Instrument Development: Modular, Multitrack, and Multifunctional Linearly Polarized Spectrometer for Synchronized Multispectral Characterization of Molecular Assembly

With support from the Chemical Measurement and Imaging (CMI) program of the Chemistry Division and the Established Program to Stimulate Competitive Research (EPSCoR), Professor Dongmao Zhang and his research group at Mississippi State University are developing a multichannel spectrometer for simultaneous acquisition of UV-visible and linearly polarized resonance synchronous (LPRS) spectra. LPRS spectroscopy is a new technique recently developed by the Zhang group that employs linearly polarized light for excitation and detection.

When used in combination with UV-visible measurements, the LPRS method enables quantitative determination of the absorption, scattering, and emission properties of natural and synthetic biological, chemical, and environmental samples. The spectral signatures obtained with the combined UV-vis and LPRS analysis provide fingerprint-like information about the geometric features (sizes and shapes) and the optical properties of materials.

However, the current UV-vis and LPRS analysis is time-consuming and applicable only to steady-state samples because it requires three sequential spectral acquisitions performed with two different instruments. Therefore, this grant supports the development of new measurement tools to enable simultaneous multidimensional spectroscopic characterization of dynamic systems with high temporal resolution.

Such techniques are crucial for many areas of science and technology, including biology, materials science, clean energy applications, and environmental protection. The broader impacts of the project also include training opportunities for students from diverse backgrounds in the cross-disciplinary areas of scientific instrumentation, optical spectroscopy, data acquisition and analysis, and materials science.

Furthermore, the Zhang group will organize two optical spectroscopy workshops to provide opportunities for HBCU (Historically Black College and University) and PUI (Predominantly Undergraduate Institution) students and faculty to learn about the theory and unique capabilities of the techniques being developed in this project.

Solution-phase processes involving the dynamical evolution of materials are ubiquitous in chemistry, biology, and materials science. Examples of such systems include protein aggregation, molecular assembly, and nanoparticle synthesis, as well as post-synthetic modifications of macromolecules, supramolecular assemblies, and nanoscale materials. Technologies that are capable of concurrently monitoring the evolution of these materials are crucial not only for deciphering correlations between structure and optical properties, but also for discovery and optimization of new materials.

Optical spectroscopic techniques that exploit the interaction of light and matter have been the methods of choice for studying such dynamic systems because of their broad accessibility and relatively high temporal resolutions. However, existing tools are limited in their information content because they are incapable of simultaneously resolving the complex interplay among the absorption, scattering, and emission processes.

The combined UV-vis and LPRS analysis is extraordinarily informative because this approach enables concurrent experimental quantification of a material’s absorption extinction spectrum, scattering extinction spectrum, scattering depolarization spectrum, fluorescence intensity and depolarization spectra, and fluorescence quantum yield. Collectively, these spectral signatures provide critical insights, many being inaccessible before, on the sizes, shapes, molecular compositions, and optical activities of materials.

The scientific investigation outlined in this project aims to create a multichannel linearly polarized spectrometer capable of concurrent acquisition of these multidimensional signatures with sub-second temporal resolution. The research team will study the formation of porphyrin assemblies as model systems for developing the measurement approach and will investigate how the absorption, scattering, and emission properties vary during assembly and disassembly.

These studies have the potential to reveal mechanistic pathways in the porphyrin assembly and disassembly processes. The measurement and data analysis strategies developed for these model systems will be extensible to numerous other dynamic systems across a range of scientific disciplines, and provide a platform for advanced student training and the engagement of researchers from diverse backgrounds.

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.