With the support of the Organic and Macromolecular Program, Professor Matthew Platz and his group plan to study the photochemistry of diazirines, diazo compounds and azides ("precursors") and the birth of carbenes and nitrene reactive intermediates. Using femtosecond time resolved UV-Vis and IR spectroscopy and computational methods they will learn which transition of the precursor molecules is pumped and which excited state of the precursor leads to fragmentation to form a reactive intermediate and nitrogen. If the pumped state and dissociative states are not the same, they will study the pathway connecting them and the time scale of the dissociative process. They will verify that rearrangement can proceed in concert with nitrogen extrusion and identify the excited state responsible for that process. They will monitor the formation of hot reactive intermediates and the structural and environmental factors that control the rate at which they transfer heat to solvent and if they rearrange as they relax. The group will learn the lifetime of singlet reactive intermediates and the factors that control their relaxation to triplet state species. The research has several broad impacts. Students are trained in classical organic chemistry as well as ultrafast spectroscopic techniques and advanced computational methods. Students will learn to work in a group that does synthetic chemistry, analytical chemistry, ultrafast spectroscopy and theory. Organic, analytical and physical chemists work together and learn from each other. Historically, the Platz Laboratory welcomes women, minority and majority high school student interns, undergraduates, graduate students, post doctoral students and visiting faculty. Students learn to work with individuals of many races, ethnicities, nationalities and educational level. Numerous graduates of the laboratory have been placed in university, college and high school positions teaching chemistry, and they are committed to continue this tradition.
of direct relevance to photolithography, an area of critical value for semiconductor manufacturering. This project emphasized the direct observation of transient species using ultrafast time resolved ultraviolet-visible (UV-vis) and infrared (IR) spectroscopy. These studies provided quantitative information on the lifetimes and reactivity of short-lived excited states, carbene and nitrene as reactive intermediates, as well as information about their electronic and geometric structures. This allowed the first detection of many species of fundamental interest that have sub-nanosecond (ns) lifetimes and answer the basic question of whether or not certain fragile molecules exist at all, and, if so, for how long. The proposed research contributed to science in a broad sense by contributing to our understanding of how the electronically excited states of precursors (azides, diazirines and diazo compounds) connect to the ground state surfaces of carbenes and nitrenes and related intermediates. We learned about the influence of structure, wavelength and solvent on the details of this connectivity and expect that general principles, applicable beyond, for examples azides and nitrenes, will emerge. Our work will stimulate the development of new theory and modeling of radiationless processes. Our results will also be of practical benefit to chemists who use these reagents in photoaffinity labeling experiments in chemical biology and to materials scientists wishing to modify surfaces and to scientists interested in photolithography. Students learned and improved their skills in classical organic chemistry (synthesis, characterization, analysis of reaction mixtures), computational chemistry, and ultrafast time-resolved laser spectroscopy. Educating students and encouraging them to pursue careers in science is another significant outcome of this project, including high school and undergraduate students.
