The gradually stabilized LUMO from DMACBP to DMACPyBP, DMACBPN and DMACPyBPN originates from the enhanced electron-withdrawing strength of acceptor with increasing nitrogen content. However, due to the enhanced electronic coupling between the donor and the acceptor, the HOMO levels of DMACPyBP and DMACPyBPN are more stabilized as these are delocalized over both DMAC and the pyridine (Py) rings, as compared to the DMAC-localized orbitals in DMACBP and DMACBPN. (Figure ). The HOMO-LUMO gap, DEHOMO-LUMO, decreases from 2.84 eV for DMACBP, to 2.75 eV for DMACPyBP, 2.72 eV for DMACBPN and 2.63 eV for DMACPyBPN, following a similar trend to that observed for the LUMO and governed by the strength of the electronacceptor moiety (Error! Reference source not found.a).