Columnar Arrangement Research Articles

Influence of Processing on Microstructure and Performance of Electron Beam Physical Vapor Deposition (EB-PVD) Thermal Barrier Coatings

Abstract The paper addresses the effect of processing parameters on microstructure and lifetime of electron beam physical vapor deposition, partially yttria-stabilized zirconia (EB-PVD PYSZ) coatings deposited onto NiCoCrAlY-coated Ni-base superalloys. In particular, the formation of a thermally grown oxide layer, an equi-axed zone, and various columnar arrangements of the highly textured PYSZ layers are discussed with respect to processing conditions. Three different microstructures were cyclically tested at 1100°C. The intermediate columnar structure was superior with respect to cyclic life times to a fine and to a coarse columnar structure which was mainly attributed to differences in the elastic properties. The effect of PYSZ microstructure on hot corrosion behavior of the thermal barrier coating (TBC) system at 950°C is briefly discussed.

Preparation and Molecular Arrangement of Novel Pyrenophanes

Abstract A stack and an offset stack geometrical arrangements based on the columnar structure have been confirmed for the molecular packing of novel pyrenophanes consisting of aniline unit or nitrobenzene unit, respectively, in contrast to a herringbone arrangement identified for the pyrenophane having benzene unit. Such a columnar stack arrangement is probably due to weak intermolecular interaction between the pyrene and the opposite aromatic component.

Reversible intercalation of volatile amines into stacks of soluble phthalocyanines

Different alkyl amines were intercalated into stacks of tetraalkenylphthalocyaninatozinc by exposing the solids to amine vapor. Since the intercalation is reversible, quantitative and kinetic aspects of the sorption were investigated using quartz crystal microbalances (QCMs) and thermal desorption mass spectrometry (TDS). Two different types of sorption were found and these were interpreted as interaction with aliphatic sidechains and preferential intercalation. At higher vapor concentration most of the interstitial spaces are occupied, suggesting a 1 ∶ 1 host–guest stoichiometry. Structure elucidation of an intercalated n-butylamine was carried out by EXAFS transmission measurements. Intercalation was found to take place while maintaining the columnar arrangement and without significant expansion of the spacing. Additional QCM measurements revealed less favorable sorption of sterically demanding amines which can be explained by morphological discrimination.

Bowl-shaped molybdenum complexes containing tris(3- p-methoxyphenylpyrazol-1-yl)borate (Tp An). Crystal structures of [Mo(Tp An)(NO)(Cl)(NHC 6H 4-p-CH 3)] and [Mo(Tp An)(NO)(Cl){NHC 6H 4-p-N(CH 3) 2}

New arylamide complexes of the type [Mo(Tp An)(NO)(Cl)(NHC 6H 4 -p-R)] (Tp An=hydrotris(3- p-methoxyphenylpyrazol-1-yl)borate; R=CH 3O ( 1), N(CH 3) 2 ( 2), Cl ( 3), CH 3 ( 4)) have been prepared in order to deduce the influence different arylamide para-substituents have on their molecular structure and properties. The single-crystal X-ray structures of [Mo(Tp An)(NO)(Cl){NHC 6H 4 -p-N(CH 3) 2}] ( 2) and [Mo(Tp An)(NO)(Cl)(NHC 6H 4 -p-CH 3)] ( 4) have been solved, both of them having a characteristic bowl-like molecular shape. The influence of electronic and steric factors on the shape of the bowl cavity is discussed. Both compounds have a columnar packing arrangement with molecular interpenetrating between neighbouring columns. Given that columnar stacking could be appropriate for liquid crystal materials, new related complexes bearing long-chain substituted arylamide ligands [Mo(Tp An)(NO)(Cl)(NHC 6H 4 -p-C n H 2 n+1 )] ( n=6, 10, 12, 14, 16; 5– 9) have been prepared.

