Wortmann, Svenja and Schloeglmann, Sylvia and Nuernberger, Patrick (2022) Sensitivity of Isomerization Kinetics of 1,3,5-Triphenylformazan on Cosolvents Added to Toluene. JOURNAL OF ORGANIC CHEMISTRY, 87 (3). pp. 1745-1755. ISSN 0022-3263, 1520-6904
Full text not available from this repository. (Request a copy)Abstract
Formazan molecules exhibit photochromism because isomerization processes following excitation may occur in both the azo group and the hydrazone group; thus, each formazan may be present in various forms with different colors. The ratio of these forms depends on the illumination conditions and the environment of the formazan with a most incisive sensibility of the thermal anti-syn relaxation of the C=N toward slight traces of impurities in toluene solutions, as reported most prominently for 1,3,5-triphenylformazan. Here, we study the latter compound with transient absorption spectroscopy to investigate the role of these traces by adding small amounts of both protic and aprotic cosolvents. Whereas the activation barrier decreases if the binary solvent mixture has a higher polarity, the role of hydrogen bonding can have a reverse impact on the thermal isomerization rate. Both the addition of an aprotic cosolvent and the addition of a protic cosolvent can slow the reaction due to their hydrogen-bond accepting and hydrogen-bond donating properties, respectively. In the case of methanol as a cosolvent, this effect outweighed that of the polarity increase for small concentrations, which was not observed for the fluorinated alcohol hexafluoroisopropanol. The results are explained in the context of a competition between solute-cosolvent and cosolvent-cosolvent hydrogen bonding.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | CURCUMIN EXCITED-STATE; PICOSECOND SPECTRAL RELAXATION; SOLVENT MIXTURES ROLE; ULTRAFAST PHOTOISOMERIZATION; INFRARED-SPECTROSCOPY; COLORIMETRIC ASSAY; FORMAZAN; DERIVATIVES; ABSORPTION; ACIDITIES; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Physical Chemistry I > Prof. Dr. Patrick Nürnberger |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 14 Nov 2023 14:17 |
| Last Modified: | 14 Nov 2023 14:17 |
| URI: | https://pred.uni-regensburg.de/id/eprint/56755 |
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