Elastic–Plastic Fully π‐Conjugated Polymer with Excellent Energy Dissipation Capacity for Ultra‐Deep‐Blue Flexible Polymer Light‐Emitting Diodes with CIEy = 0.04

Abstract Emerging intrinsically flexible fully π‐conjugated polymers (FπCPs) are a promising functional material for flexible optoelectronics, attributed to their potential interchain interpenetration and entanglement. However, the challenge remains in obtaining elastic–plastic FπCPs with intrinsic robust optoelectronic property and excellent long‐term and cycling deformation stability simultaneously for applications in deep‐blue flexible polymer light‐emitting diodes (PLEDs). This study, demonstrates a series of elastic‐plastic FπCPs (P1–P4) with an excellent energy dissipation capacity via side‐chain internal plasticization for the ultra‐deep‐blue flexible PLEDs. First, the freestanding P1 film exhibited a maximum fracture strain of 34.6%. More interestingly, the elastic behavior is observed with a low strain (≤10%), and the stretched film with a high deformation (>10%) attributed to plastic processing revealed the robust capacity to realize energy absorption and release. The elastic–plastic P1 film exhibits outstanding ultra‐deep‐blue emission, with an efficiency of 56.38%. Subsequently, efficient PLEDs are fabricated with an ultra‐deep‐blue emission of CIE (0.16, 0.04) and a maximum external quantum efficiency of 1.73%. Finally, stable and efficient ultra‐deep‐blue electroluminescence are obtained from PLEDs based on stretchable films with different strains and cycling deformations, suggesting excellent elastic–plastic behavior and deformation stability for flexible electronics.