Self-assembly controlled at the level of individual functional groups.

Molecular self-assembly is driven by intermolecular interactions between the functional groups on the component molecules. Small changes in molecular structure can make large differences in extended structure, and understanding this connection will lead to predictive power and control of the self-assembly process. Scanning tunneling microscopy is used to study self-assembly in two-dimensional clusters and monolayers, and the experimental approach is to study "families" of molecules where one or more functional groups is varied in a methodical way. Studied families include indole carboxylic acids, isatin derivatives (which have the indole backbone), quinaldic acid, thioethers, and fluorenone derivatives. In these systems, a variety of intermolecular interactions drive the assembly of the molecular monolayer, including hydrogen bonds, van der Waals forces, zwitterionic interactions, surface interactions, and halogen interactions.

A Low-Cost Beam-Scanning Second Harmonic Generation Microscope with Application for Agrochemical Development and Testing.

A low-cost second harmonic generation (SHG) microscope was constructed, and, for the first time, SHG microscopy was used for imaging agrochemical materials directly on the surface of common commercial crop leaves. The microscope uses a chromatically fixed (1560 nm) femtosecond fiber laser, a commercial 2D galvanometer mirror system, and a PCIe digital oscilloscope card, which together kept total instrument costs under $40 000 (USD), a significant decrease in cost and complexity from common systems (commercial and home-built) using tunable lasers and faster beam-scanning architectures. The figures of merit of the low-cost system still enabled a variety of measurements of agrochemical materials. Following confirmation of largely background-free SHG imaging of common crop leaves (soybean, maize, wheatgrass), SHG microscopy was used to image active ingredient crystallization after solution-phase deposition directly on the leaf surface, including at industrially relevant active ingredient concentrations (<0.05% w/w). Crystallization was also followed in real-time, with differences in crystallization time observed for different application procedures (spraying vs single droplet deposition). A strong dependency of active ingredient crystallization on the substrate was found, with an increased crystallization tendency observed on leaves vs on glass slides. Different crystal habits for the same active ingredient were also observed on different plant species. Finally, a model extended-release formulation was prepared, with a decrease in active ingredient crystallinity observed vs solution-phase deposition. These collective results demonstrate the need for making diagnostic measurements directly on the leaf surface and could help inform the next generation of pesticide products that ensure optimized agricultural output for a growing world population.