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Related Concept Videos

Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.5K
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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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
1.9K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.2K
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.
2.2K
Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

8.2K
The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
8.2K
Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

3.7K
Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
3.7K

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Related Experiment Video

Updated: Sep 22, 2025

Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering
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Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering

Published on: December 21, 2017

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Photoinduced Aggregation of Polythiophenes.

Zachary C Smith1, Robert H Pawle1, Samuel W Thomas1

  • 1Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, United States.

ACS Macro Letters
|May 24, 2022
PubMed
Summary

Thiophene-based materials with photocleavable side chains aggregate upon UV light exposure. This photoinduced aggregation enables potential applications in solid-state device construction.

Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photochemistry

Background:

  • Thiophene-based materials are explored for their unique electronic and optical properties.
  • Controlling material solubility and aggregation is crucial for device fabrication.
  • Photocleavable linkers offer a route to light-induced changes in material properties.

Purpose of the Study:

  • To synthesize and characterize thiophene-based materials with photolabile solubilizing groups.
  • To investigate the photoinduced aggregation behavior of these materials upon UV irradiation.
  • To assess the potential of these materials in solid-state device applications.

Main Methods:

  • Synthesis of quaterthiophene oligomers and a polymeric analog featuring nitrobenzyl ester linkages.

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates
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Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

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Last Updated: Sep 22, 2025

Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering
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Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

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Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates
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Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

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  • UV irradiation of materials in solution and as thin films.
  • Spectroscopic analysis (UV-Vis absorption, fluorescence) to monitor aggregation.
  • Solubility tests before and after irradiation.

    • Main Results:

    • Oligomers yielded soluble diacids after UV exposure.
    • The polymeric analog exhibited red-shifted absorbance and quenched fluorescence, indicating aggregation.
    • Photochemical cleavage of alkyl chains was confirmed as the cause of aggregation.
    • Irradiated polymer thin films demonstrated resistance to dissolution in organic solvents.

    Conclusions:

    • Thiophene-based materials with photocleavable nitrobenzyl ester side chains undergo photoinduced aggregation.
    • The aggregation behavior is dependent on the molecular structure (oligomer vs. polymer).
    • These photoresponsive materials show promise for fabricating multilayer solid-state devices.