Electrochemically triggered conversion between metacyclophan-1-ene and dihydropyrene molecular switching systems
Iluminada Gallardo1, Gonzalo Guirado, Gemma Prats
1Departament de Química, Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain.
Physical Chemistry Chemical Physics : PCCP
|February 26, 2009
Summary
Electrochemical oxidation of metacyclophanene isomers yields a fluorescent dihydropyrene intermediate. This study demonstrates dual electrochemical triggering of two distinct molecular switching systems.
Area of Science:
- Organic Chemistry
- Photochemistry
- Electrochemistry
Background:
- Metacyclophanenes are photochromic molecules exhibiting reversible color changes.
- Positive photochromic systems show greater stability in the open isomer form.
- Negative photochromic systems are more stable in the closed isomer form.
Purpose of the Study:
- To investigate the electrochemical oxidation of metacyclophanene isomers.
- To explore the potential for electrochemically triggering molecular switching systems.
- To synthesize a stable fluorescent dihydropyrene intermediate.
Main Methods:
- Electrochemical oxidation of open and closed metacyclophanene isomers.
- Characterization of the resulting products using spectroscopic techniques.
- Analysis of the photochromic properties of the intermediate.
Main Results:
- Quantitative yield of a stable fluorescent dihydropyrene intermediate.
- The dihydropyrene intermediate exhibits negative photochromism.
- Demonstration of dual electrochemical triggering of two molecular switching systems.
Conclusions:
- Electrochemical oxidation provides a viable route to generate photochromic intermediates.
- This work presents a novel method for electrochemically controlling molecular switches.
- The findings open new avenues for designing advanced functional materials.
Related Concept Videos
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
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
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.
01:17Thermal Electrocyclic Reactions: Stereochemistry
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.
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.
00:53Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)
Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
![[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12417.jpg&w=3840&q=75)
01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.