Ultrafast time-resolved studies of reactive intermediates

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TECHNICAL SUMMARY:This project will use ultrafast time-resolved UV-vis and IR spectroscopy to study the birth of carbenes and isomeric alkenes from photo-excited precursors. This research team will study both polar and non-polar alkene formation by monitoring the intense C=C and C=O bands, if available, or the out-of-plane bending region between 750 and 1000 cm(-1) using time-resolved IR spectroscopy. The primary goal of the project is to generate unique data concerning: (a) the competition between internal conversion and fragmentation in diazo and diazirine excited states; (b) to understand the chemistry of vibrationally excited, open-shell, singlet carbenes; and (c) the dynamics of fully relaxed closed-shell singlet carbenes. This study will reveal the dynamics and mechanistic pathways of chemical transformations that proceed during the first 0.3 - 2000 ps after a diazirine or diazo compound absorbs light. The secondary goal is to study the dynamics of isomerization of vibrationally relaxed alkyl substituted closed-shell singlet carbenes to alkenes using ultrafast time-resolved IR spectroscopy. The 1,2-hydrogen shift reaction is of basic fundamental interest, and these efforts will systematically vary the structure of carbenes and solvent to provide the first broad and quantitative description of this classic reaction.NON-TECHNICAL SUMMARY:This work will raise the level of understanding and predictability of photochemistry and bring it closer to the level of maturity of ground state chemistry. These efforts will spur the development of computational tools that can quantitatively predict photochemical and photophysical processes. The project will generate data that will help theorists develop methods with sufficient predictive power to aid the design of photochemical reactions. These computational and experimental investigations will work synergistically to train and educate students about reactive intermediates and the means to study them. Valuable new data will be available to evaluate the intrinsic properties and reactivity of these unusual reactive intermediates, and for which industrial applications already exist, particularly in lithography and semiconductor manufacturing. Graduate students will be trained in conducting research, both experimentally and theoretically, while the team will also reach out to the K-16 communities with research activities as well as educational outreach and engagement.