The standard electron-transfer rate constants ( k ( 0 )) are measured for redox processes of Fe versus Zn porphyrins in monolayers on Au(111); the former undergoes a metal-centered redox process (conversion between Fe (III) and Fe (II) oxidation states) whereas the latter undergoes a ring-centered redox process (conversion between the neutral porphyrin and the pi-cation radical). Each porphyrin contains three meso-mesityl groups and a benzyl thiol for surface attachment. Under identical solvent (propylene carbonate)/electrolyte (1.0 M Bu 4NCl) conditions, the Zn (II) center has a coordinated Cl (-) ion when the porphyrin is in either the neutral or oxidized state. In the case of the Fe porphyrin, two species are observed a low-potential form ( E l (0) approximately -0.6 V) wherein the metal center has a coordinated Cl (-) ion when it is in either the Fe (II) or Fe (III) state and a high-potential form ( E h (0) approximately +0.2 V) wherein the metal center undergoes ligand exchange upon conversion from the Fe (III) to Fe (II) states. The k ( 0 ) values observed for all of the porphyrins depend on surface concentration, with higher concentrations resulting in slower rates, consistent with previous studies on porphyrin monolayers. The k ( 0 ) values for the ring-centered redox process (Zn chelate) are 10-40 times larger than those for the metal-centered process (Fe chelate); the k ( 0 ) values for the two forms of the Fe porphyrin differ by a factor of 2-4 (depending on surface concentration), the Cl (-) exchanging form generally exhibiting a faster rate. The faster rates for the ring- versus metal-centered redox process are attributed to the participating molecular orbitals and their proximity to the surface (given that the porphyrins are relatively upright on the surface): a pi molecular orbital that has significant electron density at the meso-carbon atoms (one of which is the site of attachment of the linker to the surface anchoring thiol) versus a d-orbital that is relatively well localized on the metal center.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1021/la8019843 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Cathode Design Based on Nitrogen Redox and Linear Coordination of Cu Center for All-Solid-State Fluoride-Ion Batteries.
J Am Chem Soc
January 2025
Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
All-solid-state fluoride-ion batteries (FIBs) have attracted extensive attention as candidates for next-generation energy storage devices; however, promising cathodes with high energy density are still lacking. In this study, CuN is investigated as a cathode material for all-solid-state fluoride-ion batteries, which offers enough anionic vacancies around the 2-fold coordinated Cu center for F intercalation, thereby enabling a multielectron-transferred fluorination process. The contribution of both cationic and anionic redox to charge compensation, in particular, the generation of molecular nitrogen species in highly charged states, has been proved by several synchrotron-radiation-based spectroscopic technologies.
View Article and Find Full Text PDF2-Amidophenolate and 2-Iminosemiquinone Radical-Coordinated Vanadyl Complex as Catholyte for Non-Aqueous Redox-Flow Batteries.
Chem Asian J
January 2025
Indian Institute of Technology Guwahati, Department of Chemistry, Department of Chemistry, 781039, Guwahati, INDIA.
Fulfilment of energy demand by utilizing renewable energy sources that do not contribute to the production of greenhouse gases is a step forward in mitigating global warming. However, with the energy sources being intermittent in nature, renewable energy needs to be stored effectively on a grid scale. In this context, the development of redox-flow batteries has emerged as a promising technology where charging and discharging processes are accomplished by the redox shuttling of the electrolytes, namely anolytes and catholytes.
View Article and Find Full Text PDFMolecular Photoelectrocatalysis for Radical Reactions.
Acc Chem Res
January 2025
State Key Laboratory of Physical Chemistry of Solid Surfaces, Key Laboratory of Chemical Biology of Fujian Province, College of Chemistry and Chemical Engineering, and Discipline of Intelligent Instrument and Equipment, Xiamen University, Xiamen 361005, P. R. China.
ConspectusMolecular photoelectrocatalysis, which combines the merits of photocatalysis and organic electrosynthesis, including their green attributes and capacity to offer novel reactivity and selectivity, represents an emerging field in organic chemistry that addresses the growing demands for environmental sustainability and synthetic efficiency. This synergistic approach permits access to a wider range of redox potentials, facilitates redox transformations under gentler electrode potentials, and decreases the use of external harsh redox reagents. Despite these potential advantages, this area did not receive significant attention until 2019, when we and others reported the first examples of modern molecular photoelectrocatalysis.
View Article and Find Full Text PDFImplications of Charge and Heteroatom Dopants on the Thermodynamics and Kinetics of Redox Reactions in Keggin-Type Polyoxometalates.
ACS Mater Au
January 2025
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States.
The utilization of polyoxometalate-based materials is largely dictated by their redox properties. Detailed understanding of the thermodynamic and kinetic efficiency of charge transfer is therefore essential to the development of polyoxometalate-based systems for target applications. Toward this end, we report electrochemical studies of a series of heteroatom-doped Keggin-type polyoxotungstate clusters [PWO] ( ), [VWO] ( ), [P(VW)O] ( ), and [V(VW)O] ( ) to elucidate the role of the identity and spatial location of heteroatoms and overall cluster charge on the rate constants of electron transfer and redox reaction entropies.
View Article and Find Full Text PDFDynamically Cyclic Fe/Fe Active Sites as Electron and Proton-Feeding Centers Boosting CO Photoreduction Powered by Benzyl Alcohol Oxidation.
Research (Wash D C)
January 2024
School of Resources and Environment, Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 611731, China.
Solar-driven CO photoreduction holds promise for sustainable fuel and chemical productions, but the complex proton-coupled multi-electron transfer processes and sluggish oxidation half-reaction kinetics substantially hinder its efficiency. Here, we devised a rational catalyst design to address these challenges by fabricating ferrocene carboxylic acid-functionalized CsSbBr nanocrystals (CSB-Fc NCs), which facilitate simultaneous benzyl alcohol oxidation and CO reduction reactions under visible-light irradiation. The synchronized proton-coupled electron transfer processes between the reduction and oxidation half-reactions on CSB-Fc NCs resulted in a 5-fold increase in the CO reduction rate (45.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!