Supramolecular Structure and Dynamics of Organic Molecules Adsorbed on the External Surface of MFI Zeolites. A Direct and Indirect Computational EPR Analysis

Ottaviani, M. Francesca; Lei, Xuegong; Liu, and Zhiqiang; Turro, Nicholas J.

doi:10.1021/jp011110a

Cited by 17 publications

(21 citation statements)

References 26 publications

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“…A similar effect has also been observed for MFI zeolite 37. 38 This difference is illustrated in Figure 9 where three different equilibria are shown. The insertion equilibrium A has already been discussed.…”

Section: Synthesissupporting

confidence: 73%

Host–Guest Antenna Materials

et al. 2003

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The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.

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Section: Synthesissupporting

confidence: 73%

Host–Guest Antenna Materials

et al. 2003

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“…Über eine ähnliche Eigenschaft wurde in Arbeiten zum MFI‐Zeolithen berichtet 37. 38 Die auftretenden Prozesse sollen anhand der in Abbildung 9 dargestellten Gleichgewichte erläutert werden: Die Adsorption auf der äußeren Oberfläche ist zumeist der erste Schritt einer Einbaureaktion. Wir kennen bislang keinen Fall, bei dem die Adsorption wie in B dargestellt spezifisch auf der Mantelfläche erfolgt.…”

Section: Synthesenunclassified

Wirt‐Gast‐Antennenmaterialien

et al. 2003

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Wir stellen Wirt‐Gast‐Materialien vor, aufgebaut aus zylindrischen Zeolith‐L‐Kristallen, deren Kanäle mit Farbstoffmolekülen gefüllt sind. Die Synthese dieser Stoffe beruht auf der Eigenschaft der Moleküle, in einzelne Kanäle zu diffundieren. Der umgekehrte Prozess, das Herausdiffundieren der Farbstoffe, kann mithilfe eines molekularen “Korkens” unterdrückt werden. Durch Funktionalisierung dieser zapfenförmigen Moleküle lassen sich Eigenschaften wie Benetzbarkeit, Brechungsindex und chemische Reaktivität einstellen. Die supramolekulare Organisation der Farbstoffe innerhalb der Kanäle entspricht einer ersten Organisationsstufe. Damit gelingt es, Licht im Volumen eines Nanokristalls zu sammeln und Anregungsenergie strahlungslos an die Enden des Zylinders oder umgekehrt von dort zur Mitte zu transportieren. Eine zweite Organisationsstufe ist die Kupplung an einen externen Acceptor‐ oder Donor‐Zapfenfluorophor an den Kanalenden, der elektronische Anregungsenergie abfängt oder einspeist. Die dritte, zum Teil noch hypothetische Stufe umfasst die Kupplung an eine externe Funktionseinheit über Zapfenmoleküle. Die Abstimmbarkeit dieser hochorganisierten Materialien bietet attraktive Möglichkeiten zur Untersuchung von elektronischen Energieübertragungsphänomenen und zur Entwicklung von neuen photonischen Funktionseinheiten.

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“…The mean crystal diameter was 0.5 µm, as characterized by scanning electron microscopy. The external surface area was determined by EPR spectroscopy (spin probe: 2,2,6,6-tetramethyl-4-[(phenylacetyl)oxy]-1-piperidinyloxy) 19 to be 20 m 2 g Ϫ1 .…”

Section: Experimental Materialsmentioning

confidence: 99%

In situ EPR investigation of the addition of persistent benzyl radicals to acrylates on ZSM-5 zeolites. Direct spectroscopic detection of the initial steps in a supramolecular photopolymerization

Lei

Jockusch

Ottaviani

et al. 2003

Photochem Photobiol Sci

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Photolysis of dibenzyl ketone derivatives adsorbed on ZSM-5 zeolites produces persistent benzyl radicals (initiator radicals), which add to methyl acrylates (monomers) to generate persistent adduct radicals. Both initiator and adduct radicals are readily observable by conventional steady-state EPR spectroscopy at room temperature and are persistent for time periods ranging from seconds to many days. The rate of the formation and the amount of the adduct persistent radical formed depends on the structure of the initiator radical (benzyl radical derivative) and the structure of the monomer (acrylate derivative). The lifetimes of the initiator and adduct radicals depend on the supramolecular structure of the radical@zeolite complex and the diffusion and reaction dynamics of the radicals in the complex. The most intense signal and highest addition rate to methyl acrylate were observed for the smallest initiator radical, the benzyl radical, because of its high mobility and relatively rapid diffusion within the internal zeolite surface. With increasing length of an alkyl chain (methyl, ethyl, and pentyl) on either the initiator (alpha position of the radical) or monomer (alkyl group of acrylate ester), the rate of radical addition to the monomer decreased, a result that is consistent with the decreased mobility and diffusion of the initiator radical or monomer. Deuterium isotope experiments and variation of the methyl acrylate concentration demonstrated that the initial adduct radical from methyl acrylate adds to another methyl acrylate to generate a secondary adduct radical, which, in turn, can continue to propagate to form a polymer that is cross-linked to the zeolite crystals. The results demonstrate that EPR can be a powerful tool for the direct in situ analysis of supramolecular photochemistry involving radicals rendered persistent by supramolecular steric effects. The latter eliminate the need for sophisticated flash photolysis equipment to investigate the structure and dynamics of reactive radicals and require only the use of simpler steady-state lamps.

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Supramolecular Structure and Dynamics of Organic Molecules Adsorbed on the External Surface of MFI Zeolites. A Direct and Indirect Computational EPR Analysis

Cited by 17 publications

References 26 publications

Host–Guest Antenna Materials

Host–Guest Antenna Materials

Wirt‐Gast‐Antennenmaterialien

In situ EPR investigation of the addition of persistent benzyl radicals to acrylates on ZSM-5 zeolites. Direct spectroscopic detection of the initial steps in a supramolecular photopolymerization

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