Jürg Hulliger

Fluorine in crystal engineering—“the little atom that could”

In the last decade interactions of fluorine substituents in a variety of organic compounds have gained interest in life science and solid state materials. This review provides knowledge on fluorine interactions classified into phenyl-perfluorophenyl-, C-FH, FF and C-FpiF interactions. Except for phenyl-perfluorophenyl stacking featuring a stabilising energy of about 30 kJ.mol(-1), interactions involving fluorine are generally weak. Although, there is still no concise understanding of fluorine interactions, there are numerous examples showing the influence of weak synthons on chemical, physical and biological properties.

Nanoporous and mesoporous organic structures: new openings for materials research

Organic solid state and molecular architectures providing nano- or mesoporous space for the inclusion of guest species open up new opportunities for the synthesis of materials showing designed chemical and physical properties. Porous materials are reviewed by taking into account recent progress in inorganic zeolites, metalloorganic and organic networks including carbon nanotubes and condensed cyclodextrins. Various properties requiring a parallel alignment of close-packed guests are addressed. As a particular example of physical property design, spontaneous polarity formation in channel-type inclusion compounds is discussed.

A new organic nanoporous architecture: Dumb-bell-shaped molecules with guests in parallel channels

A new type of dumb-bell-shaped host molecule (6-8) has been synthesised, of which 1,8-bis((1)-adamantyl)-1,3,5,7-octatetrayne (8 = BAOT) forms an open porous architecture when cocrystallised with a number of typical solvent molecules. Adamantyl substituents attached to a tetraalkyne spacer build up the walls of parallel channels wherein guest molecules are aligned. Surprisingly, the tetraalkyne unit is significantly bent. Desolvation experiments provide evidence for a reversible inclusion of guests. In the case of the inclusion of 2-butanone, a partial substitution by symmetrical and asymmetrical long-chain chromophores during crystallisation was possible. Stained crystals showed optical frequency doubling. The crystal structure analysis revealed a centric space group, although considerable translational and orientational disorder was present. Application of scanning pyroelectric microscopy revealed that the growth of inclusion compounds with 2-butanone produced polar ordering of guest molecules, which were aligned in two macro-domains of opposing polarity. The resulting orientation of the carbonyl dipoles is in agreement with the theoretical prediction of a Markov model of spontaneous polarity formation based on molecular recognition processes on growing crystal faces. The present case represents a new example of a property-driven supramolecular synthesis.

Glutamic acid inducing kidney stone biomimicry by a brushite/gelatin composite

Brushite is a well known precursor of calcium oxalate monohydrate, the main mineral found in kidney stones having a monoclinic crystal structure. Here, we present a new method for biomimicking brushite using a single tube diffusion technique for gel growth. Brushite crystals were grown by precipitation of calcium hydrogen phosphate hydrate in a gelatin/glutamic acid network. They are compared with those produced in gel in the presence of urea. The aggregates were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and thermal gravimetric analysis (TGA). SEM revealed a change of morphology by glutamic acid from spherulitic growth to plate-shaped and mushroom-like forms consisting of crystal plates and highly ordered prismatic needles, respectively. Furthermore, brushite crystals grown in a gelatin/glutamic acid/urea network showed needle-shaped morphology being different from other brushite growth forms. The XRD method showed that cell parameters for brushite specimens were slightly larger than those of the American Mineral Society reference structure. The mushroom-like biomimetic composite bears a strong resemblance to the brushite kidney stones which may open up new future treatment options for crystal deposition diseases. Hence, suitable diets from glutamic acid rich foods could be recommended to inhibit and control brushite kidney stones.

Supramolecular synthons mediated by weak hydrogen bonding: forming linear molecular arrays via CC–H···NC and CC–H···O2N recognition

In crystalline 4-cyano-4′-ethynylbiphenyl and 4-ethynyl-4′-nitrobiphenyl, molecules are connected with the hitherto unreported Câ–·C–H···Nâ–·C and Câ–·C–H···O2N supramolecular synthons to form linear arrays.

Theoretical Characterization of Charge Transport in One‐Dimensional Collinear Arrays of Organic Conjugated Molecules

A great deal of interest has recently focused on host-guest systems consisting of one-dimensional collinear arrays of conjugated molecules encapsulated in the channels of organic or inorganic matrices. Such architectures allow for controlled charge and energy migration processes between the interacting guest molecules and are thus attractive in the field of organic electronics. In this context, we characterize here at a quantum-chemical level the molecular parameters governing charge transport in the hopping regime in 1D arrays built with different types of molecules. We investigate the influence of several parameters (such as the symmetry of the molecule, the presence of terminal substituents, and the molecular size) and define on that basis the molecular features required to maximize the charge carrier mobility within the channels. In particular, we demonstrate that a strong localization of the molecular orbitals in push-pull compounds is generally detrimental to the charge transport properties.

Cathodoluminescence and photoluminescence of Smn+ (n=2,3) in oxide environments

Abstract Cathodoluminescence (CL) and photoluminescence (PL) of Smn+ (n=2,3) in crystalline, glassy SrB4O7, and polycrystalline SrSO4, BaSO4 were traced in order to distinguish between the valence state 2+ and 3+. Whereas PL selectively excites both valence states, Sm3+ is preferentially seen by CL. Differences in measured spectra are most likely due to the effect of ionization of Sm2+ to Sm3+ by accelerated electrons and an energy transfer from the host to Sm3+.

Epitaxial Nd:YLF linear waveguide laser

We report laser operation in planar and linear Nd:YLF waveguide structures grown by liquid-phase epitaxy (LPE). We could reduce the relatively high threshold of 115-mW incident pump power observed for the planar waveguide to 8 mW in a ridge-type structure that we obtained by mechanical polishing and subsequent growth of a cladding layer. Substantial improvements seem possible with reduction of the losses caused by imperfect end-face reflection and scattering, as well as by use of techniques capable of producing smaller structures than the 40-microm-wide triangular ridge cross section that was obtained with polishing. Since the LPE technique is applicable to other activator ions as well, it might offer a route to development of low-threshold upconversion lasers.

Supramolecular control of fluorinated benzophenones in the crystalline state

Crystal structures of three fluorinated benzophenones were determined via single crystal X-ray diffraction. The occurrence of the C–F⋯H, F⋯F, C–F⋯πF interactions in these crystal structures indicates that a base limit of fluorine atoms in the molecule seems to be necessary for successful competition with the hydrogen type of interactions.

Synthesis of bone-like micro-porous calcium phosphate/iota-carrageenan composites by gel diffusion.

Brushite and octacalcium phosphate (OCP) crystals are well-known precursors of hydroxylapatite (HAp), the main mineral found in bone. In this report, we present a new method for biomimicking brushite and OCP using single and double diffusion techniques. Brushite and OCP crystals were grown in an iota-carrageenan gel. The aggregates were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and thermal gravimetric analysis (TGA). SEM revealed different morphologies of brushite crystals from highly porous aggregates to plate-shaped forms. OCP crystals grown in iota-carrageenan showed a porous spherical shape different from brushite growth forms. The XRD method demonstrated that the single-diffusion method favors the formation of monoclinic brushite. In contrast, the double diffusion method was found to promote the formation of the triclinic octacalcium phosphate OCP phase. By combining the different parameters for crystal growth in carrageenan, such as ion concentration, gel pH and gel density, it is possible to modify the morphology of composite crystals, change the phase of calcium phosphate and modulate the amount of carrageenan inclusion in crystals. This study suggests that iota-carrageenan is a high-molecular-weight polysaccharide that is potentially applicable for controlling calcium phosphate crystallization.