Density Functional Theory (DFT) calculations at the PBE0/6-31G(d,p) level of theory in the gas phase were performed in order to gain a deeper understanding of the electronic structures of all compounds (Figure ). For T-tBuCz-AQ, the highest occupied molecular orbital (HOMO) is localized on the carbazole donors, with a minor contribution from the anthraquinone, while the lowest unoccupied molecular orbital (LUMO) is localized on the anthraquinone. Similar HOMO and LUMO distributions are noted for T-MeOCz-AQ. As expected, the HOMO level for T-MeOCz-AQ is slightly destabilized compared to that of T-tBuCz-AQ due to the stronger electrondonating character of the dMeOCz donor as compared to dtBuCz, while the LUMO levels is also destabilized, though less so than the HOMO, reflecting the poor but non-trivial electronic coupling of the donors with the AQ acceptor. In the case of C-tBuCz-AQ and C-MeOCz-AQ, the HOMOs and LUMOs are exclusively localized on the carbazole donors and anthraquinone, respectively, and no overlap is observed. A consequence of the near-zero orbital overlap is that though, as expected, the HOMO of C-MeOCz-AQ is destabilized compared to that of C-tBuCz-AQ the LUMO levels are effectively the same in these two compounds. In the case of tBuCz-PA, the HOMO is delocalized on the carbazole and pyrazoloanthrone, while the LUMO is located on the pyrazoloanthrone. Due to the orthogonal conformation of the DMAC in DMAC-PA, the HOMO is mostly localized on the DMAC while the LUMO is located on the pyrazoloanthrone ring. As expected, the HOMO levels are correlated with the electron-donating strength of the donor group while the LUMO levels are similar; the more destabilized LUMO in tBuCz-PA is a reflection of the greater electronic coupling with the donor in this compound. The calculated optical gaps of 2.73 for T-tBuCz-AQ and 2.60 eV for C-tBuCz-AQ decrease to 2.45 and 2.30 eV for T-MeOCz-AQ and C-MeOCz-AQ, respectively, as expected.