Topological Transition in One-Dimensional π-Conjugated Polymers via Strain Engineering

Topological trivial and nontrivial phases can be readily realized in low-dimensional organic polymers via bottom-up synthesis. However, to effectively harness these topological phases in practical devices, it is crucial to develop strategies for achieving a controllable topological transition. Inspired by topology and pi-electron pairing, we propose a method to induce topological transitions through orbital crossover driven by continuous external strain in 10 one-dimensional (1D) pi-conjugated polymers (CPs), categorized into aromatic and quinonoid forms. Our results reveal that quinonoid polymers exhibit edge states, indicative of nontrivial topological phases (Zak invariant, Z 2 = 1), while aromatic polymers correspond to trivial topological phases (Z 2 = 0). Notably, the poly(thiophene dioxide) (TDO) quinonoid polymer undergoes a reversible topological transition under a tensile strain of 3.6%, demonstrating a strain-dependent topological phase. This phenomenon is attributed to the gap closure resulting from the orbital crossover between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). This work uncovers the topological phases in 1D organic polymers and highlights the topological transitions induced by strain engineering.