Thermally Activated Delayed Fluorescence in Phase‐Separated Nanostructures

ABSTRACT Organic light‐emitting materials that exploit thermally activated delayed fluorescence (TADF) are of wide interest for next‐generation display and lighting technologies. However, many state‐of‐the‐art organic TADF emitters use electron donor–acceptor (D–A) architectures that often crystallize, which can hamper processability. Here, we report that the spontaneous formation of supramolecular nanostructures through phase separation generates a charge transfer (CT) complex with TADF properties, providing a novel approach to the design of emissive materials. This design involves functionalizing crystalline pyromellitic diimides (PMDIs) with a discrete oligodimethylsiloxane ( o DMS) linker to induce phase separation while improving processability. Mixing the electron acceptor PMDI‐ o DMS with the electron donor 4,5‐dibromoveratrole (DBV) forms a CT complex. Using X‐ray scattering experiments, we demonstrate that the intercalation of DBVs results in lamellar nanostructures with 20% less domain spacing than PMDI‐ o DMS homo‐aggregates. Characterization of the CT complex using emission and transient absorption spectroscopy over a wide temperature range provided compelling evidence of TADF in drop‐casted thin films, in which PMDI‐ o DMS and DBV are well‐ordered. Altogether, our results demonstrate that controlled nanoscale organization can serve as a design principle for TADF materials, opening a new route to the development of modular and processable emitters.