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Macrocyclic liquid crystals combine the unique property of liquid crystals and excellent supramolecular assembly ability of macrocyclic compounds. It is a significant challenge to make rational use of the advantages of macrocyclic compounds to prepare new macrocyclic mesogens. Pillararenes, a type of macrocycles with rigid pillar-shaped frameworks and easy-to-functionalize property, are excellent building blocks to fabricate liquid crystal materials. However, the site-selective modification property of pillararene has been rarely exploited to tailor liquid crystal behaviors. Previously reported pillararene-based liquid crystal systems are almost prepared by per-functionalized pillararenes. Herein, we report the regulation of chiral liquid crystal behaviors by different derivatization of pillararene. Lyotropic and thermotropic liquid crystals with different chirality were obtained by self-assembly of pillararene with different numbers of cholesterol groups. The bridge between thermotropic liquid crystal and lyotropic liquid crystal based on pillararene is built. In addition, the chirality of the mesogens can be amplified through supramolecular self-assembly driven by noncovalent interactions. Based on the different liquid crystal behaviors, the optical signal of the pillararene-based chiral liquid crystals was used to fabricate an information encryption system. This work provides a simple strategy to regulate liquid crystal behaviors via pillararene-based mesogens and realizes information encryption through the combination of different types of liquid crystals. [ABSTRACT FROM AUTHOR]

The Schiff base N,N-bis(salicylidene)-o-phenylenediamine (salophen) was prepared by the condensation of salicylaldehyde with o-phenylenediamine in ethanol solution. Two new Zn(II) and Ni(II) salophen complexes, were synthesized, fully characterized by infrared (IR), 1H NMR spectroscopic measurements, UV–Vis spectra, photoluminescence (PL), and X-ray diffraction (XRD). The prepared complexes were used as phosphors to fabricate complexes/PMMA slab-based luminescent solar concentrators (LSC). The thermal stability of pure and doped PMMA polymer was examined by differential scanning calorimetry. Various parameters such as the optical energy gap, refractive index, AC and DC conductivity, dielectric constant, dielectric loss, Urbach energy, fluorescence quantum yield, and Stokes shift have been calculated and discussed. Optical absorption is carried out in wavelength region 200–900 nm at room temperature before and after the samples have been exposed to sunlight for up to 8 h. Photodegradation studies showed that the Zn(II) complex/PMMA LSC has the lowest rate of degradation compared with Ni(II) complex/PMMA LSC with the same concentration (0.06% weight). I–V characteristics of the photovoltaic devices with and without collectors were examined. The PV cell coupled with LSC shows an increase in maximum efficiency by about 50% compared to the normal one. This indicates that the proposed technique is very useful for improving the efficiency of solar cells. [ABSTRACT FROM AUTHOR]

Liquid crystals confined to porous materials often have different critical phenomena and ordering than in the bulk. Through the selection of pore size, structure and guest liquid crystal, these systems could enable a variety of functional materials for applications such as sensors and displays. A recent example of such a system is chiral nematic mesoporous films infiltrated with liquid crystal 4-cyano-4'-n-octylbiphenyl (8CB), which has reversible thermal switching of its optical bandgap. The optical bandgap is lost when the ordered 8CB guests are heated above ∼50 °C, where the 8CB becomes isotropic. In this study, we have used NMR cryoporometry and pulsed-field gradient diffusion measurements to determine the pore sizes and structures of various chiral nematic mesoporous silica and organosilica films. Temperature and orientation-dependent wideline (15)N NMR spectra of films infiltrated with (15)N-labelled 8CB guests show that the ordering of the 8CB mesogens is consistent with an average orientation parallel to the chiral nematic pore axes. Inclusion of a large, orientation-dependent shift was necessary to fit the spectra, probably due to susceptibility differences between the 8CB guests and the organosilica host., (Copyright © 2014 John Wiley & Sons, Ltd.)

