Unfortunately, the lPL of each of 4NICz, 5NICz and 7NICz is shorter in wavelength than the pulsed laser excitation source of the fluorimeter, and so reliable decay profiles for the prompt fluorescence could not be obtained for these emitters. However, the lifetimes of the prompt fluorescence of 6NICz and 6,10NICz (Figure ) are 1.3× faster than those of the 10 wt% doped films in PMMA, at 3.6 and 2.9 ns, respectively. There is also a delayed fluorescence with td of 489.2 and 34.0 ms for 6NICz and 6,10NICz, respectively (Figure ). Compared to the delayed fluorescence observed in the 10 wt% doped films in PMMA, the td of 6,10NICz is 2.9 times slower in the 1 wt% doped films. The 'switching-on' of TADF at this lower doping concentration in 6NICz and the simultaneous slowing of the TADF process in 6,10NICz highlight the complex interplay of the competing decay processes in these molecules, and the sensitivity of the photophysics to the environment. In the time-gated PL spectra, all five emitters exhibited phosphorescence associated with extremely long lifetimes extending to the time scale of seconds (Figure ). Notably, the phosphorescence of 4NICz was too long-lived to be accurately fitted over a 10 s time window, but it could be readily observed with the naked eye (Figure ); additionally, the phosphorescence of 6,10NICz at room temperature was too weak for the decay to be accurately fitted, but the tail of the decay can still be observed in the temperature-dependent TRPL measurement even at room temperature (Figure ). Phosphorescence lifetimes for 4NICz and 6,10NICz are thus not reported. The phosphorescence lifetimes, tPh, of 5NICz, 6NICz, and 7NICz are 1.5, 0.8, and 1.9 s at room temperature. Finally, a much shorter component to the decay associated with the phosphorescence was recorded over 100/200 ns (Figure ) in all five emitters. We attribute this process to residual prompt fluorescence, considering that the tail of the higher energy emission band clearly extends to overlap with the phosphorescence band (Figure ); we have included the decay and fitted lifetime of this process for completeness.