Abstract
The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers. Herein, learning from the hydrogen bonds in glucose, which were facilitated to the toughness enhancement of cellulose, we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains. Through tuning the copolymerization ratio, we systematically investigated their influence on the hierarchical condensed structures, rheology behavior, tensile performances, and optoelectronic properties of conjugated polymers. Compared to the reference copolymers with a low ratio of amide units, copolymers with 30% and 40% amide units present a feature of the shear-thinning process that resembled the non-Newtonian fluid, which was enabled by the interchain dynamic hydrogen bonds. Besides, we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers. We demonstrated the significant impact of hydrogen bonds in solution gelation, material crystallization, and thin film stretchability. Impressively, the breaking elongation for P4 was even up to ~30%, which confirmed the partially enhanced film ductility and toughness due to the increased amide groups. Furthermore, polymer light-emitting devices (PLEDs) based on these copolymers presented comparable performances and stable electroluminescence (EL). Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52 μJ/cm2, suggesting the wide prospective application in the field of flexible optoelectronic devices.
Highlights
Conjugated polymers (CPs) with intrinsic elasticity property are desirable for deformable optoelectronic devices, such as organic photovoltaics (OPV) [1, 2], polymer light-emitting diodes (PLEDs) [3], and wearable sensors [4, 5]
Combining the results of dynamic light scattering (DLS) and rheological measurement, we concluded that the crosslinked interchain hydrogen bonds was facilitated to the chain entanglement and aggregation in solution, which resulted in solution gelation at the amide ratio of 30% and 40%
The hydrogen bonds are favourable for realizing the long-range-order, well-organized stacking structure of polymer chains, demonstrated by the pronounced diffractions peaks in the wideangle X-ray scattering (WAXS) test
Summary
Conjugated polymers (CPs) with intrinsic elasticity property are desirable for deformable optoelectronic devices, such as organic photovoltaics (OPV) [1, 2], polymer light-emitting diodes (PLEDs) [3], and wearable sensors [4, 5]. It is meaningful to develop viscoelastic and intrinsic stretchable CPs, of which their polymer chains are incompact entanglement. Predicting and directly measuring the intrinsic mechanical properties of CPs remain a daunting task [6]. Metrics of the mechanical properties, including the elastic modulus and hardness, are helpful for evaluating their application in flexible and stretchable optoelectronic devices. The inherent π -conjugated structure and limited strain of most CPs prompt us to optimize their elastic properties with a minimal compromise of optoelectronic performances
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