Room‐Temperature Inversion of Phosphorescence and Fluorescence Emission Triggered in Twisted Dimeric Structures Displaying Excitonic Coupling

Abstract We here report the design of new thermally activated delayed fluorescence (TADF) emitters based on a dimeric binaphthalimide structure, which induces a small singlet‐triplet energy gap. The impact of dimerization and the resulting intramolecular exciton effect are highlighted through comparisons with monomeric variants. Additionally, we studied the influence of the acceptor strength, alongside global electronic effects—such as exciton coupling and charge resonance—induced by the donor/acceptor/acceptor/donor (DAAD) configurations. These effects led to the energetic merging, and even inversion, of the phosphorescence and fluorescence spectra in semi‐rigid matrices, including room‐temperature polymethyl methacrylate (PMMA) thin films, compromising the TADF response initially enhanced in fluidic environments.