Erlangen 2022 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 14: Photochemistry II

MO 14.1: Vortrag

Mittwoch, 16. März 2022, 14:30–14:45, MO-H6

Studying the photodynamics of a formazan in binary solvent mixtures — •Svenja Wortmann, Sylvia Schloeglmann, and Patrick Nuernberger — Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93040 Regensburg

1,3,5-Triphenylformazan (TPF) contains an azo group and a hydrazone group, of which both can isomerize upon excitation with visible light. Therefore, TPF can exist in different isomeric forms, which can be converted into each other accompanied by a color change of the solution [1,2]. The ratio of the present formazan isomers and their thermal stability are dependent on the solvent environment and the illumination conditions. Thus, we studied the photodynamic behavior of TPF in toluene solution and with additional admixtures of protic and aprotic cosolvents with transient absorption spectroscopy on different time scales. Especially, the thermal back-isomerization around the C=N double bond shows a high sensitivity regarding the binary solvent mixtures. Finally, it was possible to elucidate the role of solvent polarity as well as the impact of hydrogen bonding. Whereas an increased solvent polarity of the binary mixture results in a decreased activation barrier, hydrogen bonding may have the contrary effect on the thermal back-relaxation. Hence, both hydrogen-bond donors and acceptors as cosolvents can slow the isomerization reaction of TPF [3].

[1] R. Kuhn, H.M. Weitz, Chem. Ber. 86, 1199-1212 (1953)

[2] U.-W. Grummt, H. Langbein, J. Photochem. 15, 329-334 (1981)

[3] S. Wortmann, S. Schloeglmann, P. Nuernberger, J. Org. Chem. (2021), DOI:10.1021/acs.joc.1c01928.