Hyperfluorescence from 2,1,3-benzothiadiazole-containing oligomers Christopher Riggs 1 , Peter Skabara 1 , Joseph Cameron 1 , Nicola J. Fairbairn 1 , Gordon J. Hedley 1 , Sebastian Reineke 2 1 University of Glasgow, UK, 2 Technische Universität Dresden, Dresden Integrated Centre for Applied Physics and Photonic Materials (IAPP), Germany Recent developments in OLED research have yielded materials which can produce 100% IQE through harvesting triplet states via TADF. In order to enhance emissions in such molecules, a high rate of reverse intersystem crossing (rISC) is required. To achieve this, careful manipulation of molecular design can lead to narrowing the ΔEST of said molecule. This necessitates the use of charge transfer (CT) and locally excited (LE) states to facilitate conversion from the non-radiative triplet manifold to the emissive singlet state via rISC. The very nature of the CT states results in broad emission profiles unsuited to display technology, despite the high IQE. Thermally activated delayed fluorescence – assisted fluorescence (TADF-AF, or TAF) otherwise known by the Kyulux trademark, hyperfluorescence, presents a means of achieving both 100% EQE and narrow FWHM of emissions, with improved device stability. This process transfers the excited state energy of the singlet state of the TADF molecule to a carefully selected fluorescent molecule doped within a TADF host matrix via Förster resonance energy transfer (FRET). Instead of emitting from the TADF molecule, the fluorophore is excited indirectly and thus circumvents the broadly emitting CT 1 → S 0 transition. Our recently published and highly emissive fluorophore, BTF4 [1] , possesses both good absorption properties, thanks to its highly absorbing fluorene arms; and efficient transfer of energy to its highly emissive BT core. BTF4’s hexyl chains assist in solubility, as well as spatial separation resulting in reduced Dexter quenching. It is conceivable that, coupled with a TADF sensitiser with adequate emission overlap with BTF4’s absorption spectra, excitation via FRET should be possible. We explore how device performance and stability are enhanced thanks to this process, as well as investigate the effects on emission properties. References 1. DOI :10.1002/cptc.202200256
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