Photodynamics of small aromatic molecules and selected inorganic isosteres

• Applicant: Professor Dr. Ingo Fischer
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545634500

We will investigate the photochemistry, photophysics and photodissociation dynamics of small aromatic molecules in the gas phase. The work is motivated by the fundamental interest in several species, but also by their relevance in various areas of chemistry. Systems to be studied include C6H6 isomers, some of their B,N isosteres (i.e. exchanging two carbon atoms by one nitrogen and one boron atom) and finally selected C7H6 and C7H5 isomers. The C6H6 isomers fulvene and DMCB are intermediates in the formation of aromatic rings and polycyclic hydrocarbons (PAH) in environments like combustion or interstellar space. The mechansim of PAH formation is still considered to be a major unsolved problem. Fulvene, DMCB and several of the C7Hx isomers are central species, but neither their chemistry nor the spectroscopy has been more than superficially studied. Replacing two carbon atoms in aromatic molecules by one boron and one nitrogen retains the number of electrons and leads to isosteres, which exhibit dramatic modifications of the electronic structure, which make the compounds relevant for material science applications. It was e.g. suggested that B,N isosteres of PAHs might facilitate singlet fission, a process that is assumed to increase the efficiency of solar cells. Here, we will address borazine (also called "inorganic benzene") and 1,4-azaborine to improve our understanding of the photochemistry in B,N isosteres of benzene. The experiments are based on laser excitation to initiate the photochemistry and ionization to monitor the dynamics. While the primary processes will be studied by time-resolved spectroscopy in Saclay, processes on a longer time scale will be followed by the detection of photofragments in Würzburg. As a novel technique, we will employ femtosecond soft X-ray probe pulses to access steps of the reaction that are inaccessible by standard methods. The structure and reactivity in the molecular cation will be explored using synchrotron radiation to obtain a full picture of the molecular chemistry. The studies are complemented by computations and experiments will be simulated by molecular dynamics calculations. The project becomes possible by the complementary skills of the applicants. While the Würzburg team provides expertise in the chemistry of reactive species, their photodissociation and photoionization and computational simulation of their reactions, the Paris-Saclay team is a leading group in the field of ultrafast spectroscopy. The groups cherish a long-standing collaboration and the project leaders have jointly supervised two binational PhD theses (cotutelle de these). This shows that the framework for a successful cooperation is already in place.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Co-Investigator: Professor Dr. Roland Mitric
• Cooperation Partners: Dr. Lou Barreau; Professor Dr. Lionel Poisson