Zeolite L Research Articles

The Synthesis of a Large Stokes-Shift Dye and Intercalation into the Nanochannels of Zeolite L.

A host-guest-based fluorescent composite with a large Stokes shift was synthesized by intercalating 2,2'-(thiophene-2,5-diyl)bis(benzo[d]oxazol-6-amine) (BBTA) into the nanochannels of zeolite L (ZL) and sealing the pores with (3-aminopropyl)triethoxysilane (APTES). To confirm the orientation of the amino groups in BBTA, a single crystal of 2,5-bis(6-nitrobenzo[d]oxazol-2-yl)thiophene (BBTN) was grown and examined by X-ray crystallography. The evidence of successful intercalation of BBTA into the nanochannels of ZL was provided by fluorescence spectrometry, gas sorption and fluorescence microscopy. BBTA showed a Stokes shift of 6641 cm-1 (157 nm) in ethanol and 4611 cm-1 (93 nm) in toluene. The BBTA-ZL composite (BBTA-ZL-s) showed a Stokes shift of 5677 cm-1 (123 nm) in toluene, and 5450 cm-1 (124 nm) in ethanol. In addition, the degree of loading was determined and stability against leaching was confirmed. We report the synthesis of this novel composite dye material with potential applications where free dyes are not applicable and which retains a large Stokes shift, independent of its chemical environment.

Sealing of Zeolite L Channels with Ethoxysilanes: Influence of Molecular Structure and Thermal Treatment

AbstractThe suitability of silanes H2N(C3H6)Si(OC2H5)3‐x(CH3)x (x=0, 1, 2) for the sealing of zeolite pores has been investigated. The sealing efficiency was evaluated by observing the exit kinetics of the fluorescent dye resorufin from the one‐dimensional main channels of zeolite L (ZL). The best results in terms of sealing quality were obtained with x=0, indicating the importance of ensuring maximum probability for siloxane bond formation and cross‐linking during the sealing process. The amino group thereby plays a crucial role in the positioning of the silane prior to covalent bond formation. Samples sealed with 3‐aminopropyltriethoxysilane (APTES) showed excellent stability against leaching in aqueous medium even under moderately alkaline conditions. Further evidence for the ability of APTES to efficiently seal the channels of ZL was obtained by nitrogen sorption measurements.

Multiple equilibria describe the complete adsorption isotherms of nonporous, microporous, and mesoporous adsorbents

The adsorption of simple gases begins with the formation of a monolayer on the pristine surface, not always followed by the formation of a second or more monolayers. Subsequently, cluster formation or cavity filling occurs, depending on the properties of the surface. The characteristically different shape of the isotherms related to these processes allows to clearly differentiate them. We analyzed argon and N 2 adsorption isotherms quantitatively over the entire relative pressure range for adsorbents bearing different properties: the nonporous Stöber-type particles, the microporous zeolite L (ZL) and zeolite L filled with indigo (Indigo-ZL), and three mesoporous silica adsorbents of different pore size. The formal equilibria involved in cluster formation and in cavity filling have been derived and successfully applied to quantitatively describe the isotherms of the adsorbents. No indication regarding formation of a second monolayer on top of the first one was observed for the Stöber-type particles. Instead, cluster generation, which minimizes surface tension, starts early. The behavior of microporous ZL and of Indigo-ZL is different. A second monolayer sets up and cluster formation starts with some delay. The enthalpy of cluster formation is, however, practically identical with that seen for the Stöber-type particles. The difference between the experimental and the calculated inflection points is very small. The shapes of the isotherms seen for the mesoporous adsorbents differ significantly from those seen for the nonporous and for the microporous adsorbents. The quantitative analysis of the data proves that formation of a second monolayer is followed by filling of cavities which ends as soon as all cavity sites are filled. The sum of the individual fractional contributions, namely the monolayer formation Θ mL , the appearance of a second monolayer Θ 2L on top of the first one, and the cavity filling Θ cav , yields a calculated adsorption isotherm Θ calc which describes the experimental data Θ exp well. The experimental and the calculated first inflection points are in excellent agreement, which is also the case for the second inflection points. The value of the cavity filling enthalpy is roughly 10% larger than that for the cluster formation seen in the nonporous and the microporous adsorbents. The volume for cavity filling is significantly smaller than the monolayer volume for the mesoporous adsorbent with a pore diameter of 2.7 nm, while it is the same or larger for pore diameters of 4.1 nm and 4.4 nm, respectively. We conclude that understanding the adsorption isotherms as signature of several sequential chemical equilibrium steps provides additional information data for clusters, cavities, and position of the inflection points, not accessible by means of the conventional models. The theory reported herein covers type I, II, IV and to some extent also type VI isotherms. • We analyzed Argon and N 2 adsorption isotherms quantitatively over the entire relative pressure range for adsorbents bearing different properties: the nonporous Stöber-type particles, the microporous zeolite L and zeolite L filled with Indigo (Indigo-ZL), and three mesoporous silica adsorbents of different pore size. • The formal equilibria involved in cluster formation and in cavity filling have been derived and successfully applied to quantitatively describe the isotherms of the adsorbents. • The experimental and the calculated inflection points agree very well for all samples. • Understanding the adsorption isotherms as signature of several sequential chemical equilibrium steps provides otherwise hidden additional information. • The theory reported herein covers type I, II, IV and to some extent also type VI isotherms.

