Metal–Ligand Based Mechanophores Enhance Both Mechanical Robustness and Electronic Performance of Polymer Semiconductors

• Published in: Advanced functional materials Vol. 31; no. 11
• Main Authors: Wu, Hung‐Chin, Lissel, Franziska, Wang, Ging‐Ji Nathan, Koshy, David M., Nikzad, Shayla, Yan, Hongping, Xu, Jie, Luo, Shaochuan, Matsuhisa, Naoji, Cheng, Yuan, Wang, Fan, Ji, Baohua, Li, Dechang, Chen, Wen‐Chang, Xue, Gi, Bao, Zhenan
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2021; Wiley
• Subjects: Carrier mobility; charge transport; Coordination compounds; Current carriers; Iron; Ligands; MATERIALS SCIENCE; Mechanical properties; mechanophore; metal‐ligand coordination; Modulus of elasticity; polymer semiconductor; Polymers; Robustness; Semiconductors; Stretchability; stretchable electronics; Thin films
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202009201

The backbone of diketopyrrolopyrrole‐thiophene‐vinylene‐thiophene‐based polymer semiconductors (PSCs) is modified with pyridine (Py) or bipyridine ligands to complex Fe(II) metal centers, allowing the metal–ligand complexes to act as mechanophores and dynamically crosslink the polymer chains. Mono‐ and bi‐dentate ligands are observed to exhibit different degrees of bond strengths, which subsequently affect the mechanical properties of these Wolf‐type‐II metallopolymers. The counter ion also plays a crucial role, as it is observed that Py‐Fe mechanophores with non‐coordinating BPh4– counter ions (Py‐FeB) exhibit better thin film ductility with lower elastic modulus, as compared to the coordinating chloro ligands (Py‐FeC). Interestingly, besides mechanical robustness, the electrical charge carrier mobility can also be enhanced concurrently when incorporating Py‐FeB mechanophores in PSCs. This is a unique observation among stretchable PSCs, especially that most reports to date describe a decreased mobility when the stretchability is improved. Next, it is determined that improvements to both mobility and stretchability are correlated to the solid‐state molecular ordering and dynamics of coordination bonds under strain, as elucidated via techniques of grazing‐incidence X‐ray diffraction and X‐ray absorption spectroscopy techniques, respectively. This study provides a viable approach to enhance both the mechanical and the electronic performance of polymer‐based soft devices. Incorporation of metal–ligand coordination bonds into polymer semiconductors is able to simultaneously improve thin film deformability and charge transport efficiency. Such metal‐coordination bonds prove to be both dynamic and reversible under external forces, indicating that PSCs with metallated mechanophores are promising candidates for future high performance mechanically robust electronics.