Related Concept Videos
01:26Photochemical 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
Selection Rules: Photochemical Activation
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01:26Thermal 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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02:34Structural Isomerism
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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...
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...
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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02:52Stereoisomerism
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Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
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Structural Rigidification Strategy Based on Self-Assembly Enabled Reversible Excited-State Conversion of Iridium(III)
Xiangyu Liu1, Jing Liu2, Danlei Zhu1
1Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University Beijing 100084, P. R. China.
Journal of the American Chemical Society
|October 15, 2024
Summary
Researchers developed a new method using self-assembly to create stimulus-responsive iridium(III) complexes. These materials change color when exposed to different conditions, enabling multiple-stimulus-responsive data encryption.
Area of Science:
- Materials Science
- Photochemistry
- Supramolecular Chemistry
Background:
- Stimulus-responsive chromic materials change color with external stimuli, finding broad applications.
- Transition-metal complexes, particularly iridium(III) complexes, are promising for chromic materials due to tunable excited states influenced by composition and stacking.
- Achieving ordered stacking in octahedral iridium(III) complexes for multiple-stimulus responsiveness is challenging.
Purpose of the Study:
- To develop a structural rigidification strategy via self-assembly for reversible regulation of iridium(III) complex excited states.
- To achieve color switching in iridium(III) complexes under various stimuli for data encryption applications.
- To overcome the challenge of ordered stacking in octahedral iridium(III) complexes.
Main Methods:
- Preparation of cationic iridium(III) complexes with tetrakis(perfluorophenyl)-borate ([B(PhF5)4]-) counterions.
- Utilizing polar-π interactions between the counterion and iridium(III) cations to induce self-assembly and structural rigidification.
- Investigating the excited-state conversion from metal-to-ligand charge transfer (3MLCT) to ligand-centered (3LC) states in aggregated states.
Main Results:
- Structural rigidification restricted conformational changes of the 3MLCT excited state, facilitating conversion to the 3LC excited state.
- Excited-state conversion led to a 54 nm blue shift in photoluminescence spectra (yellow to sky blue).
- Developed iridium(III) complexes exhibiting distinct responses to low temperature, vapor fuming, and mechanical force for data encryption.
Conclusions:
- A novel strategy for ordered stacking of octahedral complexes was successfully implemented.
- The study provides deeper insights into the photophysical processes governing transition-metal complex behavior.
- This work offers a new perspective for designing advanced multiple-stimulus-responsive chromic materials.