Investigation of Structural Characteristics of Bis(β-diketonato)copper(II) Complexes Containing Alkoxy or Aryloxy Side Chains: X-Ray Structures of 1,3-Bis(4-butoxyphenyl)propane-1,3-dione, Bis[1,3-bis(4-butoxyphenyl)propane-1,3-dionato-κO,κO′]copper(II) and Bis[1,3-bis(4-phenoxyphenyl)propane-1,3-dionato-κO,κO′]copper(II)

Copper(II) complexes containing β-diketonato ligands of the general formula [Cu(4-RO)C 6H 4COCHCOC 6H 4(4-OR)} 2] 3 (R = Bu) or 4 (R = Ph) were prepared and their structures solved by X-ray diffraction. The crystal structure of the parent ligand (4-BuO)C 6H 4COCH 2COC 6H 4(4-OBu) 1 was also solved. The influence of the different side chains 4-RO - C 6H 4 (R = Bu or Ph) on potential liquid-crystal properties was investigated for both the ligands and the copper derivatives. The presence of BuO substituents at the aromatic rings appears to improve the molecular linearity with respect to 1,3-diphenylpropane-1,3-dione (=dibenzoylmethane; DBM), this feature being of interest for rod-like structures. On the other hand, the molecular structure of the copper(II) complexes 3 and 4 showed a flat core almost unmodified by the different peripherical substituents. A columnar arrangement was observed for both compounds 3 and 4, but, additionally, a layer-like disposition was also found in 3, which was proved to be a metallomesogen.

Effect of Intermolecular Axial Interaction on Columnar Mesomorphism in Long-Chain Metallotetraphenylporphyrins

The mesomorphic phase transition behavior of a series of long-chain metallotetraphenylporphyrin complexes (C12TPPM, M: Co, Ni, Cu, Zn, Pd, Pt, V=O, Al(OH), Mo=O(OH) and Si(OH)2) were compared to reveal that the intermolecular interaction by the axial group significantly affects the columnar arrangement. Furthermore, it was indicated that the more rigid columnar backbone with a capability of free rotation of disc-shaped molecules leads to the formation of hexagonal and tetragonal arrays of columns.

Tris(4-tolyl)methyl]benzene.

The crystal structure of the title compound, C(28)H(26), in the monoclinic space group C2/c has a columnar packing arrangement with a 7.20 A axis, a feature common to several tetraphenylmethanes.

Switchable columnar metallomesogens

Chiral columnar liquid crystals have recently appeared as a promising new type of ferroelectric materials. To date, all the columnar liquid crystals that have been reported to show ferroelectric switching consist of organic compounds. However, metal-containing liquid crystals open this field to a significant number of new structures and offer the possibility of adding to the ferroelectric behavior other properties inherent to the presence of metals in the structure, such as magnetism, as well as the use of new methods of characterization (EPR, synchrotron radiation, etc.). The potential of columnar metal-containing liquid crystals as ferroelectric materials has been demonstrated even though only a few organic columnar ferroelectric liquid crystals have been described. As a first approach to this type of material, this concepts article describes the results obtained with chiral metal beta-diketonates that show ferroelectric switching in the columnar mesophase. It has been shown that these materials have a helical columnar arrangement in the mesomorphic state, and a chiral superstructure has been proposed from circular dichroism studies. This type of supramolecular structure plays a fundamental role in the ferroelectric properties of these compounds. The discussion is mainly focused on the strategy employed for the molecular design, and on the interpretation of the mesophase structure and the electrooptic effect. The use of a diverse range of techniques, both those commonly used in the field of liquid crystals and those that are more specific will be highlighted, and the principles of these specific techniques are summarized together with a justification of their applicability to this study.

Crystal and molecular structure studies of tris (2-hydroxy-3-t-butyl-5-methylbenzene)-methane trihydrate and N-benzyl-N-phenyl benzamide

The structures of the title compounds, tris(2-hydroxy-3-t-butyl-5-methylbenzene)-methane)C34H46O3.3H2O, 3) and N-benzyl-N-phenylbenzamide (C20H17NO, 6), have been investigated by X-ray crystallography. Compound 3 crystallizes in the trigonal space group $$P\bar 3 $$ with cell parameters a = 14.090(5) A, b = 14.090(5)A, c = 10.485(5)A, Z = 2. Compound 6 crystallizes in the monoclinic space group C2/c with cell parameters a = 24.533(4)A, b = 9.176(4)A, c = 16.711(5)A, β = 125.88(2)°, Z = 8. Compound 3 has both intra-and intermolecular hydrogen bonds. It also exhibits a helical columnar arrangement of the molecules and goes into mesophase before melting into an isotropic liquid.

