An official website of the United States government
Photoredox catalysis has been prominent in many applications, including solar fuels, organic synthesis, and polymer chemistry. Photocatalytic activity directly depends on the photophysical and electrochemical properties of photocatalysts in both the ground state and excited state. Controlling those properties, therefore, is imperative to achieve the desired photocatalytic activity. Redox potential is one important factor that impacts both the thermodynamic and kinetic aspects of key elementary steps in photoredox catalysis. In many challenging reactions in organic synthesis, high redox potentials of the substrates hamper the reaction, leading to slow conversion. Thus, the development of photocatalysts with extreme redox potentials, accompanied by potent reducing or oxidizing power, is required to execute high-yielding thermodynamically demanding reactions. In this review, we will introduce strategies for accessing extreme redox potentials in photocatalytic transformations. These include molecular design strategies for preparing photosensitizers that are exceptionally strong ground-state or excited-state reductants or oxidants, highlighting both organic and metal-based photosensitizers. We also outline methodological approaches for accessing extreme redox potentials, using two-photon activation, or combined electrochemical/photochemical strategies to generate potent redox reagents from precursors that have milder potentials.
more »
« less
“How Should I Think about Voltage? What Is Overpotential?”: Establishing an Organic Chemistry Intuition for Electrochemistry
Redox reactions are ubiquitous in organic synthesis and intrinsic to organic electrosynthesis. The language and concepts used to describe reactions in these domains are sufficiently different to create barriers that hinder broader adoption and understanding of electrochemical methods. To bridge these gaps, this Synopsis compares chemical and electrochemical redox reactions, including concepts of free energy, voltage, kinetic barriers, and overpotential. This discussion is intended to increase the accessibility of electrochemistry for organic chemists lacking formal training in this area.
more »
« less
- Award ID(s):
- 1953926
- PAR ID:
- 10299685
- Date Published:
- Journal Name:
- The Journal of Organic Chemistry
- ISSN:
- 0022-3263
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Avoiding faradaic side reactions during the operation of electrochemical devices is important to enhance the device stability, to achieve low power consumption, and to prevent the formation of reactive side‐products. This is particularly important for bioelectronic devices, which are designed to operate in biological systems. While redox‐active materials based on conducting and semiconducting polymers represent an exciting class of materials for bioelectronic devices, they are susceptible to electrochemical side‐reactions with molecular oxygen during device operation. Here, electrochemical side reactions with molecular oxygen are shown to occur during organic electrochemical transistor (OECT) operation using high‐performance, state‐of‐the‐art OECT materials. Depending on the choice of the active material, such reactions yield hydrogen peroxide (H2O2), a reactive side‐product, which may be harmful to the local biological environment and may also accelerate device degradation. A design strategy is reported for the development of redox‐active organic semiconductors based on donor–acceptor copolymers that prevents the formation of H2O2during device operation. This study elucidates the previously overlooked side‐reactions between redox‐active conjugated polymers and molecular oxygen in electrochemical devices for bioelectronics, which is critical for the operation of electrolyte‐gated devices in application‐relevant environments.more » « less
-
Zinc and manganese are widely used as reductants in synthetic methods, such as nickel-catalyzed cross-electrophile coupling (XEC) reactions, but their redox potentials are unknown in organic solvents. Here, we show how open-circuit potential measurements may be used to determine the thermodynamic potentials of Zn and Mn in different organic solvents and in the presence of common reaction additives. The impact of these Zn and Mn potentials is analyzed for a pair of Ni-catalyzed reactions, each showing a preference for one of the two reductants. Ni-catalyzed coupling of N-alkyl-2,4,6-triphenylpyridinium reagents (Katritzky salts) with aryl halides are then compared under chemical reaction conditions, using Zn or Mn reductants, and under electrochemical conditions performed at applied potentials corresponding to the Zn and Mn reduction potentials and at potentials optimized to achieve the maximum yield. The collective results illuminate the important role of reductant redox potential in Ni-catalyzed XEC reactions.more » « less
-
Abstract Reduction–oxidation (redox) reactions provide a distinct modality for biological communication that is fundamentally different from the more‐familiar ion‐based electrical modality. Biology uses these two modalities for communication through different systems (immune versus nervous), and uses different mechanisms to control the flow of the charge carriers: the flow of soluble ions is controlled using structural barriers (i.e., membranes) and gates (e.g., membrane‐spanning protein channels), while the flow of insoluble electrons is controlled using redox‐reaction networks. Here, a simple electrochemical approach to pattern catechols onto a flexible polysaccharide hydrogel is reported and it is demonstrated that the patterned catechol regions serve as nodes for the mediated flow of electrons through redox reactions. Electron flow through this node involves the switching of binary redox states (oxidized and reduced) and this node's redox state can be detected (i.e., “read”) by passively observing its optical absorbance, or actively switching its redox‐state electrochemically. Further, this catechol node can be switched through biological mechanisms, and this enables the fabricated catechol node to be embedded within biochemical redox reaction networks to facilitate the spanning of bio‐electronic communication. Thus, it is envisioned that catechols can emerge as a molecular equivalent to a transistor for miniaturize‐able, deployable and sustainable redox‐linked bioelectronics.more » « less
-
null (Ed.)The ability to control the charge density of organic mixed ionic electronic conductors (OMIECs) via reactions with redox-active analytes has enabled applications as electrochemical redox sensors. Their charge density-dependent conductivity can additionally be tuned via charge injection from electrodes, for instance in organic electrochemical transistors (OECTs), where volumetric charging of the OMIEC channel enables excellent transconductance and amplification of low potentials. Recent efforts have combined the chemical detection with the transistor function of OECTs to achieve compact electrochemical sensors. However, these sensors often fall short of the expected amplification performance of OECTs. Here, we investigate the operation mechanism of various OECT architectures to deduce the design principles required to achieve reliable chemical detection and signal amplification. By utilizing a non-polarizable gate electrode and conducting the chemical reaction in a compartment separate from the OECT, the recently developed Reaction Cell OECT achieves reliable modulation of the OECT channel's charge density. This work demonstrates that systematic and rational design of OECT chemical sensors requires understanding the electrochemical processes that result in changes in the potential (charge density) of the channel, the underlying phenomenon behind amplification.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.joc.1c01520
