Christopher B. Gorman

A Unified Description of Linear and Nonlinear Polarization in Organic Polymethine Dyes

An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability α, the first hyperpolarizability β, and the second hyperpolarizability γ are seen to be derivatives, with respect to F, of their next lower order polarization (for α) or polarizability (for β and γ). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.

Relation Between Bond-Length Alternation and Second Electronic Hyperpolarizability of Conjugated Organic Molecules

The solvent dependence of the second hyperpolarizability, γ, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured γ is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with changes in molecular geometry from a highly bond-length alternated, polyene-like structure for a formyl-substituted compound in non-polar solvents, to a cyanine-like structure, with little bond-length alternation, for a dicyanovinyl-substituted compound in polar solvents. By tuning bond-length alternation, γ can be optimized in either a positive or negative sense for polymethine dyes of a given conjugation length.

Thin Films of n-Si/Poly-(CH3)3Si-Cyclooctatetraene: Conducting-Polymer Solar Cells and Layered Structures

The optical and electronic properties of thin films of the solution-processible polymer poly-(CH3)3Si-cyclooctatetraene are presented. This conjugated polymer is based on a polyacetylene backbone with (CH3)3Si side groups. Thin transparent films have been cast onto n-doped silicon (n-Si) substrates and doped with iodine to form surfacebarrier solar cells. The devices produce photovoltages that are at the theoretical limit and that are much greater than can be obtained from n-Si contacts with conventional metals. Two methods for forming layered polymeric materials, one involving the spincoating of preformed polymers and the other comprising the sequential polymerization of different monomers, are also described. An organic polymer analog of a metal/insulator/metal capacitor has been constructed with the latter method.

Substituted polyacetylenes through the ring-opening metathesis polymerization (ROMP) of substituted cyclooctatetraenes: A route into soluble polyacetylene

Abstract Ring-Opening metathesis polymerization (ROMP) of substituted cyclooctatetraenes (COT) produces polyacetylenes that are substituted, on the average, every eight carbon atoms. In several cases these polymers are soluble and highly conjugated. The effect of the side group on the optical, electrical and materials properties of the polymer will be discussed.

Soluble polyacetylenes derived from the ring-opening metathesis polymerization of substituted cyclooctatetraenes: electrochemical characterization and Schottky barrier devices

Recent developments in ring-opening metathesis polymerization (ROMP) have enabled the synthesis of poly-cyclooctatetraene (poly-COT), a material which is isostructural to polyacetylene. This liquid-phase polymerization method allows facile construction of interfaces, films, and devices with polyacetylene-like materials. The ROMP method also allows the preparation of soluble, yet highly conjugated polyacetylene analogs from substituted cyclooctatetraenes (R-COT). The redox characteristics of R-COT polymers were investigated at electrodes modified with thin polymer films. Voltammetric methods were used to characterize the redox response, band gap, electrochemical doping, and cis-trans isomerization properties of these polyenes. We have applied poly-COT technology to the fabrication of Schottky diodes and photoelectrochemical cells, by forming poly-COT films on semiconductor surfaces. The resultant semiconductor/organic-metal interfaces behave more ideally than semiconductor contacts with conventional metals, in that changes in the work function of the conducting polymer exert a large and predictable effect on the electrical properties of the resulting Schottky diodes. Transparent films of the solution-processible polymer poly- trimethylsilyl-cyclooctatetraene (poly-TMS-COT) have been cast onto n-silicon substrates and doped with iodine to form surface barrier solar cells. These devices produce photovoltages that are much larger than can be obtained from n-silicon contacts with conventional metals.

The Application of Ring-Opening Metathesis Polymerization to the Synthesis of Substituted Polyacetylenes

Ring-opening metathesis polymerization of substituted cyclooctatetraenes has been used to synthesize substituted polyacetylenes. The spacing between the side groups in the polymer allows the polymer to attain a conjugated conformation, while the twisting of the main chain induced by the substituents renders the polymer soluble. Poly(trimethylsilylcyclooctatetraene) has been used to make Schottky-type solar cells.

Synthesis, Characterization, and Applications of Substituted Polyacetylenes Derived from Ring-Opening Metathesis Polymerization of Cyclooctatetraenes

Polyacetylene and partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. The physical properties and characterization of these polymers are reported. In particular, certain poly-COT derivatives afford soluble, highly conjugated polyacetylenes. Nonlinear optical properties are highlighted by the fact that, in several cases, scattering losses are greatly minimized. These polymers have also been used in device applications such as Schottky barrier diodes and solar cells.