Thermally Activated Delayed Fluorescence beyond Through-Bond Charge Transfer for High-Performance OLEDs

Charge transfer plays an important role in ruling the exciton dynamics of organic emitters. Most likely, intermolecular/intramolecular charge transfers occur when a donor meets a matched acceptor, which shapes the radiative decays of excitons. The generation and utilization of excitons are vital for organic light-emitting devices (OLEDs). Thermally activated delayed fluorescence (TADF) emitters, which harvest the triplets via reverse intersystem crossing and thus have attracted intensive attention in the last decade, are very promising to address the issue of cost-effectiveness in the commercialized OLEDs. Conventionally, intramolecular charge transfer via through-bond interaction is ubiquitous in the state-of-the-art TADF materials. Alternatively, through-space charge transfer via either intermolecular or intramolecular interaction is found to be unique and effective in modulating the luminescent properties, such as the emissive colors, exciton lifetimes, and quantum yields. The emerging approaches to evoke the TADF mechanisms beyond through-bond charge transfer in a single molecule and the related applications of the emitters in OLEDs are highlighted here. The timely and fashionable molecular design and device engineering regarding through-space charge transfer to the emitting layers in OLEDs are compared and discussed. Finally, a conclusion and the perspectives of the electroluminescence of novel through-space systems are proposed.

Automated summary

Charge transfer is crucial in governing exciton dynamics in organic emitters, particularly in thermally activated delayed fluorescence (TADF) emitters. It plays a role in shaping radiative decays of excitons and modulating luminescent properties. Through-space charge transfer is found to be effective in changing emissive colors, exciton lifetimes, and quantum yields in OLEDs.