RUI: Selective Excitation and Charge Dynamics of Dark Molecular Transitions

About This Grant

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professors Uttam Manna and Mahua Biswas of Illinois State University is studying how light interacts with molecules. Typically, when light hits a material, it follows well-known “bright” pathways that are easy to detect. However, light can also take much weaker, hidden routes known as “dark transitions.” Understanding these lesser-known processes could lead to important scientific breakthroughs. To investigate these effects, the research team will use special materials called metasurfaces—engineered nanostructures made from extremely small particles with unique abilities to control light. These metasurfaces will help the researchers detect dark transitions in molecules containing a metal called ruthenium. By shining light on these molecules and using sensitive tools to observe their response, the team will aim to understand how energy moves within them. This research could help scientists develop better ways to use light for sustainable energy, next-generation electronics, and the design of new materials. The project will also support science education and workforce development in science, technology, engineering and mathematics (STEM) fields. Undergraduate and master’s students will gain hands-on research experience and training. The research will be integrated into the physics curriculum, particularly in experimental courses. In addition, the investigators will provide research opportunities for students and will engage local high school students in meaningful science experiences. With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professors Uttam Manna and Mahua Biswas of Illinois State University is studying dark molecular transitions enabled by the enhanced magnetic field of high refractive index dielectric nanoparticles and metasurfaces. In optical frequencies, most light–matter interactions are dominated by electric dipole transitions, while magnetic dipole transitions are generally considered "spin-forbidden" or "dark." Typically, spin-forbidden magnetic dipole transitions in molecular systems, such as those from the ground singlet state to the excited triplet state, are enabled by introducing spin-orbit coupling to break the selection rules. In this project, the transition from the ground singlet state to the excited triplet state in molecular systems will be excited using the enhanced magnetic field of high refractive index dielectric nanoparticles and metasurfaces. The research team will perform photoluminescence, photoluminescence excitation, time-resolved photoluminescence, and transient pump–probe X-ray absorption spectroscopy to measure the emission spectra, lifetimes, and oxidation states associated with the direct emission from the triplet to the singlet state in ruthenium complexes and to study their charge dynamics. Molecular light emission is typically limited to an internal quantum yield of approximately 25 percent through singlet–singlet transitions, while about 75 percent of the decay pathways are spin-forbidden singlet–triplet transitions. Therefore, direct excitation of triplet states through magnetic field enhancement would represent a breakthrough in molecular excitation and could open new directions for the application of triplet states in energy conversion and chemical reactions. 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.