Feng et al. ). The functionalization of DMAC-TRZ with either ortho-tolyl unit and a phenyl unit results in a decreased DEST from 0.13 eV for DMAC-TRZ to 0.05 for ToDMAC-TRZ and 0.11 eV for PhDMAC-TRZ, in 30 wt% doped films in PPT. Although the DEST value of DMAC-TRZ here is different to the previously reported one, 3 likely a function of a combination of the different host, emitter concentration and measurement parameters used, in both cases the value is very small. The lPL in these doped films is red-shifted from 510 nm for DMAC-TRZ to 520 and 531 nm for ToDMAC-TRZ and PhDMAC-TRZ, respectively. This is due to the strengthening of the donor due to increased conjugation between these aromatic groups and the DMAC donor core. As 30 wt% doped films in PPT, DMAC-TRZ, ToDMAC-TRZ, and PhDMAC-TRZ have FPL of 91, 99, and 73%, respectively. The trend in EQEmax of 18.8, 18.9, and 17.2% of the corresponding devices mirrors their FPL while their lEL are blue-shifted at 499 nm, 510 nm, and 524 nm, respectively, compared to their lPL. Despite the lower efficiency, the OLED with PhDMAC-TRZ possessed a much longer lifetime (LT50 of 1910 h) than that with DMAC-TRZ (LT50 of 70 h); the OLED with ToDMAC-TRZ also showed an improved lifetime, but only at 198 h. Here, we report a rationally designed family of DMAC-TRZ derivatives, CNPh-DMAC-TRZ, CF3Ph-DMAC-TRZ, dPh-DMAC-TRZ, t BuPh-DMAC-TRZ, MeOPh-DMAC-TRZ (Figure )