New Strategies for Molecular Organization for Functional Materials

Functional materials require molecular organization to transport charges. This dissertation goes beyond typical molecular organization and focuses on three types of molecular organization: an optical lattice, covalently bound cages, and disorganized liquid interactions. Aluminum monochloride (AlCl) has been proposed as a promising candidate for laser cooling for organization in an optical lattice. In chapter 3, we show that pulsed-laser ablation of stable, non-toxic mixtures of Al with alkali or alkaline earth chlorides can provide a reliable source of cold AlCl molecules. We model the AlCl production in the limits of nonequilibrium recombination dominated by first-encounter events and find that AlCl production is limited by the solid-state densities of Al and Cl atoms and the recondensation of Al atoms in the ablation plume. This new source of AlCl molecules will provide the basis for future laser cooling experiments. Covalent assemblies of conjugated organic chromophores provide the opportunity to engineer new excited states through structural organization. A newly developed triple-stranded cage architecture, where covalent aromatic caps attach three conjugated walls, can be used to tune the properties of thiophene oligomer assemblies. In chapter 4 a variety of spectroscopic experiments are used to show that excited state properties of a benzene capped cage are dominated by through-space interactions between the chromophore subunits, generating a neutral H-type exciton state. Switching to a triazine cap enables electron transfer from the chromophore-linker after the initial excitation to the exciton state, leading to the formation of a charge-transfer state. The ability to interchange structural components with different electronic properties while maintaining the cage morphology provides a new approach for tuning the properties of chromophore assemblies. In chapter 5, the ability of disorganized molecular assembly, a liquid, can be used to generate work. A high-energy nanosecond laser pulse is used to impulsively heat an aluminum plate resulting in the rapid heating of an adjacent liquid. The volume expansion from the liquid→gas transition propels the aluminum plate upward with an initial velocity up to 4 m/s. A simple model is developed to quantitatively describe the fluid dependence on the heat of vaporization. Furthermore, this method proves that pulsed later heating for liquid→gas actuation is an efficient way to convert light energy into kinetic energy, with efficiencies approaching 2%