The photophysics of the ICz-PI isomers (p-ICz-PI and o-ICz-PI), and Cz-PI in a small molecule host, [1,3-bis(N-carbazolyl)benzene] (mCP) was also characterised (Supplementary Fig. ). The results are generally very similar to those found in zeonex but with higher DF contribution in mCP, in line with the smaller ΔEST. These are described in the Supporting Information.