The absorption spectrum of cis-azobenzene

Area of Science:

• Photochemistry
• Spectroscopy
• Physical Chemistry

Background:

• Azobenzene is a key photochromic molecule with two isomers.
• Accurate molar absorption coefficients (ε) are vital for its photochemical applications.
• Previous studies reported contaminated spectra for pure azobenzene isomers.

Purpose of the Study:

• To re-determine the absorption spectra and molar absorption coefficients (ε) of trans- and cis-azobenzene.
• To establish precise values for accurate spectrophotometric analysis.
• To provide a foundation for revising previously reported quantum yields.

Main Methods:

• Re-determination of azobenzene isomer absorption spectra in methanol across a temperature range (5-45 °C).
• Preparation of trans-azobenzene via thermal isomerization.
• Utilizing three methods for cis-azobenzene spectrum determination, including derivative spectra subtraction and global analysis.
• Comparison with ¹H-NMR determined isomeric ratios.

Main Results:

• Accurate molar absorption coefficients (ε) for both trans- and cis-azobenzene were established.
• Demonstrated high precision in spectrophotometric species analysis of azobenzene mixtures using new ε values.
• Identified mutual contamination in previously reported spectra of pure azobenzene isomers.

Conclusions:

• The re-determined molar absorption coefficients (ε) are essential for accurate azobenzene research.
• New ε values necessitate revision of previously reported quantum yields.
• The methodologies are applicable to other photochromic systems and azobenzene derivatives.