP-based conjugated polymers are much more rigid than poly(3-alkylthiophenes), with persistence length ( ) at 16-18 nm versus 2-3 nm. More importantly, in contrast to the relatively flexible poly(3-alkylthiophenes) whose backbone is more flexible than the whole polymer, we found that the backbone of DPP-based polymers has the same value compared to the whole polymer chain. This indicates that side chain interference on backbone conformation is not present for the semirigid polymer, which is further confirmed by coarse-grained molecular dynamics (CG-MD) simulations. Our work provides a novel protocol to probe polymer's backbone conformation and paradigm-shifting understanding of the backbone conformation of semirigid conjugated polymers.
共轭聚合物的主链构象决定了电子的离域，最终影响其光电性质。大多数共轭聚合物可被视为半刚性棒状结构，其主链嵌入长烷基侧链之中。因此，通过实验定量共轭主链的构象具有挑战性。在此，我们对具有选择性氘代侧链的刚性共轭供体-受体（D-A）二酮吡咯并吡咯（DPP）聚合物进行了对比变化中子散射，以测量共轭主链构象。我们首先合成了具有氘代侧链的基于DPP的聚合物，并通过核磁共振（NMR）和傅里叶变换红外光谱（FTIR）进行了确认。利用对比变化中子散射，我们发现基于DPP的共轭聚合物比聚（3-烷基噻吩）刚性大得多，其持久长度（ ）为16 - 18纳米，而聚（3-烷基噻吩）的持久长度为2 - 3纳米。更重要的是，与相对灵活的聚（3-烷基噻吩）不同，聚（3-烷基噻吩）的主链比整个聚合物更灵活，我们发现基于DPP的聚合物主链与整个聚合物链具有相同的 值。这表明对于半刚性聚合物不存在侧链对主链构象的干扰，这通过粗粒化分子动力学（CG-MD）模拟得到了进一步证实。我们的工作提供了一种探测聚合物主链构象的新方法，并对半刚性共轭聚合物的主链构象有了范式转变的理解。
