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03:00Electrolysis
27.3K
In a galvanic cell, the electrical work is done by a redox system on its surroundings as electrons produced by the spontaneous redox reactions are transferred through an external circuit. Alternatively, an external circuit does work on a redox system by imposing a voltage sufficient to drive an otherwise nonspontaneous reaction in a process known as electrolysis. For instance, recharging a battery involves the use of an external power source to drive the spontaneous (discharge) cell reaction in...
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01:15Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
8.8K
Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...
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02:46Halogenation of Alkenes
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Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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01:13Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
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Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.
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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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Updated: Sep 17, 2025
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An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation
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Electrochromism Enabled by Br-/Br3- Conversion.
Jiangbei Wan1, Yingyu Chen1, Zhaotao Li1
1Key Laboratory of Research on Utilization of Si-Zr-Ti Resources of Hainan Province, School of Materials Science and Engineering, Hainan University, Haikou 570228, China.
Nano Letters
|July 2, 2025
Summary
This study demonstrates a novel electrochromic device using bromine redox reactions for reversible optical modulation. The device achieves efficient color change and stability, paving the way for new electrochromic technologies.
Area of Science:
- Electrochemistry
- Materials Science
- Optical Engineering
Background:
- Halogen ion redox reactions offer fast kinetics and reversibility, suitable for energy storage and catalysis.
- Previous applications of redox halogen systems were limited by opacity and product stability, hindering optical modulation.
- Reversible optical modulation remains an underexplored area for redox halogen systems.
Purpose of the Study:
- To achieve efficient and reversible Br-/Br3- conversion for optical modulation.
- To develop a novel electrochromic device (ECD) based on the Br-/Br3- redox reaction.
- To explore the potential of CNTs and MPI+ in catalyzing redox reactions for electrochromic applications.
Main Methods:
- Utilized carbon nanotube (CNTs) and 1-methyl-3-propylimidazolium ions (MPI+) to catalyze Br- oxidation.
- Constructed an electrochromic device (ECD) based on the Br-/Br3- redox reaction.
- Evaluated optical modulation and cycling stability of the fabricated ECD.
Main Results:
- Achieved efficient and reversible Br-/Br3- conversion.
- The ECD demonstrated optical modulation from colorless to bright yellow with 64.0% modulation.
- The device exhibited excellent cycling stability, retaining 97.0% optical modulation after 3000 cycles.
Conclusions:
- The Br-/Br3- redox system, catalyzed by CNTs and MPI+, enables effective reversible optical modulation.
- The developed ECD shows promise for diverse electrochromic technologies due to its simplified structure and ease of fabrication.
- This work opens new avenues for applying redox halogen systems in optical modulation technologies.