| Autor: |
Banu Öngel, Jörg M. Neudörfl, Axel G. Griesbeck |
| Jazyk: |
angličtina |
| Rok vydání: |
2021 |
| Předmět: |
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| Zdroj: |
Molbank, Vol 2021, Iss 2, p M1226 (2021) |
| Druh dokumentu: |
article |
| ISSN: |
1422-8599 |
| DOI: |
10.3390/M1226 |
| Popis: |
The α-methylated chalcone 3 with an electron-donor substituted A-aryl ring and an unsubstituted B-phenyl ring was synthesized by base-catalyzed aldehyde/acetophenone condensation. Compound 3 can be photo-switched from E→Z by irradiation with long-wavelength light λ > 350 nm, whereas irradiation with shorter wavelengths leads to photo-stationary states (PSS) with lower amounts of the Z-isomer. The limiting wavelength for fully equilibrated E⮀Z (PSS = 1) can be achieved around 240 nm. The stability of both E- and Z-isomers at the wavelength-dependent PSS under UV-irradiation between 250 and 350 nm is remarkably high as observed from UV and NMR spectroscopy. Compound 3 is fatigue resistant even after more than 10 days continuous irradiation and is also oxygenation-stable under singlet oxygen sensitization conditions. In remarkable contrast to many other α-methylated chalcones, no change in the E/Z-ratio was detected when PSS samples were treated with Broensted acids. The negative photochromic E→Z switch of 3 is accompanied by a conformational switch from the E-form in its preferred s-trans conformation to the Z-form in a distorted s-cis conformation (Es-c→Zs-t). |
| Databáze: |
Directory of Open Access Journals |
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