Organic thermally activated delayed fluorescence (TADF) materials have been steadily developed over the past decade for use in so-called third-generation organic light-emitting diodes (OLEDs). This is because organic TADF emitters can convert 100% of the electrically generated excitons to photons without using scarce metals, and this has garnered great interest within the display community. Typical TADF emitters consist of donor (D) and acceptor (A) moieties connected in a twisted conformation to results in a minimal orbital overlap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively). This provides a small energy splitting (DEST) between the lowest singlet (S1) and triplet (T1) excited states. However, such a longrange charge transfer (LRCT) character of these D-A TADF materials leads to a broad emission spectrum (full width of half maximum, FWHM > 45 nm) even in compounds where conformational motion is restricted. Broad emission is undesired for colour saturation. In 2016, Hatakeyama et al. reported a new class of TADF materials, so-called multi-resonant TADF (MR-TADF) compounds that typically have a narrowband emission (FWHM of < 30 nm). These compounds contain electron-rich and electron-poor dopants disposed meta or para with respect to each other within a polycyclic aromatic compound. Such compounds emit from a short-range charge transfer (SRCT) state associated with a characteristically small DEST. MR-TADF materials not only exhibit narrowband emission but also have high photoluminescence (PL) quantum yields (ΦPL) linked to fast radiative decay rate constants.