Molecular Spectroscopy-Max Planck Institut für Polymerforschung, Mainz

Prof. Dr. Mischa Bonn

The aim of the Molecular Spectroscopy group is to elucidate intermolecular interactions between the different molecular constituents (lipids, proteins and water) of model biological membranes, using (ultrafast) optical techniques.

In a second line of research, we are attempting to characterize and control optical properties and charge carrier dynamics in semi-conductor nanostructures using ultrafast TeraHertz spectroscopy.

Research Activities:

Vibrational spectroscopy and microscopy on model membranes
Membranes constitute the highly active partition between living cells and the outside world. They regulate molecular transport, cell adhesion and intercellular signaling. A detailed understanding - and control - of the many biological processes that occur at the membrane surface, such as viral infection and targeted drug delivery, requires insights at the molecular level. Recent developments in experimental techniques have opened avenues for the study of intermolecular interactions and chemical processes at surfaces and interfaces with unprecedented time and spatial resolution, without the need for (fluorescent) labels. We employ Sum Frequency Generation (SFG) and Coherent Anti-Stokes Raman Scattering (CARS) microscopy to address important issues in biological (model) membranes. We investigate, for instance, the structure and dynamics of membrane-bound water, and the role of cholesterol - the second most important membrane constituent after phospholipids - on the structure of the lipid layer.

Time-domain terahertz (THz) spectroscopy of solar cell building blocks
It is challenging to characterize charge carrier movement in semiconductor nanostructures, partly because of the complications of attaching contacts to the sample. Moreover, conductivity measurements at low frequencies are inherently limited in the information content. These drawbacks can be circumvented using freely propagating THz pulses. The rapidly varying electric field contained in these pulses with durations of ~1 picosecond allows for the investigation of key electronic properties of materials such as the electron mean-free path, exciton properties and confinement effects in nanostructured materials. Furthermore, the high time resolution of this technique allows the study of dynamic processes and/or systems far from equilibrium using a pump-probe experimental approach. Using THz spectroscopy, we investigate charge dynamics in building blocks for solar cells: conjugated polymers, nanostructured semi-conductors of CdSe, InAs and TiO2, and ZnO nanowires. A brief, incomplete overview of our activities can be found on our Time-domain terahertz (THz) spectroscopy website.

Schematic representation of a cell membrane

In the process of Sum-Frequency Generation (SFG) at a water-lipid interface, two laser beams (depicted here in red and green) are combined to generate a third color (here:blue)