Using molecular fragments of NDI and pyrene groups as examples, we then evaluated the excited states of the donor-acceptor pairs. We first treated both NDI and pyrene cores separately, adding a short part of the connecting bridge to the edges. The calculations from DFT combined with multi-reference configuration interaction (DFT/MRCI) and second-order approximate coupled cluster (CC2) gave vertical and adiabatic energies as shown in Table , and the frontier molecular orbitals are shown in Figure . With an NDI de-excitation energy of 2.57 eV (~480 nm) corresponding to the nπ1* state and pyrene de-excitation energy of 3.27 (~380 nm)