Integrating functional molecules into single-molecule devices is a key step toward the realization of future computing machines based on the smallest possible components. In this context, photoswitching molecules that can make a transition between high and low conductivity in response to light are attractive candidates. Here we present the synthesis and conductance properties of a new type of robust molecular photothermal switch based on the norbornadiene (NB)–quadricyclane (QC) system. The transport through the molecule in the ON state is dominated by a pathway through the π-conjugated system, which is no longer available when the system is switched to the OFF state. Interestingly, in the OFF state we find that the same pathway contributes only 12% to the transport properties. We attribute this observation to the strained tetrahedral geometry of the QC. These results challenge the prevailing assumption that current will simply flow through the shortest through-bond path in a molecule.

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single‐molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local‐heating mechanism for the forward reaction and catalyzed by a single charge‐transfer process for the reverse switching. This single‐molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single‐molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage‐class memories.

The configuration of the molecule–electrode contact region plays an important role in determining the conductance of a single-molecule junction, and the variety of possible contact configurations have yielded multiple conductance values for a number of molecular families. In this report, we perform simultaneous conductance and electromechanical coupling parameter measurements on a series of oligophenylene–dithiol single-molecule junctions. These molecules show two distinct conductance values, and by examining the conductance changes, the electromechanical coupling, and the changes in the I–V characteristics coupled with a combination of analytical mechanical models and density functional theory (DFT) structure calculations, we are able to determine the most-probable binding configuration in each of the conductance states. We find that the lower-conductance state is likely due to the thiols binding to each electrode at a gold top site, and in the higher-conductance state, the phenylene π orbitals interact with electrodes, drastically modifying the transport behavior. This approach provides an expanded methodology for exploring the relationship between the molecule–electrode contact configuration and molecular conductance.

Systems that are capable of robustly reproducing single-molecule junctions are an essential prerequisite for enabling the wide-spread testing of molecular electronic properties, the eventual application of molecular electronic devices, and the development of single-molecule based electrical and optical diagnostics. Here, a new approach is proposed for achieving a reliable single-molecule break junction system by using a microelectromechanical system device on a chip. It is demonstrated that the platform can (i) provide subnanometer mechanical resolution over a wide temperature range (≈77-300 K), (ii) provide mechanical stability on par with scanning tunneling microscopy and mechanically controllable break junction systems, and (iii) operate in a variety of environmental conditions. Given these fundamental device performance properties, the electrical characteristics of two standard molecules (hexane-dithiol and biphenyl-dithiol) at the singlemolecule level, and their stability in the junction at both room and cryogenic temperatures (≈77 K) are studied. One of the possible distinctive applications of the system is demonstrated, i.e., observing real-time Raman scattering in a single-molecule junction. This approach may pave a way to achieving high-throughput electrical characterization of single-molecule devices and provide a reliable platform for the convenient characterization and practical application of single-molecule electronic systems in the future.

Tao and colleagues found two conductance states for single water molecular junctions, originating with two water orientations that depend on water-water interactions. Electric fields can further switch the water molecular junction from the high-to low-conductance states. The study reveals the nature of water molecules as charge mediators and sets fundamental limits on orientation-dependent watermediated electron transfer rates.