Nonlinear Optical Analysis of Molecular Composition and Dynamics within Heterogeneous Assemblies

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Professor Garth Simpson of Purdue University is developing a new imaging tool to map the chemical composition of and dynamics in heterogeneous assemblies. Understanding chemical complexity with high sensitivity and sub-micrometer spatial resolution is important for understanding the stability and bioavailability of chemical components in therapeutic materials while the presence of trace species can influence crystallization and phase transformations in two dimensional materials. Professor Simpson and his group will develop a new imaging tool based on infrared spectroscopy and molecular chirality to map the composition and translational dynamics within structurally heterogeneous assemblies. Their discoveries could lead to new approaches for extracting chemical information from images including how active molecular components are distributed in pharmaceuticals. Professor Simpson will also lead a short course on nonlinear optics and engage students in research activities. The measurement capabilities of photothermal infrared imaging will be enhanced in the fingerprinting region of the spectrum through integration of chiral spectroscopic contrast and the creation of photobleached gratings in samples. This approach is expected to resolve inhomogeneities of diffusion in traditional infrared imaging by improving both temporal and spatial resolution. By using chiral-specific spectroscopies, molecular orientation and order within microstructured assemblies will be interpreted and predicted using a mathematical framework. Chiral-specific effects predicted in the mid-infrared transmission measurements of ordered systems will then be extended to microcrystals and tissues. Finally, a spatial Fourier transform approach for fluorescence recovery after photobleaching will be used for construction of spatially-resolved maps of molecular diffusivity within heterogeneous assemblies. These local-viscosity maps have the potential to provide key details about how composition and molecular transport govern the behavior of biologically-active materials. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.