6.2 Redox-based and photochromic molecular switches
3 min read•august 7, 2024
Redox-based molecular switches use to change properties like color or conductivity. These switches can be controlled by applying voltage, making them useful in and displays. It's all about moving electrons to create change.
, on the other hand, use light to transform between different forms. Molecules like spiropyrans and change shape when hit with UV or visible light, opening up possibilities for and .
Redox-Based Molecular Switches
Redox-Active Molecules and Oxidation States
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Nitrogen fixation catalyzed by ferrocene-substituted dinitrogen-bridged dimolybdenum–dinitrogen ... View original
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A four-state capacitance molecular switch based on a redox active tetrathiafulvalene self ... View original
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Metastable oxidation states of tetrathiafulvalenes on the surface of liposomes - Journal of ... View original
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Nitrogen fixation catalyzed by ferrocene-substituted dinitrogen-bridged dimolybdenum–dinitrogen ... View original
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A four-state capacitance molecular switch based on a redox active tetrathiafulvalene self ... View original
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Top images from around the web for Redox-Active Molecules and Oxidation States
Nitrogen fixation catalyzed by ferrocene-substituted dinitrogen-bridged dimolybdenum–dinitrogen ... View original
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A four-state capacitance molecular switch based on a redox active tetrathiafulvalene self ... View original
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Metastable oxidation states of tetrathiafulvalenes on the surface of liposomes - Journal of ... View original
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Nitrogen fixation catalyzed by ferrocene-substituted dinitrogen-bridged dimolybdenum–dinitrogen ... View original
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A four-state capacitance molecular switch based on a redox active tetrathiafulvalene self ... View original
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- Redox-based molecular switches use redox-active molecules that can change their through the transfer of electrons
- Oxidation states refer to the degree of oxidation of an atom in a compound, indicating the number of electrons gained or lost compared to its neutral state
- Different oxidation states of a molecule can have distinct properties such as color, conductivity, or magnetic behavior
- Examples of redox-active molecules include transition metal complexes () and organic compounds with multiple stable oxidation states (tetrathiafulvalene)
Electron Transfer and Electrochromic Materials
- Electron transfer is the fundamental process in redox-based molecular switches, where electrons move between different molecular orbitals or between a molecule and an electrode
- The transfer of electrons can be triggered by applying an electrical potential, allowing for the control of the molecular switch state
- change their optical properties (color or transparency) when their oxidation state is altered through an applied voltage
- These materials find applications in smart windows, displays, and optical memory devices (tungsten oxide films)
Photochromic Molecular Switches
Photochromism and Spiropyrans
- is the reversible transformation of a chemical species between two forms with different absorption spectra when exposed to light of appropriate wavelengths
- Photochromic molecular switches exploit this phenomenon to change their properties upon light irradiation
- Spiropyrans are a class of photochromic compounds that undergo a reversible structural change between a colorless closed form () and a colored open form (merocyanine) upon exposure to UV and visible light, respectively
- The spiropyran-merocyanine system has potential applications in optical memory, , and light-responsive materials
Azobenzenes and Diarylethenes
- Azobenzenes are photochromic molecules that can isomerize between a thermally stable trans form and a metastable cis form when exposed to UV light, with the reverse process occurring upon visible light irradiation or thermal relaxation
- The trans-cis of azobenzenes is accompanied by a significant change in molecular geometry and dipole moment, making them useful for light-controlled molecular switches and actuators
- are another class of photochromic compounds that undergo a reversible reaction between an open form and a closed form when exposed to UV and visible light, respectively
- The photocyclization of diarylethenes is associated with changes in electronic structure and optical properties, allowing for their application in high-density optical memory and photonic devices
UV-Visible Light Switching
- Photochromic molecular switches are typically operated using UV and visible light, which provides a non-invasive and spatially controllable means of triggering the switching process
- UV light is often used to induce the conversion from one form to another (spiropyran to merocyanine, trans to cis azobenzene, or open to closed diarylethene), while visible light or thermal relaxation can reverse the process
- The specific wavelengths of light used for switching depend on the absorption spectra of the photochromic compounds, with many systems employing UV light in the range of 300-400 nm and visible light in the range of 400-700 nm
- The ability to control molecular switches with light enables remote activation, patterning, and spatiotemporal resolution in various applications such as optical memory, photopharmacology, and light-responsive materials (photochromic lenses)
Key Terms to Review (21)
Azobenzenes: Azobenzenes are organic compounds characterized by a nitrogen-nitrogen double bond connecting two aromatic rings. They are notable for their ability to undergo reversible photoisomerization, which allows them to switch between two different structural forms, making them useful in applications like molecular switches and photochromic devices.
Cyclic voltammetry: Cyclic voltammetry is an electrochemical technique used to study the redox properties of chemical species by measuring the current response as a function of an applied voltage over time. This method involves sweeping the potential of an electrode linearly in a triangular waveform, which allows for the investigation of electron transfer kinetics and mechanisms of redox reactions. It is particularly valuable in studying molecular switches that rely on redox processes, enabling insights into their switching behavior and performance.
Diarylethenes: Diarylethenes are a class of organic compounds characterized by a double bond between two carbon atoms, each of which is connected to an aromatic ring. These compounds are known for their photochromic properties, meaning they can reversibly change structure upon exposure to light. This ability to switch between different forms makes diarylethenes valuable in various applications, particularly in molecular switches and memory devices.
Electrochromic materials: Electrochromic materials are substances that change color or transparency when an electric voltage is applied, making them valuable for various applications like displays and smart windows. These materials undergo reversible redox reactions that alter their electronic states, leading to visual changes. Their ability to switch colors based on electrical input positions them as key components in advanced technologies that integrate electronic and optical properties.
