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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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Estrategia de rigidificación estructural basada en la conversión reversible de estado excitado de iridio habilitado
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
Resumen
Los investigadores desarrollaron un nuevo método que utiliza el autoensamblaje para crear complejos de iridio (III) que responden al estímulo. Estos materiales cambian de color cuando se exponen a diferentes condiciones, lo que permite la encriptación de datos que responden a múltiples estímulos.
Área de la Ciencia:
- Ciencias de los materiales
- La fotoquímica
- Química supramolecular
Sus antecedentes:
- Los materiales crómicos sensibles al estímulo cambian de color con estímulos externos, encontrando amplias aplicaciones.
- Los complejos de metales de transición, particularmente los complejos de iridio (III), son prometedores para los materiales crómicos debido a los estados excitados sintonizables influenciados por la composición y el apilamiento.
- Lograr el apilamiento ordenado en complejos de iridio octaédrico para la respuesta a estímulos múltiples es un desafío.
Objetivo del estudio:
- Desarrollar una estrategia de rigidificación estructural mediante autoensamblaje para la regulación reversible de los estados excitados complejos de iridio.
- Para lograr el cambio de color en complejos de iridio (III) bajo varios estímulos para aplicaciones de cifrado de datos.
- Para superar el desafío del apilamiento ordenado en complejos de iridio octaédrico.
Principales métodos:
- Preparación de complejos catiónicos de iridio ((III) con tetracis ((perfluorofenil) borato ([B ((PhF5) 4) -) contraiones.
- Utilizando las interacciones polar-π entre el counterion y el iridium (III) para inducir el autoensamblaje y la rigidificación estructural.
- Investigando la conversión de estado excitado de transferencia de carga de metal a ligando (3MLCT) a estados centrados en ligando (3LC) en estados agregados.
Principales resultados:
- La rigidificación estructural restringió los cambios conformacionales del estado excitado 3MLCT, facilitando la conversión al estado excitado 3LC.
- La conversión de estado excitado condujo a un cambio azul de 54 nm en los espectros de fotoluminiscencia (amarillo a azul cielo).
- Se han desarrollado complejos de iridio (III) que muestran respuestas distintas a bajas temperaturas, vapor y fuerza mecánica para la encriptación de datos.
Conclusiones:
- Se implementó con éxito una nueva estrategia para el apilamiento ordenado de complejos octaédricos.
- El estudio proporciona una visión más profunda de los procesos fotofísicos que rigen el comportamiento complejo de los metales de transición.
- Este trabajo ofrece una nueva perspectiva para el diseño de materiales crómicos avanzados que responden a múltiples estímulos.