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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Oxymercuration-Reduction of Alkenes02:36

Oxymercuration-Reduction of Alkenes

Oxymercuration–reduction of alkenes is one of the major reactions converting alkenes to alcohols. It involves the hydration of alkenes with mercuric acetate in a mixture of tetrahydrofuran and water, forming an organomercury adduct. This is followed by a demercuration step in which the adduct is reduced to an alcohol using sodium borohydride.
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...

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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
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Overcrowded Alkene Photo-Redox-Switches Based on Quinolinium/Carbene Building Blocks.

Chris Burdenski1, Patrick W Antoni1, Marcel E Baumert1

  • 1Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Dortmund, Germany.

Angewandte Chemie (International Ed. in English)
|May 21, 2026
PubMed
Summary
This summary is machine-generated.

Novel overcrowded alkene photo/redox switches offer multi-stimuli responsiveness. Electrochemical switching enables rapid E/Z-isomerization, while photochemical switching demonstrates excellent photostability for advanced molecular devices.

Keywords:
carbeneselectron hole catalysisphoto‐switchradicalsredox‐switch

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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Supramolecular Chemistry

Background:

  • Overcrowded alkenes are key components in molecular switches.
  • Tetrasubstituted alkenes offer unique structural and electronic properties.
  • Photo/redox switching requires precise control over molecular conformation.

Purpose of the Study:

  • To design and characterize novel overcrowded alkene-based photo/redox switches.
  • To investigate multi-stimuli responsive properties including electrochemical and photochemical switching.
  • To elucidate the mechanisms governing these switching processes.

Main Methods:

  • Modular synthesis of folded and twisted tetrasubstituted alkenes from quinolinium salts and stable carbenes.
  • Electrochemical characterization and redox-state isolation.
  • Photochemical E/Z-isomerization studies.
  • X-ray diffraction, UV-vis, NMR spectroscopy, and computational methods (TD-DFT, nonadiabatic molecular dynamics).

Main Results:

  • Successful synthesis of a novel class of overcrowded alkene photo/redox switches.
  • Demonstration of multi-stimuli responsive properties: electrochemical redox-switching and photochemical E/Z-switching.
  • Isolation and full characterization of different oxidation states, including structural analysis by X-ray diffraction.
  • Excellent photostability for E/Z-switching in selected compounds.
  • Accurate prediction of absorption properties and substituent effects by TD-DFT calculations.
  • Identification of a high-energy barrier for thermal back-switching versus instantaneous electrochemical E/Z-isomerization via electron hole catalysis.

Conclusions:

  • The developed overcrowded alkenes represent a versatile platform for photo/redox switches.
  • Electrochemical switching offers a rapid and catalytic pathway for E/Z-isomerization.
  • Photochemical switching exhibits high stability, suitable for applications requiring light-induced changes.
  • Computational studies provide deep mechanistic insights into the switching processes.