Photoswitching Molecular Junctions: Platforms and Electrical Properties

Abstract

Remarkable advances in technology have enabled the manipulation of individual molecules and the creation of molecular electronic devices utilizing single and ensemble molecules. Maturing the field of molecular electronics has led to the development of functional molecular devices, especially photoswitching or photochromic molecular junctions, which switch electronic properties under external light irradiation. This review introduces and summarizes the platforms for investigating the charge transport in single and ensemble photoswitching molecular junctions as well as the electronic properties of diverse photoswitching molecules such as diarylethene, azobenzene, dihydropyrene, and spiropyran. Furthermore, the article discusses the remaining challenges and the direction for moving forward in this area for future photoswitching molecular devices.

Light-Driven Charge Transport and Optical Sensing in Molecular Junctions

“…Thanks to the rapid development of experimental techniques in MJ fabrications and measurements, researchers are now able to expand their investigations beyond pure charge transport. Many interesting transport phenomena in MJs have been reported to date, including the transistor (or gating) effect [15][16][17][18], conductance switching [19][20][21], thermal [22,23], thermoelectricity [24,25], photoswitching [26][27][28] and spintronics [29][30][31][32][33]. While most of these topics have been previously reviewed [34][35][36], we, in this work, will focus our attention on the optoelectronic phenomena in MJs, a topic that has been rarely surveyed in detail yet is rather important for furthering the development of the field.…”

Beyond Simple Structure–Function Relationships: The Interplay of Geometry, Electronic Structure, and Molecule/Electrode Coupling in Single-Molecule Junctions

“…One such case where this is quite evident is cis vs trans isomers of stilbene-like moieties, 9−13 a structural element that commonly appears in molecular scaffolds considered for electronics applications, especially in the context of photoactivated switches. 14,15 Single-molecule conductancethe most fundamental transport propertyhas been investigated both theoretically and experimentally for a stilbene-like molecule, 16 as well as for several derivatives of the structurally similar azobenzene moiety. 17−22 However, such studies have produced results varying from an ∼2× higher conductance for cis over trans, 16 to the exact opposite, 21 and even all the way up to ∼100× higher conductance for trans 18 or ∼30× higher conductance for cis.…”

“…One such case where this is quite evident is cis vs trans isomers of stilbene-like moieties, − a structural element that commonly appears in molecular scaffolds considered for electronics applications, especially in the context of photoactivated switches. , Single-molecule conductancethe most fundamental transport propertyhas been investigated both theoretically and experimentally for a stilbene-like molecule, as well as for several derivatives of the structurally similar azobenzene moiety. − However, such studies have produced results varying from an ∼2× higher conductance for cis over trans, to the exact opposite, and even all the way up to ∼100× higher conductance for trans or ∼30× higher conductance for cis . Aside from differences in measurement methodology and slight variations in molecular design, an important reason for this inconsistency is likely that changing from trans to cis unavoidably causes multiple structural changes at once, each of which can affect conductance (Figure ): the length of the molecule decreases, which is expected to increase conductance by reducing the tunneling barrier width; steric hindrance causes each ring in the cis molecule to twist out of plane by ∼35°, which is expected to decrease conductance by partially breaking the conjugated π-system; − the electronic structure of cis and trans isomers and their respective energy-level alignments with the electrodes may differ; and the modified geometry of the molecule, especially the angles at which linkers attached in the standard para positions extend out from the backbone, may impact the orbital alignment between metal and molecule and hence the efficiency of electronic coupling between the two.…”

Donor–Acceptor Stenhouse Adducts for Stimuli-Responsive Self-Assembly of Gold Nanoparticles into Semiconducting Thin Films

“…The focus of nanotechnology has shifted from static to dynamic designs. The ultimate goal is to create lifelike abiotic systems, which could perform complex tasks and create chemical networks. − One of the approaches to achieve this goal is to utilize molecular switches that can change their properties upon external stimulation. − The said stimuli can vary from chemical ones, such as the change of pH, presence of a particular compound, , or change in the oxidation state, to physical ones like the change in temperature, mechanical force, or illumination . Photoswitches are the most popular, easy to manipulate, robust, and provide an efficient and precise way to control the complex system …”