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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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01:24Types of Reversible Electrodes
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For electrode reversibility to be maintained, all the reactants and products involved in the half-reaction must be present at the electrode. There are several types of reversible electrodes (half-cells).In metal-metal-ion electrodes, a metal balances electrochemically with a solution of its own ions. Examples are Cu2+|Cu and Zn2+|Zn. Metals that react with the solvent, like group 1 and most group 2 metals, which react with water, and zinc, which reacts with aqueous acidic solutions, cannot be...
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01:11Aryldiazonium Salts to Azo Dyes: Diazo Coupling
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The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the...
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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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Towards electrochromic devices having visible color switching using electronic push-push and push-pull cinnamaldehyde
Daminda Navarathne1, W G Skene
1Laboratoire de caractérisation photophysique des matériaux conjugués, Department of Chemistry, Pavillon JA Bombardier, Université de Montréal , CP 6128, succ. Centre-ville, Montreal, Quebec H3C 3J6, Canada.
ACS Applied Materials & Interfaces
|November 22, 2013
Summary
New conjugated azomethines were synthesized and studied for their tunable optical and electrochemical properties. These materials show potential for applications in electrochromic devices due to their distinct color changes upon oxidation.
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Area of Science:
- Organic Chemistry
- Materials Science
- Electrochemistry
Background:
- Conjugated azomethines are organic compounds with potential applications in electronic devices.
- Tuning electronic properties of organic molecules is crucial for developing advanced materials.
Purpose of the Study:
- To synthesize and characterize novel symmetric and unsymmetric conjugated azomethines.
- To investigate the optical, electrochemical, and spectroelectrochemical properties of these azomethines.
- To evaluate the potential of these azomethines in electrochromic devices.
Main Methods:
- Synthesis of azomethines from cinnamaldehyde and 2,5-diaminothiophene-3,4-dicarboxylic acid diethyl ester.
- Optical spectroscopy to determine absorbance and solvatochromism.
- Electrochemical methods (cyclic voltammetry) to study redox properties.
- Spectroelectrochemistry to correlate color changes with electrochemical states.
Main Results:
- Successfully prepared a series of conjugated azomethines with tunable electronic properties.
- Observed positive solvatochromism in symmetric push-push derivatives, with absorbance shifts up to 31 nm.
- Demonstrated significant color transitions (215 nm) between neutral and radical cation states.
- Showcased reversible color changes in electrochromic devices, with oxidation leading to a shift into the near-infrared (NIR) region.
Conclusions:
- The electronic and optical properties of these azomethines can be effectively tuned by substituents.
- These azomethines exhibit promising electrochromic behavior, including distinct color changes upon oxidation.
- The synthesized azomethine triads are suitable for applications in electrochromic devices.