The Effect of π-Coupling on the Electronic Properties of 1,4-Dithiol Benzene Stacking

We have studied the influence of π-coupling on electronic and structural properties of self-assembled 1,4-dithiol benzene (HSC₆H₄SH) molecule with the first principle DFT-KS method. The isolated molecule shows well defined electronic properties, which drastically change once the molecule is packed into a dense 1-D molecular wire. The HOMO-LUMO gap for a dimer decreases by 1.2 eV when intermolecular distance changes from 6.9 to 3.3 Å, while it sharply decreases by 2.2 eV for a wire containing seven (7) molecular units. It is found that intermolecular distances between molecular units, as well as the number of molecules in the molecular wire are the two main correlated factors that influence the magnitude of the changes. In fact, the two parameters that influence the electronic structure properties of the wires are clearly related to magnitude of π-electron interaction in the vicinity of the HOMO-LUMO gap region.