Probing and Designing Cascade Reactivity in Consecutive Mechanoactivation of Covalent Bonds

With support of the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division, Yan Xia and Todd Martinez of the Department of Chemistry at Stanford University are designing mechanically responsive molecules, mechanophores, to understand new force-driven reaction pathways that are inaccessible under thermal or photochemical reaction manifolds. The proposed research aims to experimentally and computationally investigate the kinetic energy transduction, non-statistical dynamic effects, and cascade reactivity in consecutive mechanoactivation events across multiple coupled mechanophores. The project lies at the interface of physical organic, polymer, and computational chemistry, and is therefore well suited to the education of next-generation scientists at all levels. These groups will build on their record of collaborative research and education and aim to provide high level of education and training for students underrepresented in science. Demonstrating mechanochemistry using interactive mechanochromic experiments and virtual reality molecular stimulation is planned with the goal of sparking the interest of K-12 students in science. Mechanical stress is ubiquitous in nearly all terrestrial settings and technological applications. The proposed research aims to understand, explore, and develop cascade reactivity, non-statistical dynamic effects, and control product distribution in closely coupled ladder-type multi-mechanophore systems. Dynamic effects have been found to account for the reactivity and product distribution in many multistep thermal and photochemical reactions, where the reaction barrier becomes so small that transition state theory can no longer be used to rationalize the reactivity. Because the application of force significantly lowers the reaction barrier, dynamic effects are potentially much more common but rarely explored in mechanochemistry. The proposed research seeks to fill a knowledge gap in understanding how different molecular parameters influence the extent dynamic effects and control of mechanochemical reactivity of covalent bonds. Understanding and designing mechanochemical cascade reactivity and strong dynamic effects is expected to enable the design of chemical systems that exhibit a high efficiency of transducing mechanical energy into multifaceted chemical responses. 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.