Intrinsically Flexible Thermally Activated Delayed Fluorescence Polymers with High Reverse Intersystem Crossing Rates Enabled by an Intramolecular Sensitization Strategy

Intrinsically flexible thermally activated delayed fluorescence (TADF) polymers are attractive candidates for developing high-efficiency stretchable organic light-emitting diodes (OLEDs). However, most of the intrinsically flexible TADF polymers, which involve embedding soft alkyl chains into backbones, are confronted with inefficient reverse intersystem crossing rates (kRISC) and severe nonradiative losses, suffering from unsatisfied device performances. Herein, we present a design concept of integrating assisted TADF sensitizing units into optimized intrinsically flexible polymers that achieve excellent photoluminescence quantum yields of exceeding 70% together with an attractive kRISC of 23.0 × 105 s–1, significantly confirming the improved spin flip of triplet excitons. The maximum external quantum efficiency of solution-processed OLEDs can reach 11.3%, further demonstrating that the intramolecular sensitization strategy is valid to improve device performance by elevating exciton utilization. Moreover, the flexible OLEDs fabricated on polymer substrates also exhibit almost undiminished device performance even in highly bent flexible OLEDs, directly evidencing that the structural design of intrinsically flexible TADF polymers can significantly form emitting films with stable morphology and thus enhance device long-term mechanical stability. Morphological analysis and mechanical property tests demonstrate that the unique advantages of newly designed intrinsically flexible polymers can potentially be employed in the fabrication of flexible high-efficiency display equipment.