CUI: AIM

B2.1 - Charged directed chemistry

The ATTO group is part of the CUI: Advanced Imaging of Matter (AIM) excellence cluster of the Universität Hamburg, focused on the investigation of emerging functionalities in systems of increasing complexity. More specifically, our group is involved in AIM’s research area that targets molecules of small to medium size which, despite their limited number of atomic constituents, already possess a large number of degrees of freedom. Emergent behaviour in these systems arises through an intimate coupling between the electronic and nuclear sub-systems, and may be further promoted through interaction with a solvent or surface environment.

Highly efficient energy conversion from light to molecular function plays a fundamental role in artificial and biological light harvesting as well as in mitigating radiation damage. Investigating the problem at the molecular level allows the mechanisms leading to efficient electron and energy transfer to be unraveled. Recent advances in ultrafast laser technology have given access to the electron time scale in matter, and real-time tracing of the photo-induced electron dynamics in biologically relevant molecules has been demonstrated. In this project, we endure in a joint experimental and theoretical approach to understand and control ultrafast processes with unprecedented spatio-temporal resolution in free molecular systems relevant for chemistry and biology. Ultrashort UV/XUV light pulses are used to excite/ionize the system and prepare electronic coherences. Our goal is to then investigate the dynamical emergence of strongly coupled vibronic (non-Born-Oppenheimer) degrees of freedom and attempt to control the fate of these electronically excited systems. These studies will unravel the role of underlying molecular processes (including charge migration, charge transfer and localization) on the subsequent photochemistry and photobiology of the system. Tailored laser fields are being developed to steer and optimize charge flow with the aim of obtaining a charge-directed reactivity.

We use high-energy photons to activate a strongly nonadiabatic molecular dynamics. After sudden ionization the electronic charge density rapidly oscillates, and theoretical calculations indicates that charge can be driven by vibronic couplings from one site to another of the molecule within a few femtoseconds. S₁₁₈, S₁₁₉ and S₁₂₀ are calculated electronic states. Image credit: https://doi.org/10.1103/PhysRevLett.115.143002.

On the experimental side, where the ATTO group has a prominent role, we coherently excite/ionize molecules of biological relevance such as many aromatic compounds, amino acids, purines and pyrimidines and subsequently probe the coupled electron and nuclear dynamics with attosecond pulses from the XUV to the soft-X spectral region. Different approaches can be used to track the charge flow with site specificity, including transient absorption and photoelectron-photoion detection. Experiments are performed at first in gas-phase molecules, and will be gradually extended to a micro-solvated environment.

Main collaborators:

• Markus Drescher
• Franz Kärtner
• Daniela Pfannkuche
• Robin Santra