Cooperative Self-Assembly of Dimer Junctions Driven by π Stacking Leads to Conductance Enhancement

Abstract

We demonstrate enhanced electronic transport through dimer molecular junctions, which self-assemble between two gold electrodes in π−π stabilized binding configurations. Single molecule junction conductance measurements show that benzimidazole molecules assemble into dimer junctions with a per-molecule conductance that is higher than that in monomer junctions. Density functional theory calculations reveal that parallel stacking of two benzimidazoles between electrodes is the most energetically favorable due to the large π system. Imidazole is smaller and has greater conformational freedom to access different stacking angles. Transport calculations confirm that the conductance enhancement of benzimidazole dimers results from the changed binding geometry of dimers on gold, which is stabilized and made energetically accessible by intermolecular π stacking. We engineer imidazole derivatives with higher monomer conductance than benzimidazole and large intermolecular interaction that promote cooperative in situ assembly of more transparent dimer junctions and suggest at the potential of molecular devices based on self-assembled molecular layers.

Conductance and assembly of quasi-1D coordination chain molecular junctions with triazole derivatives

“…1b and c, right). 22,41 Notably, the extension lengths that junctions can sustain for both isomers in low-G are ∼4 Å, approximately double that of high-G plateaus, as shown in 2D conductance-displacement histograms (Fig. 2b and c).…”

“…1c and their methylated derivatives discussed further below in organic solvents, N , N -dimethylformamide (DMF) and 1,2,4-tricholorobenzene (TCB), or dip-coated onto the substrates out of aqueous solutions as described in the ESI† and in our previous work. 22,40,41 Measurements in aqueous liquid conditions using the wax-coated tip are also performed and shown in the ESI† for comparison to the dip-coated measurements. Both dried and aqueous conditions yield the same molecular conductance values, but the signal-to-noise is higher in dried dip-coated samples (Fig.…”

Reliable Dimerization Energies for Modeling of Supramolecular Junctions

“…Intermolecular noncovalent interactions are of importance in current investigations in biology (see the book [ 1 ]), chemistry (see the review by Stoddard et al [ 2 ]), physics (see reference [ 3 ] and the works cited therein), and materials research [ 4 , 5 , 6 ]. In the area of materials science, certain types of noncovalent interactions are crucial for the design of novel electronic materials [ 7 , 8 , 9 , 10 , 11 , 12 ]. Specifically, supramolecular junctions containing π-conjugated molecules have frequently been studied (see the review [ 13 ]).…”