Tuning the number and position of triphenylamine substituents on a benzo[b]furan core to achieve high-efficiency deep-blue and blue emitters

In recent years, the need for high-efficiency deep-blue emitters has become more urgent for outstanding full-color organic light-emitting diode (OLED) displays. Considering that combining relatively weak acceptor and donor units is expected to raise the energy of the charge-transfer (CT) state and achieve deep blue emission, herein, two deep-blue emitters (56dTPA-BF and 356tTPA-BF) and one blue emitter (2356fTPA-BF) are synthesized by incorporating benzo[b]furan (BF) acceptor and triphenylamine (TPA) donor units, respectively. The emission color, fluorescence efficiency, and excited state features can be adjusted by introducing TPA units at different substitution positions on BF. Due to the weak electron-attracting effect of BF, the CT S-1 states of 56dTPA-BF and 356tTPA-BF can emit bright deep-blue fluorescence (412 nm and 428 nm) with photoluminescence quantum yields (PLQYs) of 0.68-0.77 in toluene, while the local excited S-1 state of 2356fTPA-BF gives blue emission (446 nm) with a PLQY of 0.98. Fortunately, both non-doped and doped devices based on 2356fTPA-BF show maximum external quantum efficiencies (EQEs) of over 3.42% and pure blue emission with CIE coordinates of (0.152, 0.114), while the doped devices based on 56dTPA-BF and 356tTPA-BF all afforded deep-blue emission and EQEs of over 3.0%. These results demonstrate that the benzo[b]furan could be a promising acceptor unit for designing high-efficiency deep-blue emitters.