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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
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.
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

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...
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Plants and other photosynthetic organisms comprise pigments capable of absorption of direct sunlight. These pigments are present in the reaction center - the main site of photochemical reactions as well as in the antenna complex. Under average light conditions, the rate at which reaction center pigments absorb light is far below the electron transport chain's capacity. As a result, the reaction center alone cannot provide enough energy to drive photosynthesis. The photosynthetic efficiency can...
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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.
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Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals
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Compartmentalized photoreactions within compositionally anisotropic Janus microstructures.

Kyung Jin Lee1, Sangyeul Hwang, Jaewon Yoon

  • 1Department of Chemical Engineering, Macromolecular Science and Engineering, and Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.

Macromolecular Rapid Communications
|March 25, 2011
PubMed
Summary

Researchers created spatially controlled photoreactions in microparticles and microfibers using photocrosslinkable poly(vinyl cinnamate). This novel EHD co-jetting method enables mask-free, selective photocrosslinking for advanced material fabrication.

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Area of Science:

  • Materials Science
  • Polymer Chemistry
  • Microfluidics

Background:

  • Microparticles and microfibers are crucial in various applications.
  • Achieving spatial control over reactions within these structures is challenging.
  • Existing methods for selective modification often require complex masking or laser techniques.

Purpose of the Study:

  • To demonstrate spatially controlled photoreactions in bicompartmental microparticles and microfibers.
  • To develop a mask-free method for selective photocrosslinking.
  • To create novel Janus-type particles and fibers with controlled morphology.

Main Methods:

  • Bicompartmental particles and fibers synthesized via electrohydrodynamic (EHD) co-jetting of distinct polymer solutions.
  • Anisotropic incorporation of photocrosslinkable poly(vinyl cinnamate) into one compartment.
  • Characterization using confocal laser scanning microscopy, Fourier-transformed infrared spectroscopy, and scanning electron microscopy.
  • Photoreaction induced by UV light (254 nm) for selective crosslinking.
  • Solvent treatment (chloroform) to generate hemishell structures.

Main Results:

  • Successful synthesis of bicompartmental microparticles and microfibers with confirmed physical and chemical anisotropy.
  • Demonstration of spatially controlled photocrosslinking of poly(vinyl cinnamate) upon UV exposure.
  • Formation of unique half-moon shaped hemishells with porous morphology (70 nm pores) after solvent treatment.
  • Adjustment of polymer concentrations in EHD co-jetting solutions determined particle and fiber structures.

Conclusions:

  • EHD co-jetting provides a versatile platform for creating anisotropic bicompartmental microstructures.
  • Selective photocrosslinking can be achieved without masks or laser writing, enabling efficient fabrication of Janus-type particles and fibers.
  • The developed method offers a novel route to porous hemishell structures with potential applications in advanced materials and devices.