Cellulose-based materials have been and continue to be exceptionally important for humankind. Considering the bioavailability and societal relevance of cellulose, turning this renewable resource into an active material is a vital step towards sustainability. Herein we report a new form of cellulose-derived material that combines tunable photonic properties with a unique mesoporous structure resulting from a new supramolecular cotemplating method. A composite of cellulose nanocrystals and a urea-formaldehyde resin organizes into a chiral nematic assembly, which yields a chiral nematic mesoporous continuum of desulfated cellulose nanocrystals after alkaline treatment. The mesoporous photonic cellulose (MPC) films undergo rapid and reversible changes in color upon swelling, and can be used for pressure sensing. These new active mesoporous cellulosic materials have potential applications in biosensing, optics, functional membranes, chiral separation, and tissue engineering., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chiral nematic structures with different helical pitch from layer to layer are embedded into phenol-formaldehyde bilayer resin composite films using cellulose nanocrystals (CNCs) as templates. Selective removal of CNCs results in mesoporous resins with different pore size and helical pitch between the layers. Consequently, these materials exhibit photonic properties by selectively reflecting lights of two different wavelengths and concomitant actuation properties., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cellulose nanocrystals (CNCs) are obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose. The nanocrystals have diameters of ~5-15 nm and lengths of ~100-300 nm (depending on the cellulose source and hydrolysis conditions). This lightweight material has mostly been investigated to reinforce composites and polymers because it has remarkable strength that rivals carbon nanotubes. But CNCs have an additional, less explored property: they organize into a chiral nematic (historically referred to as cholesteric) liquid crystal in water. When dried into a thin solid film, the CNCs retain the helicoidal chiral nematic order and assemble into a layered structure where the CNCs have aligned orientation within each layer, and their orientation rotates through the stack with a characteristic pitch (repeating distance). The cholesteric ordering can act as a 1-D photonic structure, selectively reflecting circularly polarized light that has a wavelength nearly matching the pitch. During CNC self-assembly, it is possible to add sol-gel precursors, such as Si(OMe)4, that undergo hydrolysis and condensation as the solvent evaporates, leading to a chiral nematic silica/CNC composite material. Calcination of the material in air destroys the cellulose template, leaving a high surface area mesoporous silica film that has pore diameters of ~3-10 nm. Importantly, the silica is brilliantly iridescent because the pores in its interior replicate the chiral nematic structure. These films may be useful as optical filters, reflectors, and membranes. In this Account, we describe our recent research into mesoporous films with chiral nematic order. Taking advantage of the chiral nematic order and nanoscale of the CNC templates, new functional materials can be prepared. For example, heating the silica/CNC composites under an inert atmosphere followed by removal of the silica leaves highly ordered, mesoporous carbon films that can be used as supercapacitor electrodes. The composition of the mesoporous films can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica films are obtained. These materials are flexible and offer the ability to tune the chemical and mechanical properties through variation of the organic spacer. Chiral nematic mesoporous silica and organosilica materials, obtainable as centimeter-scale freestanding films, are interesting hosts for nanomaterials. When noble metal nanoparticles are incorporated into the pores, they show strong circular dichroism signals associated with their surface plasmon resonances that arise from dipolar coupling of the particles within the chiral nematic host. Fluorescent conjugated polymers show induced circular dichroism spectra when encapsulated in the chiral nematic host. The porosity, film structure, and optical properties of these materials could enable their use in sensors. We describe the development of chiral nematic mesoporous silica and organosilica, demonstrate different avenues of host-guest chemistry, and identify future directions that exploit the unique combination of properties present in these materials. The examples covered in this Account demonstrate that there is a rich diversity of composite materials accessible using CNC templating.

We illustrate a new approach toward the synthesis of a porous supramolecular honeycomb based on triptycene. A coordination polymer has been prepared where the triptycene groups are linked through triptycenesemiquinonediimine platinum complexes, but the product is disordered rather than the intended honeycomb structure. A model platinum complex and its (15)N-labeled isotopomer have been prepared and characterized.

We have discovered that the self-assembly of cellulose nanocrystals (CNCs) into chiral nematic phases varies significantly with the substrate and evaporation rate. These variables allow the reflectance peak of iridescent chiral nematic films of CNCs and mesoporous silica templated from CNCs to be tuned over a wide range of wavelengths.

