As two such monomers are linked by a single bond into d1, both the HOMO and LUMO shift toward the Fermi level to -1.05 eV and 1.82 eV, respectively (Figure ). The HOMO-LUMO gap thus shrinks notably to 2.87 eV, as expected from a bonding motif that maintains the conjugation at the inter-monomer level and thus results in an overall extension of the electron conjugation and delocalization. A similar coupling with a single bond but with the monomers in a collinear and staggered position (d3) results in an only slightly larger gap of 2.97 eV (Figure ) with the HOMO and LUMO at -1.12 eV and 1.85 eV, respectively. As the two monomers become linked with two covalent bonds that form a new four membered ring at the junction (d2), the changes in the frontier orbital energies are not so pronounced either.