Theoretical study of the electron transport through aromatic molecular wires with different levels of conjugation

The electron transport behaviors of three typical aromatic molecules (planar p-terphenyl, dibenzo[cd, Im]perylene, and dibenzo[bc, kl]coronene) with different levels of conjugation were studied theoretically using a combination of density functional theory and non-equilibrium Green’s functions method. The results demonstrate that although the planar p-terphenyl is the least conjugated one among the three molecules, its conductance is significantly higher than those of dibenzo[cd, Im]perylene and dibenzo[bc, kl]coronene. The conductance of the three molecular wires decreases with an order of planar p-terphenyl > dibenzo[cd, Im]perylene > dibenzo[bc, kl]coronene, which is reverse to the order of the levels of conjugation of the three molecules. This unanticipated electron transport feature was analyzed from the transmission spectra and the molecular projected self-consistent Hamiltonian states of the three molecular wires under different applied bias. It is found that the orbital density at the molecule–electrode interface is the essential reason for generating this unanticipated electron transport behavior of the three aromatic molecular wires. The finding is expected to be helpful in designing and rationalization of high performance molecular wires for nanoscale applications.