Understanding How Reaction Kinetics and Morphology Affect Photomechanical Molecular Crystals

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Non-Technical Abstract:In this project funded by the Solid-State and Materials Chemistry Program of the Division of Materials Research, Professor Christopher Bardeen of the University of California, Riverside is using a combination of novel chemical methods and characterization techniques to take organic crystals closer to practical applications. Organic crystals composed of light-sensitive molecules can undergo a variety of light-induced shape changes such as bending, twisting, and coiling. These materials could have application across a broad range of fields spanning from engineering to medicine to cell biology, by making it possible to create microdevices powered by light. One example of such a device would be a light-powered swimmer for microsurgery or drug delivery. The application of these photomechanical materials is hampered by a limited understanding of how they work and how their performance can be optimized. The PI will address these challenges by controlling important parameters like molecular structure and crystal shape, while designing new optical experiments to examine how the light-induced changes occur inside the crystals. Technical Abstract:The creation of stable photoreactive molecules is a prerequisite for better performing materials. One phase of the research concentrates on making new molecules to make crystalline structures that can survive exposure to air and solvents. For example, the use of fluorine substitution will raise the molecular oxidation potential and may also enhance crystal plasticity. Molecular crystals can also exhibit nonlinear spatio-temporal reaction kinetics that can lead to autocatalysis, enhanced mechanical response, and oscillatory motion under steady-state illumination. Oscillatory motion can potentially be harnessed to provide locomotion for micro-swimmers. Along with new theoretical approaches, a novel standing-wave fluorescence experiment will be developed to directly probe the nonlinear reaction kinetics in single crystals. Finally, both bottom-up solution growth and top-down laser cutting will be used to create crystals with well-defined orientations and shapes. By controlling both crystal shape and the orientation of the strain tensor with respect to that shape, a detailed investigation into how both variables determine the crystal's response to light will become possible. The broader impacts of this work include potential societal impacts resulting from new materials that transform photons into mechanical motion and enable new devices. Participating graduate and undergraduate students will receive training in spectroscopy, materials characterization, and data analysis that will enable them to contribute in economically important areas like photonics. The PI will also continue ongoing outreach efforts at Taft Elementary School that impact hundreds of underrepresented minority students each year.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.