Over the last decade, thermally activated delayed fluorescence (TADF) emitters have been widely explored as emitters in OLEDs, in part owing to their ability to harness all of the singlet and triplet excitons to produce light and thus achieve up to 100% internal quantum efficiency (IQE). A weak overlap between the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbital (LUMO) is required to achieve a small singlet-triplet energy gap (ΔEST) that is necessary to promote the required endothermic reverse intersystem crossing (RISC) underpinning the TADF mechanism. This is typically achieved by the emitter adopting a strongly twisted donor-acceptor (D-A) architecture. However, the longrange charge transfer (LRCT) character of the emissive excited state and the corresponding relatively large structural relaxation upon exciton formation lead to an undesired broadening of the emission envelope, which result in devices having poor color saturation. In 2016, Hatakeyama et al. reported a new type of organic TADF material, so-called multiresonant TADF (MR-TADF) emitters. The short-range charge transfer (SRCT) character of the emissive lowest singlet (S1) state that exists as a result of the HOMO/LUMO separation on adjacent atoms and the rigid structure of the molecule result in narrowband emission, small Stokes shifts, and high photoluminescence quantum yields (FPL), all of which contribute to devices having both high color purity and high maximum external quantum efficiencies (EQEmax). However, the commonly rigid and planar geometries of MR-TADF emitters lead to poor solubility in organic solvents, making them tend to aggregate. The resultant poor film-forming properties from solution and severe aggregation-caused quenching (ACQ) are detrimental to their performance in SP-OLEDs. In this report, a new MR-TADF emitter 2,7-tBuCzNB has been developed to address these outstanding issues in the context of SP-OLEDs (Figure ). The asymmetric B-N core (named Cz-SCz), reported recently by Ni et al., has been confirmed to have an emissive SRCT state in both toluene and doped films in mCP. The eight tert-butyl groups in 2,7-tBuCzNB are responsible for its good solubility in organic solvents. This property coupled with the relatively high molecular weight of 2,7-tBuCzNB (1525 g mol -1 ) contribute to the good film-forming ability of this compound. The peripheral tert-butyl carbazole and twisted secondgeneration tert-butyl carbazole donors help to increase the intermolecular distance between adjacent emitter molecules and to suppress ACQ. As a result, 2,7-tBuCzNB emits at an emission peak wavelength (lPL) of 501 nm (Full width at half maximum, FWHM, of 41 nm) in 5 wt% doped film in mCP. It has a high FPL of 93% in toluene, and the FPLs in doped films are around 80% at concentrations ranging from 1 to 10 wt%. The SP-OLEDs using this emitter at a doping concentration of 5 wt% in the DMIC-TRZ host showed an EQEmax of 11.6%, with a low turn on voltage (Von) of 3.4 V. The device with 10 wt% emitter showed nearly the same performance as that with 5 wt% emitter.