The epiphyseal cartilage and growth of long bones in Rana catesbeiana

The structure of the epiphyseal cartilage of the bullfrog Rana catesbeiana and its role in the growth of long bones were examined. The epiphyseal cartilage was inserted into the end of a tubular bone shaft, defining three regions: articular cartilage, lateral articular cartilage and growth cartilage. Joining the lateral cartilage to the bone was a fibrous layer of periosteum, rich in blood vessels. Osteoblasts with alkaline phosphatase activity were found on the surface of the periosteal bone, which presented a fibrous non-mineralised tip. The growth cartilage was inside the bone. The proliferative chondrocytes presented perpendicular separation of daughter cells and there was no columnar arrangement of the cells. Furthermore, chondrocyte hypertrophy was not associated with either calcification or endochondral ossification, in apparent contrast to the avian and mammalian models. Finally, there was no reinforcement system capable of directing cell volume increase into longitudinal growth. Since bone extension depends on the intramembranous ossification of the periosteum, the growth cartilage is inside and not at the end of the bone and the cells in the growth cartilage show no columnar arrangement and separate in a direction perpendicular to the long bone axis, we conclude that the growth cartilage mainly contributes to the radial expansion of the bone.

Electronic structure and mechanical properties of resistant coatings: The chromium molybdenum nitride system

Cr1−xMoxNy thin films were deposited on silicon by radio-frequency reactive magnetron sputtering. The phase, texture, and residual stress were determined by x-ray diffraction analysis. All the films crystallize in the face-centered-cubic phase. The chemical composition was measured by electron probe microanalysis. Scanning tunneling microscopy revealed a finely grained surface morphology. Scanning electron microscopy showed a columnar crystal arrangement in every film of this study. The binary compounds Mo2N and CrN exhibit grain sizes of about 5 nm, whereas the ternary compounds show grain sizes up to 23 nm. The electronic structure was analyzed using x-ray photoelectron spectroscopy (XPS). The valence band N 2s and metal d peak separations show a minimum for films with about equal content of chromium and molybdenum. Hardness values, obtained by nanoindentation, exhibit also a pronounced minimum for x=0.4. The similarity between the trends of the XPS peak separation and hardness suggests that the differences in the mechanical properties of the films are mainly due to changes in the bonding character, caused by a different charge distribution between Cr and N.

Metabolic activity patterns in the monkey visual cortex as revealed by spectral analysis.

The metabolic activity pattern of the monkey visual cortex was mapped quantitatively with [14C]-2-deoxyglucose during the performance of a visually guided reaching task. After bandpass filtering of the reconstructed two-dimensional metabolic maps of areas V1 and V2, alternating bands of high and low metabolic activity were apparent in control and experimental hemispheres. The spatial arrangement of active bands was studied with two-dimensional spectral analysis, and bands were found to be more organized in the experimental monkey. In area V1 of the control monkey the spectral amplitude was spread over a wider range of directions and frequencies than in the experimental subject. The finding that layer IV is characterized by more complex spectra than layers I through III suggests the coexistence of more than one active columnar system in the geniculorecipient layer. In area V2, stripes running almost perpendicular to the V1/V2 border were found along with superimposed patches of enhanced metabolic activity. In the experimental hemispheres, the corresponding spectra were extremely sharp yielding a constant periodicity. It is suggested that the well-organized columnar arrangement within areas V1 and V2 of the experimental hemispheres emerges from the diffusely organized background network of activity patterns in the control state.

The corticocortical projections of the physiologically defined eye field in the rat medial frontal cortex

This study investigated in the rat the corticocortical projections of the frontal eye field (FEF), which is located within the medial frontal cortex. The experiments were carried out on Wistar rats. Seven animals received a single iontophoretic injection of Phaseolus vulgaris leucoagglutinin in an FEF site within the medial frontal cortex where intracortical microstimulation elicited eye movements. In these cases, anterogradely labeled fibers and terminal-like elements were found in both hemispheres. The densest labeling was seen in the injected hemisphere, where labeled fibers prevailed in the visual cortex and their laminar distribution differed between the primary and secondary visual cortices. Dense labeled fibers were also seen in the frontal and retrosplenial cortex, whereas a columnar arrangement of terminal-like elements was detected in a restricted part of area 1 of the somatosensory cortex. Contralaterally to the injection site, labeled fibers were distributed mainly in the homotopic region. In two animals, the tracer was injected in a site at the FEF border whose stimulation evoked eye and whisker movements. In these animals, a different distribution of labeling was observed with respect to the other rats in which the tracer was deposited within the FEF, and anterograde labeling was observed in areas 1 and 2 of the parietal cortex of both hemispheres; in addition, no labeling was observed in these cases in the primary visual cortex. These findings suggest that cortical sites confined within the rat FEF are implicated in the control of orienting and exploring behaviors in addition to the control of eye movement.

