In 1979 the Air Force undertook a program to establish the principles for the design, synthesis, and processing of ultrastructured, electroactive polymers. The promising candidates were determined to be rigid rod polymers. In 1982 this approach was expanded to include the investigation of nonlinear optical properties in rigid rod polymers. The initial results in 1985, demonstrating the concept of multifunctionality, were quite startling. The polymers, PBT and PBO, which were designed as structural polymers with high strength, high modulus, and excellent thermaloxidative stability, were found to possess large nonresonant macroscopic third order optical susceptibilities. Their origin resides in the ultrafast, lossless excitations of highly-charged π- electron states. The state-of-the-art for nonlinear optical rigid rod polymers is reviewed.

One of the requirements in the theoretical determination of optical nonlinearities is the structure of the molecule. Since most of the molecules that we are interested in examining have not been made, we deemed it necessary to determine their molecular geometries. The structures of 2,6-diphenylbenzo[1,2-d:4,5-d']bisoxazole, 2,6-diphenylbenzo[ 1,2-d:5,4-d']bisoxazole, and 2,2'-p-phenylenebisbenzoxazole, and their corresponding donor- and acceptor-substituted derivatives were determined computationally using the AM1 (Austin Model 1) molecular orbital program. The quadratic polarizabilities (β's) of these model compounds were then computed using the CNDO/S (Complete Neglect of Differential Overlap/ Spectroscopy) program and frontier molecular orbital theory. Results from these calculations will be expounded.

The prediction of nonlinear optical properties of molecules and polymers is an important goal toward which a considerable effort has been recently applied. It entails the calculation of the polarizability and first and second hyperpolarizability tensor, for the systems under study, using their quantum wavefunctions. In principle several approaches are possible. The wavefunctions themselves can be calculated at the ab initio or semi-empirical levels of approximation and then the calculations can proceed via the sum over states (SOS) or the finite field (FF) formalisms.

Since we intend to calculate large systems we decided on the semi-empirical MNDO/AMI approaches for the calculation of the wavefunction. We also used the FF approach and numerical methods for finding the necessar) derivatives. The comparison between calculated and available experimental results is very encouraging. We also calculated the tensors for considerably large molecules, providing the first theoretical prediction of these values. The effect of different substituents on a given structure and the result of doping, were also studied. The polarizabilities of some oligomers as functions of the number of repeat units were calculated to assess the convergence properties. Because of the required periodicity of the perturbations, calculations cannot be made for infinite polymers in the same fashion as for small molecules. This problem is currently being addressed.

This review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include the cis- and trans-poly(p-phenylene benzobisoxazole) (PBO), the cis- and trans-forms of the corresponding poly(pphenylene benzobisthiazole) (PBT), and the structurally similar poly(5,5ʹ-bibenzoxazole-2.2ʹ-diyl-l,3-phenylene) (AAPBO) and poly(2,5-benzoxazole) (ABPBO) and their sulfurcontaining analogues. Because of their rigidity, these polymers become highly oriented in solution and some display liquid crystalline behavior. The purpose of this paper is to summarize the authorsʹ theoretical work on the structures, conformational energies, intermolecular interactions, electronic properties, electrical conductivity, and electrooptical properties of these chains, including, in some cases, the so-called articulated forms and the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.

Picosecond and femtosecond degenerate four-wave mixing have been used to measure third-order nonlinear optical susceptibility of several rigid-rod polymers and model compounds. A significant X(3) with femtosecond response was observed. The effects of processing conditions and structural variations on X(3) were studied. Four-wave mixing studies can also be conveniently used to generate ultrasonic phonons of well defined wave length and propagation direction. From this result one can investigate mechanical properties of polymers. Using this technique both the longitudinal and shear components of the elastic moduli for a uniaxially oriented rigid-rod polymer, poly-p-phenylene bis benzooxazole (PBO), were determined.

Second order non-linear optical (NLO) polymers have been the focus of intense research effort in recent years [1]. This effort is justified by the potential value of these materials in a range of attractive optical signal processing applications with lower device costs and enhanced device performance.

Nonlinear optics (NLO) is increasingly important for a variety of military and commercial needs ranging from new types of laser weapons to fiber optic communications networks, to optical computing applications. Rapid advances in optical phase conjugation, optical switching, and logic have demonstrated the enormous potential for practical applications with concurrent fast-paced materials development. A new class of organic materials called rigid rod (also known as ordered polymers) have the excellent intrinsic properties and tailorability to meet the requirements of a wide range of nonlinear optical devices. This manuscript provides a multidisciplinary effort to target key applications and material and processing requirements for ordered polymers. This manuscript provides the framework for the applications development required for the rapidly growing field of NLO devices from ordered polymeric materials.

Third-order optical susceptibilities (γijkl) can be efficiently analyzed for a variety of molecular structures employing perturbation theory and a PPP-SCF-SECI-DECI π-electron model Hamiltonian. The key, frequency tripling second hyperpolarizability γijkl(−3ω;ω,ω,ω) is calculated with full single and double CI. It is found that double excitations play a major role in third-order processes, and that γijkl, like the polarizability αij, is sensitive largely to the overall size (volume) of the π system, although charge transfer excitations may also contribute. The frequency dependence of v and correlations between γijkl and conjugation length are found for a series of trans polyenes.

Mechanically strong, environmentally stable, and electrically conductive polymeric films and fibers can be fabricated by processing (dry-jet, wet-spinning) solutions of PPBT and metallophthalocyanine molecular metal precursors, followed by chemical or electrochemical oxidation. X-ray diffraction, and resonance Raman measurements on (PPBT)-[Ni(Pc)I]x fibers indicate a microstructure consisting of small Ni(Pc)I crystallites imbedded in a PPBT matrix. Cyclic voltammetry and controlled potential coulometry indicate that PPBT/NiPc films can be reversibly doped.

We would like to report the synthesis of new third order nonlinear optical materials formed from reaction of dibromothiophenes with p-phenylenediamines under Ullmann condensation conditions. Initial measurements of the third harmonic NLO susceptibilities (X3~= 4 × 10−10 esu ), high laser damage thresholds ( 4 GW/cm2 ), and low absorptions have provided promising materials for device applications. Composite films in poly(vinylalcohol), poly(methylmethacrylate). or poly(carbonate) also gave significant X3 values in less than 10 percent w/w concentrations.

We report on ESR and electric conductivities of BBB and BBL ladder polymers with emphasis on the former. Both the ESR and the electrical conductivities are strongly anisotropic suggesting that the polymer backbones are plannar. The ESR data implies the existence of two different types of spin species. The hyperfine spectrum of one of these species is analyzed in terms of a Spin Hamiltonian and anisotropic transferred hyperfine interaction with the 14N nuclei (I = 1). We found that “annealing” the BBB and BBL films to high temperatures, To, increase the spin susceptibility for To ≤ 850K (BBB). However annealing to To ≥ 900K results in a dramatic reduction in the spin susceptibility and dramatic incise in the conductivity. The room temperature in-plane conductivity of annealed samples at To ≥ 900K exceeds σ = 1 Ω−1 cm−1. This high intrinsic conductivity is probably associated with the formation of cross-linked condensed aromatic structure. The 'phase transition” temperature to this structure is higher by 50K for BBB compared to BBL. The conductivity versus temperature of annealed samples (700K ≤ To) can be described by the onisotropic version of Mott's law for variable range hopping. We demonstrate that the anisotropic conductivity is due to the anisotropic localization lengths (ξ∥ and ξ⊥) of the wave function of the localized states.