Correlation Between Exciplex Binding Energies and Molecular Structures in Organic Donor–Acceptor Mixtures

Abstract An exciplex, a charge‐transfer state formed at a donor–acceptor (D–A) heterojunction, plays a crucial role in organic photonic devices. Although binding energy significantly influences the exciplex energy and is often decisive in the relative alignment to Frenkel exciton levels, its exact determination remains challenging due to the disordered arrangement of heterodimers in amorphous mixture, leading to heterogeneous energy broadening. In this study, the distribution of the binding energies in organic D–A mixtures is investigated, focusing on the impact of different acceptor molecules in different shapes. A model is introduced that incorporates molecular size and ionic charge localization as key parameters, which successfully reproduces the statistical results of the exciplex binding energies in amorphous mixtures using TD‐DFT calculations. Furthermore, the model predicts that large molecules with ionic charges confined to their edges exhibit low exciplex binding energies, whereas smaller molecules with delocalized ionic charges across their molecular planes result in higher binding energies, which is consistent with experimental observation. These findings provide valuable insights for designing exciplex hosts for photonic applications, particularly for blue OLEDs, which are critical for advancing display technology, where the energy budget for developing higher‐energy exciplexes than a deep blue emitter is rather limited.