Silver−Thioether Crown Complexes as Templates for the Synthesis of Extended Polyiodide Networks: Synthesis and X-ray Crystal Structures of [Ag2([15]aneS5)2]I12, [Ag([18]aneS6)]I7, [Ag([18]aneS6)]I3, and [Ag([9]aneS3)2]I5

Silver(I) complexes of [9]aneS3, [15]aneS5, and [18]aneS6 have been used as templates for the self-assembly of polyiodide ions. The complexes [Ag2([15]aneS5)2]I12, [Ag([18]aneS6)]I7, [Ag([18]aneS6)]I3, and [Ag([9]aneS3)2]I5 have been synthesized and structurally characterized. In [Ag2([15]aneS5)2]I12 [C10H20AgI6S5, orthorhombic, space group Pna21 with a = 21.688(4) Å, b = 27.748(4) Å, c = 8.623(2) Å, Z = 8], a discrete I122- polyiodide anion describable as a [2I-·5I2] charge-transfer adduct is bound to two [Ag([15]aneS5)]+ cations by Ag−I bonds. I···S interactions contribute to build up an extended three-dimensional superstructure featuring spirals of I122- and [Ag([15]aneS5)]+ ions alternating along the c axis. In [Ag([18]aneS6)]I7 [C12H24AgI7S6, trigonal, space group R3̄m with a = b = c = 9.458(4) Å, α = β = γ = 103.79(3)°, Z = 1], the Ag(I) complex cation is embedded in a unique three-dimensional polyiodide matrix in which I- ions occupy the lattice points of a primitive rhombohedral lattice with one I2 molecule bridging two I- ions along each cell edge to give a pseudo-perovskite structure. [Ag([18]aneS6)]I3 [C12H24AgI3S6, monoclinic, space group C2/m with a = 18.5767(11) Å, b = 11.9188(7) Å, c = 5.2714(5) Å, β = 95.634(9)°, Z = 2] features discrete [Ag([18]aneS6)]+ cations and I3- in a columnar stacking arrangement. Using the [Ag([9]aneS3)2]+ cation as template, an I5- salt has been obtained; this contrasts with the cubelike [I7-]∞ polyiodide array and I3- salt isolated with the [Ag([18]aneS6)]+ cation. In [Ag([9]aneS3)2]I5 [C12H24AgI5S6, monoclinic, space group C2/c with a = 17.1117(12) Å, b = 12.612(2) Å, c = 14.016(2) Å, β = 118.65(4)°, Z = 4], I···S interactions contribute to an extended structure featuring polymeric successions of cations and I5- ions. The solid-state FT-Raman spectra of these polyiodides are discussed on the basis of their crystal structures.

Investigation of the cluster substructure of icosahedral Al-Pd-Mn quasicrystals by means of exit-plane wavefunction reconstruction in high-resolution electron microscopy

The exit-plane wave reconstruction technique has been used for the first time to investigate the structure of icosahedral Al-Pd-Mn quasicrystals. The complexvalued exit-plane wavefunction along a fivefold direction was reconstructed with a resolution of 0.135 nm on the basis of a series of high-resolution electron microscopy images taken at different defocus values of the objective lens. In contrast with the original electron microscopic images, the exit-plane wavefunction is free from imaging artefacts. The result fits well with that expected from the Mackay-type cluster model for the Al-Pd-Mn icosahedral quasicrystal derived from X-ray and neutron diffraction structure investigations. Different columnar arrangements of clusters were identified; clusters whose projections barely interfere with those of other clusters display almost perfect tenfold symmetry, while the local symmetry of strongly overlapping projected clusters is degraded.

