Inverted Singlet-Triplet Gaps Reduce Radiative Exciton Processing Times in TADF and Hyperfluorescence Applications

Molecules exhibiting inverted singlet-triplet energy gaps violate Hund's rule and represent a distinct class of emitters in which reverse intersystem crossing is energetically favored over intersystem crossing. While this property has been linked to shorter triplet exciton lifetimes, its implication on the device's quantum efficiency and stability remain unclear. Here, we introduce the radiative exciton processing time (REPT)-the average period from exciton generation to light emission-which provides a more relevant performance metric than isolated singlet or triplet lifetimes. We derive the expressions for exciton processing rates in both TADF and hyperfluorescence architectures, applying them to a series of inverted-gap molecules and a conventional donor-acceptor benchmark. The results show that that the singlet-triplet inversion enables orders of magnitude faster exciton processing despite comparable triplet lifetimes. Consequently, such materials lead to suppressing bimolecular losses and delaying efficiency roll-off, potentially enabling brighter, more efficient, and longer-lived OLEDs.