In air, the trend found for the FPL of the emitters in 10 wt% doped films in PMMA differs slightly from that measured in toluene (Table ). The positions of 6,10NICz and 4NICz are now reversed, where 6,10NICz shows the lowest FPL (10%), followed by 4NICz (15%). Meanwhile, 5NICz and 7NICz have equivalent FPL of 23%, whereas in toluene 7NICz was slightly brighter, and 6NICz remains the brightest at 31%. The average FPL across all five emitters remains the same as in toluene (20% in PMMA, 19% in toluene), but the spread in FPL values is reduced. There is effectively no change in FPL under deaerated conditions in 10 wt% doped films in PMMA. Time-resolved PL decay of the prompt emission show biexponential (4NICz, 6NICz, and 7NICz) or triexponential (5NICz and 6,10NICz) decay kinetics, with average lifetimes that are comparable to those measured in toluene (Figure , Table and Table ). The trend in the magnitude of the prompt lifetimes of the 10 wt% doped films in PMMA is also the same as that in toluene, except that 5NICz has a shorter lifetime than 6,10NICz in the doped PMMA film, while the opposite is true in toluene. Finally, 6,10NICz exhibits delayed fluorescence, with a lifetime, td, of 11.9 ms, which accounts for the high-energy band observed in the gated PL spectrum (Figure ). We attribute this delayed emission to TADF. Evidence for this assignment is given when we discuss our findings for the 1 wt% PMMA films (vide infra), but for now we note that 6,10NICz exhibits simultaneous TADF/RTP biluminescence at 10 wt% doping in PMMA films. No delayed emission was observed for the other emitters at room temperature. We next prepared films at 1 wt% emitter doping to mitigate against the formation of aggregates and their potential contribution to the photophysical picture. In air, the steady-state PL spectra were significantly narrowed (Figure , Table ) compared to those of the 10 wt% doped films, with FWHM of 30 nm or less for all five emitters. The PL spectra were also blue-shifted by ca.