Griesbeck, Axel G., Oengel, Banu, Brullingen, Eric and Renner, Melissa (2021). New Photochromic alpha-Methylchalcones Are Highly Photostable, Even under Singlet Oxygen Conditions: Breaking the alpha-Methyl Michael-System Reactivity by Reversible Peroxybiradical Formation. Molecules, 26 (3). BASEL: MDPI. ISSN 1420-3049
Full text not available from this repository.Abstract
The alpha-methylated chalcones 7a-7e behave as P-type photochromic substances with photo-stationary states (PSS) as high as 15:85 when irradiated at 350 nm. These compounds are easily accessible in pure E-configuration by aldol condensation or by oxidative coupling/elimination. The alpha-methyl groups make these compounds potentially reactive with singlet oxygen following the gem-rule that predicts O-1(2) regioselectivity. Even after long irradiations times in the presence of the singlet oxygen sensitizer tetraphenylporphyrin (TPP) and oxygen, however, no oxygenation products were detected. Under these conditions, all substrates were converted into 9:1 E/Z-mixtures despite the use of low-energy light that does not allow direct or sensitized excitation of the substrates 7. Additionally, chalcone 7a reduced the singlet oxygen reactivity of the tiglic ketone 3a by about a factor of two, indicating substantial physical quenching of singlet oxygen by the alpha-methylated chalcones 7a-7e. Thus, a singlet oxygen-induced E/Z-isomerization involving 1,2-dioxatetra-methylene biradicals that leads to triplet oxygen and thermodynamic E/Z-mixtures is postulated and supported by quantum chemical (DFT)-calculations.
| Item Type: | Journal Article | ||||||||||||||||||||
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| URN: | urn:nbn:de:hbz:38-563453 | ||||||||||||||||||||
| DOI: | 10.3390/molecules26030642 | ||||||||||||||||||||
| Journal or Publication Title: | Molecules | ||||||||||||||||||||
| Volume: | 26 | ||||||||||||||||||||
| Number: | 3 | ||||||||||||||||||||
| Date: | 2021 | ||||||||||||||||||||
| Publisher: | MDPI | ||||||||||||||||||||
| Place of Publication: | BASEL | ||||||||||||||||||||
| ISSN: | 1420-3049 | ||||||||||||||||||||
| Language: | English | ||||||||||||||||||||
| Faculty: | Unspecified | ||||||||||||||||||||
| Divisions: | Unspecified | ||||||||||||||||||||
| Subjects: | no entry | ||||||||||||||||||||
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| URI: | http://kups.ub.uni-koeln.de/id/eprint/56345 |
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