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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.
2.5K
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

1.4K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
1.4K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.9K
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
Deactivation Processes: Jablonski Diagram01:25

Deactivation Processes: Jablonski Diagram

985
Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
985
Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control01:23

Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control

3.0K
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
3.0K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.1K
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.
2.1K

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Related Experiment Video

Updated: Oct 7, 2025

X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050
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X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050

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Elucidating complex triplet-state dynamics in the model system isopropylthioxanthone.

Nikolaos Liaros1, Sandra A Gutierrez Razo1, Matthew D Thum1

  • 1Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA.

Iscience
|January 10, 2022
PubMed
Summary
This summary is machine-generated.

Researchers developed new methods to study triplet states in photoresists. They found that light used for excitation also depletes triplet states via reverse intersystem crossing (RISC), offering control over photochemical processes.

Keywords:
ChemistryNonlinear opticsTheoretical photophysics

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Area of Science:

  • Photochemistry
  • Chemical Physics
  • Materials Science

Background:

  • Triplet states are crucial intermediates in many photochemical processes.
  • Understanding triplet state dynamics is key to controlling photoresist behavior.
  • Isopropylthioxanthone (ITX) is a common photoinitiator in advanced polymerization techniques.

Purpose of the Study:

  • To develop novel techniques for probing triplet state dynamics.
  • To elucidate the complex photochemistry of a radical photoresist system initiated by ITX.
  • To identify the mechanisms of triplet state population and depopulation.

Main Methods:

  • Utilized advanced spectroscopic tools for real-time monitoring.
  • Employed kinetic modeling to analyze reaction pathways.
  • Applied conventional techniques alongside novel methods for comprehensive analysis.

Main Results:

  • Identified a dual role for excitation light: promoting triplet population and causing depletion via reverse intersystem crossing (RISC).
  • Distinguished between a reactive and a non-reactive triplet state.
  • Provided evidence for RISC from an excited triplet state to a vibrationally excited ground state.

Conclusions:

  • The photophysics of ITX-based photoresists involves a complex interplay of excitation and deactivation pathways.
  • Reverse intersystem crossing (RISC) is a significant deactivation channel.
  • This research paves the way for controlling triplet state photochemistry in various applications.