(1<i>R</i>,2<i>S</i>)‑Ephedrine: A New Self-Assembling Chiral Template for the Synthesis of Aluminophosphate Frameworks

(1<i>R</i>,2<i>S</i>)-(−)-Ephedrine is used as a new structure-directing agent for the synthesis of nanoporous aluminophosphates. This molecule is selected based on the self-aggregating behavior through π–π type interactions between the aromatic rings and the presence of H-bond-forming groups. Additionally, this molecule possesses two chiral centers, which could enhance a potential transfer of chirality to the inorganic framework. Synthesis results showed that (1<i>R</i>,2<i>S</i>)-(−)-ephedrine is very efficient in directing the crystallization of the AFI-type structure in the presence of several catalytically active dopants. A combination of fluorescence spectroscopy and molecular mechanics simulations shows that ephedrine displays a great trend to self-assemble in water solution, establishing not only π–π type interactions between the aromatic rings but also intermolecular H-bonds between NH₂ and OH moieties which compete with the formation of H-bonds with water. These molecules are invariably incorporated as aggregates within the AFI structure, regardless of the dopant introduced, showing a very strong trend to self-assemble within nanoporous frameworks as well. The stability of this supramolecular arrangement within the framework is due to a molecular recognition phenomenon based on the establishment of two H-bonds between the H atoms of the amino group and the O atoms of the hydroxyl group of the consecutive dimer, leading to an infinite supramolecular π–π H-bonded chainlike arrangement within the AFI channels

Correction to Controlling the Aluminum Distribution in the Zeolite Ferrierite via the Organic Structure Directing Agent

Correction to Controlling the Aluminum Distribution in the Zeolite Ferrierite via the Organic Structure Directing Agen

Synthesis of the Aluminophosphate ICP‑1 by Self-Assembly of 1,3-Diphenylguanidine: Insights into Supramolecular Aggregation

1,3-Diphenylguanidine (DPG) has distinguishable polar and apolar groups, aromatic rings that can self-assemble through π–π type interactions, and high conformational flexibility. These features make it a potential self-assembling structure-directing agent in the synthesis of hybrid host–guest aluminophosphates. Computational simulations show that the molecule has a strong tendency to self-assemble in aqueous solution. Large supramolecular organic aggregates are produced, with the hydrophobic aromatic rings located in the center of the aggregates, stabilized by π–π type interactions, and the hydrophilic guanidine groups on the external surface in close contact with water molecules. With this organic molecule, a new 1-D AlPO framework material (ICP-1) was formed. Its structure, characterized by a combination of single-crystal and powder diffraction techniques, consists of AlP₂O₈H chains connected to the polar groups of the organic DPG molecules through a complex H-bonding network. This material has an extremely high organic content, close to that of typical mesoporous materials. However, DPG molecules are part of the ICP-1 network, rather than guest molecules in the pores, so removal of DPG results in a collapse of the structure, limiting its potential applications. Nevertheless, this work demonstrates the potential of using self-assembling organic molecules for producing very open-framework materials

Highly Luminescent and Optically Switchable Hybrid Material by One-Pot Encapsulation of Dyes into MgAPO-11 Unidirectional Nanopores

In this work a highly fluorescent hybrid material with strong anisotropic response is obtained by “one-pot” synthesis. The system is based on the “in situ” encapsulation of two chromophores, acridine (AC) and pyronine Y (PY), with similar molecular structure but perpendicular dipole moment vectors, into the 1D-nanochannels of MgAPO-11 aluminophosphate crystals (AEL structure). This non-diffusional-limited synthetic approach allows the filling of very long channels, reducing considerably the time of sample preparation (>10 μm rectangular-like AEL particles), as well as a perfect fit between the molecular and channel dimensions, avoiding the leakage of the guest dyes and any Davidov coupling. As a consequence, both dyes are embedded only in momomeric units and preferentially aligned with their long molecular axes along the channels. Interestingly, the less bulky nature of AC without pendant groups leads to a much stronger incorporation with respect to PY (48:1), enabling an efficient FRET process between them. The final solid hybrid material shows fluorescent quantum yields higher than the respective dyes in diluted solution together with blue (AC)/green (PY) fluorescence color switching depending on the direction of the polarizers upon UV light excitation

ICP-2: A New Hybrid Organo-Inorganic Ferrierite Precursor with Expanded Layers Stabilized by π–π Stacking Interactions

In this work we present the synthesis, characterization, and molecular modeling of ICP-2, a new layered ferrierite precursor with expanded layers. ICP-2 is obtained in fluoride medium from aluminosilicate gels with low H₂O content, using the chiral cation (1<i>R</i>,2<i>S</i>)-dimethylephedrinium (DMEP) as the organic structure-directing agent; ICP-2 can also be obtained as the Al-free form. The combination of physicochemical characterization of the material with molecular modeling indicates that ICP-2 is a layered material composed of ferrierite layers, where the organic cations play a dual structural role through the formation of supramolecular aggregates. On one hand, the organic cations stabilize the formation of the ferrierite layers with a core–shell structure, directing the formation of both the pseudo-10R channels (by supramolecular dimers aligned with the channel direction) and of the pseudocavities, with the trimethylammonium groups of DMEP fitting within. On the other hand, the aromatic rings of these organic cations in the pseudocavities develop π–π stacking interactions with equivalent cations in adjacent layers, holding together the ferrierite layers expanded at a distance of ∼20 Å, hence preventing the formation of H-bonds between the inorganic layers. The diastereoisomer (1<i>S</i>,2<i>S</i>)-dimethylpseudoephedrinium instead cannot direct the formation of ICP-2, which is explained because of its distinct conformational space which fits worse in the core–shell structure of ICP-2

One-Directional Antenna Systems: Energy Transfer from Monomers to J‑Aggregates within 1D Nanoporous Aluminophosphates

A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mg-containing aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å × 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance