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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.
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
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
UV–Vis Spectroscopy: Woodward–Fieser Rules01:29

UV–Vis Spectroscopy: Woodward–Fieser Rules

UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
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.
Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions01:20

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...

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Related Experiment Video

Updated: Jun 8, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
14:11

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Published on: June 10, 2021

Thiophene-containing Pechmann dye derivatives.

Tyler B Norsten1, Eric Assen B Kantchev, Michael B Sullivan

  • 1Institute of Materials Research and Engineering, A*STAR, 3 Research Link, Singapore 117602. norstent@imre.a-star.edu.sg

Organic Letters
|September 28, 2010
PubMed
Summary

New thiophene-based Pechmann dyes were synthesized and characterized. These dyes exhibit strong visible light absorption and emission, with solubility enhanced by alkyl chains.

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Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

Published on: October 24, 2017

Area of Science:

  • Organic chemistry
  • Materials science
  • Photophysics

Background:

  • Pechmann dyes are a class of organic compounds with potential applications in various fields.
  • Thiophene-containing compounds offer unique electronic properties.
  • Developing novel dyes with tunable solubility and optical properties is crucial for advanced materials.

Purpose of the Study:

  • To synthesize novel thiophene-containing Pechmann dyes.
  • To investigate the effect of alkyl chains on dye solubility.
  • To characterize the electronic and optical properties of these new dyes.

Main Methods:

  • Copper-catalyzed dehydration of β-aroylacrylic acids to form thiophene-containing Pechmann dyes.
  • Solubility enhancement via introduction of long alkyl chains.
  • Spectroscopic analysis including CV, UV/vis, and fluorescence spectroscopy.
  • Computational studies using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT).

Main Results:

  • Successful synthesis of thiophene-containing Pechmann dyes as unsaturated exo-5,5-dilactones.
  • Long alkyl chains significantly improved dye solubility.
  • Isomerization yielded the corresponding endo-6,6-dilactone.
  • Dyes exhibited strong absorption and emission in the visible region.
  • Redox and electronic properties were elucidated through experimental and computational methods.

Conclusions:

  • Thiophene-containing Pechmann dyes are readily synthesized and possess tunable solubility.
  • These novel dyes display promising strong absorption and emission characteristics in the visible spectrum.
  • The study provides insights into the structure-property relationships of these thiophene-based dyes for potential applications.