This paper describes a comparative study of self-assembled monolayers of different discoid molecules containing thioether, thiol, or disulfide substituents on gold. Discotic liquid crystalline hexaalkylthio-substituted triphenylenes and tricycloquinazolines, and derivatized triphenylenes with a single long ω-thioalkyl or ω-dithioalkyl substituent, are shown to self-assemble from dilute solution onto gold surfaces. Monolayers are formed owing to the known strong interaction of these functional groups with the gold. The characterization of the monolayers includes contact angle, polarized grazing incidence Fourier transform infrared spectroscopy (FTIR), quartz crystal microbalance (QCM), and atomic force microscopy (AFM) measurements. The discotic hexaalkyl thioethers assemble essentially face-on and without detectable lateral order onto the gold substrate. The alkyl chains do not lie flat on the gold but cover the aromatic cores. In contrast, the aromatic cores of the molecules in the monolayers of the discoid monosubstituted triphenylenes with a single thiol or disulfide substituent are shown to be in edge-on orientation. Furthermore, AFM reveals lateral order in these monolayers. Ordered areas, in the form of columns of edge-on oriented molecules, extend over length scales exceeding 100 nm. Domains of different orientation can be observed.

A series of monofunctionalized triphenylene-based discotic liquid crystals were synthesized starting from 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene. These compounds are unique in that they possess a single electron-withdrawing group (and consequently a large dipole moment) connected directly to the polyaromatic core. All of the new liquid crystals show a significantly broader range of mesogenicity relative to the parent compound 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene. Moreover, some of the new mesogens exhibit a more ordered mesophase relative to the hexagonal columnar phase (D h ) at lower temperatures. Monofunctionalization of the triphenylene core has a dramatic effect on the photophysical properties of the mesogens such as the color and efficiency of fluorescence.

The helical nanofilament (HNF) liquid crystal phase is a complex, hierarchical self-assembly in which bentcore molecules cooled from the isotropic melt form dense periodic arrays of nanoscale filaments of twisted smectic layers, a structure driven by an inherent tendency of the layers to be locally saddle-splayed. Here we report the results of a study of mixtures of an HNF-forming bent-core liquid crystal with a variety of organic guest molecules, showing that the high temperature, isotropic phase is completely mixed but that upon cooling the filaments form and grow, expelling the guest material from their internal volume. The nanofilaments form a network which acts as a porous nanoconfinement medium of large internal area ($100 m 2 cm À3 ), with the guest material confined to nanoscale interstitial volumes between the filaments. Such helical nanofilament networks represent a robust platform for potential applications in chiral separations, asymmetric synthesis, and photonic metamaterials.

Study of a diverse set of chiral smectic materials, each of which has twist grain boundary (TGB) phases over a broad temperature range and exhibits grid patterns in the Grandjean textures of the TGB helix, shows that these features arise from a common structure: ''giant'' smectic blocks of planar layers of thickness l b > 200 nm terminated by GBs that are sharp, mediating large angular jumps in layer orientation between blocks (60°< ⌬ < 90°), and lubricating the thermal contraction of the smectic layers within the blocks. This phenomenology is well described by basic theoretical models applicable in the limit that the ratio of molecular tilt penetration length-to-layer coherence length is large, and featuring GBs in which smectic ordering is weak, approaching thin, melted (nematic-like) walls. In this limit the energy cost of change of the block size is small, leading to a wide variation of block dimension, depending on preparation conditions. The models also account for the temperature dependence of the TGB helix pitch.liquid crystal ͉ chirality ͉ screw dislocation ͉ helix T he nearly simultaneous prediction of the twist grain boundary (TGB) phase, the liquid crystal (LC) analog of the Abrikosov type II superconductor (1), and its discovery in the nP1M7 series of chiral smectics (2) has led to a class of soft-matter phases exhibiting particularly striking manifestations of chirality. Although fluidlayered smectics in general tend to expel twist of the layer normal, the TGB phases adopt a state of layer twist, driven by molecular chirality in a way analogous to the accommodation of magnetic field by the formation of flux vortices in a type II superconductor. In the LC case twist is enabled by formation of GBs, which behave as arrays of screw dislocations, mediating change in layer orientation between blocks of planar smectic layers, and acting as the ''flux tubes'' in deGennes' smectic͞superconductor analogy (3).The early TGBs (2, 4, 5) exhibited a set of common characteristics, including narrow TGB phase temperature (T) ranges, T R Ϸ 1°C, small angular jumps in layer orientation at the GBs (5), and Grandjean-like textures of the director rotation (TGB) helix (2). However, beginning with the 1993 report of the nitrotolane system having homologs with TGB phase ranges of up to 100°C (6), a distinct class of TGB materials has emerged (6-11) characterized by: (i) large T R values (10°C Ͻ T R Ͻ 100°C); (ii) modulated and͞or undulated Grandjean textures, first described in the ''UTGBC'' phase of the Bangalore S1014͞CE8 mixture (7) and observed in other mixtures (10, 11), as well as in neat materials (6,8,9) § § ; (iii) evidence for large angular jumps between blocks, 90°in the case of the UTGBC square lattice (7) and 60°inferred from nitrotolane x-ray data showing 6-fold symmetric block orientation (9); and (iv) electric field-induced unwinding of the TGB helix (6, 12). Here, we report detailed structural studies using freeze-fracture electron microscopy (FFEM), x-ray diffraction (XRD), and depolarized transmission li...