In the left panel of Figure , the HOMO for DMeO-BTBT, the LUMO for TCNQ, and the HOMO and LUMO of their dimer complex are visualized; this D-A dimer has the greatest S1 DCT in the data set. The visual similarity between the monomer orbitals and those in the complex is apparent, and the localization onto donor and acceptor moieties in the complex is striking. In the right panel of Figure , the HOMO of DPTTA HOMO, the LUMO of F4TCNQ, and HOMO and LUMO of their dimer complex are visualized; this D-A dimer has the smallest S1 DCT in the data set. While there is significant visual similarity between the monomer MOs and those in the complex, there is also substantial delocalization of the HOMO onto the acceptor molecule and similar delocalization of the LUMO onto the donor. To maximize S1 DCT, the electron density must be localized on the electron donor in the HOMO and transferred completely to the acceptor LUMO. The value of η quantifies the degree to which the isolated HOMO (LUMO) of the donor (acceptor) correlates with that in the complex, which predicts S1 DCT.