New cryogels based on polymers and zeolite L for controlled Enalapril maleate release

New composite cryogels for controlled release of Enalapril Maleate (EM) were developed based on two biodegradable polymers, poly(vinyl alcohol) (PVA) and pullulan (PU) as polymer matrix, and zeolite L (ZL) as inorganic filler. The cryogels were prepared by freeze-thaw technique using different concentrations of the components, the EM being introduced directly during the cryogel preparation. The samples were characterized by FTIR spectroscopy, scanning electron microscopy and water vapor sorption-desorption isotherms. The presence of PU and ZL in the cryogels led to the modification of FTIR characteristic absorption bands of EM and contributed to the modification of the cryogel morphology. The sample moisture absorption was in the range 5.28–18.20%, determined at a relative humidity RH = 82%. Cryogels based on PVA, PU and ZL components showed a longer EM release period compared to cryogels containing only PVA. The analysis of in vitro EM release kinetics was performed using three predictable models: zero and first order kinetics, and Korsmeyer-Peppas model. Korsmeyer-Peppas model best fitted the release data.

Indigo in the nanochannels of zeolite L: Towards a new type of colorant

A host-guest based colorant was synthesized by intercalating indigo molecules into the nanochannels of zeolite L (ZL). Reductive washing thereby ensured the efficient and selective removal of non-intercalated indigo molecules. The UV-vis diffuse reflectance spectrum of the product after intercalation and reductive washing (designated as indigo-ZL) was found to resemble the solution spectrum of indigo, leading to the conclusion that the formation of indigo aggregates is prevented due to the steric constraints imposed by the microporous structure of ZL. The application of indigo-ZL on cotton was tested by roll coating. The light absorption properties of the resulting textile prints showed no significant alteration when compared to the pure indigo-ZL powder. The UV-vis diffuse reflectance spectra of mixtures consisting of indigo-ZL and a further ZL-based colorant were successfully predicted by the weighted addition of the respective primary spectra.

The spatial distribution of the photostability of thionine in zeolite L nanochannels investigated by Photobleaching Lifetime Imaging Microscopy.

Dye photobleaching is a photochemical reaction that can be investigated locally using fluorescence microscopy techniques. In this study, a user-friendly computational tool to assist photobleaching experiments called Photobleaching Lifetime Imaging Microscopy (PbLIM) is presented. With this tool it is possible to recover the photobleaching kinetics spatially, where a photobleaching lifetime is generated for each pixel of the image. Our model was applied to the photobleaching process of thionine encapsulated into the one-dimensional nano-channels of Zeolite L (ZL), from where we gained insight into the molecular oxygen distribution inside the ZL channels, as well as the detailed photobleaching of the confined thionine.

Supramolecular Organization of Dye Molecules in Zeolite L Channels: Synthesis, Properties, and Composite Materials.

Sequential insertion of different dyes into the 1D channels of zeolite L (ZL) leads to supramolecular sandwich structures and allows the formation of sophisticated antenna composites for light harvesting, transport, and trapping. The synthesis and properties of dye molecules, host materials, composites, and composites embedded in polymer matrices, including two- and three-color antenna systems, are described. Perylene diimide (PDI) dyes are an important class of chromophores and are of great interest for the synthesis of artificial antenna systems. They are especially well suited to advancing our understanding of the structure-transport relationship in ZL because their core fits tightly through the 12-ring channel opening. The substituents at both ends of the PDIs can be varied to a large extent without influencing their electronic absorption and fluorescence spectra. The intercalation/insertion of 17 PDIs, 2 terrylenes, and 1 quaterrylene into ZL are compared and their interactions with the inner surface of the ZL nanochannels discussed. ZL crystals of about 500 nm in size have been used because they meet the criteria that must be respected for the preparation of antenna composites for light harvesting, transport, and trapping. The photostability of dyes is considerably improved by inserting them into the ZL channels because the guests are protected by being confined. Plugging the channel entrances, so that the guests cannot escape into the environment is a prerequisite for achieving long-term stability of composites embedded in an organic matrix. Successful methods to achieve this goal are described. Finally, the embedding of dye-ZL composites in polymer matrices, while maintaining optical transparency, is reported. These results facilitate the rational design of advanced dye-zeolite composite materials and provide powerful tools for further developing and understanding artificial antenna systems, which are among the most fascinating subjects of current photochemistry and photophysics.

