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Related Concept Videos

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.
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
Heterogeneous Catalysis01:22

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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.
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...

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Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications
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Triple-Regulation Strategy toward Multivariate Isomeric Covalent Organic Frameworks for Efficient Photocatalysis.

Pei Huang1, Yixin Ouyang2, Qiang Li3

  • 1Guangdong Provincial Key Laboratory of Carbon Dioxide Resource Utilization, School of Chemistry, South China Normal University, Guangzhou 510006, P. R. China.

Journal of the American Chemical Society
|June 12, 2026
PubMed
Summary
This summary is machine-generated.

Researchers developed a new triple synergic regulation strategy to create 15 novel isomeric covalent organic frameworks (Iso-COFs). This breakthrough enables precise control over structure-property relationships for enhanced photochemical hydrogen peroxide production.

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A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks
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A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

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Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications
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Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications

Published on: July 25, 2025

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks
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A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Published on: April 28, 2023

Area of Science:

  • Structure Chemistry
  • Materials Science
  • Photochemistry

Background:

  • Isomer structural chemistry is a rapidly advancing field.
  • Isomerization of periodic framework materials, particularly covalent organic frameworks (COFs), presents significant challenges due to structural complexity and a lack of systematic strategies.
  • Controlling isomerism in COFs is crucial for tailoring material properties.

Purpose of the Study:

  • To develop a systematic strategy for synthesizing isomeric covalent organic frameworks (Iso-COFs).
  • To investigate the influence of different isomerism types (geometric, positional, linkage) on photochemical properties.
  • To establish a structure-property relationship for Iso-COFs in H2O2 photosynthesis.

Main Methods:

  • A triple synergic regulation strategy combining geometric, positional, and linkage isomerism was employed.
  • Synthesis of 15 novel Iso-COFs with identical chemical formulas (C48H36N6O3) but distinct structures.
  • Photochemical evaluation of 6 model Iso-COFs for H2O2 production, supported by Density Functional Theory (DFT) calculations and in situ characterization.

Main Results:

  • Successfully synthesized a record number of 15 Iso-COFs using the developed multidimensional regulation strategy.
  • TDA-BTD COF demonstrated superior photochemical H2O2 production efficiency (2016.26 μmol g-1h-1) and an apparent quantum yield (AQY) of 3.67% at 420 nm.
  • DFT calculations and characterization confirmed that isomerism types regulate substrate adsorption, charge separation, and electronic structure.

Conclusions:

  • A pioneering multidimensional strategy for designing periodic framework-based isomers was established.
  • The study achieved the synthesis of a record number of Iso-COFs with identical chemical formulas.
  • This work provides a foundational understanding of how isomerism impacts the performance of COFs in photochemical applications.