Figure shows the time-resolved emission of 1 wt.% p-ICz-PI in zeonex films. p-ICz-PI exhibit a clear prompt emission with an onset at 401 nm (λmax. = 434 nm). This band red-shifts with time, which is attributed to the presence of aggregates at 1 wt.% doping, confirmed by their absence in 0.1 wt.% films (Supplementary Fig. ). At long time-delays, >800 µs, strong blue long-persistent emission, distinct from the phosphorescence (Figure ), is observed when the laser is turned-off. This slow DF is consistent with the relatively high ∆EST = 0.37 eV in zeonex (Figure and Supplementary Fig. ). 0.1 wt.% doped films (Supplementary Figures ), also show this delayed fluorescence confirming its monomolecular origin. In contrast, 1 wt.% o-ICz-PI in zeonex film show distinctively different emission (Figure ). Prompt fluorescence (λonset = 411 nm and λmax = 451 nm) lasts until 150 ns with no aggregate contribution. Delayed emission is seen at the same wavelengths as prompt fluorescence at time-delays >630 µs. In addition, a new red-shifted band appears at around 516 nm. Similar emission features are also observed in 0.1 wt.% and 0.02 wt.% zeonex and neat films (Supplementary Fig. ). Steady-state fluorescence onset in these films is independent of doping ratio, unlike the p-ICz-PI isomer (Supplementary Fig. ). At 80 K, at long time-delays we observe only well-structured phosphorescence onset at 461 nm, (Figure and Supplementary Fig. ). These observations suggest there is additional low levels of exciplex gives key insight into the differences in electronic structure between the two isomers. Cz-PI clearly behaves like a typical twisted D-A TADF molecule showing much higher PLQY in non-polar zeonex films, than in highly polar solvent (Supplementary Fig. and Supplementary Table ). No exciplex emission is observed for o-Cz-PI at 80 K in the 1 wt. % zeonex films which is fully in line with the thermally activated nature of exciplex formation (Supplementary Fig. ). Notably, a clear dispersion in the CT emission maxima is observed for Cz-PI, whereas, the ICz-PI isomers are completely dispersion-free as evident from their timeresolved emission characteristics, owing to their rigidified co-planar structures (Supplementary Fig. ).