STM study of oligo(phenylene-ethynylene)s

Abstract

A detailed scanning tunneling microscopy (STM) study of two variants of oligo(phenylene ethynylene) (OPE) molecules is presented. These molecules might serve as molecular wires up to ≈ 5 nm in length. Self-assembled arrangements as well as single molecules on a Au(111) surface were analyzed. The molecular orbitals were directly imaged and are compared to density functional theory calculations. Sub-molecular resolution images of both molecules directly display the chemical structure. One of the OPE variants was lifted off the surface by the STM tip to measure the singlemolecule conductance in order to explain previously reported low conduction values. Furthermore, we present a detailed analysis of a tip-induced conformational switching of the hexyl side groups from all-trans to a nonlinear conformation, which was observed for both variants.

A review of oligo(arylene ethynylene) derivatives in molecular junctions

“…van der Waals forces, can effect molecular assembly. 130 There is no clearly defined limit on the molecular length for which measurements are practical, as conductance properties are influenced by many other factors. However, most conductance studies investigate OAE5 molecules or shorter, as will be seen in the discussion below.…”

“…76,77 6 has also been partially lifted from a Au(111) surface using an STM tip and the properties of the resulting Au-(sub-)molecule-tip junctions investigated. 130 Graphene nanogaps have been bridged using porphyrin-based OAEs bearing (substituted) pyrene or alkylated hexa-peri-hexabenzocoronene (HBC) anchoring groups. [73][74][75] Continued interest in the unique properties of graphene means that the development of additional specialised anchoring groups of this type can be expected.…”

Molecular bridge-mediated ultralow-power gas sensing

“…Generally, the electrical properties of organic molecules can be determined by using AFM/STM 29,30 , or (mechanically controllable breaking) MCB techniques [31][32][33][34] or can be simulated using computational chemistry methods [25][26][27] . Electrical transport through conventional alkane(di)thiol SAMs has been described as pure quantum tunneling across a thin dielectric film that has a rectangular potential barrier with image charge effects included, as described by J. Simmons in 1963 35 .…”

“…Figure. 13 Normalized conductance response to one period of cadaverine exposure to nanogap device and subsequent removal curve-fitted to 2 nd order adsorption-desorption models.…”