Electrical molecular switch addressed by chemical stimuli

Multi-stimuli actuation of a photoresponsive azobenzene based molecular switch

There has been considerable interest in building switching functions into self-assembled monolayers with switching actuated by external stimuli such as light, electrical current, heat, pressure or chemical changes. In this study, dual switching functionality has been built into azobenzene based molecular monolayers. Switching behaviour has been compared for unsubstituted azobenzene monolayer adsorbates and two other monolayers whose ortho position on the terminal phenyl group is substituted by ethyl and isopropyl chains, respectively. The dual molecular switching functionality with light or protonation actuation is compared. EGaIn contacts to the monolayers have been used to record the J-V curves and characterize the on/off switching. This is complemented with further characterization by transition voltage spectroscopy (TVS), ultraviolet photoelectron spectroscopy (UPS), water contact angle determination, atomic force microscopy (AFM) and theoretical computations. It is concluded that side chains (the ethyl and isopropyl groups) are able to decouple neighbouring azobenzene adsorbates which promotes the photo-efficiency of isomerisation and switching. In addition, acid treatment is also applied to these three molecular layers to try to achieve dual stimuli actuation. The absorption wavelength of the azobenzene moiety red shifts by ∼100 nm for all the three protonated molecules. In the case of the unsubstituted azobenzene, its triggering wavelength is totally reversed once it is protonated. A logic truth table has been constructed for the SAM device, which shows that the simple azobenzene molecular layers exhibit the behaviour of an 'AND' logic gate which uses blue light and acid as two inputs.

Electrical monitoring of single-event protonation dynamics at the solid-liquid interface and its regulation by external mechanical forces

Detecting chemical reaction dynamics at solid-liquid interfaces is important for understanding heterogeneous reactions. However, there is a lack of exploration of interface reaction dynamics from the single-molecule perspective, which can reveal the intrinsic reaction mechanism underlying ensemble experiments. Here, single-event protonation reaction dynamics at a solid-liquid interface are studied in-situ using single-molecule junctions. Molecules with amino terminal groups are used to construct single-molecule junctions. An interfacial cationic state present after protonation is discovered. Real-time electrical measurements are used to monitor the reversible reaction between protonated and deprotonated states, thereby revealing the interfacial reaction mechanism through dynamic analysis. The protonation reaction rate constant has a linear positive correlation with proton concentration, whereas the deprotonation reaction rate constant has a linear negative correlation. In addition, external mechanical forces can effectively regulate the protonation reaction process. This work provides a single-molecule perspective for exploring interface science, which will contribute to the development of heterogeneous catalysis and electrochemistry.

Toward Practical Single-Molecule/Atom Switches

Electronic switches have been considered to be one of the most important components of contemporary electronic circuits for processing and storing digital information. Fabricating functional devices with building blocks of atomic/molecular switches can greatly promote the minimization of the devices and meet the requirement of high integration. This review highlights key developments in the fabrication and application of molecular switching devices. This overview offers valuable insights into the switching mechanisms under various stimuli, emphasizing structural and energy state changes in the core molecules. Beyond the molecular switches, typical individual metal atomic switches are further introduced. A critical discussion of the main challenges for realizing and developing practical molecular/atomic switches is provided. These analyses and summaries will contribute to a comprehensive understanding of the switch mechanisms, providing guidance for the rational design of functional nanoswitch devices toward practical applications.

Design, Transport/Molecular Scale Electronics, Electric Properties, and a Conventional Quantum Study of a New Potential Molecular Switch for Nanoelectronic Devices

In this study, we examined the influence of an external electric field applied in two directions: horizontal (X-axis) and vertical (Y-axis) on the electronic and vibrational properties of a field-effect molecular switch, denoted as M. We employed density functional theory and quantum theory of atoms in molecules for this analysis. The current-voltage (I-V) characteristic curve of molecular switch system M was computed by applying the Landauer formula. The results showed that the switching mechanism depends on the direction of the electric field. When the electric field is applied along the X-axis and its intensity is around 0.01 au, OFF/ON switching mechanisms occur. By utilizing electronic localization functions and localized-orbital locator topological analysis, we observed significant intramolecular electronic charge transfer "back and forth" in Au-M-Au systems when compared to the isolated system. The noncovalent interaction revealed that the Au-M-Au complex is also stabilized by electrostatic interactions. However, if the electric field is applied along the Y-axis, a switching mechanism (OFF/ON) occurs when the electric field intensity reaches 0.008 au. Additionally, the local electronic phenomenological coefficients (Lelec) of this field-effect molecular switch were determined by using the Onsager phenomenological approach. It can also be predicted that the molecular electrical conductance (G) increases as Lelec increases. Finally, the electronic and vibrational properties of the proposed models M and Au-M-Au exhibit a powerful switching mechanism that may potentially be employed in a new generation of electronic devices.

Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

Like hydroquinones and quinones, aromatic compounds with multiple NH2 groups and the corresponding quinonediimines have the potential to serve as components of useful redox-active organic materials. Benzene-1,2,4,5-tetramine (BTA) and its oxidized form BTA-H2 offer a promising redox pair of this type, and the compounds have proven to be useful in many areas of chemistry. However, key aspects of their behavior have remained poorly studied, such as the nature of their protonated forms, their preferred molecular structures, their reactivity, and their organization in condensed phases. In the present work, we have used a combination of improved methods of synthesis, computation, spectroscopic studies, and structural analyses to develop a deeper understanding of BTA, BTA-H2, their salts, and related compounds. The new knowledge is expected to accelerate exploitation of the compounds in areas of materials science where desirable properties can only be attained by properly controlling the organization of molecular components.

Recent Advances in Single-Molecule Sensors Based on STM Break Junction Measurements

Single-molecule recognition and detection with the highest resolution measurement has been one of the ultimate goals in science and engineering. Break junction techniques, originally developed to measure single-molecule conductance, recently have also been proven to have the capacity for the label-free exploration of single-molecule physics and chemistry, which paves a new way for single-molecule detection with high temporal resolution. In this review, we outline the primary advances and potential of the STM break junction technique for qualitative identification and quantitative detection at a single-molecule level. The principles of operation of these single-molecule electrical sensing mainly in three regimes, ion, environmental pH and genetic material detection, are summarized. It clearly proves that the single-molecule electrical measurements with break junction techniques show a promising perspective for designing a simple, label-free and nondestructive electrical sensor with ultrahigh sensitivity and excellent selectivity.

Hard-Soft Chemistry Guides the Adaptable Charge Transport in Lysine-doped Heptapeptide Junctions

Counterions always coexist with charged peptides in charge transport process, which are excellent candidate components for tunable molecular electronic devices. Here, we introduced hard-soft acid base theory to analyze the...