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Related Concept Videos

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

70.5K
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

9.4K
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...
9.4K
Photosystem II01:22

Photosystem II

79.2K
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...
79.2K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.8K
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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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
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Leveraging Multiproton-Coupled Electron Transfer to Improve Ir(III) Photocatalyst Efficiency.

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
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Researchers developed new iridium photocatalysts inspired by Photosystem II. These catalysts use intramolecular multiproton-coupled electron transfer (MPCET) to significantly reduce charge recombination and boost photocatalytic efficiency.

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Area of Science:

  • Photocatalysis
  • Organometallic Chemistry
  • Energy Conversion

Background:

  • Charge recombination (CR) in photoredox reactions limits quantum yields and hinders efficient light energy conversion.
  • Inspiration drawn from redox relays in Photosystem II (PSII) to overcome CR limitations.
  • Development of advanced photocatalyst designs is crucial for efficient solar energy applications.

Purpose of the Study:

  • To design and synthesize novel iridium(III) complexes with covalently attached benzimidazole-phenol-pyridine (BIP-Py) groups.
  • To investigate the role of intramolecular multiproton-coupled electron transfer (MPCET) in enhancing photocatalytic activity.
  • To mitigate rapid charge recombination (CR) by utilizing an extended hydrogen-bond network.

Main Methods:

  • Synthesis of iridium(III) complexes featuring BIP-Py moieties.
  • Infrared spectroelectrochemistry to monitor pyridine protonation.
  • Visible spectroelectrochemistry and transient absorption spectroscopy to study charge-separated states (CSS).

Main Results:

  • Evidence of pyridine protonation upon phenol oxidation and formation of CSS via intramolecular proton-coupled electron transfer (PCET).
  • Demonstrated a ~106-fold reduction in CR rate in a photocatalytic N-hydroxyphthalimide ester reduction.
  • Achieved up to a 157% enhancement in quantum yield using the BIP-Py photocatalyst platform.

Conclusions:

  • MPCET-based redox relays integrated into photocatalyst frameworks effectively enhance photocatalytic efficiency.
  • The BIP-Py platform offers a promising strategy for designing next-generation photocatalysts.
  • This work provides a new avenue for improving light energy conversion in catalytic systems.