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  • HU Berlin  (5)
  • Heinrich-Mann-Bibl. Strausberg
  • 2020-2024  (5)
  • Berger, Fabian  (5)
  • 1
    UID:
    b3kat_BV048641574
    Format: XV, 18, 10, 19-48, 10, 49-72, 2, 73-106, 24, 107-114 Seiten , Illustrationen, Diagramme (überwiegend farbig)
    Note: Tag der mündlichen Prüfung: 17.12.2021 , Dissertation Humboldt-Universität zu Berlin 2021 , Zusammenfassung englisch und deutsch
    Language: English
    Keywords: Heterogene Katalyse ; Komplexes System ; Zeolith ; Freie Energie ; Hochschulschrift
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  • 2
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin
    UID:
    edochu_18452_24650
    Format: 1 Online-Ressource (5 Seiten)
    Content: Dimerization of linear butenes and pentenes at zeolitic Brønsted acid sites yields, rather than branched alkenes, alkanes featuring a cyclohexane ring. The absence of any C=C double bond in the latter explains not only the observed change of the IR spectra, but also the observation that oligomerization stops at the dimer. Quantum chemical evidence is produced to show that dimerization of linear butenes and pentenes at zeolitic Brønsted sites in H-MFI yields alkanes featuring cyclohexane rings rather than branched alkenes. The absence of any C=C double bond in the formed cyclic alkane explains the observations that oligomerization stops at the dimer. The calculated reaction enthalpies for the dimerization of 2-pentene in the gas phase are −84 kJ mol−1 for branched alkenes, but −153 and −154 kJ mol−1 for alkyl-cyclopentane and -hexane, respectively. Together with calculated adsorption enthalpies of the dimers, −111 and −127 kJ mol−1, respectively, this implies surface dimer formation enthalpies of −264 and −281 kJ mol−1, respectively, in close agreement with the experimental value of −285 kJ mol−1. In contrast, the predicted enthalpy for formation of branched alkoxides, −198 kJ mol−1, deviates by 87 kJ mol−1 from experiment. Calculated IR spectra for the Brønsted OH group show the observed conversion of the band at approximately 3000 cm−1 (hydrogen bond with alkene) to a less intense band at approximately 3450–3500 cm−1 ( interaction with alkane ).
    Content: Peer Reviewed
    In: Weinheim : Wiley-VCH, 60,7, Seiten 3529-3533
    Language: English
    URL: Volltext  (kostenfrei)
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  • 3
    UID:
    edochu_18452_22784
    Format: 1 Online-Ressource (5 Seiten)
    Content: Proton‐responsive photochromic molecules are attractive for their ability to react on non‐invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero‐atoms, which are orthogonal to the photo‐active π‐center. Here, we incorporate azulene, an acid‐sensitive pure hydrocarbon, into the skeleton of a diarylethene‐type photoswitch. The latter exhibits a novel proton‐gated negative photochromic ring‐closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero‐atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its π‐system, supported by 1H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non‐alternant hydrocarbons into photochromic systems for the development of multi‐responsive molecular switches.
    Content: Peer Reviewed
    In: Weinheim : Wiley-VCH, 59,42, Seiten 18532-18536
    Language: English
    URL: Volltext  (kostenfrei)
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  • 4
    UID:
    edochu_18452_27713
    Format: 1 Online-Ressource (5 Seiten)
    ISSN: 1433-7851 , 1521-3773 , 1433-7851 , 1521-3773
    Content: The location of Brønsted-acid sites (bridging OH groups, b-OH) at different crystallographic positions of zeolite catalysts influences their reactivity due to varying confinement. Selecting the most stable b-OH conformers at each of the 12 T-sites (T=Si/Al) of H-MFI, a representative set of 26 conformers is obtained which includes free b-OH groups pointing into the empty pore space and b-OH groups forming H-bonds across five- or six-membered rings of TO4 tetrahedra. Chemically accurate coupled-cluster-quality calculations for periodic models show that the strength of internal H-bonds and, hence, the OH bond length vary substantially with the framework position. For 11 of the 19 H-bonded b-OH groups examined, our predictions fall into the full width at half maximum range of the experimental signals at 3250±175 cm−1 and 7.0±1.4 ppm which supports previously debated assignments of these signals to H-bonded b-OH sites.
    Content: Peer Reviewed
    In: Weinheim : Wiley-VCH, 62,25, 1433-7851
    In: 1521-3773
    Language: English
    URL: Volltext  (kostenfrei)
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  • 5
    UID:
    edochu_18452_27028
    Format: 1 Online-Ressource (6 Seiten)
    Content: Auf Protonen ansprechende photochrome Moleküle sind aufgrund ihrer Fähigkeit, auf nicht-invasive schnelle optische Stimuli zu reagieren, und wegen der ubiquitären Bedeutung von Protonierungs- und Deprotonierungsprozessen, sehr interessant. Üblicherweise befinden sich die sauren/basischen Stellen dieser Moleküle an Heteroatomen, die orthogonal zum photoaktiven π-Zentrum ausgerichtet sind. In dieser Arbeit wird Azulen, ein protonensensitiver reiner Kohlenwasserstoff, in das Gerüst eines Diarylethen-Photoschalters eingebaut. Dieser zeigt einen bisher ungekannten, protonenvermittelten, negativ photochromen Ringschluss. Veränderungen seiner optischen Eigenschaften durch Protonierung, sowohl in der offenen, als auch in der geschlossenen Form, sind viel ausgeprägter als die von Diarylethen-Photoschaltern mit Säure/Base-Gruppen auf Heteroatombasis. Das einzigartige Verhalten des neuen Photoschalters kann auf die direkte Protonierung seines π-Systems zurückgeführt werden, was sowohl durch 1H-NMR als auch durch theoretische Berechnungen belegt wird. Unsere Ergebnisse zeigen das große Potenzial der Einbindung nicht-alternierender Kohlenwasserstoffe in photochrome Systeme für die Entwicklung von molekularen Schaltern, die auf unterschiedliche Stimuli reagieren.
    Content: Peer Reviewed
    In: Weinheim : Wiley-VCH, 132,42, Seiten 18690-18695
    Language: German
    URL: Volltext  (kostenfrei)
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