Time-resolved emission measurements of the two ICz-PI isomers were recorded in degassed DCM. p-ICz-PI emits the same prompt (1 ns -40 ns) and a weak delayed fluorescence (2 µs -1 ms) (Figure -d and Supplementary Fig. ). In contrast, o-ICz-PI showed a more pronounced enhancement in emission intensity upon degassing (Supplementary Fig. , Supplementary ) similar to Cz-PI (Supplementary Fig. and). Time-resolved emission in MCH shows clear vibronic features for p-ICz-PI, and a shorter lifetime compared to both o-ICz-PI and Cz-PI (Supplementary Fig. ). We did not observe any delayed fluorescence in MCH, presumably due to a larger ∆EST in all cases.