This paper describes an approach to crystal engineering based on designing and analyzing hierarchical levels of crystalline architecture. The system under study consists of 1:1 co-crystals of melamines and barbituric acids that self-assemble into crystallographically infinite hydrogen-bonded tapes. The formation of structural elements can be rationalized and controlled using familiar molecular concepts such as steric repulsion.

Novel rigid rod polymers substituted with NLO-active chromophores have been developed towards application in electrooptical signal Modulation. The Materials are based on rigid polyesters and polyesteramids, in which the chromophores are either covalently linked to the backbone by short flexible spacers or directly incorporated into the main chain. In the bulk these systems form macroscopically ordered structures with layers of rigid rod backbones separated by the side chain segments. The properties and stability of the induced polar order can thus be adjusted by morphological parameters like the layer distance or the orientation of the main chains relative to the substrate. The relaxation of the NLO activity with time is described by a Multi-exponential decay and shows enhanced time-temperature stability even above 100°C. The temperature dependence of the relaxation times exhibits unusual features that distinguishes these systems from conventional NLO side chain polymers.

The construction of covalently self-assembled second-order nonlinear optical (NLO) Materials containing stilbazole or alkynyl-type high-β chromophores acentrically organized on inorganic oxide substrates is discussed. These structurally different chromophores exhibit differing packing densities on the surface when introduced under the same reaction conditions. In the stilbazolium chromophores, ion-exchange of the chloride counter-anion with very large anionie organic dyes results in appreciably enhanced second harmonic generation (SHG) efficiency. The frequency-dependent SHG response for self-assembled Monolayers derived from the alkynyl-type chromophore was also investigated. The linear absorption spectra exhibit two maxima in the visible region which are assigned to electronically isolated chromophores (480 nm) and aggregated species (540 nm). The dispersion of the second-order NLO coefficient reveals that both microstructures are NLO-active. The origin of the SHG response from both assemblies is discussed.

Recently, it has been discovered that crystalline organic thin films can be deposited in nearly single crystalline form on a variety of substrates such as glass, polymers, etc. Since then, this discovery has led to the growth of crystalline organic quantum wells, waveguides, coupler/switches, and organic/ inorganic heterojunction devices such as field effect transistors and avalanche photodiodes. Organic light emitting diodes (LEDs) which luminesce in the red, green and blue have also been demonstrated. In this paper, we will report on several recent advances in the growth of organic thin films deposited by organic molecular beam deposition. We report on modeling of organic monolayer growth based on the atom-atom potential Method. The Model provides insight into the factors which control “quasi-epitaxial growth” i.e. the ordered growth of one layer of an organic film which is incommensurate with the substrate lattice. We also observe large optical nonlinearities which are a feature of both single and Multi-layer crystalline organic films. The growth of organic, nonlinear optically active crystalline organic compounds are also discussed.

Conjugated oligomers form a fascinating class of molecular semiconductors, which open the perspective of control of electronic and structural properties through the variation of their chemical structure. For analysing the correlation between charge transport and structural properties, sexithiophene, 6T, was substituted by hexyl groups, both on the terminal α positions (α,ωDH6T) and as pendant groups in β position (β,β′DH6T). Structural characterizations by X-ray diffraction show that vacuum evaporated thin films of 6T and α,ωDH6T consist of layered structure in a monoclinic arrangement, with all-planar Molecules standing on the substrate, and that a much longer range ordering is observed when passing from 6T to α,ωDH6T, evidencing a large increase of molecular organization at the mesoscopic level. Electrical characterizations also indicate a significant enhancement of anisotropy of conductivity, with a ratio of 120 in favor of the conductivity along the stacking axis for α,ωDH6T. The charge carrier mobility, measured on field-effect transistors fabricated from these conjugated oligomers, also shows a large increase by a factor of 25 when passing from 6T to α,ωDH6T, and reaches a value close to 10-1cm2V-1s-1. In contrast, ββ′DH6T presents very low conductivity and mobility. These observations are attributed to the self-assembly properties brought by alkyl groups in α,ω position, and confirm the large potential of molecular engineering of organic semiconductors.

A novel type of photorefractive polymers, containing a conjugated backbone and a second order NLO chromophore, has been developed. A new polymerization method based on the Stille coupling reaction was explored to synthesize these materials. It was expected that the conjugated backbone would absorb photons in the visible region and play the triple role of charge generator, charge transporter and backbone. Several physical measurements demonstrated this expectation. Two beam coupling experiments clearly indicated an asymmetric optical energy exchange between two beams without applying an external electrical field. This is a conclusive demonstration for photorefractivity. Also, large optical gain of 5.7 cm-1 was observed under zero-field condition, which is comparable to most inorganic photorefractive materials. The versatility of the reaction makes possible the advancement of new polymer structures.

