| Self-assembly of nanostructure is a potential solution to the achievement of the necessary components for organic electronics and ultimately, molecular electronics. In the present work, we have studied the assembly of molecular unit consisting of a substituted benzene core with polar side chains especially chosen to favor the cohesion of molecules into a columnar structure, rigidly stacked together by hydrogen bonding. Such dense molecular stacking provides an elegant manner to produce highly organized systems with significant pi-orbital coupling. In our theoretical investigation, we focused on the formation, the structural and the electronic properties of organic molecular wires with sophisticated methods such as Hartree-Fock (HF) and Density Functional Theory (DFT). The high dipole moment (2,60 D) found for the monomer constitutes a good indicator for the cohesion of molecular units within the wire, and the HOMO-LUMO gap (5,34 eV) provides an upper value for the expected bandgap of a long wire. The formation of a dimer is characterized by an increasing stability ( De = 0,75) of the assembly, a relatively short intermolecular distance (4,44 A) and by a decreasing HOMO-LUMO gap (4,47 eV) relative to the monomer (5,34 eV). The formation of the trimer leads to an improved stability over the monomer (De = 1,70 eV) to a decreasing HOMO-LUMO gap (3,88 eV) and to an unexpected geometry. The results of our calculations for these elements of the organic wires is discussed in terms of intra and intermolecular changes relative to the conformation of the molecular units. We focused our attention on calculated parameters such as the charge transfer, the stability of the different molecular conformations considered, and the electronic properties of the assembly near the HOMO-LUMO gap. |