Molecular Order within Langmuir−Blodgett Films of Two Amphiphilic Octasubstituted Phthalocyanines Studied by Atomic Force Microscopy

Y-type Langmuir-Blodgett films of the octasubstituted amphiphilic phthalocyanines 1 and 2 deposited onto hydrophobic glass have been investigated by atomic force microscopy (AFM). The technique has been used to measure the thicknesses of one, two, and three bilayer films, and the results show that each bilayer is of the same thickness. This characteristic thickness is the same as the repeat spacing measured using low-angle X-ray diffraction methods on thicker samples, and thus we demonstrate that the order of the molecules in the monolayers after several cycles of deposition remains constant. We have detected considerable differences with respect to the consistency of the films of 1 and 2 and their resistance to the pressure exerted by the AFM tip during the scanning process required to obtain the images. Films of 1 are more robust and we have observed the columnar arrangement of the molecules at the surfaces of one, two, and three bilayers. However, under the same imaging conditions it was not possible to observe molecular order before perturbing the surface of the films formed by 2. The lateral extent of the ordered regions at the surfaces of the films of 1 covers areas of at least 10 μm 2 . There is very clear evidence that there is a predominant alignment. Inspection of 82 images taken of different regions of the film indicates that ca. 83% show columns whose axes are aligned to within ±30° of the dipping direction.

(Pyrazolato)gold Complexes Showing Room-Temperature Columnar Mesophases. Synthesis, Properties, and Structural Characterization

Mesogenic (pyrazolato)gold complexes of formula [Au(pz)]3 (pz = 3,5-bis(3‘,4‘-di-n-decyloxyphenyl)pyrazole (1), 3-(3‘,4‘,5‘-tri-n-decyloxyphenyl)-5-(3‘‘,4‘‘-di-n-decyloxyphenyl)pyrazole (2), 3-(2‘,3‘,4‘-tri-n-decyloxyphenyl)-5-(3‘‘,4‘‘,5‘‘-tri-n-decyloxyphenyl)pyrazole (3), 3,5-bis(3‘,4‘,5‘-tri-n-decyloxyphenyl)pyrazole (4)) have been prepared by reaction of the potassium salts of the nonmesogenic pyrazolate ligands with [AuCl(tht)] (tht = tetrahydrothiophene) in a 1:1 molar ratio. All these compounds show columnar mesophases that remain stable, at room temperature, for long periods of time. The formation of isomers for the nonsymmetrical derivativesdetected by spectroscopic studiesare suggested to be responsible for the subtle changes observed in the transition temperatures. Powder X-ray diffraction measurements show clearly that the supramolecular columnar arrangement appears in the crystalline solids as well as in the mesomorphic phase. An analogue of the mesogenic trinuclear complexes 1−4, having a methoxy group at the phenyl substituents of the pyrazolate ligands, [Au{3,5-(MeOPh)2Pz}]3 (5), has been synthesized and characterized by an X-ray single-crystal diffraction experiment. The molecular structure of 5 is based on a nine-membered metallacycle core. The whole molecule exhibits a rough planarity that favors a crystalline structure formed from columnar arrangements of trinuclear complexes. A simple and clear relationship could be established between the solid-state crystal structure of 5 and the X-ray-deduced structure of the mesophases.

The Chemistry of Vanadium−Carbon Bond Functionalities over an Oxo-Surface Defined by the Calix[4]arene Skeleton: The Redox Relationship between Vanadium(III) and Vanadium(IV) Assisted by Carbon−Oxygen Bond Cleavage

This report deals with the chemistry of V−C functionalities anchored to a quasi-planar O4 matrix represented here by the [p-But-calix[4]-(OMe)2(O)2]2- macrocycle. The starting material [p-But-calix[4]-(OMe)2(O)2V−Cl], 2, has been converted into the corresponding alkyl and aryl derivatives [p-But-calix[4]-(OMe)2(O)2V−R] (R = Me, 3; R = CH2Ph, 4; R = p-MeC6H4, 5) by conventional procedures. The structure of 5 reveals the self-assembling of the monomeric unit into a columnar arrangement with the p-tolyl substituent functioning as a guest moiety in a neighboring unit. Complexes 3−5 undergo migratory insertion reactions with CO and ButNC to the corresponding η2-acyls [p-But-calix[4]-(OMe)2(O)2V(η2-COR)] (R = Me, 6; R = CH2Ph, 7) and η2-iminoacyls [p-But-calix[4]-(OMe)2(O)2V{η2-C(NBut)R}] (R = Me, 8; R = CH2Ph, 9; R = p-MeC6H4, 10), the reaction with CO being strongly dependent on the R substituent. The structural model for the hexacoordinate intermediate leading to the inserted product is exemplified by the d2 high-spin [p-But-calix[4]-(OMe)2(O)2V(Cl)(CNBut], 11, and proves the presence of four available orbitals at the metal for driving the reactivity in the [p-But-calix[4]-(OMe)2(O)2V] fragment. The bonding mode of the organic functionalities at the metal and the conversion of the alkyl substituent into the η2-acyl have been inspected by extended Hückel calculations. The oxidative demethylation of 3 and 5 by a controlled amount of iodine opened an interesting synthetic route to the corresponding vanadium(IV) organometallic derivatives [p-But-calix[4]-(OMe)(O)3V−X] (X = Cl, 12; X = p-MeC6H4, 13). A structural report on 2, 5, and 9 is included.