We describe an approach to prepare polymer composites with chiral nematic photonic structures through the self-assembly of cellulose nanocrystal (CNC) dispersions in organic solvents. Contrary to previous reports, we demonstrate that dispersions of neutralized sulfated CNCs in polar organic media readily form lyotropic chiral nematic liquid crystalline phases. We have investigated the effect of the neutralizing base on the CNC self-assembly, observing chiral nematic ordering for all counterions studied. The self-assembly of the organic CNC dispersions can be exploited to prepare iridescent polymeric composites simply by casting the CNC dispersion with a suitable polymer soluble in the organic solvent. Photonic properties of the composite films can be easily controlled by either varying the ratio of CNCs to polymer or adding salts.

Liquid crystalline phases can be used to impart order into inorganic solids, creating materials that mimic natural architectures. Herein, mesoporous silica and organosilica films with layered structures and high surface areas have been templated by nanocrystalline chitin. Aqueous suspensions of spindle-shaped chitin nanocrystals were prepared by sequential deacetylation and hydrolysis of chitin fibrils isolated from king crab shells. The nanocrystalline chitin self-assembles into a nematic liquid-crystalline phase that has been used to template silica and organosilica composites. Removal of the chitin template by either calcination or sulfuric-acid-catalyzed hydrolysis gave mesoporous silica and ethylene-bridged organosilica films. The large, crack-free mesoporous films have layered structures with features that originate from the nematic organization of the nanocrystalline chitin., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pd nanoparticles were well dispersed on a new triptycene-based microporous polymer support by the gas bubbling-assisted membrane reduction (GBMR) method. The stability of Pd nanoparticles is improved by the porous support, and the materials show excellent performance for CO oxidation.

The conjugated polymer poly(p-phenylenevinylene) (PPV) was polymerized in the pores of chiral nematic mesoporous organosilica to give a composite film showing the strong characteristic fluorescence of PPV as well as the iridescence due to the photonic band gap of the host material. Detailed circular dichroism (CD) studies reveal a chiral structure of the polymer within the pores. These new fluorescent materials undergo fluorescence quenching upon exposure to electron deficient aromatics such as 2,4,6-trinitrotoluene (TNT), indicating that they may be useful for developing chemical sensors.

A family of new amino resin-cellulose nanocrystal composites is reported. Owing to the chiral nematic order of the cellulose nanocrystals (CNCs) embedded in the amino resin polymer, the materials appear highly iridescent and their color can be controlled by the addition of salt. The freshly prepared samples are highly flexible and their color can be manipulated by applying pressure to the films. Colored chiral nematic patterns can be permanently recorded in the composite films, suggesting their application for security features, pressure sensors, and decoration.

Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays.

Four distinct triptycene-containing metal-organic frameworks, including three that are structural isomers, were synthesized and characterized. Structural isomerism was observed in the secondary building units of TMOF-2 giving rise to no fewer than three distinct [Zn4O](6+) clusters. Structural integrity upon guest solvent removal was confirmed using powder X-ray diffraction and thermogravimetric analysis, but gas adsorption experiments were conducted and revealed no appreciable surface area. Triptycenyl groups incorporated into MOFs appear to enhance structural diversity, but also crowd the pores of the MOF, reducing accessible surface area.

Helium ion microscopy (HIM) has been used to image mesoporous silica and organosilica for the first time. Images of chiral nematic silica, ethylenesilica, and new benzenesilica reveal the structural organization, pore dimensions and connectivity of these materials on the nanometer length scale.

The study of traditional organic cavitands has been central in the development of supramolecular chemistry. As the field of supramolecular chemistry matures, a new class of cavitand, the metallocavitand, is quietly emerging. No central theme currently exists to unify these relatable supramolecules due to the structural diversity of metallocavitands. To provide a concrete foundation for future metallocavitand research, we define metallocavitands here as multimetallic complexes where metal coordination is necessary for cavity formation. This tutorial review highlights synthetic routes based on self-assembly and macrocycle-templating strategies to isolate bowl-shaped metallocavitands, and highlights interesting supramolecular phenomena observed with metallocavitands such as dimerization, host-guest encapsulation, catalysis, unique regioselective reactivity, and enantioselective guest recognition.

