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Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

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Visible Light [2 + 2] Cycloadditions of Thermoresponsive Dendronized Styryltriazines To Exhibit Tunable

Sijie Zhou¹, Mengjie Zhang¹, Yue Yuan¹

¹International Joint Laboratory of Biomimetic and Smart Polymers, School of Materials Science and Engineering, Shanghai University, Nanchen Street 380, Shanghai 200444, China.

ACS Macro Letters

|June 27, 2024

Summary

This study introduces visible light-induced, catalyst-free cycloadditions of thermoresponsive dendronized styryltriazines in water. These molecules create tunable microenvironments for dyes and enable light-triggered release, offering eco-friendly material design.

Area of Science:

Supramolecular Chemistry
Photochemistry
Materials Science

Background:

Visible light photochemistry offers eco-friendly routes for molecular modification.
Catalyst-free reactions in aqueous media are desirable for sustainable chemistry.
Thermoresponsive polymers and dendrimers enable tunable material properties.

Purpose of the Study:

To develop visible light-induced, catalyst-free [2+2] cycloadditions of thermoresponsive dendronized styryltriazines.
To investigate the formation of tunable microenvironments for guest molecules in aqueous media.
To explore the light-triggered release of encapsulated dyes.

Main Methods:

Synthesis of dendronized styryltriazines with oligoethylene glycol (OEG) pendants.
Visible light (400 nm) irradiation to induce [2+2] cycloaddition reactions in water.
Characterization of thermoresponsive properties and microenvironment formation using solvatochromic dyes.

Main Results:

Efficient catalyst-free [2+2] cycloadditions of dendronized styryltriazines were achieved under visible light.
Dendronized structures exhibited tunable thermoresponsive behavior with phase transition temperatures between 36-65 °C.
Encapsulation of Nile red within tunable microenvironments led to variable photophysical properties, with light-induced release observed.

Conclusions:

Dendronized styryltriazines are effective building blocks for photoresponsive and thermoresponsive materials in aqueous systems.
The tunable microenvironments created can modulate guest molecule properties and enable controlled release.
This work presents a sustainable approach for designing smart materials using visible light.

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Cycloaddition Reactions: MO Requirements for Thermal Activation

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Cycloaddition 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.

Cycloaddition Reactions: Overview

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

[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.

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical 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

Thermal Electrocyclic Reactions: Stereochemistry

Thermal 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.

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