Investigations of singlet and triplet diffusion in thermally activated delayed-fluorescence emitters: Implications for hyperfluorescence

摘要

Exciton transport is particularly intriguing in molecules with intramolecular charge-transfer states that show thermally-activated delayed fluorescence (such as 4CzBN), as in these cases it is defined by multiple cycles through singlet and triplet spin configurations that have significantly different transport properties. Thus, the overall exciton transport has contributions from both the singlet and triplet exciton diffusion. Herein, we investigate with Monte Carlo simulations how the singlet and triplet diffusion lengths can be experimentally established for this unique class of molecules. We then consider how the efficiency of diffusive transfer to a fluorescence acceptor (hyperfluorescence) is affected by modifications of the triplet and singlet transfer rates. Importantly, we theoretically predict that high-efficiency hyperfluorescence can be achieved in an active layer by ensuring that triplet transport between thermally-activated delayed fluorescence molecules is poor.