Transient Structural Evolution and Dissipation in Organic-Inorganic Hybrids

Northwestern University, Evanston IL

Investigators

Abstract

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Richard Schaller of Northwestern University is using sophisticated time-resolved spectroscopies to examine the changes in lattice structure that occur after photoexcitation of hybrid crystals containing both organic and inorganic components. Establishing a connection between the photoinduced structural changes that take place in these materials and their functional behavior is challenging. The Schaller group will selectively deposit energy in particular bonds within the hybrid crystals and use ultrafast spectroscopies and time-resolved x-ray methods to watch the vibrational motion of the atomic sites in the crystal that ensues. The project aims to quantify excitation-induced structural changes in bond angles, bond strengths, strains and symmetries under a variety of experimental conditions. Such discoveries could aid in the design of functional organic-inorganic materials for next generation clean energy technologies. The project will also provide research opportunities for graduate students in physical chemistry methods and sustainable energy science, and the project participants will engage in educational outreach activities for high school students. Organic-inorganic hybrids used in sustainable energy technologies, including metal halide perovskites, polyoxometalates, and metal-organic-frameworks, share characteristics of highly disparate chemical species in close proximity. Transient structural changes and atypical vibrational coupling are suspected to play key roles in these systems, which prompts time-resolved investigation of lattice and vibrational evolution with control over electronic and vibrational energy deposition. The Schaller laboratory will experimentally investigate excited-state structural changes that impact function for organic-inorganic hybrids. Activities to be performed include femtosecond stimulated Raman spectroscopy, infrared-pumped transient absorption, and transient X-ray diffraction with visible or infrared excitation for a series of promising compositions. The project has the potential to advance fundamental understanding of the mechanisms by which these hybrid materials exhibit long carrier lifetimes and transfer vibrational energy through inhomogeneous environments. 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.