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

Abstract

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.

Molecular Design of Stretchable Polymer Semiconductors: Current Progress and Future Directions

“…Chemical structures of DPPTVT-based polymer semiconductors with various types of ligands (Bpy and Py) and Fe salts. Reprinted with permission from ref . Copyright 2021 Wiley.…”

Optimizing Morphology to Trade Off Charge Transport and Mechanical Properties of Stretchable Conjugated Polymer Films

“…Generally, the conjugated polymers possess heterogeneous structures with rigid backbones and flexible side chains, where the backbones determinate the optoelectronic properties, and the flexible side chains increase the solubility in processing solvents . Thus, different molecular design strategies can be employed to balance the mechanical and electrical properties of conjugated polymers, that is, preparing triblock copolymers with soft building blocks, − partially breaking the conjugation in backbones, − and incorporating long flexible side chains − or self-healed cross-linking moieties. , These strategies have greatly improved the ductility of conjugated polymers without significantly decreasing the charge mobility (Table ). For example, Bao et al successfully fabricated intrinsically stretchable conjugated polymer films with high mobility of 1.12 cm 2 V –1 s –1 at 100% strain by introducing alkyl spacers with hydrogen-bonding moiety into backbones of conjugated polymers.…”

A robust and self-healing elastomer achieved by a thio-β-diketone-Cu(ii) coordination and H-bonding dual crosslinked system

“…To investigate the M-L coordination change at the molecular level, X-ray absorption fine structure (XAFS) analysis is an efficient measurement, considering that X-ray absorption spectroscopy has been proved to be useful to monitor the reconfiguration of M-L coordination in polymeric systems. 59 The dynamics of coordination in PU-SO-Cu during stretching were investigated through the technique, as exhibited in Fig. 4a and b.…”