The LTP emission profiles overlap very well with the phosphorescence spectrum of 1 wt% TPhCor in PMMA measured at 77 K (Figure ). Based on these results, we can conclude that the LTP originates from the LE T1 state localized on TPhCor. Notably, there is a remarkable difference in the phosphorescence spectra at 298 K and 77 K of both TDMACPhCor and TPXZPhCor (Figures 5a), also reflected in the different phosphorescence afterglows at 298 K and 77 K (Figures 5c). Based on similar observations in our previous report, we assign this dual phosphorescence to T1 H and T1 L , associated with phosphorescence from two conformers. Considering the broad RTP of TDMACPhCor and TPXZPhCor, we contend that the spectra consist of contributions from both T1 H and T1 L , which is only possible if there is thermally activated excitonic coupling between T1 H and T1 L (vide infra). To validate this hypothesis, temperature-dependent phosphorescence spectra were measured from 77 to 298 K. As shown in Figure , the phosphorescence emission of TCzPhCor shows a negligible change across this temperature range; the weak emission band centred at ~460 nm is ascribed to steady- state fluorescence due to the residual background excitation, evidenced by the unchanged PL intensity as a function of temperature (Figure ). A similar background excitation was observed in the phosphorescence spectrum of the TCzPhCor-doped PMMA film (Figure ). However, for TDMACPhCor and TPXZPhCor, distinctly red-shifted phosphorescence spectra were obtained with decreasing temperature, also reflected by the change in the phosphorescence afterglows (Figures ), which is the result of loss of the phosphorescence from T1 H . Figure illustrates a plausible mechanistic explanation, where excitonic coupling between T1 H and T1 L is temperature dependent, which explains why at different temperatures, differing phosphorescence afterglows were recorded.