We have demonstrated a novel cyclosulfation chemistry for the functionalization of C60 Molecules and a new route to the synthesis of fullerol. The cyclosulfation reaction of C60 was performed in neat fuming sulfuric acid at 55–60 °C under N2. Hydrolysis of these derivatives in the presence of water at 85–90 °C or in aqueous NaOH solution at ambient temperature gave the corresponding polyhydroxylated fullerenes (fullerols) in high yield. Various spectroscopie methods were used to resolve the chemical structure of fullerol. An average of 10 to 12 hydroxyl addends was found in fullerols that can be correlated to the structure of polycyclosulfated fullerene precursors containing 5 to 6 cyclosulfate units. The cyclosulfation chemistry is, presumably, initiated by an one-electron oxidation reaction on C60 Molecules, followed by the attack of nucleophilic anionie sulfate species onto the resulting cationic C60 radical intermediates. Further electron oxidation and intramolecular cyclization of the resulting hydrogen sulfated C60 yielded the desired polycyclosulfated C60 products.

We have successfully synthesized single crystals of C60 fullerene complex with a symmetrical triplet donor of 2,3,6,7,10,11-hexamethoxytriphenylene (HMT). All spectroscopie data and analyses support the chemical composition of this complex as C60(HMT)2. Single crystals of C60(HMT)2 are, at 20±1 °C, cubic, space group Fd3c-Oh8 (No. 228) with a = 30.251(9) Å, α = 90.00°, V = 27682(30) Å3, Z = 16 (dcalcd = 1.476 gcm-3), and Ru (unweighted) = 0.098.

A second order nonlinear optical susceptibility inversion structure in the thickness direction (NIST) is proposed for enhancing the efficiency of Cerenkov radiation type phase matched second harmonic generation (CRPM-SHG). With the aid of the coupled-mode theory, it is analyzed that the efficiency is enhanced by 50 to 100 times by introducing the NIST structure to a waveguiding layer made of a 2-docosylamino-5-nitropyridine (DCANP) Langmuir-Blodgett (LB) film, and that the optical conditions for the most efficient CRPM-SHG are equivalent to those for guided mode SHG at the cutoff points of the modes. Several fabrication methods are possible for NIST waveguides. For the first time, a NIST waveguide has been fabricated using a DCANP-LB film by employing a novel and simple technique in which the substrate inversion is carried out during the dipping process. The inversion in nonlinearity was confirmed using the maker fringe method and polarized absorption spectra. A NIST planar waveguide of 260 Monolayers of DCANP (570 nm thick) was fabricated. Intense CRPM-SHG was observed from the waveguide when a YAG laser was coupled into it. The intensity was 20 to 30 times larger than that of a conventional waveguide of the same thickness.

Subjecting crystals of the thermochromic polydiacetylene (PDA) from the bis (ethyl ure thane) of 5,7-dodecadiyne-1, 12-diol (ETCD) to the solvents chlorobenzene and ?,?-dimethylformamide above the thermochromic transition temperature of PDA-ETCD irreversibly converts the material to nonthermochromic forms. These new forms have been characterized by their structural, thermal, and spectral properties. The materials isolated after exposure to chlorobenzene are highly crystalline with a structure that has expanded and disordered, yet is still related to that of the pristine polymer. The observed properties are discussed in the framework of the crystal structure-thermochromism relationship for urethane-substituted PDA.

Crystal engineering has been invoked to design structural analogues of two prototypal SHG active solids, p-nitroaniline (pNA) and potassium dihydrogenphosphate (KDP). pNA exists as linear polar strands because of head-to-tail hydrogen bonding between adjacent molecules whereas KDP is a self-assembled hydrogen bonded diamondoid network that becomes polar when the hydrogen bonds align. We detail preparation and crystallographic characterization of two classes of multicomponent solid, organic cation hydrogen sulfates and cocrystals of the cubane cluster [M (CO)3(μ3-OH)]4, which structurally mimic pNA and KDP, respectively. Several of the Multi-component solids are polar and they represent a generic approach to designing new polar materials since one component can be changed without altering the basic architecture within the crystal.

A novel thin film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with angstrom-level control over thickness and multilayer architecture. Molecular self-assembly of in-situ polymerized conjugated polymers consists of a layer-by-layer process in which a substrate is alternately dipped into a solution of a p-doped conducting polymer (e.g. polypyrrole, polyaniline) and a solution of a polyanion. In-situ oxidative polymerization produces the more highly conductive, underivatized form of the conjugated polymer, which is deposited in a single layer of precisely controlled thickness (30 to 60 Å). The thickness of each layer can be fine-tuned by adjusting the dipping time and the solution chemistry. The surface chemistry of the substrate (e.g. hydrophobic, charged, etc.) also strongly influences the deposition, thereby making it possible to selectively deposit conducting polypyrrole onto well defined regions of the substrates. Typical multilayer films exhibit conductivities in the range of 20–50 S/cm, but samples with conductivities as high as 300 S/cm have been realized. There is no limit to the number of layers that can be built up nor to the complexity of the multilayer architecture of the film; achieved simply by alternating the sequence of dips into solutions of various polycations and polyanions. This new self-assembly process opens up vast possibilities in applications which require large area, ultrathin films of conducting polymers and, more importantly, in applications that can take advantage of the unique interactions achievable in the complex, supermolecular architectures of multilayer films.

