Finally, the trend in the measured HOMO/LUMO energies matches that predicted by DFT, although the absolute energies of the LUMO were more stabilised than the predictions. emitting in the sky-blue regime. In particular, the difference between the two singly substituted structures demonstrates that the emission energy of this class of donor-naphthalene type emitters is influenced not only by the number of donors but also their substitution pattern around the naphthalene ring. We hypothesise that the apparent difference in behaviour of the CT absorption band and the CT emission band in relation to molecular structure is caused by the CT absorption band being partially masked by the much larger LE absorption band, which makes its peak position difficult to ascertain accurately. TDA-DFT calculations at the relaxed excited state of all three emitters show an equivalent stabilisation of ca. 0.56 eV (Table ) compared to the vertical excited state. We thus conclude that there is no increased stabilisation of the conformation of 2-PXZ-Nap in the relaxed excited state that is responsible for its apparent reduced Stokes shift compared to 1-PXZ-Nap.