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Related Concept Videos

Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

3.2K
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.
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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
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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.7K
Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview01:27

Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview

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Wilhelm Rudolph Fittig discovered the pinacol coupling reaction in 1859. It is a radical dimerization reaction and involves the reductive coupling of aldehydes or ketones in the presence of hydrocarbon solvent to yield vicinal diols.
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Related Experiment Video

Updated: Apr 8, 2026

Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes
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Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes

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Microenvironment Engineering Vinylene-Linked Covalent Organic Frameworks for Highly Efficient CO2 Photoreduction.

Yushu Zhang1,2, Zelong Liang1,2, Kaiyuan Wang1,2

  • 1College of Chemistry, State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, China.

Journal of the American Chemical Society
|April 7, 2026
PubMed
Summary

Researchers developed a novel covalent organic framework (COF) to efficiently convert carbon dioxide (CO2) to carbon monoxide (CO) using photocatalysis. This metal-free system operates without solvents or additives, achieving record-breaking gas-solid conversion rates.

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Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface
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CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light
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CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

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Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface
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CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light
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CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

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Area of Science:

  • Materials Science
  • Catalysis
  • Photochemistry

Background:

  • Efficient photocatalytic reduction of carbon dioxide (CO2) to carbon monoxide (CO) in gas-solid systems without solvents, cocatalysts, or sacrificial agents remains a significant challenge.
  • Covalent organic frameworks (COFs) offer tunable structures for photocatalytic applications, but optimizing their performance under demanding conditions requires precise control over the microenvironment.

Purpose of the Study:

  • To design and construct a robust pyridazine-based COF platform for tunable CO2 photoreduction.
  • To establish a structure-reactivity relationship by modulating the nitrogen content in aldehyde linkers.
  • To investigate the performance of a hybrid COF material with coordinated rhenium complexes for enhanced CO2-to-CO conversion.

Main Methods:

  • Synthesis of vinylene-linked pyridazine COFs with varying nitrogen content in aldehyde linkers.
  • Photocatalytic CO2 reduction experiments under gas-solid conditions without solvents, cocatalysts, or sacrificial agents.
  • Characterization using in situ infrared spectroscopy and isotopic labeling.
  • Computational analysis using density functional theory (DFT).
  • Coordination of Re(CO)5Cl to specific nitrogen sites within the COF structure.

Main Results:

  • A pyridine-containing COF demonstrated superior charge separation and the highest CO production rate among metal-free photocatalysts under gas-solid conditions.
  • The optimized COF microenvironment, when functionalized with Re(CO)5Cl, created molecular catalytic centers enhancing the acceptor-donor-acceptor (A-D-A) charge-transfer pathway.
  • The resulting hybrid material achieved a record gas-solid CO2-to-CO activity, outperforming existing heterogeneous CO2 reduction systems.
  • DFT calculations and spectroscopic studies elucidated the mechanism, highlighting the role of N-site configuration in intermediate binding and transition state energetics.

Conclusions:

  • N-microenvironment engineering in COFs is a versatile strategy for developing high-performance photocatalysts for CO2 conversion.
  • The designed pyridazine COF platform enables precise tuning of electronic properties and catalytic activity.
  • This work presents a significant advancement in heterogeneous photocatalysis for CO2 reduction, offering a solvent-free and additive-free approach.