Solution-processible 1,3,4-oxadiazole/spiro[fluorene-9,9′- xanthene] hybrid as efficient host for green thermally activated delayed fluorescence devices

A novel bulky 1,3,4-oxadiazole-based spirocyclic compound 2,5-bis(2-spiro[fluorene-9,9′-xanthene]-7-yl)phenyl)-1,3,4-oxadiazole (D- [2-SFXP]-o-OXD) has been synthesized successfully by incorporating spiro[fluorene-9,9′-xanthene] (SFX) into 2,5-biphenyl-1,3,4-oxadiazole reaction via Suzuki cross-coupling with Pd(PPh ₃ ) ₄ as catalyst. The electrochemical properties of the compound were researched via cyclic voltammetry (CV) and obtained the HOMO, LUMO, and energy gap (E _g , 3.57 eV). The green TADF OLEDs hosted D[2-SFXP]-o-OXD and D[2-SFXP]-o-OXD:mCP by solution-processing techniques with maximum current efficiency (CE) and EQE (external quantum efficiency) of 15.2 cd A ⁻¹ /4.8% and 25.9 cd A ⁻¹ /8.5% as the doping concentration increasing from 5% to 10%, respectively. The electroluminescent (EL) spectra are independent of the concentration changes, which exhibits the three dimensional bulky D[2-SFXP]-o-OXD with large steric hindrance could successfully suppress the concentration quenching and excimer emission.