Integrating Dot‐Coil TADF Polymer With SFX Side‐Chained Encapsulation for Simultaneous Enhancement of Stretchability and Electroluminescent Efficiency

ABSTRACT Integrating high‐efficiency thermally activated delayed fluorescence (TADF) emitters with molecular designs that confer both mechanical durability and long operational lifespan remains a fundamental challenge. This integration is vital for enabling low‐cost, flexible OLEDs manufactured via solution processing, a pathway that promises to supersede vacuum‐deposited technologies and their associated limitations in energy efficiency and scalability. Here we present a design strategy that integrates spiro[fluorene‐9,9′‐xanthene] (SFX) endcapping with dot‐coil architectures in TADF copolymers. A dot‐coil copolymer incorporating SFX (PCNSFX) is synthesized, along with three reference copolymers that do not contain SFX modification. PCNSFX achieves an external quantum efficiency of 13.4% and 30% stretchability in polyurethane (PU) blends, representing a fivefold increase in radiative exciton utilization relative to the non‐endcapped analogue. The PU/PCNSFX composite‐based devices exhibit a luminance of 4572 cd m − 2 , and a current efficiency of 22.3 cd A − 1 , maintaining stable emission under repeated mechanical deformation. The outstanding performance arises from the molecular encapsulation and bulky SFX units, which suppress aggregation‐induced quenching by spatially isolating the emissive cores, while the oxygen atoms form hydrogen bonds with the carbamate groups of PU, preventing phase separation and enhancing mechanical compliance. This side‐chain‐mediated dynamic compatibility establishes a general approach for intrinsically stretchable TADF films in deformable optoelectronic devices.