The TADF character of all the materials was confirmed by temperature dependent TRPL measurements, where the contribution from the delayed emission increases with increasing temperature (Figure ). The delayed emission of both t BuPh-DMAC-TRZ and OMePh-DMAC-TRZ is only modestly quenched at 80 K, attributed to the highly efficient RISC process in these two emitters, thus at this temperature triplet harvesting is not fully suppressed. This effect is also observed for their 80 K temperature phosphorescence spectra, which are not structured, resulting to a misleading triplet energy value, while their 20 K phosphorescence spectra are more structured (indicating mixed CT/LE character) and the triplet energy value appears similar in both molecules, around 2.65 eV (Figure ). This results in a ΔEST of 30 meV for both emitters and is in good agreement with the DFT calculations (Figure ). For CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, and dPh-DMAC-TRZ, 80 K is a sufficiently low temperature to effectively suppress TADF, and structured phosphorescence is observed with energy onset at 2.5, 2.63, and 2.54 eV, respectively (Figure ). The resulting ΔEST values are 290, 210, and 150 meV for CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, and dPh-DMAC-TRZ, respectively (Table ). From the modelled lowest triplet value of the aryl decorated donor units (Figure The FPL of the six emitters in 10 wt% mCP are compiled in Table . In all cases, the FPL of the mCP films is lower than in toluene. It has already been established that the FPL of DMAC-TRZ is higher in higher dipole moment matrices. For these reasons a screening of the FPL in high triplet energy hosts mCP, mCBPCN and DPEPO host was conducted using t BuPh-DMAC-TRZ as a representative example (Table ). As well, mCBPCN and DPEPO have high MW and Tg, which would be beneficial to influence the horizontal orientation of the TDM of these materials. At concentrations below 10 wt% the FPL values are similar in the three hosts, because the measurement error is higher. At higher concentrations, the FPL values in mCBPCN and DPEPO are similar and higher than those in mCP. Thus, mCBPCN was chosen as the host material to carry on the solid-state photophysical analysis, as DPEPO is recognized to be unstable in the OLEDs and this would thus negatively impact the device lifetime. Further, 10 wt% was chosen as the doping concentration as at this concentration there are few intermolecular interactions as already observed in films of DMAC-TRZ. The FPL values in 10 wt% mCBPCN are 87, 34, 70, 70, 72, and 72% for DMAC-TRZ, CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, dPh-DMAC-TRZ, t BuPh-DMAC-TRZ, and OMePh-DMAC-TRZ, respectively (Table ). ). The average room temperature tp are 7.8 ns, 9.5 ns, 10.5 ns, 16.2 ns, and 18.5 ns for CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, dPh-DMAC-TRZ, t BuPh-DMAC-TRZ, and OMePh-DMAC-TRZ, respectively (Table ). As was observed in both solution and in mCP films, longerlived prompt fluorescence is observed when the DMAC contains electron-donating substituents. The magnitude of the delayed component is similar to that of the doped mCP films for all emitters except t BuPh-DMAC-TRZ and OMePh-DMAC-TRZ, which have higher DF contribution in their decay profile. The average td is 1.2 ms, 163, 305, 2.64, and 1.99 µs for CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, dPh-DMAC-TRZ, t BuPh-DMAC-TRZ, and OMePh-DMAC-TRZ, respectively (Table ). These lifetimes also follow the same trend as previously discussed for toluene where the delayed lifetimes become shorter in emitters containing more electron-rich donors. DMAC-TRZ was measured in the same environment as a comparison, showing lifetimes that are intermediate, with an average tp and td of 12.1 ns and 15.6 µs, respectively.