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01:26Photochemical 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
Selection Rules: Photochemical Activation
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
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.
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
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Related Experiment Video
Updated: Jun 11, 2026
10:21
Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
Published on: October 5, 2019
Supramolecular cobaloxime assemblies for H2 photocatalysis: an initial solution state structure-function analysis.
Karen L Mulfort1, David M Tiede
1Division of Chemical Sciences and Engineering, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
The Journal of Physical Chemistry. B
|July 3, 2010
Summary
Researchers studied cobaloxime-based supramolecular photocatalysts for hydrogen production. A "push-pull" design showed promising ultrafast excited state quenching for efficient solar energy conversion.
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Published on: July 25, 2025
Area of Science:
- Supramolecular Chemistry
- Photocatalysis
- Renewable Energy
Background:
- Cobaloxime-based supramolecular photocatalysts are investigated for proton reduction to hydrogen.
- Understanding structure-activity relationships is crucial for efficient solar energy conversion.
Purpose of the Study:
- To investigate the correlation between structure and light-induced electron transfer in cobaloxime-based photocatalysts.
- To evaluate new supramolecular photocatalyst designs for hydrogen production.
Main Methods:
- Solution-phase X-ray scattering to assess structural integrity in solution.
- Ultrafast transient optical spectroscopy to analyze electron transfer and charge separation dynamics.
- Investigated one known and three new axially coordinated cobaloxime assemblies.
Main Results:
- Biphasic excited state decay kinetics observed, indicating configurational dispersion impacts electron transfer.
- An assembly with a "push-pull" donor-photosensitizer-acceptor motif showed significant ultrafast excited state quenching.
- This specific assembly presents a strong potential for efficient solar energy conversion.
Conclusions:
- Structural integrity and configurational dispersion influence photoinduced electron transfer in these photocatalysts.
- The "push-pull" triad motif is a promising architecture for next-generation supramolecular photocatalysts.
- Findings guide the design of advanced materials for solar fuel production.