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Related Concept Videos

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
1.9K
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

6.5K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
6.5K
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

2.0K
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
2.0K
Radical Formation: Homolysis00:54

Radical Formation: Homolysis

3.8K
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
3.8K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.2K
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.
2.2K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.5K
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.
2.5K

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Accessing Highly Efficient Photothermal Conversion with Stable Open-Shell Aromatic Nitric Acid Radicals.

Zejun Wang1, Jiawen Zhou1, Yiheng Zhang1

  • 1Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China.

Angewandte Chemie (International Ed. in English)
|January 3, 2022
PubMed
Summary

Stable aromatic nitric acid radicals were synthesized for efficient solar-driven water desalination. These novel organic small molecules demonstrate high photothermal conversion efficiency and stability, crucial for sustainable water purification applications.

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Electron SpinOpen-ShellOrganic SemiconductorPhotothermal ConversionRadicals

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Area of Science:

  • Materials Science
  • Organic Chemistry
  • Photochemistry

Background:

  • Stable radical preparation is challenging due to inherent instability in ambient conditions.
  • Aromatic radicals often require protective groups to prevent degradation.
  • Developing robust organic materials for energy applications is a key research area.

Purpose of the Study:

  • To synthesize and characterize novel star-shaped aromatic nitric acid radicals.
  • To evaluate the photothermal properties and stability of these radicals for solar-driven applications.
  • To assess their performance in seawater desalination.

Main Methods:

  • Facile demethylation and oxidation reactions were employed for radical synthesis.
  • Electrochemical and thermal stability were assessed.
  • Spectroscopic analysis (UV-Vis-NIR) and solar-driven water evaporation tests were conducted.

Main Results:

  • A series of stable star-shaped aromatic nitric acid radicals were successfully prepared.
  • TPA-TPA-O6 exhibited broad solar absorption (300-2000 nm) and high photothermal conversion efficiency.
  • Under one sun irradiation, TPA-TPA-O6 achieved 89.41% water evaporation efficiency and a rate of 1.293 kg m-2 h-1 with negligible photobleaching.

Conclusions:

  • The synthesized aromatic nitric acid radicals possess excellent electrochemical and thermal stability due to extensive resonance structures.
  • TPA-TPA-O6 demonstrates superior performance as a pure organic small molecule photothermal material for efficient solar seawater desalination.
  • These findings highlight the potential of stable organic radicals in advanced solar energy conversion technologies.