Transient absorption measurements were performed to study the initial excited state formation dynamics for all three derivatives in degassed solution state (DCM and MCH) (Figure and Supplementary Fig. ). In MCH, p-ICz-PI gives an instantaneous excited state absorption (ESA) at 570 nm, followed by the emergence of an 870 nm band within 5 ps (Supplementary Fig. ). The 870 nm ESA decays in 6.3 ns which correlates well with the fluorescence decay time of 6 ns (Supplementary Table ), identifying this as the ESA from the emissive, highly delocalised and conjugated mixed LE/CT species. A residual ESA observed at 520-650 nm with a lifetime of 3.9 ns could potentially arise from the LE state as it is not observed in DCM.