Chiral nematic mesoporous materials decorated with metal nanoparticles have been prepared using the templated self-assembly of nanocrystalline cellulose (NCC). By adding small quantities of ionic compounds to aqueous dispersions of NCC and tetramethoxysilane (TMOS), the helical pitch of the chiral nematic structure could be manipulated in a manner complementary to the ratio of NCC/TMOS previously demonstrated by our group. We have studied the transformation of these ion-loaded composites into high surface area mesoporous silica and carbon films decorated with metal nanoparticles through calcination and carbonization, respectively. This general and straightforward approach to prepare chiral nematic metal nanoparticle assemblies may be useful in a variety of applications, particularly for their chiral optical properties.

We report a template-free strategy based on steric repulsion for the isolation of discrete columnar aggregates of macrocycles. Specifically, introduction of sterically-demanding trityl-derived substituents at the periphery of Pt(4) Schiff base macrocycles limits the otherwise infinite one-dimensional columnar aggregation to discrete tetrameric and hexameric assemblies. Single crystal X-ray diffraction studies of these compounds reveal discrete nanotubes of finite length that pack inefficiently resulting in three-dimensional networks of interconnected void space. The discrete assemblies were studied by N(2) adsorption and show enhanced surface area when stacked. In the absence of bulky substituents the macrocycles are nonporous. This strategy for engineering discrete supramolecular macrocyclic aggregates may be generalized to other columnar assembling systems., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This combined experimental (STM, XPS) and molecular dynamics simulation study highlights the complex and subtle interplay of solvent effects and surface interactions on the 2-D self-assembly pattern of a Schiff-base macrocycle containing catechol moieties at the liquid-solid interface. STM imaging reveals a hexagonal ordering of the macrocycles at the n-tetradecane/Au(111) interface, compatible with a desorption of the lateral chains of the macrocycle. Interestingly, all the triangular-shaped macrocycles are oriented in the same direction, avoiding a close-packed structure. XPS experiments indicate the presence of a strong macrocycle-surface interaction. Also, MD simulations reveal substantial solvent effects. In particular, we find that co-adsorption of solvent molecules with the macrocycles induces desorption of lateral chains, and the solvent molecules act as spacers stabilizing the open self-assembly pattern.

Anatase TiO(2) nanocrystals have been organized into high-surface-area (150-230 m(2) g(-1)) mesoporous films with long-range chiral nematic ordering. The chiral structure of the anatase films causes them to selectively reflect circularly polarized light and appear iridescent. These materials show replication of structural features found in the silica template on nanometer to millimeter length scales., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The supramolecular chemistry of bowl-shaped heptazinc metallocavitands templated by Schiff base macrocycles has been investigated. Dimerization thermodynamics were probed by (1)H NMR spectroscopy in benzene-d(6), toluene-d(8), and p-xylene-d(10) and revealed the process to be entropy-driven and enthalpy-opposed in each solvent. Trends in the experimentally determined enthalpy and entropy values are related to the thermodynamics of solvent autosolvation, solvent molecules being released from the monomeric metallocavitand cavity into the bulk solvent upon dimerization. The relationship established between experimentally measured dimerization thermodynamics and autosolvation data successfully predicts the absence of dimerization in CH(2)Cl(2) and CHCl(3) and was used to estimate the number of solvent molecules interacting with the monomeric metallocavitand in solution. Host-guest interactions between heptazinc metallocavitands and fullerene C(60) have also been investigated. Interestingly, metallocavitand-C(60) interactions are only observed in solvents that facilitate entropy-driven dimerization suggesting entropy and solvent autosolvation may be important in explaining concave-convex interactions., (© 2012 American Chemical Society)

Nanocrystalline cellulose (NCC) has been used to template ethylene-bridged mesoporous organosilica films with long-range chirality and photonic properties. The structural color of the organosilica films results from their chiral nematic ordering, can be varied across the entire visible spectrum, and responds to the presence of chemicals within the mesopores. To synthesize these materials, acid hydrolysis was used to remove the NCC template without disrupting the organosilica framework. The resulting mesoporous organosilica films are much more flexible than brittle mesoporous silica films templated by NCC. These materials are the first of a novel family of chiral mesoporous organosilicas with photonic properties., (© 2011 American Chemical Society)

