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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
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.
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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.
Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Radical Reactivity: Overview01:11

Radical Reactivity: Overview

Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Formation: Homolysis00:54

Radical Formation: Homolysis

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.

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Related Experiment Video

Updated: May 19, 2026

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera
06:08

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Published on: December 27, 2018

Persistent Halogenated Perylenediimide Organic Radical Anions Orchestrating Three-Photon Energy Conversion and

Tarun Kumar Dinda1,2, Sathi Sahoo1,2, Manoranjan Ojha1,2

  • 1School of Chemical Sciences, National Institute of Science Education and Research (NISER), Jatni, Odisha, India.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|May 18, 2026
PubMed
Summary

A stable perylenediimide radical anion (PDI-Br8•‒) acts as a robust photocatalyst. This breakthrough enables efficient, multi-photon organic synthesis under ambient conditions.

Keywords:
air stable radical aniondouble Z‐schemeone‐pot three‐components coupling reactionthree‐photon absorptionvisible light photocatalysis

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Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst
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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: May 19, 2026

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera
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Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Published on: December 27, 2018

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst
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Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

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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
  • Photochemistry
  • Materials Science

Background:

  • Persistent radical ions are crucial for light harvesting but are often unstable.
  • Developing stable radical ions for photocatalysis remains a significant challenge.

Purpose of the Study:

  • To engineer a stable perylenediimide radical anion for advanced photocatalysis.
  • To explore its potential in multi-photon processes and organic synthesis.

Main Methods:

  • Halogen engineering of perylenediimide to create PDI-Br8•‒.
  • Characterization of its stability, absorption, redox cycling, and excited-state lifetime.
  • Application as a photocatalyst in a stereoselective coupling reaction.

Main Results:

  • PDI-Br8•‒ exhibits exceptional air stability (>18 months) and broad visible light absorption.
  • It demonstrates reversible two-electron redox cycling and a long excited-state lifetime (∼2 ns).
  • Efficiently catalyzes the one-pot synthesis of (E)-enenitriles from alkynes, acrylonitrile, and bromotrihalomethanes at low loading.

Conclusions:

  • Halogen substitution stabilizes the radical anion, enabling its use as a robust photocatalyst.
  • This work presents a molecular design for multi-photon radical photochemistry.
  • The developed radical unifies energy storage, charge transport, and synthetic reactivity.