Absorption spectra and photoisomerization quantum yields of azobenzene re-determined

Vít Ladányi, Ľubica Vetráková, Jamaludin Al Anshori, Pavel Dvořák, Jacob Wirz, Dominik Heger


Azobenzene is a photochromic molecule existing in two isomeric forms the cis- and trans- isomers.

It is widely used in various applications for photoswitching e. g. in biochemical and material
science. 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
redetemined them.

Pure trans-azobenzene was prepared by warming the solution in the dark and used for determination
of trans-azobenzene molar absorption coefficients at various temperatures (5–45 °C). The molar
absorption coefficients of cis-azobenzene were determined using three independent techniques. For
these purposes the cis-isomer was prepared by irradiation to the photostationary state (λ[irr]
= 348 nm) to obtain ~97 % cis-form 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
re-determined 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 poster will compare the obtained
results to the previously published data and detail the newly developed methods for QY
determination.