Hollow polymer-based particles are useful for the encapsulation, protection, and release of active compounds. Adding a metal-organic coordination framework shell to nanocontainers is an attractive goal because it should help control their stability and permeability while yielding new properties and functions. We have discovered that polymer capsules with a Prussian blue analogue inner shell can be synthesized by emulsion-induced assembly of a metal-containing amphiphilic block ionomer. The capsules are selectively permeable and were used as nanocontainers to encapsulate and release a model compound. Further, these nanomaterials are tunable in size and organize into 2-D close-packed arrays in the solid state. Potential applications for these materials include the encapsulation and nanopatterning of pharmaceutical, biological, and catalytic compounds.

By subtly varying crystallization conditions, four distinct cadmium acetate coordination networks with unit cell formulas Cd(87)(H(2)O)(36)(EtOH)(18)(OH)(12)(CH(3)CO(2))(162) (1), Cd(87)(H(2)O)(72)(OH)(12)(CH(3)CO(2))(162) (2), Cd(10)(H(2)O)(6)(OH)(2)(CH(3)CO(2))(18) (3), and Cd(20)(H(2)O)(20)(OH)(4)(CH(3)CO(2))(36) (4) have been isolated. The coordination networks exhibit interesting structural diversity and have been investigated by powder X-ray diffraction, elemental analysis, thermal gravimetric analysis, infrared spectroscopy, and single-crystal X-ray diffraction. All four complexes are composed of secondary building units with the general formula [Cd(4)(OAc)(9)(μ(3)-OH)](2-). Complexes 1 and 2 exhibit a remarkable three-dimensional network composed of aligned columns, each 4.5 nm long, containing three different cadmium acetate clusters. Complexes 3 and 4 extend in two-dimensions with each unit cell repeating a different linkage isomer of the [Cd(4)(OAc)(9)(μ(3)-OH)](2-) cluster.

Silver nanoparticles (NPs) have been synthesized inside mesoporous silica films with chiral nematic structure. Circular dichroism measurements of the silver NP-loaded silica films show NP-based optical activity in the vicinity of the surface plasmon resonance. These materials, with an optical response associated with the chiral assembly of metal NPs, may be useful for developing new sensors.

Dinitrodialkoxybenzene derivatives are important precursors for Schiff base macrocycles and a variety of other molecules. During our investigations, we have found that the dinitration reaction of 1,2-dialkoxybenzenes proceeds with unusual regioselectivity, giving exclusively the desired 1,2-dialkoxy-4,5-dinitrobenzene product, but we have been unable to find a good explanation for this result. The dinitration of 1,4-dialkoxybenzene derivatives also exhibits surprising regioselectivity that has hitherto been left unexplained. Herein, we report a detailed DFT analysis of the regioselective dinitration of both 1,2- and 1,4-dimethoxybenzene. These results show that the reaction mechanism likely involves a single electron transfer (SET) process. In the case of the former isomer, the regioselectivity is mainly determined by the symmetry of the HOMO of the aromatic moiety that defines the structure of the SHOMO of the aromatic radical cation formed by the SET process. In the case of the latter isomer, the selectivity is due mainly to solvation effects and may thus be altered depending on the solvent environment. Synthetic studies of the nitration of 1,4-dialkoxybenzene derivatives using different solvent conditions support this conclusion and provide practical information for tuning the regioselectivity of the reaction.

A simple 1-step procedure yields a family of easily modifiable, stable, conjugated Schiff base macrocycles with 5-fold symmetry mediated by 3-center hydrogen bonding.

Chirality at the molecular level is found in diverse biological structures, such as polysaccharides, proteins and DNA, and is responsible for many of their unique properties. Introducing chirality into porous inorganic solids may produce new types of materials that could be useful for chiral separation, stereospecific catalysis, chiral recognition (sensing) and photonic materials. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant. Efforts to impart chirality at a larger length scale using self-assembly are almost unknown. Here we describe the development of a photonic mesoporous inorganic solid that is a cast of a chiral nematic liquid crystal formed from nanocrystalline cellulose. These materials may be obtained as free-standing films with high surface area. The peak reflected wavelength of the films can be varied across the entire visible spectrum and into the near-infrared through simple changes in the synthetic conditions. To the best of our knowledge these are the first materials to combine mesoporosity with long-range chiral ordering that produces photonic properties. Our findings could lead to the development of new materials for applications in, for example, tuneable reflective filters and sensors. In addition, this type of material could be used as a hard template to generate other new materials with chiral nematic structures.

