Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers

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.