The experimentally derived ET values of the PCs (Table ) can then be applied to the target E/Z isomerization of E-stilbene (Figure ). Given that the ET of the E and Z isomers of stilbene are determined from the onset of the absorption spectra in ethyl iodide and the ET of the PCs are determined from the onset of emission spectra (steady-state or gated emission at 77 K), the triplet energies are not strictly directly comparable since different methods and solvents have been used for their estimation. However, since triplet energies only serve to predict whether an ), with 89% of Z-stilbene remaining. This mirrors the results of the forward E/Z isomerisation reaction; 91% of Z-isomer is formed when irradiating E-stilbene, indicating that the same Z/E ratio is obtained whether irradiating E-stilbene or Z-stilbene for 24 h.