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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.8K
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
1.8K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

2.8K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
2.8K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.3K
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.
2.3K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.0K
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.
2.0K
Stability of Conjugated Dienes01:28

Stability of Conjugated Dienes

3.3K
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.
3.3K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
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.
2.0K

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Related Experiment Video

Updated: Jun 12, 2025

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light
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Stabilizing Dye-Sensitized Upconversion Hybrids by Cyclooctatetraene.

Yuxi Liu1, Lulu Ning1, Yijun Luo1

  • 1College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, Shaanxi, P.R. China.

Nano Letters
|September 18, 2024
PubMed
Summary

Cyclooctatetraene (COT) enhances the photostability of dye-sensitized upconversion nanoparticles by quenching triplet states and consuming singlet oxygen. This strategy significantly extends the operational lifetime of these valuable nanomaterials.

Keywords:
cyclooctatetraenenear-infrared dyephotostabilityupconversion nanoparticles

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Area of Science:

  • Nanotechnology
  • Materials Science
  • Photochemistry

Background:

  • Lanthanide-doped upconversion nanoparticles (UCNPs) convert near-infrared (NIR) light to visible light for diverse applications.
  • Dye antennas improve UCNP light-harvesting but are susceptible to photobleaching in ambient conditions.

Purpose of the Study:

  • To develop a synergistic approach to mitigate photobleaching in dye-sensitized UCNPs.
  • To enhance the photostability and operational lifetime of UCNP-based nanohybrids.

Main Methods:

  • Incorporation of cyclooctatetraene (COT) as a triplet state quencher and singlet oxygen scavenger.
  • Investigating the effect of COT on the photostability of IR806 dye and dye-UCNPs.
  • Evaluating emission intensity, dynamics, and half-life under continuous laser irradiation.

Main Results:

  • COT effectively quenched dye triplet states and consumed singlet oxygen, preventing dye oxidation.
  • The half-life of the IR806 dye was extended by 4.7-fold.
  • Dye-UCNPs exhibited a 3.9-fold increase in half-life without compromising emission properties.

Conclusions:

  • COT offers a novel strategy to significantly enhance the photostability of NIR dyes and dye-sensitized UCNPs.
  • This approach improves the durability of UCNP nanohybrids for advanced applications.
  • Mitigating photobleaching is crucial for the practical utility of UCNP-based systems.