Efficiency Boost in Through Space Charge Transfer Emitters: Insights from Spiro Lateral Rocking Confinement

Intramolecular through-space charge-transfer (TSCT) excited states have emerged as promising candidates for thermally activated delayed fluorescence (TADF) emitters. This study addresses the challenges in tuning excited state dynamics through conformational engineering, which significantly impacts exciton utilization. An effective strategy is presented to enhance the performance of TSCT-TADF molecules by restricting the lateral rocking of the spiro unit via immobilizing groups, which indirectly adjusts the conformations of the donor and acceptor subunits. This approach is successfully illustrated with two TSCT-TADF emitters, 8PhDM-B and 8PyDM-B, featuring sterical aryl phenyl and pyridine substitutions at the C8 site of a rigid spiro-fluorene bridge. Organic light-emitting diodes (OLEDs) utilizing these emitters demonstrated impressive maximum external quantum efficiencies of 33.1% and 31.0%, respectively. The findings underscore the importance of the rocking confined strategy in refining excited state dynamics, thereby providing valuable insights for the design of highly efficient OLED emitters.