Structure of nanochannel entrances in stopcock-functionalized zeolite L composites.

Multifunctional hybrid materials are obtained by modifying zeolite L (ZL) with stopcock molecules, consisting of a tail group that can enter the ZL nanochannels and a head group too large to pass the channel opening. However, to date no microscopic-level structural information on modified ZL materials has been reported. Herein we draw atomistic pictures of channel openings and stopcock-functionalized ZL based on first-principles calculations. We elucidate the interactions of the tail group with the inner surface of ZL channels and the space-filling properties of the stopcocks, revealing cork- or lid-sealing modes. Water is essential to obtain stable modifications. AlOH groups are the preferred modification sites, bipodal modifications suffer from strain, and tripod binding is ruled out. Our results suggest the viability of recursive functionalization by cross-linking.

Structure of Nanochannel Entrances in Stopcock‐Functionalized Zeolite L Composites

AbstractMultifunctional hybrid materials are obtained by modifying zeolite L (ZL) with stopcock molecules, consisting of a tail group that can enter the ZL nanochannels and a head group too large to pass the channel opening. However, to date no microscopic‐level structural information on modified ZL materials has been reported. Herein we draw atomistic pictures of channel openings and stopcock‐functionalized ZL based on first‐principles calculations. We elucidate the interactions of the tail group with the inner surface of ZL channels and the space‐filling properties of the stopcocks, revealing cork‐ or lid‐sealing modes. Water is essential to obtain stable modifications. AlOH groups are the preferred modification sites, bipodal modifications suffer from strain, and tripod binding is ruled out. Our results suggest the viability of recursive functionalization by cross‐linking.

Novel multi-component hybrids through double luminescent lanthanide unit functionalized zeolite L and titania

Zeolite L (ZL) is functionalized with inside-outside double modification paths (gas disperse (“ship in bottle”) and covalently grafting) with two kinds of luminescent lanthanide species (Tb3+ complex of acetylacetone (AA), lanthanide polyoxometalate (NaLnW10O36·32H2O, abbreviated as LnW10, Ln=Eu, Tb)) to prepare the hybrid materials. The prepared hybrids show the red and green luminescence, which provides a useful path to obtain multi-component lanthanide hybrids.

Efficient and Robust Host–Guest Antenna Composite for Light Harvesting

We report discovery of a new efficient and robust antenna composite for light harvesting. The organic dye hostasol red (HR) is strongly luminescent in aprotic solvents but only weakly luminescent in potassium zeolite L (ZL) at ambient conditions. We observed a dramatic increase of the luminescence quantum yield of HR–ZL composites if some or all exchangeable potassium cations of ZL are substituted by an organic imidazolium cation (IMZ+) and if the acceptor HR is embedded in the middle part of the channels, so that it is fully protected by the environment of the perylene dye tb-DXP. This led to the discovery of a highly efficient donor,acceptor-ZL antenna material where tb-DXP acts as donor and HR acts as acceptor. The material has a donor-to-acceptor (D/A) absorption ratio of more than 100:1 and a nearly quantitative FRET efficiency. Synthesis of this host–guest material is reported. We describe a successful procedure for achieving full sealing of the ZL channel entrances such that the guests cannot escap...

Luminescent hybrid materials based on zeolite L crystals and lanthanide complexes: Host–guest assembly and ultraviolet–visible excitation

Several kinds of host–guest hybrid materials have been synthesized employing a ship in a bottle method by loading 9-hydroxy-2-methylphenalenone (MHPO) or 9-hydroxyphenalen (HPNP) from gas phase into the nanochannels of Ln3+-exchanged zeolite L (ZL) crystals (Ln=Gd or Eu). The resulting hybrids without lanthanide ions, MHPO–ZL, HPNP–ZL and the hybrids with lanthanide ions Ln–MHPO–ZL and Ln–HPNP–ZL are characterized with FT-IR, UV–vis DRS and photoluminescence spectroscopy. The photoluminescence properties of these hybrid materials have been analyzed and discussed, exhibiting the luminescence of Eu3+ and ligands under the excitation at ultraviolet–visible region. These results provide useful data and can be expected to have potential application in the practical fields.

