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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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.
Photosystem I01:27

Photosystem I

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...
Photosystem II01:22

Photosystem II

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 molecules...
The Z-Scheme of Electron Transport in Photosynthesis01:34

The Z-Scheme of Electron Transport in Photosynthesis

The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
Oxygenic Photosynthesis01:26

Oxygenic Photosynthesis

Oxygenic photosynthesis is a fundamental process in which light energy is harnessed to drive the oxidation of water, leading to the production of molecular oxygen (O₂), adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). This process is essential for sustaining aerobic life on Earth and is primarily carried out by cyanobacteria, algae, and plants. The core of oxygenic photosynthesis lies in the thylakoid membranes, where chlorophyll pigments facilitate light...

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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
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Cyclodextrin-based systems for photoinduced hydrogen evolution.

Nikos Mourtzis1, Pablo Contreras Carballada, Marco Felici

  • 1Organic Chemistry, Institute for Molecules and Materials, Faculty of Science, Radboud University Nijmegen, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.

Physical Chemistry Chemical Physics : PCCP
|March 29, 2011
PubMed
Summary
This summary is machine-generated.

New iridium-based photocatalysts efficiently produce hydrogen fuel from water. These light-driven systems, using cyclodextrin-appended iridium complexes and platinum nanoparticles, show significantly higher yields than traditional methods.

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Area of Science:

  • Photocatalysis
  • Hydrogen production
  • Supramolecular chemistry

Background:

  • Developing efficient artificial photosynthesis systems for sustainable energy is crucial.
  • Previous photocatalytic systems for hydrogen production often suffer from low yields and stability issues.

Purpose of the Study:

  • To design and synthesize novel light-driven catalytic systems for efficient molecular hydrogen production in water.
  • To explore a modular approach for creating versatile photo-active systems using self-assembly.

Main Methods:

  • Utilized cyclodextrin-appended iridium complexes as photosensitizers.
  • Employed viologen-based electron relays and cyclodextrin-modified platinum nanoparticles as catalysts.
  • Investigated the self-assembly of these components into three-component systems for proton reduction.

Main Results:

  • Achieved effective molecular hydrogen production in water using a sacrificial electron donor.
  • Demonstrated that iridium complexes of the formula [Ir(ppy)(2)(pytl-R)]Cl yield 20-35 times more hydrogen than classical [Ru(bpy)(3)]Cl(2) systems.
  • Found a direct correlation between the hydrogen yield and the emission quantum yield of the photosensitizer.

Conclusions:

  • The developed modular, light-driven catalytic systems offer a highly efficient route for hydrogen production.
  • Iridium-based photosensitizers significantly outperform ruthenium-based counterparts in this photocatalytic application.
  • The emission quantum yield of the photosensitizer is a key factor determining the efficiency of hydrogen generation.