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The miracle of single electron transfer: How miraculous is the electron transfer from metal to ligand?
In the field of modern chemistry, photocatalysis has triggered a new wave of research, especially in the field of "single electron transfer". This process not only plays an important role in chemical synthesis, but also shows broad application potential in environmental science and materials science. This article will explore the metal-to-ligand electron transfer process in photochemistry and how it changes our understanding of chemical reactions.
Photocatalysts can use the energy of light to transfer electrons from metals to ligands. How does this process work?
Basics of Photocatalysis
The core of photocatalysis lies in the light absorption and energy transfer of photosensitizers. As the photocatalyst is excited, electrons are transferred from the d orbital of the metal to the π* orbital of the ligand, thereby forming an excited state. This process goes through a complex series of electron transfer and energy redistribution steps, which ultimately enables the catalyst to promote a variety of chemical reactions.
Peripheral Electron Transfer
According to Marcus theory, the rate of peripheral electron transfer depends on the thermodynamic advantage and the level of its intrinsic barrier. Specifically, when electron transfer is energetically favorable, the reaction rate is faster. Interpreted in terms of older molecular systems, this process is analogous to the movement of nuclei and the transformation of degrees of freedom.
This process actually involves the transfer of electrons between the catalyst and the substrate through the "tunneling" effect.
Catalyst regeneration
In the catalytic cycle, catalyst regeneration is also crucial. Such processes usually involve a second peripheral electron transfer, during which the catalyst is affected by various reaction additives, such as the Stern-Volmer experiment to measure the intensity of phosphorescence. changes, helps to understand the efficiency of this transfer.
Photophysical properties
The redox potential of photocatalysts also has a profound influence on chemical reactions. Although common electrochemical methods can conveniently measure the red oxygen position in the ground state, it is difficult to directly measure the red oxygen position in the excited state. Therefore, by comparing the transfer rates of different ground state reactants, the potential of the excited state can be indirectly inferred.
To measure the redox potential of the excited state, an advanced technique called "phase modulation voltammetry" can be used.
Effect of ligand electronegativity
When studying photocatalysts, the electronegativity differences between ligands cannot be ignored. Ligands with higher electronegativity can better stabilize the electrons they bring, thereby affecting the redox properties of the entire catalytic complex. This not only affects its reactivity, but also increases its potential for application in synthetic chemistry.
Application Scope
Photocatalysis has a wide range of applications, from reductive dehalogenation to generate iminium ions to oxidative generation of oxycarbonyl ions. These chemical transformations not only improve the efficiency of synthesis, but also open up many new reaction modes. For example, the carbon-iodine bond reduction reaction catalyzed by Ir(ppy)3 is highly efficient and easy to operate.
End of Thought
With the in-depth exploration of photocatalytic technology, this field is facing unprecedented challenges and opportunities. Can we use this knowledge to design more efficient photocatalysts to tackle more complex chemical synthesis problems in the future?
