Dynamic Chain-Extension and Crosslinking Behavior of End-Group Functionalized Stretchable Deep-Blue Light-Emitting Conjugated Polymers for Flexible Light-Emitting Diodes.

The development of flexible light-emitting diodes requires conjugated polymers that simultaneously possess excellent stretchability, efficient luminescence, and stable performance under strain. Dynamic covalent chemistries, including Diels-Alder cycloaddition, have been widely exploited to improve the mechanical robustness of polymeric materials, and stretchable light-emitting polymers based on various dynamic interactions have also been extensively reported. Nevertheless, most existing dynamic crosslinking motifs contain polar functional groups that induce severe exciton quenching, which is particularly destructive to deep-blue conjugated emitters. Here, we develop a low-polarity Diels-Alder dynamic topological strategy via end-group functionalization specifically for deep-blue light-emitting conjugated polymers. Terminal vinyl-functionalized deep-blue polymer BTT is reacted with a bifunctional pyrrole crosslinker (Pyr2), enabling continuous structural evolution from chain-extended to crosslinked states by simply tuning crosslinker loading. The constructed low-polarity dynamic network endows the films with a maximum fracture strain of ∼30.7% and reversible stress recovery, while well preserving deep-blue photoluminescence quantum yield. The optimized cross-linked BTT-2 film achieves superior electroluminescent performance in flexible PLEDs, and device efficiency can be further boosted when the emissive layer is subjected to static pre-strain. Blending BTT derivatives with MEH-PPV is conducted as preliminary proof of material compatibility, which drastically increases the electroluminescence brightness of composite films.