Intrinsically Stretchable Ortho‐Steric Engineered MR‐TADF Polymers With in Situ Hypercrosslinking for Narrowband Deep‐Blue OLEDs

ABSTRACT Intrinsically stretchable organic light‐emitting diodes (OLEDs) are the core building blocks for next‐generation wearable electronics and flexible ultra‐high‐definition (UHD) displays. However, intrinsically stretchable deep‐blue polymers with narrowband emission and ultra‐high color purity (CIE y < 0.1) have remained an unmet challenge. Herein, we propose an in situ free‐radical hypercrosslinking strategy to construct multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) crosslinked polymers that simultaneously achieve narrowband deep‐blue emission and intrinsic stretchability. Using a carbonyl‐nitrogen fused ring (QAO) MR framework as the emissive core, we employ ortho/para‐styrene substitution steric engineering to modulate excited‐state properties and exciton dynamics. Combined with in situ copolymerization with acrylic polyurethane, a three‐dimensional elastic network is formed, enabling synergistic optimization of optoelectronic and mechanical performance. The ortho‐substitution exhibits deep‐blue emission at 424 nm with a full‐width at half‐maximum (FWHM) of only 34 nm, a photoluminescence quantum yield (PLQY) of 79%, and a maximum external quantum efficiency (EQE) of 13.3%. The flexible OLED based on hypercrosslinked polymer oQAOPU20 shows an electroluminescence peak at 440 nm with an FWHM of 42 nm, CIE coordinates of (0.151, 0.072) (CIE y < 0.1), which represents the first reported narrowband deep‐blue MR‐TADF polymer with intrinsic stretchability, and enables flexible OLEDs with stable emission under mechanical deformation.