Effect of Fluorination on the Properties of 9,9′-(Sulfonylbis(4,1-Phenylene))bis(3-(tert-Butyl)-6-Fluoro-9 H-Carbazole) as Host for Thermally Activated Delayed Fluorescent Emitters
Document Type
Article
Publication Date
10-1-2024
Abstract
To enhance organic light emitting diode (OLED) performance, host materials with high triplet energies are crucial for confining excitons, despite increasing driving voltages due to the singlet-triplet energy gap. We synthesized sulfonylbis(4,1-phenylene)bis(3,6-disubstituted-9H-carbazole) derivatives as donor-acceptor-donor host materials, namely compounds 3, 5 and 7, with varying fluorination levels. These compounds show moderate singlet-triplet energy splitting and molecular dipole moments, allowing for fine-tuning of hole-transport mobilities, deeper frontier orbital energies, and a red shift in singlet emission while maintaining high triplet energy levels. These adjustments impact a range of physical, electronic and optical properties. The materials exhibit exceptional thermal stability, with decomposition starting above 400 degrees C and glass transition temperatures over 130 degrees C. Used with the green TADF emitter DACT-II, these hosts enable reverse intersystem crossing rates between 7.43x104 s(-1) and 1.77x105 s(-1). While OLEDs using mCP as a reference host achieve a maximum quantum efficiency of 18.5 %, those with host 5 show lower efficiency roll-off, leading to higher external quantum efficiency at brightness levels above 2000 cd/m(2) without colour shift. The reduced roll-off in devices with host 5 compared to mCP is attributed to effective F & ouml;rster and Dexter energy transfers to DACT-II at high currents, enhancing light emission pathways.
Keywords
efficiency roll-off, host, TADF, fluorination
Divisions
CHEMISTRY,PHYSICS
Publication Title
ChemPhotoChem
Volume
8
Issue
10
Publisher
Wiley
Publisher Location
POSTFACH 101161, 69451 WEINHEIM, GERMANY