The same level of theory was used to additionally compare the HOMO energies of Cz-Ph-TRZ (-5.69 eV), DMAC-TRZ (-5.13 eV) and azasiline-Ph-TRZ (-5.39 eV), each with structures analogous to AZB-Ph-TRZ (Figure ). The first of these exactly matches the HOMO level of AZB-Ph-TRZ (-5.69 eV) while the HOMO levels of the latter two compounds are significantly shallower in energy, evidencing that the AZB donor has indeed a deep HOMO level (and weaker donating strength) than that of the other six-membered-central-ring DMAC and azasiline counterparts. The HOMO-LUMO energy gap (∆EHL) values of 3.68 eV and 3.59 eV for AZB-Ph-TRZ and AZB-TRZ, respectively, are consequently larger in comparison to the 2.91 eV and 3.17 eV for DMAC-TRZ and azasiline-Ph-TRZ (also known as DTPDDA in the literature), respectively, and most like the 3.82 eV for Cz-Ph-TRZ.