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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
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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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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Photosystem I01:27

Photosystem I

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Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
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Electron Transport Chain: Complex III and IV01:43

Electron Transport Chain: Complex III and IV

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During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...
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Photosystem II01:22

Photosystem II

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The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across  two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment...
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Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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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.
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Updated: Feb 26, 2026

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
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Aprovechamiento de la Transferencia de Electrones Acoplada a Múltiples Protones para Mejorar la Eficiencia de

Eris Villalona1, Rodrigo E Domínguez2, Edwin J Gonzalez Lopez2

  • 1Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.

The journal of physical chemistry. C, Nanomaterials and interfaces
|February 25, 2026
PubMed
Resumen

Los investigadores desarrollaron nuevos fotocatalizadores de iridio inspirados en el Fotosistema II. Estos catalizadores utilizan la transferencia intramolecular de electrones acoplada a múltiples protones (MPCET) para reducir significativamente la recombinación de carga y aumentar la eficiencia fotocatalítica.

Palabras clave:
fotocatálisistransferencia de electrones acoplada a protonescomplejos de iridiorecombinación de cargarendimiento cuánticoenergía solarquímica organometálicaconversión de energía

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Área de la Ciencia:

  • Fotocatálisis
  • Química organometálica
  • Conversión de energía

Sus antecedentes:

  • La recombinación de carga (CR) en reacciones de fotorredox limita los rendimientos cuánticos y dificulta la conversión eficiente de energía lumínica.
  • Inspiración extraída de los relés redox en el Fotosistema II (PSII) para superar las limitaciones de CR.
  • El desarrollo de diseños avanzados de fotocatalizadores es crucial para aplicaciones eficientes de energía solar.

Objetivo del estudio:

  • Diseñar y sintetizar nuevos complejos de iridio(III) con grupos benzimidazol-fenol-piridina (BIP-Py) unidos covalentemente.
  • Investigar el papel de la transferencia intramolecular de electrones acoplada a múltiples protones (MPCET) en la mejora de la actividad fotocatalítica.
  • Mitigar la rápida recombinación de carga (CR) utilizando una red de enlaces de hidrógeno extendida.

Principales métodos:

  • Síntesis de complejos de iridio(III) con grupos BIP-Py.
  • Espectroelectroquímica infrarroja para monitorizar la protonación de piridina.
  • Espectroelectroquímica visible y espectroscopia de absorción transitoria para estudiar estados de carga separada (CSS).

Principales resultados:

  • Evidencia de protonación de piridina tras la oxidación de fenol y formación de CSS a través de transferencia intramolecular de electrones acoplada a protones (PCET).
  • Demostró una reducción de ~106 veces en la tasa de CR en una reducción de éster de N-hidroxiftalimida fotocatalítica.
  • Logró hasta un 157% de mejora en el rendimiento cuántico utilizando la plataforma de fotocatalizador BIP-Py.

Conclusiones:

  • Los relés redox basados en MPCET integrados en marcos de fotocatalizadores mejoran eficazmente la eficiencia fotocatalítica.
  • La plataforma BIP-Py ofrece una estrategia prometedora para diseñar fotocatalizadores de próxima generación.
  • Este trabajo proporciona una nueva vía para mejorar la conversión de energía lumínica en sistemas catalíticos.