Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs

All ortho-linked D-A and D-A-D molecules exhibit non-TADF feature due to broad spatial overlap at triplet excited state for large ΔEST, while A-D-A compounds show strong TADF property owing to efficient spatial separation for small ΔEST. [Display omitted] The highest efficiency thermally activated delayed fluorescence (TADF) emitters in OLEDs are mostly based on twisted donor/acceptor (D/A) type organic molecules. Herein, we report the rational molecular design on twisted all ortho-linked carbazole/oxadiazole (Cz/OXD) hybrids with tunable D-A interactions by adjusting the numbers of donor/acceptor units and electron-donating abilities. Singlet-triplet energy bandgaps (ΔEST) are facilely tuned from ∼0.4, 0.15 to ∼0 eV in D-A, D-A-D to A-D-A type compounds. This variation correlates well with triplet-excited-state frontier orbital spatial separation efficiency. Non-TADF feature with solid state photoluminescence quantum yield (PLQY)