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Photoisomerization of azo-derivatives: the effect of protonation
Wann 26.05.2020
von 11:00 bis 12:00
Wo Zoom-Meeting
Teilnehmer Universitätsoffen / open to university members
Termin übernehmen vCal

Photoisomerization of azo-derivatives:
the effect of protonation

One of the most used organic chromophores for optical switching applications are azobenzenes. Azobenzenes exhibit a reversible isomerisation process between its trans and cis isomers of different stability. After a photochemical conversion, the spontaneous thermal back reaction occurs. While the photoinduced trans-to-cis isomerisation reaction can be performed in a few femtoseconds, the rate of the thermal cis-to-trans back reaction depends greatly on the chemical architecture of the system and the environment [1]. While slow thermally back-isomerising azoderivatives are valuable photoactive basic materials for information storage purposes, transmitting at the molecular scale with response times within the nanosecond or picosecond range will enable the potential application of azobenzene-based materials in micropumps and autonomous valves. Novel absorption spectroscopy experiments have shown that the rate of thermal back-isomerization is strongly dependent on pH [2]. With the purpose of understanding the mechanism underlying the isomerization and the changes in reaction paths and energy barriers due to protonation, in collaboration with the group of Andreas Walther from the Institute of Macromolecular Chemistry in Freiburg, we investigated the protonation sites of an azo-derivative (Arylazopyrazole structure (AAP)). Large effects on back reaction rates were observed experimentally. We computationally explored the relative energy profiles for the isomerization along the CNNC-dihedral angle of unprotonated and protonated AAP to give insight into experimental findings. The precise calculations enable to predict the properties of newly designed molecular photoswitches, which represents a timesaving alternative to laborious synthetic efforts.

M. Ari (Institute of Physics, University of Freiburg, Germany), S. Kalthoum  (Institute of Physics, University of Freiburg, Germany), and M. Walter (Fraunhofer IWM, MikroTribologie Centrum TC, Freiburg, Germany )

[1] Beilstein J. Org. Chem. 2012, 8, 1003.
[2] J. Phys. Chem. A 2009, 113, 13144