Through Space Charge Transfer for Efficient Sky-Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection

Through-space charge transfer, which exists in nonconjugation linker based thermally activated delayed fluorescence (TADF) materials, excites chemists to explore more possibilities in organic light-emitting diodes (OLEDs). Herein, an sp³-hybrid carbon-centered donor–σ–acceptor type chromophore, QAFCN, is tentatively developed by exploring bi-acridine based electron-donor, i.e., 5,5-dimethyl-5,9-dihydroquinolino[3,2,1-de]acridine (QA). It is interesting to find that the QA moiety shows downshift in highest occupied molecular orbital because of its deformed geometry, which makes it qualified for sky-blue electroluminescence emission. Together with the blue-shift, enhanced photoluminescence quantum yield and faster reverse intersystem crossing rate are also observed in QAFCN, which can be attributed to the close through-space distance between donor/acceptor. As compared to the ACRFLCN without these special features, QAFCN has obvious TADF property and achieves efficient OLEDs of ≈18% external quantum efficiency.