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Related Concept Videos

Nucleophilic Aromatic Substitution: Elimination–Addition01:11

Nucleophilic Aromatic Substitution: Elimination–Addition

Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
Electrophilic Aromatic Substitution: Sulfonation of Benzene01:22

Electrophilic Aromatic Substitution: Sulfonation of Benzene

Sulfonation of benzene is a reaction wherein benzene is treated with fuming sulfuric acid at room temperature to produce benzenesulfonic acid. Fuming sulfuric acid is a mixture of sulfur trioxide and concentrated sulfuric acid.
meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H

All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for the...
Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

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 para position.
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene01:13

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

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.
Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN101:14

Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1

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, or cyano...

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Updated: Jul 15, 2026

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine
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Deactivating Emission in Azulene via Solvent-Induced (Anti)Aromaticity.

Kiser Z Colley1, Shilpa Debnath2, Ulrike Salzner3

  • 1Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, United States.

Journal of the American Chemical Society
|July 14, 2026
PubMed
Summary

Azulene exhibits anti-Kasha emission, crucial for optoelectronics. This study reveals how aromatic solvents tune its excited-state lifetime and aromaticity, offering new control over light emission properties.

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Area of Science:

  • Photophysics and Optoelectronics
  • Organic Chemistry
  • Materials Science

Background:

  • Anti-Kasha emission is rare in organic molecules but prominent in azulene, making it promising for optoelectronic applications like imaging and LEDs.
  • Despite its potential, the photophysical mechanisms governing azulene's behavior, including its aromaticity and emission deactivation in derivatives, remain poorly understood.
  • Existing models of azulene's reactivity and aromaticity lack experimental verification, hindering the development of new materials.

Purpose of the Study:

  • To investigate the solvent-dependent photophysics of azulene using advanced spectroscopic techniques.
  • To elucidate the mechanisms behind the deactivation of anti-Kasha emission in azulene derivatives.
  • To explore methods for controlling excited-state aromaticity and anti-Kasha emission in azulene-based materials.

Main Methods:

  • Utilized fluorescence spectroscopy to analyze emission properties.
  • Employed transient absorption spectroscopy to probe excited-state dynamics.
  • Investigated the influence of various solvents, including aromatic and polar solvents, on azulene's photophysical behavior.

Main Results:

  • Discovered that weak complexation with aromatic solvents can tune and reduce the S2 state lifetime of azulene.
  • Observed that solvent polarity has minimal impact, emphasizing the role of 10-π Hückel aromaticity over zwitterionic character.
  • Found that enhanced dipolar character in functionalized azulenes leads to greater sensitivity to solvent aromaticity and faster excited-state quenching via conical intersections.

Conclusions:

  • Provided crucial mechanistic insights into the photophysics of azulene and its derivatives.
  • Demonstrated a straightforward method to control excited-state aromaticity and anti-Kasha emission by leveraging solvent interactions.
  • Highlighted the potential of azulene as a versatile platform for designing novel optoelectronic materials.