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Related Concept Videos

[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.
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 Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
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...

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Related Experiment Video

Updated: Jun 18, 2026

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Published on: February 7, 2017

Chemically responsive supramolecular assemblies of pyrene-beta-cyclodextrin dimer.

Tomoki Ogoshi1, Masayoshi Hashizume, Tada-aki Yamagishi

  • 1Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. ogoshi@t.kanazawa-u.ac.jp

Langmuir : the ACS Journal of Surfaces and Colloids
|November 10, 2009
PubMed
Summary

This study details supramolecular assemblies formed by a beta-cyclodextrin dimer and a fluorescent pyrene unit. These assemblies exhibit wire-like structures in water and transform upon guest addition, showing potential for molecular electronics.

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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
16:24

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

Published on: August 2, 2012

Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Nanotechnology

Background:

  • Beta-cyclodextrin (beta-CD) dimers are known for their host-guest chemistry.
  • Fluorescent molecules like phenylethynylpyrene can be incorporated into supramolecular structures.
  • Understanding self-assembly in aqueous media is crucial for developing functional nanomaterials.

Purpose of the Study:

  • To synthesize and characterize a novel beta-cyclodextrin dimer linked to a fluorescent phenylethynylpyrene moiety (Py-beta-CD dimer).
  • To investigate the self-assembly behavior of the Py-beta-CD dimer in aqueous media.
  • To explore the structural and electronic responses of these assemblies to different guests.

Main Methods:

  • Synthesis of the Py-beta-CD dimer.
  • Tapping mode atomic force microscopy (AFM) for structural analysis.
  • Spectroscopic methods to study guest interactions and electron transfer.

Main Results:

  • The Py-beta-CD dimer self-assembles into wire-shaped supramolecular structures in water via pi-pi stacking.
  • Addition of sodium adamantane carboxylate induces a structural transition to J-type assemblies.
  • Electron transfer occurs from the phenylethynylpyrene moiety to electron-deficient guests.

Conclusions:

  • The Py-beta-CD dimer effectively forms ordered supramolecular assemblies in aqueous solution.
  • The assemblies exhibit tunable structures and electronic properties in response to guest molecules.
  • This system holds promise for applications in molecular sensing and electronics.