Beyond the D-A type emitters, in 2016, Hatakeyama and co-workers firstly reported pure-blue boron-containing multi-resonance (MR) type TADF emitters that feature narrowband emissions and high photoluminescence quantum yields (PLQYs). The narrowband emission behaviour of MR type emitters is the most suitable for high-definition display with a wide colour gamut, i.e., BT 2020 standard. Since then, the development of MR-TADF emitters has attracted much attention. Nowadays, there have been numerous reports on high-efficiency OLEDs based on MR-TADF emitters with blue, green, and red emissions. Nonetheless, there is a limited report on high-efficiency MR emitters that can fulfil the high requirement of color gamut for blue pixel, i.e., CIEx,y = (0.131, 0.046). As a result, it is necessary to develop high-efficiency deep-blue MR emitters that satisfy the color gamut requirement of the BT 2020 standard, i.e., CIEy ≤ 0.05.