Optimizing OLED efficiency through thermally activated delayed fluorescence: Computational insights into position...

Next-generation OLEDs require more than just incremental improvements; they necessitate a fundamental rethinking of how excited-state dynamics are controlled. Central to this challenge is the singlet-triplet energy gap (ΔE_ST), which plays a crucial role in determining whether the abundant triplet excitons are dissipated as heat or harvested as light. When ΔE_ST decreases below 0.2 eV, reverse intersystem crossing (RISC) occurs with remarkable efficiency. This process unlocks the full potential of thermally activated delayed fluorescence (TADF) without relying on scarce heavy metals. In this context, position isomers of BN-perylenes represent a significant breakthrough. By embedding isoelectronic B-N units at different sites of the perylene scaffold, we can reshape the orbital topology, enhance molecular polarity, and spatially confine excitons. The variation in the position of BN substitution directly tunes ΔE_ST, allowing for precise control over excited-state energetics and emission behavior. As a result, these isomers produce a new generation of emitters that combine high internal quantum efficiency with long-term stability and color purity. Such molecular innovations transform ΔE_ST from a passive limitation into an active design variable, marking a significant step toward OLED devices that are brighter, more efficient, and sustainable at scale.