Theoretical studies on phthalimide-based efficient thermally activated delayed fluorescence emitters

The donor units significantly impact the nature of excited states, energy levels and dynamics. The designed compounds AI-Pxz and AI-Dmac are expected to be potential efficient TADF emitters owing to its small ΔEST, large , and high radiative rate. [Display omitted] •Three thermally activated delayed fluorescence compounds are designed.•Folded structure leads to a spatially well-separated HOMO and LUMO.•Singlet-triplet energy gaps are facilely tuned to ~0.020 eV for designed compounds.•n → π* transition in T1 leads to a large spin–orbit coupling between S1 and T1 states. Three thermally activated delayed fluorescence (TADF) emitters integrating N-phenylphthalimide acceptor with different electron-donating units via an ortho-phenyl linker were theoretically designed and investigated. Results indicate the folded structure leads to a spatially well-separated HOMO and LUMO. Singlet-triplet energy gaps (ΔEST) are facilely tuned to ~ 0.020 eV for AI-Dps, AI-Pxz and AI-Dmac. The slightly hybridized charge transfer and local-excitation character induced by n → π* transition in T1 lead to a remarkably large . Simultaneously maintaining high radiative rate, AI-Pxz and AI-Dmac are expected to be potential efficient TADF emitters.