10 nm, both in terms of the lPL and the onset, and the expected relationship between the λPL and molecular structure was re-established. Further, the broad, low-energy emission band at ca. 470 nm is absent at this doping concentration in the presence of oxygen. Yet, under vacuum, the low-energy band returns with an equal or greater intensity to that observed in the 10 wt% doped film, relative to the high-energy band (Figure , dashed line). This highlights the intense oxygen sensitivity of this emission process, which we assign to the same room-temperature phosphorescence from T1 that we observed in the 10 wt% doped film. Under vacuum, the time-gated PL spectra (1-10 ms) of 4NICz, 5NICz, 6NICz and 7NICz exhibit the same broad phosphorescence that was observed in the 10 wt% doped films, but here the band is structured and clearly resolved into two distinct peaks in each of these four emitters. The positions of these peaks are largely invariant with structure, with a minor peak at ~440 nm and a major peak at ~470 nm. For 6,10NICz, the phosphorescence remains largely hidden by the tail of the delayed fluorescence emission at lPL of 389 nm, a slight bump is nonetheless observed at ca. 485 nm corresponding to emission from T1. Meanwhile, the time-gated PL spectrum of 6NICz shows delayed fluorescence at 384 nm that is approximately equal in intensity to the phosphorescence at 473 nm. This behaviour is distinct from the 10 wt% doped films in PMMA, where only delayed emission from T1 was observed. Therefore, at this lower doping concentration in PMMA, both 6NICz and 6,10NICz exhibit dual TADF/RTP emission at room temperature. c Peak of the phosphorescence, as determined by the time-gated emission (1 -10 ms), under vacuum.