A Twist in biphthalimide-based chromophores enables thermally activated delayed fluorescence

Abstract

Thermally activated delayed fluorescence (TADF) emitters, which convert nonemissive triplets into emissive singlets, have garnered tremendous impetus as next-generation organic electroluminescent materials. Employing donor−acceptor (D−A) designs to produce intramolecular charge transfer (ICT) states is considered an attractive strategy to effectively reduce the singlet− triplet ($ΔE_{ST}$) gap, thereby enhancing reverse intersystem crossing (rISC) in TADF emitters. Herein, we report two ICT chromophores (BP-1TPA and BP-2TPA) utilizing a rational design strategy based on a twisted biphthalimide acceptor core integrated with varying triphenylamine donors. We accomplish efficient TADF emission with a high photoluminescence quantum yield (PLQY) of ∼80% at ambient conditions from poly(methyl methacrylate)-doped films of these chromophores. Twisting the acceptor core ensures the separation of natural transition orbitals, leading to small $ΔE_{ST}$ and generates an intermediate triplet excited state to facilitate rISC. The present study, therefore, sheds light on how delayed fluorescence can be realized from a simple twisted phthalimide core by rational molecular engineering and enables new insights toward exploring the aromatic imide class of molecules as potential organic light-emitting materials.