Bhattacharjee Rameswar, Kertesz Miklos
Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, United States.
J Am Chem Soc. 2024 Sep 25;146(38):26497-26504. doi: 10.1021/jacs.4c10064. Epub 2024 Sep 13.
A topological quantum phase transition has been identified for the first time for 24 π-conjugated polymers as a function of external longitudinal strain due to a level crossing of the frontier orbitals at the topological phase transition. Topological phase is determined by the presence/absence of edge states. Out of the 24 polymers 15 are traditionally assigned an aromatic character, and 9 are traditionally assigned a quinonoid character. We find that all aromatic ones correspond to the trivial topological phase (Zak invariant, = 0), while all of the quinonoid ones to the nontrivial topological phase ( = 1) replacing the intuitive characterization of aromatic/quinonoid with the physically well-defined Zak invariant. Unique topological phase transition as a function of tensile strain can be achieved for four of the quinonoid ones. Tensile strain in these cases leads to a reduction of the bandgap. We introduced a figure of merit for indicating the efficiency of achievable very small bandgap upon the application of external strain.
首次在24种π共轭聚合物中确定了拓扑量子相变，它是外部纵向应变的函数，这是由于在拓扑相变处前沿轨道的能级交叉所致。拓扑相由边缘态的存在与否决定。在这24种聚合物中，传统上有15种被归为具有芳香性，9种被归为具有醌型特征。我们发现，所有具有芳香性的聚合物都对应于平凡拓扑相（Zak不变量，= 0），而所有具有醌型特征的聚合物都对应于非平凡拓扑相（= 1），用物理上定义明确的Zak不变量取代了芳香性/醌型的直观表征。对于其中四种具有醌型特征的聚合物，可以实现独特的作为拉伸应变函数的拓扑相变。在这些情况下，拉伸应变会导致带隙减小。我们引入了一个品质因数，用于指示在施加外部应变时实现非常小的带隙效率。