Metal complexes composed of two zinc(II) salphen units that are bridged by a flexible hydrocarbon chain have been synthesized and characterized. Their self-assembled supramolecular structures were studied with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that all of the complexes displayed nanofibrillar morphology and that the surface texture and diameter can be altered by the addition of 4,4'-bipyridine and hydrophobic effects, respectively.

A new nickel-containing bis(bromobenzyl)salphen monomer suitable for Gilch polymerization was prepared. Reaction with KO(t)Bu in THF-DMF afforded primarily gels, but also soluble, conjugated oligomers that are red-shifted in the absorption spectrum when compared to the monomer. This spectral change, consistent with an enhanced conjugation length, was also compared with a suitable model compound for the polymer. Our results indicate that Gilch polymerization may be a useful route to fully conjugated metal-containing polymers if attention is paid to ensuring solubility of the product.

Coordination of Pt(2+) to a family of tunable Schiff base proligands directs the 12-component self-assembly of disk-shaped Pt(4) rings in a head-to-tail fashion. Aggregation of these S(4) symmetric Pt(4) macrocycles into columnar architectures was investigated by dynamic and static light scattering, NMR spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Data from these experiments support the formation of columnar architectures for all of the structures studied except when bulky tris(4-tert-butylphenyl)methyl substituents were present. In this case, aggregation was limited to dimers in CHCl(3) (K(dim) = 3200 +/- 200 L mol(-1) at 25 degrees C) and a thermodynamic analysis revealed that dimerization is an entropy driven process. Columnar architectures of Pt(4) rings with branched 2-hexyldecyl substituents organize into lyotropic mesophases in nonpolar organic solvents. These new self-assembled supramolecules are promising candidates to access nanotubes with multiple linear arrays of Pt(2+) ions.

A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests. Strong host-guest interactions explain the exceptionally high packing coefficient (0.80) observed for encapsulated N,N-dimethylformamide (DMF). The guest-accessible hydrogen-bonding sites arise from an unusual mu(3)-OH ligand bridging three cadmium ions. Thermodynamic and kinetic studies show that dimerization is an entropy-driven process with a highly associative mechanism. In DMF the exchange rate of peripheral cluster supporting carboxylate ligands is intrinsically linked to the rate of dimerization and these two seemingly different events have a common rate-determining step. Investigation of guest dynamics with solid-state (2)H NMR spectroscopy revealed 3-fold rotation of an encapsulated DMF molecule. These studies provide a solid understanding of the host-guest and dynamic properties of a new family of metallocavitands and may help in designing new supramolecular catalysts and materials.

Two new unsymmetrical Schiff base macrocycles with isosceles triangle shapes have been prepared. The macrocycles adopt cone-shaped conformations that rapidly interconvert at high temperature. Dynamic NMR studies show that the macrocycle that is tautomerized to the keto-enamine isomer is slower to flip than is the one in the enol-imine state. These macrocycles are good hosts for binding organic cations in their interiors.

Schiff base macrocycle 1, which has a crown ether like central pore, was combined with different alkali-metal and ammonium salts in chloroform, resulting in one-dimensional supramolecular aggregates. The ion-induced self-assembly was studied with solid-state NMR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was found that the lengths and widths of the superstructures depend on the cation and counteranion of the salts. Among the salts being used, Na(+) and NH(4) (+) ions with BF(4) (-) ions showed the most impressive fibrous structures that can grow up to 1 mum in diameter and hundreds of microns in length. In addition, the size of the fibers can be controlled by the evaporation rate of the solvent. A new macrocycle with bulky triptycenyl substituents that prevent supramolecular assembly was prepared and did not display any nanofibers with alkali-metal ions in chloroform when studied with TEM.