Novel cool white-luminescent hybrids through host–guest assembly of 6-hydroxybenz[de]anthracen-7-one and europium ion exchanged zeolite L

Zeolite L (ZL) is functionalized with europium ions through ion exchange and then 6-hydroxybenz[de]anthracen-7-one (HBAO) ligand is fabricated with coordination to Eu3+ by a so-called gas disperse (so-called ship-in-bottle) method. It is worthy pointing out that the europium hybrids show emission of both europium ion and HBAO, which can be integrated to show close white luminescence. This result provides a useful path to obtain white emissive lanthanide hybrids.

Orientation and Order of Xanthene Dyes in the One-Dimensional Channels of Zeolite L: Bridging the Gap between Experimental Data and Molecular Behavior

Supramolecular organization in nanochannels is governed by both the nature of the channels and the size, shape, and charge of the guests, and may also depend on the cosolvent in the host. Oxonine (Ox+) and pyronine (Py+) cationic dyes in zeolite L (ZL) could provide important insight on this issue, but their orientation in the composite materials is not understood yet. Theoretical modeling of Ox+/ZL and Py+/ZL composites indicates that the 70–80° orientation, deduced from optical microscopy data but incompatible with host–guest geometry contraints, is not stable and reveals two possible orientations for these dyes in ZL nanochannels: perpendicular or parallel to the channel axis. In the hydrated composite, corresponding to optical microscopy experiments conditions, perpendicular Ox+/Py+ is the favored orientation, suggesting a larger portion of perpendicularly oriented dye molecules and a smaller fraction aligned. Optical microscopy data might therefore be reinterpreted as the vector sum of components ari...

Nanochannels: Hosts for the Supramolecular Organization of Molecules and Complexes

Nanochannels have been used as hosts for supramolecular organization for a large variety of guests. The possibilities for building complex structures based on 2D and especially 3D nanochannel hosts are larger than those based on 1D nanochannel hosts. The latter are, however, easier to understand and to control. They still give rise to a rich world of fascinating objects with very distinguished properties. Important changes are observed if the channel diameter becomes smaller than 10 nm. The most advanced guest-nanochannel composites have been synthesized with nanochannels bearing a diameter of about 1 nm. Impressive complexity has been achieved by interfacing these composites with other objects and by assembling them into specific structures. This is explained in detail. Guest-nanochannel composites that absorb all light in the right wavelength range and transfer the electronic excitation energy via FRET to well-positioned acceptors offer a unique potential for developing FRET-sensitized solar cells, luminescent solar concentrators, color-changing media, and devices for sensing in analytical chemistry, biology, and diagnostics. Successful 1D nanochannel hosts for synthesizing guest-host composites have been zeolite-based. Among them the largest variety of guest-zeolite composites with appealing photochemical, photophysical, and optical properties has been prepared by using zeolite L (ZL) as a host. The reasons are the various possibilities for fine tuning the size and morphology of the particles, for inserting neutral molecules and cations, and for preparing rare earth complexes inside by means of the ship-in-a-bottle procedure. An important fact is that the channel entrances of ZL-based composites can be functonalized and completely blocked, if desired, and furthermore that targeted functionalization of the coat is possible. Different degrees of organizational levels and prospects for applications are discussed, with special emphasis on solar energy conversion devices.

Self-Assembling Zeolite Crystals into Uniformly Oriented Layers

We report important progress made in the synthesis of oriented functional layers of nanochannel materials by using coordination chemistry as a tool. Zeolite L (ZL) crystals have been arranged into oriented layers through the coordinative interactions between a functional organic linker (L) and metal cations used for connecting the different parts. As organic linker we used a terpyridyl ligand bearing a urea group and a reactive siloxane part. Two strategies that lead to monolayers with different properties are described. The first consists of reacting the siloxane group of ligand L with OH groups of the substrate (S), and selectively reacting the siloxane group of L with OH groups located at the base of the ZL crystals. Next, metal cations M(n+), for example, Zn(2+) or Cu(2+), are coordinated to the terpy group on the modified substrate. To this the modified ZL is added and coordinatively bound by the terpy(Mn(n+))terpy interaction, leading to oriented ZL layers. The second method consists of reacting substrate S and ligand L in the presence of a metal cation. A layer with reactive siloxane groups is formed on S to which the ZL crystals are bound by the reaction of the hydroxyl groups of their base. Zn(2+), Cu(2+), and lanthanide ions Eu(3+) and Tb(3+)have been tested successfully, all of them leading to high-quality ZL monolayers with open channels, accessible for accepting guests, oriented perpendicularly with respect to the surface of S.

