Absorption spectra and photoisomerization quantum yields of azobenzene
redetermined
Vít Ladányi, Ľubica Vetráková, Jamaludin Al Anshori, Pavel Dvořák, Jakob
Wirz, Dominik Heger
Azobenzene is a photochromic molecule existing in two isomeric forms the cis- and trans-
isomers.
N N
N
N
cis-azobenzene trans-azobenzene
h
h
Azobenzene is widely used in various applications for photoswitching e.g., in biochemical
and material science, and as a chemical actinometer. For its best performance, the knowledge
of the correct molar absorption coefficients and its isomerization quantum yields is essential.
Our attempt to apply the azobenzene isomerization for chemical actinometry reviled
inconsistencies in the published values and therefore we redetermined them [1,2].
Pure trans-azobenzene was prepared by warming the solution in darkness and used for
determination of trans-azobenzene molar absorption coefficients at various temperatures (5–
45 °C). The molar absorption coefficients of cis-azobenzene were obtained using three
independent techniques. For these purposes the cis-isomer was prepared by irradiation to the
photostationary state (λirr = 348 nm) to obtain ~97 % cis-isomer and later the kinetic
experiments were utilized to reach the molar absorption coefficients calculations.
Quantum yields of trans–cis and cis–trans photoisomerization in methanol were then
redetermined for the monochromatic irradiation at range of wavelenghts 280–434 nm. The
concentrations were obtained from the analysis of UV-vis spectra performed in Matlab
program. The photon flux was determined by ferrioxalate actinometer. The presentation
compares the obtained results to the previously published data and detail the newly developed
methods for QY determination.
[1] Ľ. Vetráková, V. Ladányi, J. Al Anshori, P. Dvořák, J. Wirz, D. Heger, Photochem. Photobiol. Sci., 2017, 16,
1749-1756.
[2] V. Ladányi, P. Dvořák, J. Al Anshori, Ľ. Vetráková, J. Wirz, D. Heger, Photochem. Photobiol. Sci., 2017, 16,
1757-1761.