Metallosalphen complexes with peripheral glucose and galactose substituents were synthesized and characterized. Their self-assembled supramolecular structures were then studied with transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that all of the complexes displayed aggregation in the solid-state. Zinc-salphen complexes showed a remarkably homogeneous helical nanofibrillar morphology, whereas the other metal complexes only displayed micron-sized clusters.

Iptycenes, including triptycene as the smallest member, are rigid molecules with shapes that lead them to form open structures with substantial "free volume". There is a great deal of excitement in the application of these molecules to supramolecular chemistry, where researchers have taken advantage of their unique properties to construct new molecules and materials, including molecular machines, novel liquid crystals, and porous polymers for chemical sensing. This tutorial review highlights the application of iptycenes to the supramolecular chemistry of crystal engineering, host-guest complexes, molecular machines, polymers, and liquid crystals.

Conjugated Schiff base macrocycles with wide bores and conformational flexibility bind organic cations in their interiors, and can be used to assemble larger supramolecular structures.

The preparation of bent anthradithiophenes (BADTs) using an oxidative photocyclization-based synthetic strategy is reported. The optical properties of the new compounds were characterized by UV-vis and fluorescence spectroscopies, and the redox properties were probed by cyclic voltammetry. Structural studies using single crystal X-ray crystallography show that the unsubstituted BADT adopts a slipped cofacial stacking arrangement in the solid state with pi-pi interactions along the intermolecular stacking axis. The dialkylated derivatives adopt similar packing motifs with varying degrees of slipping along their long and short molecular axes while the diphenyl derivative packs into an edge-to-face herringbone arrangement. Powder diffraction data show that in thin films prepared by vacuum evaporation, molecules of the unsubstituted BADT are oriented nearly perpendicular to the substrate surface whereas the dialkylated derivatives adopt either multiple phases or new polymorphs. A thiahelicene prepared from the oxidative photocyclization of two isomers of 2,5-dithienyl-1,4-distyrylbenzene is described and the crystal structure reported.

New Schiff base ligands with two metal binding sites have been prepared. Copper and zinc complexes of the ligands, which serve as models for rigid, conjugated metallopolymers, were synthesized and characterized. The copper complexes display only weak intramolecular antiferromagnetic interactions, suggesting that the polymer structure is not useful for developing magnetic materials. Preliminary investigations of the novel polymers, including the preparation of a conjugated zinc-containing polymer, are reported.

Although micro- and mesoporous materials have each been extensively studied separately, very little work has been done to combine both porosity ranges into a single material. Materials with bimodal porosity could have attractive properties for a wide range of applications and could open new areas of study. Here, we present a strategy to develop micro-mesoporous materials using coordination chemistry, and illustrate the concept with the formation of mesostructured Prussian blue analogues.

Two new conjugated macrocycles have been prepared in high yield using Schiff base condensation. These are the first Schiff base macrocycles to incorporate phenanthrene, and they contain 66 and 78 atoms, respectively, in their smallest closed ring. Although the backbones of the two macrocycles have nearly the same constitution, one aggregates in chloroform while the other does not. This is rationalized based on the differential overlap of aromatic components in the dimers.

We have developed methodology for the formation of a new family of metal-free Schiff base macrocycles utilizing the differential exchange rates of aldimines and ketimines. The more robust ketimine bond is kinetically inert under the milder conditions used for aldimine bond formation. In particular, this route enables access to the first conjugated macrocycles with four unsymmetrical N2O2 salphen-like pockets.

A new [3 + 3] Schiff base macrocycle incorporating three N2O2 salphen-type binding sites and peripheral neopentyloxy substituents has been prepared. The incorporation of Zn2+ ions into this and related conjugated Schiff base macrocycles has been studied by NMR spectroscopy, mass spectrometry, and X-ray diffraction. When reacted with 7 equiv of zinc acetate, the macrocycles template the formation of heptanuclear complexes. Two tetranuclear Zn2+ complexes that are plausible intermediates in the assembly of the heptanuclear complexes have been isolated and structurally characterized. These reactive intermediates are promising substrates for the synthesis of polynuclear, mixed-metal clusters. We also demonstrate that this chemistry may be generalized to other bridging carboxylate ligands, such as methacrylate.