Surface modification and controlled assembly of molecular materials

Organic materials were prepared to gain an understanding of how to control the surface and bulk properties of molecular materials. Surfaces were modified by growing thin films of electronically relevant phenylene vinylene hyperbranched polymers from silicon using the Heck reaction with triiodobenzene and divinylbenzene monomers. Hyperbranched polymers enabled continued film growth regardless of random chain termination. Films were grown by reacting one monomer with the surface at a time and washing the unreacted monomer away. Films grown from patterned surfaces indicated monomers reacted with chemisorbed initiator molecules on the surface and did not physisorb onto unpatterned regions. Films were characterized using XPS, ellipsometry, SEM, and AFM.; Bulk organization of molecular materials was studied using oligomers and single crystals. A series of oligo(m-phenylene ethynylene)s having triethylene glycol ester-linked side chains were studied with regard to their supramolecular organization in the solid-state. Small angle X-ray diffraction indicated that the oligomers with a chain length of eight or more monomers organized longitudinally with a d-spacing linearly dependent on the chain length, suggestive of lamellar packing. This is in contrast to the helical conformation observed in acetonitrile.; Single crystal molecular organization was investigated using coordination network crystals. Crystals that had molecules arranged as chains, such as catena-poly[dicyanobenzene-silver(I)]-triflate, were exposed to inhibitors specifically designed to bind at the growing surface. It was found that inhibitors had qualitative effects on the morphology and on the surface composition of the crystals and that the surface and bulk properties had potential to be modified independently. Copper-pyridine crystals were studied to determine how the steric bulk on pyridine influenced the pyridine coordination to copper. It was found that as the steric bulk of the pyridine increased, the probability that all the copper coordination sites were occupied with pyridine decreased, and that solvent molecules and ancillary ligands also coordinated to copper. A single crystal of 4'-undecyloxy-4-biphenyl carbonitrile revealed that the molecules in the crystalline form had similar organization as the molecules in the smectic phase.