Le-Quyenh Dieu

Nanochannels for supramolecular organization of luminescent guests

Zeolites and mesoporous silica are versatile host materials for the supramolecular organization of a large variety of guests. The inclusion of luminescent molecules, complexes, or nanoclusters into ordered one-dimensional channel systems is particularly intriguing, as the resulting host–guest compounds may exhibit unique properties such as optical anisotropy, efficient energy transfer, and enhanced stability. Several levels of organization have been realized for zeolite L, extending from the interior of a given crystal to the channel entrances and the external surface as well as from the microscopic to the macroscopic scale. The diverse chemistry that is involved in the development of a highly organized and functional host–guest material is illustrated by the design of molecules which are able to selectively adsorb at the channel entrances and establish communication between included guests and external objects. The importance of phthalocyanines as chromophores for this particular concept is exemplified. Based on the extensive research on zeolite L, possibilities and recent developments in the field of mesoporous silica hosts are discussed, revealing that despite the obvious differences between microporous and mesoporous host–guest materials, many similarities and analogies exist.

Probing Molecular Order in Zeolite L Inclusion Compounds Using Two-Photon Fluorescence Polarimetric Microscopy

We investigate the local static molecular orientational behavior in zeolite L inclusion compounds by polarimetric two-photon fluorescence microscopy. This technique, based on the polarized read-out of the signal under a tunable incident polarization state, provides refined information on molecular disorder that is not achievable using traditional fluorescence anisotropy. Moreover, the polarimetric microscopy imaging scheme permits a spatial investigation of possible heterogeneities, with a submicrometric resolution. The study performed on different fluorescent molecules inserted in zeolite L channels evidence a degree of disorder for either small or flexible structures.

On the Significance of the Anchoring Group in the Design of Antenna Materials Based on Phthalocyanine Stopcocks and Zeolite L

The synthesis of stopcocks based on zinc phthalocyanine for selective adsorption at the channel entrances of zeolite L is reported. The introduction of either an inert SiMe₃ moiety, an imidazolium cation or a reactive isothiocyanate (NCS) group allows attachment to the channel entrances of zeolite L through van der Waals interactions, electrostatic interactions, or covalent binding, respectively. Stopcocks that rely on van-der-Waals-driven adsorption require careful selection of the solvent used for the deposition onto the zeolite surface to avoid a nonspecific distribution of the molecules. Regarding the design of photonic antenna systems, a stopcock with a cationic tail was found to be the most convenient, based on the observation that efficient energy transfer from molecules located in the zeolite nanochannels is more readily obtained than in the other cases.

Novel phthalocyanine-based stopcock for zeolite L

We report the first phthalocyanine-based stopcock for selective adsorption to the channel entrances of zeolite L and realisation of a new electronic dipole moment coupling situation.

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.

Controlling Size and Morphology of Zeolite L

The synthesis of zeolite L crystals of high purity and well-defined morphology is described. Four procedures are detailed, leading to (a) large elongated cylindrical crystals, (b) medium-sized disc-shaped crystals, (c) nano-sized crystals, and (d) medium-sized cylindrical-shaped crystals.