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Photochemical Electrocyclic Reactions: Stereochemistry01:26

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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
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Fully Sensitized Upconversion Nanoparticles as Efficient Catalysts for NIR-Driven UV Photochemistry.

Naomi Weitzel1, Armaz Tsutskiridze2, Julia Bramowski1

  • 1Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Universitätsstraße 31, 93040, Regensburg, Germany.

Angewandte Chemie (International Ed. in English)
|September 17, 2025
PubMed
Summary
This summary is machine-generated.

Upconversion nanoparticles (UCNPs) efficiently convert low-energy light into high-energy photons, enabling demanding chemical reactions. These bright, recoverable UCNP catalysts show great promise for synthetic and biomedical applications.

Keywords:
CycloadditionDopingLuminescenceNanoparticlesPhotocatalysis

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Area of Science:

  • Materials Science
  • Photochemistry
  • Nanotechnology

Background:

  • Chemical photocatalysis typically uses single-photon excitation, limiting its use in high-energy reactions.
  • Biological photosynthesis utilizes multi-photon energy for complex chemical transformations.
  • Upconversion nanoparticles (UCNPs) convert multiple low-energy photons into one high-energy photon, addressing this limitation.

Purpose of the Study:

  • To synthesize and optimize NaYbF4:Tm@NaYF4 nanoparticles for enhanced UV and blue emission.
  • To investigate the application of these UCNPs as heterogeneous photocatalysts for energy-demanding reactions.
  • To establish a framework for tailoring UCNPs for synthetic and biomedical applications.

Main Methods:

  • Systematic optimization of UCNP synthesis, focusing on sensitizer concentration, dopant spacing, and shell thickness.
  • Characterization of UCNP optical properties, including UV and blue emission enhancement.
  • Testing UCNPs as photocatalysts for [2+2] photocycloadditions and Paternò-Büchi reactions under 980 nm excitation.

Main Results:

  • Achieved a 210-fold enhancement in UV emission at 345 nm compared to lower-doped systems.
  • Demonstrated efficient photocatalysis with turnover numbers (TON) > 290,000 and turnover frequencies (TOF) up to 8.52 s⁻¹.
  • Confirmed UCNP catalyst recoverability and suitability for deep-tissue applications.

Conclusions:

  • Optimized UCNPs offer a viable solution for high-energy photochemical transformations.
  • UCNPs show significant potential as efficient, recoverable photocatalysts.
  • This work provides a pathway for UCNP development in synthetic chemistry and biomedicine.