Molecular design of ordered transition metal thin film interfaces by coordination chemistry and self-assembly

This dissertation explores the development of ordered thin films of transition metal complexes via self-assembly and coordination chemistry. Particular emphasis is placed on nano-scale structural characterization through spectroscopic and scanning probe techniques. The photoactive and catalytic properties of metal porphyrins and diimines, as well as their constrained geometries, make them excellent building blocks for molecular architectures. The structural and functional reproducibility of this approach suggests applications including electronics packaging, sensors, displays, and molecular electronics.; In the first generation of thin films, Zn-porphyrin/phenylene ethynylene co-polymers were separated into multilayers by ligation of bidentate “spacers.” The resulting 3-dimensional architectures were coordinated to pyridine-functionalized self-assembled alkylsilane monolayers on hydroxylated glass; a stable interface for chemically binding the arrays to the substrates. X-ray diffraction, UV-vis, and AFM indicated long-range order. Short-range defects were suggested by the unprecedented appearance of two N 1s XPS signals for Zn-porphyrin. XPS investigations on a series of porphyrin polymers revealed multiple chemical environments at the N atoms caused by interpolymer interactions. Analogous interactions in multilayers resulted from inadequate metal coordination and the inability to align polymer chains.; Second generation films employed Ru-porphyrin(carbonyl) monomers, which form stable 6-coordinate complexes in monolayers and bilayers, and avoid destabilizing interpolymer interactions. Ru-bis(bipyridine) dichloride was also coordinated to pyridine surfaces by substitution of Cl ligands. Absorbance spectroscopy indicated reproducible sub-monolayer coverage for both Ru-complexes, with strong evidence of surface coordination from XPS binding energy shifts. AFM revealed homogenous surfaces of close-packed particles of exceptionally low RMS roughness. UV-vis, contact angles, and AFM indicated that additional material was physisorbed onto the coordinated species, presumably via π-interactions.; These surfaces were used as substrates for the in-situ polymerization of polyaniline. Relative to silica, the metalated thin films qualitatively improved polymer adhesion, and increased the rate of polymer growth and secondary nucleation. Notably, the conductivity of the polymer films was as high as ∼40 S/cm, compared to ∼0.4 S/cm on bare silica. These effects were attributed to conformational expansion and enhanced crystallinity of the conjugated polymer via interfacial interactions with the π-systems of the aromatic surface species.