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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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
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Deactivation Processes: Jablonski Diagram01:25

Deactivation Processes: Jablonski Diagram

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Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
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Electrophilic Aromatic Substitution: Overview01:16

Electrophilic Aromatic Substitution: Overview

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In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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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.
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π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Updated: Jan 4, 2026

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst
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Two-electron transfer stabilized by excited-state aromatization.

Jinseok Kim1, Juwon Oh1, Seongchul Park2

  • 1Spectroscopy Laboratory for Functional π-electronic Systems and Department of Chemistry, Yonsei University, Seoul, 03722, Korea.

Nature Communications
|November 3, 2019
PubMed
Summary
This summary is machine-generated.

Excited-state aromaticity in TMTQ involves a two-electron transfer, forming a Baird aromatic 8π core annulene. This process stabilizes charge separation in functional photoactive materials.

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Area of Science:

  • Photochemistry
  • Organic Chemistry
  • Aromaticity Studies

Background:

  • Excited-state aromaticity is crucial for understanding photochemical processes.
  • Oligomers with donor-acceptor systems offer tunable electronic properties.

Purpose of the Study:

  • Investigate a two-electron transfer process in TMTQ, an acceptor-donor-acceptor oligomer.
  • Elucidate the role of excited-state aromaticity in stabilizing this process.

Main Methods:

  • Spectroscopic measurements to observe electron transfer.
  • Analysis of excited-state properties and aromaticity.

Main Results:

  • Quantitative observation of two π-electron shift between donor and acceptors.
  • Excited-state aromatization forming a Baird aromatic 8π core annulene.
  • Stabilization of a two-charge separated state via multiexcitonic nature.

Conclusions:

  • TMTQ exhibits excited-state aromaticity driven by two-electron transfer.
  • Baird aromaticity stabilizes charge-separated states in photoactive materials.
  • Provides insights for designing novel functional photoactive materials.