Circularly Polarized Electroluminescence of Thermally Activated Delayed Fluorescence-Active Chiral Binaphthyl-Based...

Two pairs of thermally activated delayed fluorescence (TADF)-active chiral luminogens (R/S-1 and R/S-2) can be achieved by introducing D-A-type groups to chiral BINOL skeletons. The resulting chiral luminogens can exhibit aggregation-induced emission properties in THF-water mixtures and TADF emission in a doped-film state. The absolute photoluminescence quantum yield (Φ_PL) and delayed fluorescence lifetimes (τ_delayed) were measured to be 18.5% and 1.03 μs for R-1 and 15.7% and 0.97 μs for R-2. However, only R/S-1 with the fixed conjugation structure can emit circularly polarized luminescence signals, and g_lum can reach 1.6 × 10^-3 in toluene solution and 9.2 × 10^-4 in the neat film. Most importantly, R/S-1 was chosen as the emitting layers for orange-red circularly polarized organic light-emitting diodes, which can display low turn-on voltage (V_on) of 3.4 V, high maximum brightness (L_max) up to 40 470 cd m^-2, moderate external quantum efficiency of 4.1%, as well as circularly polarized electroluminescence signal with g_EL = -0.9 × 10^-3/+1.0 × 10^-3.