Are the rates of dexter transfer in TADF hyperfluorescence systems optically accessible?. Issue 6 (19th April 2021)

• Record Type: Journal Article
• Authors: Haase, Nils; Danos, Andrew; Pflumm, Christof; Stachelek, Patrycja; Brütting, Wolfgang; Monkman, Andrew P.
• Is Part Of: Materials horizons. Volume 8:Issue 6(2021)
• Page Start: 1805
• Page End: 1815
• Publication Date: 2021-04-19
• Subjects: Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0mh01666g
• Languages: English
• ISSNs: 2051-6347

Abstract

Abstract : Dexter quenching is a likely loss mechanism in hyperfluorescent OLEDS, but changes in delayed emission kinetics in analogous optical experiments come from something else. Abstract : Seemingly not, but for unexpected reasons. Combining the triplet harvesting properties of TADF materials with the fast emission rates and colour purity of fluorescent emitters is attractive for developing high performance OLEDs. In this "hyperfluorescence" approach, triplet excitons are converted to singlets on the TADF material and transferred to the fluorescent material by long range Förster energy transfer. The primary loss mechanism is assumed to be Dexter energy transfer from the TADF triplet to the non-emissive triplet of the fluorescent emitter. Here we use optical spectroscopy to investigate energy transfer in representative emissive layers. Despite observing kinetics that at first appear consistent with Dexter quenching of the TADF triplet state, transient absorption, photoluminescence quantum yields, and comparison to phosphor-sensitised "hyperphosphorescent" systems reveal that this is not the case. While Dexter quenching by the fluorescent emitter is likely still a key loss mechanism in devices, we demonstrate that – despite initial appearances – it is inoperative under optical excitation. These results reveal a deep limitation of optical spectroscopy in characterizing hyperfluorescent systems.