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Related Concept Videos

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
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
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.
Diels–Alder Reaction: Characteristics of Dienes01:29

Diels–Alder Reaction: Characteristics of Dienes

The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...

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Updated: Jul 16, 2026

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
12:07

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Published on: April 1, 2013

Isomeric Dibenzodiindenophenanthrene Diradicaloids: Synthesis, Structures, Properties, and Efficient NIR Photothermal

Qing Jiang1, Xinyi Zheng1, Jianchao Li2

  • 1College of Chemistry and Bioengineering, Hunan University of Science and Engineering, Yongzhou, China.

Angewandte Chemie (International Ed. in English)
|July 15, 2026
PubMed
Summary

Structural isomerism in polycyclic hydrocarbons (PHs) creates novel organic diradicaloids with tunable electronic properties. These PHs exhibit unique redox behavior and serve as advanced near-infrared photothermal materials.

Keywords:
aromaticitynear‐infrared photothermal conversionorganic diradicaloidspolycyclic hydrocarbonsstructural isomerism

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

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

Published on: November 29, 2018

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Last Updated: Jul 16, 2026

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
12:07

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

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

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
12:19

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

Published on: November 29, 2018

Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photochemistry

Background:

  • Structural isomerism is key to tuning organic diradicaloid properties.
  • Polycyclic hydrocarbons (PHs) are versatile molecular platforms.

Purpose of the Study:

  • Synthesize and characterize isomeric open-shell PHs based on dicyclopenta[b,j]phenanthrene.
  • Compare their diradical properties with anthracene-based isomers.
  • Investigate their potential as near-infrared photothermal materials.

Main Methods:

  • Synthesis and characterization of isomeric PHs (1-3).
  • Experimental and theoretical studies of electronic structures and diradical properties.
  • Electrochemical analysis for redox behavior.
  • X-ray crystallography for structural confirmation.
  • Near-infrared laser irradiation studies for photothermal properties.

Main Results:

  • Isomeric PHs exhibit large diradical characters (y0 = 0.54-0.72).
  • Small singlet-triplet energy gaps (ΔEST = -0.99 to -2.79 kcal/mol) and narrow HOMO-LUMO gaps (0.90-1.16 eV) were observed.
  • Compounds show multistage reversible redox behavior, forming stable radical ions and dications.
  • Excellent photothermal stability, conversion efficiency, and imaging performance under NIR irradiation.

Conclusions:

  • Subtle structural isomerism significantly influences the electronic structure and properties of diradical PHs.
  • These PHs represent a robust molecular platform for advanced near-infrared photothermal materials.
  • The study provides deep insights into structure-property relationships in isomerism-engineered diradical PHs.