Ultrafast Spectroscopy of Hydroxy-Substituted Azobenzenes in Water.
Ultrafast UV/Vis pump/probe experiments on ortho-, meta- and para-hydroxy-substituted azobenzenes (HO-ABs), as well as for sulfasalazine, an AB-based drug, were performed in aqueous solution. For meta-HO-AB, AB-like isomerisation behaviour can be observed, whereas, for ortho-HO-AB, fast proton transfer occurs, resulting in an excited keto species. For para-HO-AB, considerable keto/enol tautomerism proceeds in the ground state, so after excitation the trans-keto species isomerises into the cis form. Aided by TD-DFT calculations, insight is provided into different deactivation pathways for HO-AB, and reveals the role of hydroxy groups in the photochemistry of ABs, as well as their acetylation regarding sulfasalazine. Hydroxy groups are position-specific substituents for AB, which allow tuning of the timescale of thermal relaxation, as well as the amount and contribution of the keto species to photochemical processes.
Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Sabrina
S
Steinwand
Institute for Organic Chemistry and Chemical Biology, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Thomas
T
Halbritter
Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Dominique
D
Rastädter
Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Juan Manuel
JM
Ortiz-Sánchez
Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Irene
I
Burghardt
Institute for Organic Chemistry and Chemical Biology, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany).
Alexander
A
Heckel
Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt (Germany). wveitl@theochem.uni-frankfurt.de.
Josef
J
Wachtveitl
azobenzenes; photochemistry; tautomerism; time-resolved spectroscopy; water chemistry