Kenneth E. Maly

Assembly of nanoporous organic materials from molecular building blocks

Microporous organic solids are a relatively new class of materials that have potential applications in areas such as gas storage, molecular separations, and catalysis. In this Highlight article, the design considerations and main strategies for preparing these materials will be discussed. The properties of these remarkable materials, and their potential utility in a variety of applications will also be outlined.

Synthesis of Substituted Trinaphthylenes via Aryne Cyclotrimerization

The first synthesis of a series of substituted trinaphthylene derivatives via a palladium-catalyzed aryne cyclotrimerization is reported. This method provides an approach for the preparation of novel disk-shaped polycyclic aromatic hydrocarbons that self-assemble via pi-pi interactions and may form columnar liquid crystal phases. Although the trinaphthylenes prepared in this study do not exhibit columnar mesophases, variable concentration (1)H NMR studies provide evidence for aggregation in solution.

Solid-state 11B and 13C NMR, IR, and X-ray crystallographic characterization of selected arylboronic acids and their catechol cyclic esters.

Nine arylboronic acids, seven arylboronic catechol cyclic esters, and two trimeric arylboronic anhydrides (boroxines) are investigated using 11B solid‐state NMR spectroscopy at three different magnetic field strengths (9.4, 11.7, and 21.1 T). Through the analysis of spectra of static and magic‐angle spinning samples, the 11B electric field gradient and chemical shift tensors are determined. The effects of relaxation anisotropy and nutation field strength on the 11B NMR line shapes are investigated. Infrared spectroscopy was also used to help identify peaks in the NMR spectra as being due to the anhydride form in some of the arylboronic acid samples. Seven new X‐ray crystallographic structures are reported. Calculations of the 11B NMR parameters are performed using cluster model and periodic gauge‐including projector‐augmented wave (GIPAW) density functional theory (DFT) approaches, and the results are compared with the experimental values. Carbon‐13 solid‐state NMR experiments and spectral simulations are applied to determine the chemical shifts of the ipso carbons of the samples. One bond indirect 13C‐11B spin‐spin (J) coupling constants are also measured experimentally and compared with calculated values. The 11B/10B isotope effect on the 13C chemical shift of the ipso carbons of arylboronic acids and their catechol esters, as well as residual dipolar coupling, is discussed. Overall, this combined X‐ray, NMR, IR, and computational study provides valuable new insights into the relationship between NMR parameters and the structure of boronic acids and esters. Copyright

Tampering with Molecular Cohesion in Crystals of Hexaphenylbenzenes

Hexaphenylbenzene (HPB) and analogous compounds have properties of broad utility in science and technology, including conformationally well-defined molecular structures, high thermal stability, high HOMO-LUMO gaps, little self-association, inefficient packing, and high solubilities. Previous structural studies of HPB and its analogues have revealed persistent involvement of the central aromatic ring in strong C-H...pi interactions. These interactions can be blocked by adding simple ortho alkyl substituents to the peripheral phenyl groups. Comparison of the structures of HPB and a series of ortho-substituted derivatives has shown systematic changes in molecular cohesion and packing, as measured by packing indices, densities, solubilities, temperatures of sublimation, melting points, and ratios of H...H, C...H, and C...C contacts. These results illustrate how crystal engineering can guide the search for improved materials by identifying small but telling molecular alterations that thwart established patterns of association.

Environmentally benign aqueous oxidative catalysis using AuPd/TiO2 colloidal nanoparticle system stabilized in absence of organic ligands

The use of nanoparticles (NPs) for efficient, environmentally benign catalysis is receiving increasing attention, with gold and palladium NPs being an important area of research. Herein we present a simple, reliable and cost-effective preparation of a catalytically active gold-palladium NP system that is stabilized by an aqueous titania dispersion (AuPd/TiO2) in the absence of organic ligands. The major advantages of this system are that it is catalytically active in the as-prepared colloidal state, eliminating the need for drying and sintering before use and is colloidally stable in oxidative conditions. The AuPd/TiO2 system exhibits efficient oxidative catalysis in both the presence of hydrogen peroxide and atmospheric oxygen, even at ambient temperatures for our model aqueous phase reaction of 1-phenylethanol oxidation. The preparation and characterization of the AuPd/TiO2 system is described with respect to the effects of colloidal stability, particle size and morphology on aqueous oxidative catalysis. The major finding is that NPs with a gold core and thin palladium shell (70 mol% gold, 30 mol% palladium, Au70Pd30/TiO2) provides the most catalytically active system. The ability of the catalyst to use atmospheric oxygen at ambient temperatures in aqueous media highlights the strong potential of the developed catalytic system for green oxidative processes. The presented approach provides a new platform of all-inorganic colloidal nanoparticle systems for future development of industrially viable, environmentally friendly catalysts.

Design of photonic liquid crystal materials: synthesis and evaluation of new chiral thioindigo dopants designed to photomodulate the spontaneous polarization of ferroelectric liquid crystals

Irradiation of a ferroelectric S C * liquid crystal phase induced by the photochromic dopants (R,R)-6,6′-bis(2-octyloxy)-5,5′-dinitrothioindigo and (R,R)-5,5′-dichloro-6,6′-bis(2-octyloxy)thioindigo at λ=514 and 532 nm, respectively, causes an increase in spontaneous polarization (P S ) by a factor ranging from 1.4 to 4.0. This increase in P S is achieved without concomitant destabilization of the S C * phase, and is consistent with an increase in transverse dipole moment of the thioindigo core as a result of trans-cis photoisomerization. The contribution of the thioindigo core towards P S is achieved through stereo-polar coupling with the chiral side-chains, which is enhanced by the presence of the nitro and chloro substituents.

Synthesis and Mesomorphic Properties of Novel Dibenz[a,c]anthracenedicarboximides

The synthesis and characterization of a novel series of dibenz[a,c]anthracenedicarboximides is reported. Incorporating electron-withdrawing imides bearing flexible alkyl chains allowed for the production of materials that self-assemble into hexagonal columnar mesophases featuring broad temperature ranges. Furthermore, longer N-alkyl chains or branched N-alkyl chains broaden the mesophase temperature range by lowering the melting transition without greatly influencing the clearing point.

Dibenz[a,c]anthracene derivatives exhibiting columnar mesophases over broad temperature ranges

We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges.

Synthesis and characterization of novel dibenz[a,c]anthracenedicarboxythioimides: the effect of thionation on self-assembly

We report the synthesis and properties of a series of novel dibenzanthracenedicarboxythioimides and an investigation of the effects of thionation on self-assembly in these systems. These compounds all display columnar mesophases over broad temperature ranges and self-associate to form dimers in solution. Overall, thionation slightly improves self-assembly in these systems. Furthermore, increasing the thionation of these materials leads to a lowering of the LUMO energy and a narrowing of the HOMO–LUMO band gap.

Anthra- and pentacenequinone derivatives: influence of structure on the formation of columnar liquid crystal phases

We report the synthesis and mesophase characterization of a series of novel di- and tetra-aryl acenequinones. Diphenyl-acenequinones 1 and 2 exhibit monotropic mesophases while tetra-aryl acenequinones 4 and 5 exhibit stable columnar hexagonal mesophases. Compound 4 exhibits a more stable columnar mesophase than 5, consistent with a packing motif where molecules are stacked in perpendicular arrangement.