The genesis of organic TADF materials as emitters for OLEDs was in 2011 and relied on a triazine-based compound (Figure ). A sufficient separation between HOMO and LUMO was induced by strengthening the electron-donor by extending the conjugation length as was done in PIC-TRZ (DEST = 0.11 eV), the first example of a purely organic TADF emitter. The design of PIC-TRZ also paved the way for the adoption of one of the most successful design strategies for TADF emitters, which is based on a strongly twisted donor-p-acceptor motif. Exciplex systems are another route to small DEST as the weak intermolecular interactions between electron-donor and electron-acceptor compounds ensure suitable physical separation of the HOMO and LUMO. Triazine-containing electron-acceptors appear prominently in exciplex systems due to their largely planar conformation. PO-T2T, for instance, has been widely used as the acceptor for exciplex since it was first reported in 2014. Triazine electron-acceptors were incorporated into some of the first TADF dendrimer emitters in 2015, such as G3TAZ, this due in part to the D3-symmetric structure of the TRZ and the ease with which chemical modification of this core can occur. High-efficiency non-doped OLEDs (EQEmax = 20%) using the small molecule emitter DMAC-TRZ showed comparable performance to the the doped device, indicating that it is possible to design a compound that shows significantly suppressed concentration quenching in neat films. DMAC-TRZ is still one of the most widely studied donor-acceptor type TADF emitters. Disposing the electron-donor adjacent to the TRZ results in improved performance in the OLED, as exemplified by TRZ-oCz (EQEmax = 9.3%). This is partially due to the more strongly twisted conformation that must be adopted for this compound and the additional through space charge transfer (TSCT) state that is induced. Since the first example in 2017, TRZ-containing TSCT TADF emitters have developed rapidly. Presently, the highest performing TRZ-based TADF emitter is SpiroAC-TRZ. Compared to the OLED with DMAC-TRZ, the EQEmax of the OLED with SpiroAC-TRZ is improved to 36.7%. Here, by employing a related electron-donor in 10H-spiro[acridine-9,9'-fluorene] (SpiroAC), a highly horizontally orientated transition dipole moment (TDM) was achieved, leading to enhanced light outcoupling. Recently, a triazine-containning TADF emitter 5Cz-TRZ with five carbazoles closely packed onto a central phenylene bridge afforded a material with one of the fastest reverse intersystem crossing (RISC) rate constants of kRISC = 1.5×10 7 s -1 .