Photochromic Phenoxyl-Imidazolyl Radical Complex via Homolytic C-O Bond Cleavage
Daisuke Tanaka1, Shunsuke Kobashi1, Hiroaki Yamashita2
1Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
The Journal of Physical Chemistry Letters
|July 28, 2025
Summary
Researchers developed a novel photochromic phenoxyl imidazolyl radical complex (PIC) that rapidly switches states. This new molecular system demonstrates tunable photochromic kinetics for faster molecular switching applications.
Area of Science:
- Photochemistry
- Molecular Engineering
- Materials Science
Background:
- Photochromic materials undergo reversible changes in color or other properties upon light exposure.
- Phenoxyl imidazolyl radical complexes (PICs) are known photochromic systems, but their switching speed can be limited.
- Controlling bond dissociation and isomerization pathways is crucial for optimizing photochromic performance.
Purpose of the Study:
- To synthesize and characterize a new photochromic phenoxyl imidazolyl radical complex (PIC).
- To investigate the mechanism and kinetics of UV-induced C-O bond cleavage and subsequent isomerization.
- To demonstrate how structural modifications can accelerate the photochromic switching process.
Main Methods:
- Synthesis of a novel photochromic phenoxyl imidazolyl radical complex (PIC).
- Ultrafast transient absorption spectroscopy to study excited-state dynamics.
- Time-resolved infrared absorption spectroscopy to confirm biradical character and isomer equilibrium.
Main Results:
- The new PIC exhibits reversible homolytic C-O bond cleavage upon UV irradiation.
- Nanosecond spectral evolution indicates rotational isomerization between two open-form isomers.
- The thermal back-reaction is ~1000 times faster than conventional PICs due to phenoxyl unit modifications.
Conclusions:
- Rational control over bond dissociation geometry is key to tuning photochromic kinetics.
- The developed PIC offers a significant acceleration in switching speed compared to previous systems.
- This work presents a novel strategy for designing fast-switching molecular systems for advanced applications.
Related Concept Videos
00:54Radical Formation: Homolysis
3.7K
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
3.7K
00:51Radical Formation: Elimination
1.9K
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions...
1.9K
01:20Radical Autoxidation
2.2K
The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
2.2K
01:17Oxidation of Phenols to Quinones
3.5K
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...
3.5K
01:11Radical Reactivity: Overview
2.2K
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
2.2K
01:03Radical Formation: Overview
2.2K
A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
2.2K