Biradicals play an important role in the chemistry of reactive environments like combustion engines, the atmosphere or interstellar clouds. Furthermore electronic states with a biradical character are key intermediates in the formation of light-emitting states in optoelectronic materials. It is therefore of relevance for many areas of chemistry and physics to understand and correctly describe the dynamic processes in biradicals and molecules with biradical electronic states. It is the goal of this graduate research school to investigate biradical systems with an electronic structure that is characterized by two unpaired electrons in degenerate or near-degenerate molecular orbitals. Their chemical and physical properties differ significantly from those of closed-shell molecules due to the interactions between the energetically close-lying states that result from the degenerate molecular orbitals.
Specifically we want to
- study the relationship between molecular structure and properties of biradicals, like the influence of substituents on stability and spin multiplicity.
- understand the formation and photophysics of charge-separated biradical states and long-lived triplet states and the influence of the environment on these processes.
- investigate experimentally and describe theoretically the structure of excited electronic states of biradicals and their chemical reaction mechanisms in the gas phase and solution.
To achieve these goals, we combine synthesis, spectroscopy and theory. Among the experimental methods that will be applied are laser spectroscopy in the time- and frequency-domain, also under the influence of an external magnetic field, electron paramagnetic resonance and spectroelectrochemistry. The electronic structure will be studied by quantum chemistry, while the influence of the environment will be modelled by quantum-classical hybrid methods. Insight into the molecular dynamics will be obtained from surface hopping dynamics und model Hamiltonians. We want to advance the understanding of bonding in organic biradicals, but also in inorganic species like diborenes, in order to reduce phenomena in complex open-shell systems to fundamental principles.