A New Approach to Materials Discovery for Electronic and Thermoelectric Properties of Single-Molecule Junctions

Abstract

We have investigated a large set of symmetric and asymmetric molecules to demonstrate a general rule for molecular-scale quantum transport, which provides a new route to materials design and discovery. The rule states "the conductance GXBY of an asymmetric molecule is the geometric mean of the conductance of the two symmetric molecules derived from it and the thermopower SXBY of the asymmetric molecule is the algebraic mean of their thermopowers". The studied molecules have a structure X-B-Y, where B is the backbone of the molecule, while X and Y are anchor groups, which bind the molecule to metallic electrodes. When applied to experimentally measured histograms of conductance and thermopower, the rules apply to the statistically most probable values. We investigated molecules with anchors chosen from the following family: cyano, pyridl, dihydrobenzothiol, amine and thiol. For the backbones B, we tested 14 different structures. We found that the formulas (GXBY)(2) = GXBX*GYBY and SXBY = (SXBX + SYBY)/2 were satisfied in the large majority of the cases, provided the Fermi energy is located within the HOMO-LUMO gap of the molecules. The circuit rules imply that if measurements are performed on molecules with nA different anchors and nB different backbones, then properties of nA(nA + 1)nB/2 molecules can be predicted. So for example, in the case of 20 backbones and 10 anchors, 30 measurements (or reliable calculations) can provide a near quantitative estimate for 1070 measurements of other molecules, at no extra cost.

A Magic Ratio Rule for Beginners: A Chemist's Guide to Quantum Interference in Molecules

“…As an example, from a measurement of the conductance of 1 in Figure and from knowledge of the magic numbers of 1 and 2 , the conductance of 2 could be predicted ahead of its synthesis. Finally, we note that weak coupling, locality, connectivity, mid‐gap transport and phase coherence can be utilized to yield further quantum circuit rules, which relate the transport properties of molecules of the form A‐B‐C, B‐A‐C and B‐C‐A . Such rules are also useful for the purpose of materials discovery, since from measurements of the electrical conductance or Seebeck coefficient of two such molecules, the electrical and thermoelectrical properties of a third can be predicted.…”

Turning the Tap: Conformational Control of Quantum Interference to Modulate Single‐Molecule Conductance

“…[13] Following theoretical predictions of the introduction of DQI effects due to interactions of pendant oxygen and bipyridene groups with conjugated molecular cores [14] as well as subsequent experimental confirmation, [15] as tudy of QI effects in molecular junctions of p-conjugated systems was carried out by GuØdon et al using the conducting atomic force microscopy technique. [16] Arroyo et al studied QI effects in acentral phenyl ring by varying the coupling to av ariety of anchor groups. [17] Manrique et al have also demonstrated tuning of QI effects through heteroatom substitution within amolecular core,a nd proposed aq uantum-circuit rule for designing molecular devices and materials.…”

Thermal and Thermoelectric Properties of Molecular Junctions

“…C) Comparison between the thermopowers S XBY and the arithmetic means ( S XBX + S YBY )/2 for different molecules. Reproduced with permission . Copyright 2015, American Chemical Society.…”