Interactions of Perylene Bisimide in the One-Dimensional Channels of Zeolite L

Supramolecularly organized host guest systems have been prepared by inserting three perylene dyes with differing end substituents into the nanosized channels of zeolite L (ZL) by gas-phase adsorption under vacuum conditions. The end substituents allowed controlling the core-to-core distances of the molecules in the channels. The three perylene dyes investigated have very similar absorption and fluorescence spectra in diluted solutions, as well as fluorescence lifetimes ∼ 4 ns. Large ZL crystals in the size range of 1500−3000 nm in length and about 1000 nm in diameter as well as nanosized NZL crystals of about 30 nm in length and diameter were used as hosts. Different loadings have been investigated. The photophysical properties of the materials were analyzed as suspensions in refractive index matching solvents, such as toluene or ethyl benzoic acid ester; as bulk materials in glass ampules; and by means of time-, space-, and spectrally resolved single-crystal fluorescence microspectrocopy techniques. The inserted dyes can form J-aggregates if the structure of the perylene derivative allows for short distances between the electronic transition moments in an in-line arrangement. J-coupling was not seen for the molecules with substituents that keep them further apart. Aligned and stabilized J-aggregates in one-dimensional channels provide new options for preparing optical devices, where coherent exciton delocalization over nanometer-to-micrometer scales may result in efficient photonic wires. The exciton coupling can be controlled by varying the molecular tail groups.

Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping

We discuss artificial photonic antenna systems that are built by incorporating chromophores into one-dimensional nanochannel materials and by organizing the latter in specific ways. Zeolite L (ZL) is an excellent host for the supramolecular organization of different kinds of molecules and complexes. The range of possibilities for filling its one-dimensional channels with suitable guests has been shown to be much larger than one might expect. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The arrangement of dyes inside the ZL channels is what we call the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also the radiationless transport of energy to either the channel ends or center. One-dimensional FRET transport can be realized in these guest-host materials. The second stage of organization is realized by coupling either an external acceptor or donor stopcock fluorophore at the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate. A possibility to achieve higher levels of organization is by controlled assembly of the host into ordered structures and preparation of monodirectional materials. The usually strong light scattering of ZL can be suppressed by refractive-index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials. The concepts are illustrated and discussed in detail on a bidirectional dye antenna system. Experimental results of two materials with a donor-to-acceptor ratio of 33:1 and 52:1, respectively, and a three-dye system illustrate the validity and challenges of this approach for synthesizing dye-nanochannel hybrid materials for light harvesting, transport, and trapping.

Transparent, luminescent, and highly organized monolayers of zeolite L

Herein we report on the fabrication of very dense, highly homogenous, well-oriented and highly organized luminescent monolayers by arranging zeolite L (ZL) microcrystals onto the multi-functional linker modified quartz plates. ZL microcrystals readily assemble in the form of a c-oriented monolayer with perfect coverage and close packing on the 2-thenoyltrifluoroacetone (TTA)-functionalized quartz plates. Additional functionalization through coordination to Eu3+ ions to the TTA moieties leads to ZL monolayers with very high quality exhibiting strong luminescence. Alternatively, the luminescence color of the layers is fine tuned by arranging ZL microcrystals with Tb3+ ions and sensitizer loaded in the nanochannels on the luminescent quartz plates. Transparent, luminescent and uniformly oriented layers are obtained by coating the polymer of PVA on top of the ZL monolayers in a facile way. SEM and photoluminescence spectroscopy were employed to characterize the oriented monolayers.

Surprising Properties of a Furo‐Furanone

The electronic absorption, fluorescence, and excitation spectra of furo[3,4-c]furanone (1) have been measured in different solvents at different concentrations. We observed a complex dependence of absorption and excitation spectra as a function of the concentration in CH(2)Cl(2) and THF due to aggregate formation. Interestingly, the fluorescence spectra were not affected. Resolving the puzzle was made possible by the fact that 1 fits perfectly into the channels of zeolite L (ZL) microcrystals to form 1-ZL guest-host composites. The geometry of the ZL channel system ensures a well-defined orientation of the embedded dye molecules, thereby leading to a preferred orientation of their electronic transition dipole moment (ETDM) and thus to objects with pronounced optical anisotropy properties. This enabled us to understand that in solution the monomers that are present at low concentration form an aggregate in which the molecules sit on top of each other and arrange into a J-type aggregate configuration at higher concentrations. The signature of the latter is observed in the 1-ZL composites. This seems to be the first example in which the insertion of molecules into a nanochannel microcrystal has helped in understanding the weak intermolecular interactions that take place in solution.