First Principles Studies of Molecular Junctions on the Basis of Tolane Derivatives

EZEQUIEL P. M. LEIVA; M. EZEQUIEL CASTILLO; MARTIN E. ZOLOFF MICHOFF; PATRICIO VÉLEZ

Lausana

Congreso; 65 th Annual Meeting of the International Society of Electrochemistry,; 2014

ISE

The possibility of building ultra small electronic and electrochemical devices using single molecules has triggered numerous experimental as well as theoretical studies in the last few years. Molecules are attractive building blocks since it is possible to tailor the properties of the contact modifying the nature of the anchoring group and also by introducing substituents on the molecule. In the present work, Density Functional Theory calculations are used to study the evolution of a variety of molecular systems (wires)attached to a gold nanolead, which is subjected to a pulling force. The nanowires analyzed in the present work are based on the diphenylacetylene structure (tolane), a molecule joining two benzene rings through an acetylene breach (HCCH). The head (or anchoring) groups studied involve the exchange of these benzenic rings of the base structure by each one of the following moieties: pyridyl (PY), tiophenol (SH),anyline (NH2), benzonitrile (CN) and dihydrobenzothiophene (BT1). These compounds have been recently studied for their conductive properties due to the conjugated p system. Energy and force profiles were obtained for the stretching process of the described systems. The results reveal that the starting geometry is crucial, as significant force values are not always found upon elongation of the junction. When meaningful forces are obtained, the following sequence (in descending order) of absolute forces is observed:SH > PY > CN > BT1 ~ NH2. In order to consider the effect of the structure of the tip, we have repeated all the previous calculations with different geometries of its ending atoms.Conductance traces were calculated for several stretching processes. The trends observed are compared with the experimental results.