The HOMO/LUMO levels are -6.23/-2.56 eV. A similar electron density distribution pattern of the orbitals of TPPQ has been previously reported, though those calculations diverge from those reported here as they included a THF environment and were carried out at the lower B3LYP/6-31G(d) level. However, the literature calculated HOMO level was slightly shallower at -6.15 eV, whilst the LUMO level was deeper at -2.80 eV. Both 4DMAC-TPPQ and 4PXZ-TPPQ exhibit a similar pattern in the distribution of the electron densities to TPPQ, with the HOMO distributed across the four donors and the LUMO localized mainly on the PQ acceptor (Figure ). Consequently, the HOMO levels are shallower compared to TPPQ at -5.29 eV for 4DMAC-TPPQ and -4.79 eV for 4PXZ-TPPQ, in line with their increasing donor strength, and the LUMO levels are stabilized compared to TPPQ, at -2.87 eV for 4DMAC-TPPQ and -2.99 eV for 4PXZ-TPPQ. The HOMO-LUMO gap, ΔEHOMO-LUMO, thus decreases from 3.67 eV for TPPQ to 2.42 eV for 4DMAC-TPPQ and 1.80 eV for 4PXZ-TPPQ.