Azothiophenes as Visible-Light Photoswitches via n-π∗ Excitations

Area of Science:

• Organic Chemistry
• Photochemistry
• Materials Science

Background:

• Selective photoisomerization of azoswitches is crucial for applications.
• Current methods are limited, primarily to ortho-substituted azobenzenes.
• The potential of n-π* band excitation for azoswitches is underexplored.

Purpose of the Study:

• To introduce a novel heteroaryl azo scaffold, azothiophenes, for visible-light photoisomerization.
• To investigate the role of thiophene-2-ester units in promoting n-π* band separation.
• To achieve selective E→Z and Z→E isomerizations using distinct visible light wavelengths.

Main Methods:

• Synthesis of novel azothiophene derivatives with ortho-electron-withdrawing substituents.
• Spectroscopic analysis to characterize n-π* band separation.
• Photoirradiation experiments using green and blue light to induce isomerizations.
• Evaluation of photochromic properties, including switching wavelength, photoconversion yields, and stability.

Main Results:

• Azothiophenes with thiophene-2-ester units exhibit well-separated n-π* bands in the visible-light region.
• Selective E→Z isomerization is achieved with green light, and Z→E isomerization with blue light.
• The azoswitches display significant photochromic characteristics: large absorption separation, long switching wavelengths (up to 549 nm), high photoconversion yields, and prolonged half-lives.
• Excellent stability against reductants was observed.

Conclusions:

• Azothiophenes represent a promising new class of visible-light responsive azoswitches.
• The design principles involving heteroaryl scaffolds and electron-withdrawing groups facilitate selective n-π* excitations.
• This work provides a foundation for advancing visible-light azoswitches through targeted molecular design.