While the FPL of 1 wt% zeonex films of dBr-tBu-DiKTa, tBr-DiKTa, and Mes3-DiKTa are 20, 15, and 47% respectively, these values change dramatically in mCP (1 wt%) to 82, 61, and 90% (Table ). This big difference in FPL in the two hosts cannot be explained by guest-guest interactions at such low film doping concentrations. Focusing on dBr-tBu-DiKTa, this emitter has a good FPL in mCP (promising for devices) but is also sensitive to intermolecular interaction because of its reduced peripheral shielding groups. We observe that the FPL for dBr-tBu-DiKTa increases to 45% in UGH-3 host, but this remains far below the 82% measured in mCP. This indicates that the transition to an inert small molecule host (UGH-3)