The ΦPL under Ar of 67 and 59% are lower than those in toluene. This behavior was also observed in 1B-DTACrs and 2B-DTACrs, but the degree of spectral broadening and the ΦPL drop in 1B-CzCrs and 2B-CzCrs are more pronounced. These data suggest that these planar carbazole-containing emitters more easily form either aggregates and/or intermolecular interactions with the host in their film state, despite the introduction of tert-butyl groups in the skeleton of these compounds in addition to the bulky o-tolyl group. This was also confirmed by the narrowing of the emission spectra and the higher ΦPL at lower doping concentrations (Figs. S23, S24, and Table ). Notably, the delayed emission lifetime of 1B-CzCrs and 2B-CzCrs (0.33 and 2.98 ms, respectively)