Multilayer thin film heterostrutuctures comprised of alternating layers of a poly (phenylene vinylene) (PPV) precursor and various polyanions were fabricated using a new self-assembly technique. Thermal treatment of these films produced multilayers of the fully conjugated form of PPV. Alternating Multilayers fabricated with inert polyanions such as sulfonated polystyrene exhibited a very strong photoluminescence whereas alternating multilayers fabricated with electron acceptor polyanions such as sulfonated C?O and poly (thiophene acetic acid) displayed a highly quenched luminescence. This latter behavior suggests that self-assembled Multilayers can be used to examine photoinduced charge transfer interactions between PPV and various electron acceptors.

A new facility for growing single crystals of urea by physical vapour transport in effusive cells is reported. The best crystals, as characterised by X-ray diffraction topography, are largely dislocation-free and do not contain microprocipitates.

Since their discovery 16 years ago, the field of intrinsically conducing polymers — “synthetic Metals” — has developed at an unexpectedly rapid rate. The concept of “doping” is the unifying theme which distinguishes this class of organic polymers — “conducting polymers” — from all others. Doping results in dramatic electronic and magnetic changes with a concomitant increase in conductivity to, or approaching, the metallic regime. Doping phenomena and the chief types of dopable organic polymers are described with particular emphasis on polyaniline, which is now probably the most actively-studied conducting polymer. It has been commercialized on a relatively large scale and presently appears to be the leading conducting polymer for technology. It shows considerable promise for electromagnetic interference (EMI) shielding and as a gas separation Membrane, and is currently used in commercial rechargeable batteries. Polypyrrole is used commercially in capacitors and as an electrically conductive coating on conventional fabrics. Additional potential uses of conducting polymers such as light-emitting diodes, electrochromic windows, chemical sensors, etc. are also described briefly.

Recent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, ε, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, ε increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative ε is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm-1. Below 600 cm-1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm-1) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative ε demonstrating the intrinsic metallic nature of the new generation of conducting polymers.

We have demonstrated that the solubility characteristics of undoped polyaniline can be understood from the point of view of standard solubility parameters which measure the propensity for the polymer and the solvent to engage in dispersive, polar, and hydrogen bonding interactions. By empirical measures and group additive calculations, emeraldine base has been shown to be characterized by solvent interaction parameters: δd = 17.4 MPa1/2, δp = 8.1 MPa1/2, and δh = 10.7 MPa1/2, which together are equivalent to a total solubility parameter: δ = 22.2 MPa1/2. In the case of doped polyanilines, the solubility parameters can influence or even dominate the interactions of the doped polymer. Without the modifying influence of the dopant anion, the doped polyaniline compositions are more strongly polar and hydrogen bonding than the undoped polymer.

Conducting polymers, e.g. polyaniline, generally lack stability in their electrically conductive form due to heat and moisture induced loss of dopant. Using a template-guided synthesis scheme, we synthesized a polymeric complex of polyaniline and polyelectrolyte that showed stability against dedoping by moisture and heat. The polymeric complex consists of a strand of polyaniline twisted tightly with a strand of polyelectrolyte. The polyelectrolyte in the complex serves as a macromolecular dopant for polyaniline. These two components of the complex are tightly bound so that the dopant is not lost during tests for thermal stability and stability in water and Moisture. Since the dopant is a polyelectrolyte with high linear anion charge density, the complex resists deprotonation by water or weak base (pH < 10).

A new class of water soluble conducting polyanilines have been developed. This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid. The resulting polyanilines readily dissolve in water. These Materials can be applied as removable discharge layers for electron-beam (e-beam) lithography and for SEM Mask Metrology. Cross-linkable functionality can be incorporated on the polyanilinc backbone resulting in water soluble polyanilines that are radiation curable. Upon irradiation these materials cross-link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge (ESD) applications. In addition, the cross-linkable polyanilines can be made into water developable conducting resists. 1.0μm conducting lines have been patterned with e-beam irradiation.

The synthesis and properties of polythiophenes, polypyrroles and their oligomers has evolved into a major area of conducting polymer research. Mixed systems containing both thiophene and pyrrole units have received much less attention. In this paper, the chemistry of thiophene-pyrrole oligomers containing up to seven heterocyclic units is reviewed.