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Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

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The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the...
3.0K
Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN101:14

Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1

2.1K
Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo,...
2.1K
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

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

6.1K
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...
6.1K
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)01:30

Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

3.9K
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
3.9K
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene01:13

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

6.2K
Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.
6.2K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

2.8K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
2.8K

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From Terminal to Spiro-Phosphonium Acceptors, Remarkable Moieties to Develop Polyaromatic NIR Dyes.

Iida Partanen1, Andrey Belyaev1,2,3, Bo-Kang Su4

  • 1Department of Chemistry, University of Eastern Finland, Yliopistokatu 7, 80101, Joensuu, Finland.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|May 22, 2023
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Summary

Researchers developed novel phosphonium-based ionic dyes for photofunctional materials. These donor-acceptor dyes exhibit tunable absorption and emission, with a phospha-spiro derivative achieving efficient near-infrared fluorescence.

Keywords:
donor-acceptor systemsfluorescencephosphonium saltphosphorus heterocyclesspiro compounds

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Area of Science:

  • Materials Science
  • Organic Chemistry
  • Photochemistry

Background:

  • Phosphonium-based compounds are emerging as versatile photofunctional materials.
  • Donor-acceptor (D-A) ionic dyes offer tunable optical properties for advanced applications.

Purpose of the Study:

  • To design and synthesize novel phosphonium-based ionic dyes with tailored photophysical properties.
  • To investigate the impact of structural modifications on absorption, emission, and fluorescence efficiency.

Main Methods:

  • Synthesis of a series of D-A ionic dyes incorporating phosphonium and extended π-NR2 fragments onto an anthracene framework.
  • Spectroscopic analysis (absorption and emission) in dichloromethane.
  • Evaluation of fluorescence quantum yields (Φ).

Main Results:

  • Dyes with varied π-spacers and terminal phosphonium groups showed absorption up to 527 nm and near-infrared (NIR) emission (805 nm), albeit with low quantum yields (<0.01).
  • Incorporation of a P-heterocyclic acceptor significantly reduced the optical bandgap and enhanced fluorescence efficiency.
  • A phospha-spiro derivative achieved NIR emission at 797 nm with a high quantum yield of Φ=0.12.

Conclusions:

  • The electron-accepting strength of the phospha-spiro moiety surpasses that of monocyclic and terminal phosphonium acceptors.
  • This study highlights a promising strategy for designing efficient charge-transfer chromophores and NIR emitters using phosphonium-based systems.