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Related Concept Videos

Radical Formation: Elimination00:51

Radical Formation: Elimination

Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to...
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
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 Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
Radical Formation: Abstraction00:47

Radical Formation: Abstraction

The electron of an atom can be abstracted from a compound by a relatively unstable radical to generate a new radical of relatively greater stability. For example, an initiator which forms radicals by homolysis can abstract a suitable species like a hydrogen atom or a halogen atom from a compound to generate a new radical. This ability of radicals to propagate by abstraction is a crucial feature of radical chain reactions.
Even though homolysis produces radicals, it is different from radical...

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Updated: Jun 11, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
10:44

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

Why Are Verdazyl Radicals Nonemissive?

Alexandre Malinge1, Pierre-Luc Thériault1, Stéphane Kéna-Cohen1

  • 1Department of Engineering Physics, École Polytechnique de Montréal, PO Box 6079, succ. Centre-Ville, Montreal, QC H3C 3A7, Canada.

The Journal of Physical Chemistry. A
|June 10, 2026
PubMed
Summary
This summary is machine-generated.

Verdazyl radicals are nonemissive due to ultrafast decay from excited states. This decay is caused by a common conical intersection geometry, hindering light emission in these organic radicals.

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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Quantum Chemistry

Background:

  • Verdazyl radicals are air-stable organic molecules with diverse applications.
  • Existing verdazyl derivatives are consistently nonemissive, limiting their potential.
  • Understanding the excited-state dynamics is crucial for designing new functional materials.

Purpose of the Study:

  • Investigate the reasons for nonemissivity in verdazyl radicals.
  • Elucidate the excited-state dynamics of verdazyl compounds.
  • Identify design strategies for potentially emissive verdazyl derivatives.

Main Methods:

  • Femtosecond pump-probe spectroscopy to study excited-state dynamics.
  • Steady-state spectroscopy for characterization.
  • Quantum chemical calculations (Spin-flip time-dependent density functional theory) to model electronic states and decay pathways.

Main Results:

  • Observed ultrafast internal conversion (0.5 ± 0.1 ps) in carbazole-substituted 2,4,6-triphenylverdazyl (TPV-Cz).
  • Measured vibrational relaxation lifetime of 3.7 ± 0.4 ps.
  • Identified a low-energy conical intersection between D1 and D0 states, driven by verdazyl ring distortion, as the cause of nonradiative decay.

Conclusions:

  • The conical intersection geometry, accessible via verdazyl ring distortion, is a recurring feature explaining the nonemissivity of functionalized verdazyls.
  • This study provides a mechanistic understanding of verdazyl photophysics.
  • The findings offer a roadmap for designing novel emissive verdazyl derivatives.