Electron transfer: Electron transfer is the movement of electrons from one atom or molecule to another, which is a fundamental process in various chemical reactions and electrical phenomena. This process is crucial in the context of redox reactions, where oxidation and reduction occur simultaneously, leading to energy changes that are often harnessed in molecular switches and devices. Understanding electron transfer is essential for exploring how molecules can switch states in response to external stimuli, such as light or changes in chemical environment.
Ferrocene: Ferrocene is a metallocene compound consisting of a central iron (Fe) atom sandwiched between two cyclopentadienyl anions (C5H5) in a unique 'sandwich' structure. This compound exhibits interesting redox properties, making it an important model system for studying electron transfer processes and molecular switches that respond to changes in oxidation states.
Functionalization: Functionalization refers to the process of adding specific functional groups to a molecule to alter its properties and reactivity. This modification enhances the molecule's performance in applications like electronic conduction, switching, and self-assembly by enabling tailored interactions at the molecular level.
Isomerization: Isomerization is the process by which a molecule is transformed into one of its isomers, changing the arrangement of atoms within the molecule while maintaining the same molecular formula. This process is significant in various molecular systems, particularly in the context of molecular switches where different isomers can represent distinct states or functions. In the case of redox-based and photochromic molecular switches, isomerization allows for reversible changes triggered by external stimuli such as light or electron transfer, making it essential for designing responsive materials.
Light-controlled materials: Light-controlled materials are substances that can change their properties or behaviors in response to light exposure. These materials often incorporate molecular switches that can undergo reversible transformations when stimulated by specific wavelengths of light, enabling applications in fields like molecular electronics, data storage, and photonic devices.
Optical Memory: Optical memory refers to a data storage technology that uses light to read and write information. This type of memory typically utilizes lasers and optical media, like CDs, DVDs, or Blu-rays, to encode data as patterns of pits and lands on the surface of the disc. In the context of molecular electronics, optical memory can also involve the use of molecules that can change their state in response to light, allowing for the storage and retrieval of data at the molecular level.
Oxidation state: The oxidation state is a measure of the degree of oxidation of an atom in a chemical compound, representing the hypothetical charge that an atom would have if all bonds to atoms of different elements were completely ionic. This concept is crucial for understanding redox reactions, as changes in oxidation states indicate the transfer of electrons, which is fundamental to processes like molecular switches that respond to light or electrical stimuli.
Photochromic switches: Photochromic switches are molecular systems that can reversibly change their structure and properties upon exposure to light. This unique characteristic allows them to function as switches, toggling between different states based on light stimuli, making them significant in various applications including data storage, sensors, and molecular electronics.
Photochromism: Photochromism refers to the reversible transformation of a chemical compound between two forms upon exposure to light, typically resulting in a change in color. This phenomenon is significant in molecular switches, where the light-induced structural changes can affect the electronic properties of a material, making it useful for applications in sensors, memory devices, and other molecular electronics.
Photocyclization: Photocyclization is a photochemical reaction where a molecule undergoes a cyclization process upon absorption of light, leading to the formation of cyclic structures. This process is significant in the context of molecular switches, particularly photochromic systems, where the switching mechanism relies on light-induced changes in molecular conformation and connectivity.
Redox-based switches: Redox-based switches are molecular systems that can reversibly change their state or configuration in response to oxidation and reduction (redox) reactions. These switches exploit the electron transfer properties of molecules to toggle between different conformations, enabling potential applications in molecular electronics and memory devices.
Self-assembly: Self-assembly is a process where molecules automatically organize themselves into structured, functional arrangements without external guidance or direction. This spontaneous organization is crucial in molecular electronics as it allows for the creation of complex nanostructures and devices that can outperform traditional methods of assembly.
Sensors: Sensors are devices that detect and respond to physical stimuli from the environment, converting those stimuli into measurable signals. These signals can then be analyzed to provide valuable information about the surrounding conditions, making sensors crucial in various applications, including molecular electronics. They can influence the conductance of single molecules, interact with self-assembled monolayers, and enable the functionality of molecular switches based on redox reactions or light.
Smart windows: Smart windows are advanced glazing technologies that can change their light transmission properties in response to external stimuli, such as electric current, light, or heat. This dynamic ability allows them to regulate indoor temperatures and control sunlight, providing energy efficiency and enhancing user comfort while reducing the reliance on traditional heating and cooling systems.
Spectroscopy: Spectroscopy is the study of the interaction between matter and electromagnetic radiation, enabling the analysis of the energy levels and transitions within molecules. This technique allows scientists to gain insights into molecular structure, dynamics, and electronic states by measuring how matter absorbs, emits, or scatters light. It's crucial in understanding various phenomena, such as energy levels, electron transfer processes, and charge transport mechanisms in different materials.
Spintronics: Spintronics, or spin transport electronics, is a technology that exploits the intrinsic spin of electrons, along with their charge, to develop advanced electronic devices. This field is rooted in understanding how electron spins can be manipulated in materials to create new functionalities, including non-volatile memory and quantum computing. Spintronics connects closely with the concepts of magnetism and molecular switches, as it relies on the magnetic properties of materials to harness and control electron spins effectively.
Spiropyran: Spiropyran is a type of organic compound that acts as a photochromic molecular switch, capable of reversibly changing its structure in response to light. This switch-like behavior allows it to transition between two forms, typically a colorless form and a colored form, depending on exposure to specific wavelengths of light. This property makes spiropyran a key component in various molecular switch designs and mechanisms, particularly in systems that utilize light as a trigger for functional changes.