Exploring the Impact of the Presence of 9,9’-Spirobifluorene Moieties on the Performance of Carbonyl-based Multiresonant Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

The impact of the decoration of the multiresonant thermally activated delayed fluorescence (MR-TADF) core DiKTa with 9,9’-spirobifluorene (SBF) groups was investigated with respect to the impact of number, position, and incorporation-type of the SBF unit on the photophysical and optoelectronic properties. This approach allows for the development of narrowband, high-efficiency organic light emitting diodes (OLEDs) with moderate efficiency roll-off by alleviating aggregation-caused quenching. The MR-TADF emitters DiKTaSBF, 3-SBF-DiKTa, 7-SBF-DiKTa, and 7-SBF-DiKTaSBF, differ in the number, position, and incorporation-type of the SBF unit. Sky-blue OLEDs with DiKTaSBF and 3-SBF-DiKTa showed superior performance with maximal external quantum efficiencies (EQEmax) of 26.1 and 27.0%, respectively, while all four families of OLEDs showed a moderate efficiency roll-off. Narrowband emissions with full-width at half maximum (FWHM) of 32 and 35 nm were observed for 7-modified emitters, whereas for the devices with emitters containing SBF groups at the 3-position showed a broadened emission, with FWHM of about 50 nm. These findings highlight the effect of the regiochemistry of the SBF group on the optoelectronic properties and the corresponding impact on the performance of the OLEDs.