Amphitropic Mesomorphic Phthalocyanines—A New Approach to Highly Ordered Layers

Phthalocyanines (Pcs), like many flat-shaped aromatic macrocycles, often arrange themselves into cofacial stacks (columnar arrangements) either in their crystalline and liquid-crystalline phases or in concentrated solutions. The main driving force for this particular supramolecular arrangement is s-overlap between the large p-systems of adjacent Pc macrocycles. Such a columnar architecture of pstacked Pc units is, among other potential applications, a promising structure for new materials with low-dimensional (photo)conducting properties. Therefore, they might present a new generation of organic photoconducting materials in xerographic processes or as components in organic photovoltaic cells of enhanced photovoltaic efficiency. The main advantage of Pcs, when compared with other aromatic macrocycles, is their strong absorption in the visible and near infrared (NIR) region. Pcs have long been known in industry as dyes, pigments, and catalysts, but more recently have found application as photoconducting materials in xerographic processes. However, the potential of Pcs for new functional materials with special optical, electrical, photoand semiconducting properties is currently being investigated. One of the main advantages of Pcs over many other discotic macrocycles is their strong absorption in the visible and NIR regions. For many of these new potential applications, thin layers of defined supramolecular order and reasonable stability have to be prepared. One of the most promising approaches for the preparation of ordered layers is to use the columnar liquid-crystalline phases (mesophases) of suitably substituted Pcs. In general, mesomorphic compounds have the advantage of good solubility and processability as well as a rather unique combination of supramolecular order and molecular mobility within their mesophase. However, the mesomorphism of Pcs needs to satisfy several requirements in order to obtain optimal materials properties. First, the columnar mesophase should display a hexagonal arrangement with a high degree of intracolumnar order; second, the mesophase should be easy to orient for the preparation of monodomains of macroscopic dimension and homeotropic orientation (the columns are oriented perpendicular to the surface of the substrate). This particular supramolecular architecture is probably the most favorable one for optical and electrical applications and is outlined in Figure 1. Finally, a afrozen ino mesophase (glass phase) rather than a return to the crystalline phase should be obtained upon cooling to ambient temperatures. This is important, because crystallization usually destroys the supramolecular architecture of the preceding mesophase and the molecular mobility within the mesophase has been found to disturb the conducting properties enormously. Although the thermotropic mesomorphic behavior of Pcs has been investigated extensively for 15 years, a satisfying synthetic approach covering all the aforementioned requirements has not yet been found. In fact, a molecular design that intrinsically leads to the ideal supramolecular behavior seems to be a contradiction. For example, most of the known mesomorphic Pcs display a very viscous mesophase with a clearing point above their decomposition temperature of about 300 C and are therefore not easy to orient. A fluid mesophase, or even an isotropic liquid phase, of monomeric Pcs could be introduced when the macrocycle was surrounded by bulky flexible side chains (e.g., very long or branched side chains) or was substituted at the non-peripheral positions. This kind of substitution pattern, on the other hand, led to less intracolumnarily ordered mesophases. In fact, it has been pointed out that alkane side chains are already responsible for what is in general, a low long-range order within the columns. This was explained by intracolumnar density fluctuations caused by the different optimal van der Waals distances between

Amphitropic Mesomorphic Phthalocyanines—A New Approach to Highly Ordered Layers

The columnar arrangement of π-stacked phthalocyanines (Pcs) is a promising structure for materials with special optical, electrical, and photo- and semiconducting properties. The requirements for obtaining optimal materials properties are discussed, and approaches towards the synthesis of mesomorphic Pcs that satisfy these requirements and the problems encountered are described. An approach that uses the thermotropic and lyotropic mesomorphism of Pcs with a special substitution pattern is demonstrated to be successful.