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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
[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.
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.
Diels–Alder Reaction: Characteristics of Dienes01:29

Diels–Alder Reaction: Characteristics of Dienes

The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
Stability of Conjugated Dienes01:28

Stability of Conjugated Dienes

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

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Photochromic dithienylethenes with extended pi-systems.

Oliver Tosic1, Kai Altenhöner, Jochen Mattay

  • 1Organische Chemie I, Universität Bielefeld, Postfach 100131, 33501, Bielefeld, Germany.

Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology
|February 4, 2010
PubMed
Summary

Six novel photochromic dithienylethenes were synthesized and their properties studied. These compounds feature unique substitutions on conjugated double bonds, impacting their photochromic behavior.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photochemistry

Background:

  • Photochromic materials reversibly change color upon exposure to light.
  • Dithienylethenes are a well-established class of photochromic compounds.
  • Tuning molecular structure is key to optimizing photochromic performance.

Purpose of the Study:

  • To synthesize novel photochromic dithienylethenes.
  • To investigate the impact of varied substitutions on conjugated double bonds.
  • To characterize the photochromic properties of the new compounds.

Main Methods:

  • Multi-step organic synthesis of six dithienylethene derivatives.
  • Spectroscopic analysis (UV-Vis, NMR) for structural confirmation.
  • Photochromic performance evaluation under UV irradiation and thermal/visible light annealing.

Main Results:

  • Successful synthesis of six new dithienylethene compounds.
  • Demonstrated photochromic behavior, including coloration and fading.
  • Substitutions influenced the absorption spectra and switching kinetics.

Conclusions:

  • The synthesized dithienylethenes exhibit promising photochromic properties.
  • Structural modifications offer a pathway to tailor photochromic responses.
  • These findings contribute to the development of advanced photochromic materials.