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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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[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

2.6K
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
2.6K
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

3.0K
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
3.0K
Regioselectivity of Electrophilic Additions-Peroxide Effect02:35

Regioselectivity of Electrophilic Additions-Peroxide Effect

8.4K
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
8.4K
Stereoisomerism02:52

Stereoisomerism

11.7K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
11.7K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
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.
2.0K

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Related Experiment Video

Updated: May 28, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy

Published on: February 20, 2020

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B←N Lewis Pair-Functionalized Perylenes: Tuning Optoelectronic Properties via Regioisomerization.

Yufeng Zhang1,2, Junqing Shi1, Lei Ji1,2

  • 1Frontiers Science Center for Flexible Electronics (FSCFE), Shaanxi Institute of Flexible Electronics (SIFE) & Shaanxi Institute of Biomedical Materials and Engineering (SIBME), Northwestern Polytechnical University, Xi'an 710072, China.

The Journal of Organic Chemistry
|February 14, 2025
PubMed
Summary

We synthesized two perylene isomers functionalized with boron-nitrogen Lewis pairs. Mirror-symmetric functionalization significantly improved photoelectronic properties, enhancing fluorescence and tuning energy levels.

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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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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Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photophysics

Background:

  • Perylene derivatives are widely studied for their optoelectronic applications.
  • Tuning the electronic properties of organic semiconductors is crucial for device performance.
  • Lewis pair functionalization offers a novel approach to modify molecular structures and properties.

Purpose of the Study:

  • To synthesize and characterize two peri-regioisomers of boron-nitrogen Lewis pair-functionalized perylenes.
  • To investigate the impact of regiochemistry on the photoelectronic properties.
  • To explore the potential of these compounds in optoelectronic applications.

Main Methods:

  • Synthesis of peri-regioisomers of B←N Lewis pair-functionalized perylenes.
  • Spectroscopic characterization (absorption, emission).
  • Electrochemical measurements to determine LUMO energy levels.

Main Results:

  • Two peri-regioisomers, PBNPf1 (centrosymmetric) and PBNPf2 (mirror-symmetric), were successfully synthesized.
  • Mirror-symmetric functionalization (PBNPf2) led to more effective tuning of photoelectronic properties.
  • LUMO energy levels were stabilized to -3.00 eV (PBNPf1) and -3.30 eV (PBNPf2).
  • Emission maxima shifted to 574 nm (PBNPf1) and 628 nm (PBNPf2).
  • High fluorescence quantum yields were achieved: up to 96% (PBNPf1) and 87% (PBNPf2).

Conclusions:

  • The regiochemistry of B←N Lewis pair functionalization significantly influences the optoelectronic properties of perylenes.
  • Mirror-symmetric functionalization is a promising strategy for enhancing fluorescence and tuning energy levels.
  • These functionalized perylenes show potential for advanced optoelectronic applications.