Abstract:
For understanding the functioning of many photo-driven molecular machines, it is crucial to capture the temporal evolution of their chirality and thus structure upon photo-excitation. This is especially relevant for understanding many biological systems, such as photo-active proteins and the kinetics of novel synthetic machines, such as unidirectional molecular motors. Steady-state circular dichroism (CD) has become a standard analytical tool to obtain solution-phase structural information via a molecule’s chiral properties. Especially in the deep ultraviolet (UV) spectral range (< 300 nm), it is sensitive to the UV-transitions in proteins and many organic ligands in functional chiral complexes. However, pushing CD spectroscopy into the time-domain has remained a challenge, with only few isolated reports with sub-nanosecond resolution [1].
In this context, I will present a novel broadband time-resolved CD spectrometer in the deep-UV region (250–370 nm) with sub-picosecond time-resolution [2]. With this instrument, it is possible to extract broadband CD spectra of photo-excited states and track their temporal evolution. From the characterisation of the structurally well-defined photo-excited triplet metal-to-ligand charge transfer (MLCT) state in [Ru(bpy)3]2+, I will proceed to the more complicated dynamics of photo-excited supramolecular systems: [Fe(bpy)3]2+ is configurationally labile in solution and its configuration needs to be controlled by supramolecular complex formation with enantiopure counterions [3]. Here, we study the transfer of the underlying diastereomeric interaction to the photo-excited neutral quintet state, which couples to an accompanying ultrafast expansion of the metal-ligand distances.
I will conclude the talk by introducing a site-specific CD-label for time-resolved studies of ultrafast conformational dynamics in peptides and proteins [4]. In this way I hope to demonstrate that the measurement of ultrafast chirality changes in photo-active functional complexes and biological systems is now feasible, opening novel avenues in chiroptical spectroscopy and structural dynamics research.
[1] J. Meyer-Ilse et al., Laser Photon. Rev. 7, 495 (2013)
[2] M. Oppermann et al., Optica 6, 56 (2019)
[3] J. Lacour et al., Angew. Chem. Int. Ed. 37, 2379 (1998)
[4] M. Oppermann & J. Spekowius et al., J. Phys. Chem. Lett. 10, 2700 (2019)
Biography:
Malte Oppermann obtained his PhD from Imperial College London in 2013. Under the supervision of Prof. Jon Marangos, he used intense laser pulses to fix gas-phase molecules in space and study the stereo-dependence of their ultrafast ionisation dynamics. After a gap-year abroad, Malte obtained a postdoctoral fellowship from the German Academic Exchange Service to join the group of Prof. Majed Chergui at École polytechnique fédérale de Lausanne (EPFL), with the aim to shift his research focus to the investigation of ultrafast chemical and biological processes in liquid phase. There, he coordinates the group’s laboratory for time-resolved spectroscopy in the ultraviolet (UV), which houses a range of laser-based setups to probe important UV-chromophores, such as amino acid residues in proteins and peptides, the nucleobases in DNA-systems and many organic ligands in coordination complexes. Malte’s own work focusses on using the polarization of light to capture the fastest structural changes in these systems in real-time and he has recently developed a novel time-resolved circular dichroism spectrometer to achieve this by tracking ultrafast chirality changes in molecular systems with femtosecond time-resolution.