Stereoelectronic Effect-Induced Conductance Switching in Aromatic Chain Single-Molecule Junctions

Abstract

Biphenyl, as the elementary unit of organic functional materials, has been widely used in electronic and optoelectronic devices. However, over decades little has been fundamentally understood regarding how the intramolecular conformation of biphenyl dynamically affects its transport properties at the single-molecule level. Here, we establish the stereoelectronic effect of biphenyl on its electrical conductance based on the platform of graphene-molecule single-molecule junctions, where a specifically designed hexaphenyl aromatic chain molecule is covalently sandwiched between nanogapped graphene point contacts to create stable single-molecule junctions. Both theoretical and temperature-dependent experimental results consistently demonstrate that phenyl twisting in the aromatic chain molecule produces different microstates with different degrees of conjugation, thus leading to stochastic switching between high- and low-conductance states. These investigations offer new molecular design insights into building functional single-molecule electrical devices.

Origin and mechanism analysis of asymmetric current fluctuations in single-molecule junctions

“…This is partially because current uctuations, the ubiquitous noise within molecular nanocircuits, is one of the biggest challenges. Except for ordinary uctuations existing in conducting bulk systems (for instance, thermal noise), charge transport through molecules would be readily inuenced by other factors, for example, conformational changes of the conducting molecules, 10,16,17 variable molecule-electrode coupling, [18][19][20] inelastic electron tunneling, [21][22][23][24] and electro-induced redox processes, 9,25-28 thus generating noises highly related to the electronic structure or behavior of the "molecularly" conducting path. Insights into the noise analysis of the single-molecule conducting processes could not only pave the way to revealing the essence of charge transport but also provide valuable information toward extensive applications in the evaluation of vibration modes, 23,29 Fano factor, 30,31 and even the identication of the number of conduction channels contributing to the transport.…”

Nanoimaging of Organic Charge Retention Effects: Implications for Nonvolatile Memory, Neuromorphic Computing, and High Dielectric Breakdown Devices

“…These are shown in Figure S5. DFT calculations including Van der Waals corrections (6,7) show that mode C is a bit more stable than mode L by 0.21 eV, so that at RT both modes should coexist. A Bader analysis shows that the amount of electron charge transferred to the Au NP in this arrangement is larger: -0.23 e -.…”

“…On one hand, this has been utilized to fabricate flexible and wearable devices, where the electronic functionalities are not affected by mechanical bending and stretching (1,2). On the other hand, in certain organic materials, the structural reconfiguration is strongly coupled to the electronic states, which can offer new electronic functionality (5)(6)(7). Remarkably, such strong coupling, or polaronic effect, can occur in the size scale as small as a single layer of molecules.…”

“…Remarkably, such strong coupling, or polaronic effect, can occur in the size scale as small as a single layer of molecules. Previously, it has been shown that the conformation, charge, or spin states of certain organic monolayers or single molecules can have two or multiple stable configurations that can be switched in the presence of external stimuli such as light or electric current (6)(7)(8)(9)(10)(11)(12). This effect is appealing for a variety of applications ranging from non-volatile memory, neuromorphic computing, and high dielectric breakdown devices (13)(14)(15).…”

A single-molecule porphyrin-based switch for graphene nano-gaps

“…16 Another is based on conformational change, in which the conductance is tuned by decreasing the pi-pi orbital overlap within a bridging moiety by rotating adjacent phenyl rings. 15,22 Recently, in an effort to overcome the limitations of gold electrodes for coming in contact with single molecules, graphene electroburnt nanogaps [23][24][25][26][27][28] have been developed, which can be electrostatically tuned by a nearby buried gate electrode. 29,30 This opens the way to the design of new molecular switches, which takes advantage of specific properties of such planar geometries.…”