Enhancing multi-resonance thermally activated delayed fluorescence emission via through-space heavy-atom effect

Abstract

Recent research has focused on the heavy-atom effect in organic luminescent materials, especially in multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters. Traditional strategies involve directly conjugating heavy atoms to the chromophore, which often broadens the emission spectrum. This study explores an unconventional approach using the through-space heavy-atom effect, positioning heavy-atom moieties with nonconjugated short-range interaction with the chromophore. This method successfully demonstrates the “intramolecular external heavy-atom effect” proposed in the 1970s in cutting-edge high-efficiency emissive materials. Comparative analysis of these emitters confirms the spatial heavy-atom effect, maintaining the spectroscopic properties of MR chromophore while significantly improving external quantum efficiency in organic light-emitting diodes (OLEDs). These emitters also mitigate efficiency roll-off, showcasing the potential of spatial interactions to enhance MR-TADF materials for OLED applications.