RESEARCH

'Confinement-controlled Chemistry' is a common factor in outstanding fundamental scientific problems in fields such as energy technology, environmental studies, catalysis, and biomedicine. Confinement may also influence environmental issues, for example in ion selective membranes for desalination, morphologically controlled heterojunctions in photovoltaics, electrodes for battery materials in energy technology, or selective ion receptors in nuclear waste. In catalysis artificial enzymes or porous solids are used. In GRK 2376, state-of-the-art experiments and theoretical models are employed to explore how confinement to nanoscale dimensions alters the transition states and pathways of chemical reactions.

0d-2d Small

The collaborative research will determine how the nature of the confining environment, e.g. surface chemistries, surface roughness, or geometry (2D vs. 1D vs. 0D), can ultimately be used to control key features that guide important chemical transformations. For this, a range of new experimental and theoretical tools is developed and applied in order to address the fundamental problem of 'Confinement-controlled Chemistry': the complementary scientific approach will combine supra-molecular chemistry, fast laser spectroscopy, synchrotron X-ray spectroscopy, linear and nonlinear vibrational spectroscopies, single molecule imaging, and theoretical techniques in quantum chemistry, force field and ab initio molecular dynamics and free energy simulations.

The following research projects are conducted by the members of the Graduate School GRK 2376:

A1: Confinement in Supramolecular Cages

The aim of the project is to determine the propensity for guest binding and ability to promote encapsulated chemical reactions of organic cages. Among the studied compounds are switchable Pd2L4 cage and Pd2L3 bowl systems or photoswitchable diarylethene Pd2L4 cages for which guest exchange dynamics are of special interest. A further goal is the exploration of neutral guest binding interpenetrated Pd4L8 cages for investigating light-initiated radical reactions. The synthetic methods are complemented by UV/Vis, fluorescence, and NMR spectroscopy, HR-ESI-MS, ion mobility mass spectrometry, isothermal titration calorimetry, cyclic voltammetry, X-ray crystallography, and DFT calculations.

Principal investigator: Guido Clever
2. Supervisor: Karina Morgenstern
Co-advisor: Martin Head-Gordon

PhD students: Kristina Ebbert, André Platzek

A2: Optical Activity in 0D–confined Spaces

The aim of the project is to gain insight into the importance of the chemistry of the walls onto the induction of optical activity into the vibrational modes of small chiral guest molecules. This is investigated for organic cages composed of achiral side-arms and chiral head groups by solution-phase vibrational circular dichroism. This spectroscopic method is sensitive for chiral molecular structures and intermolecular interactions and is employed in combination with DFT-based spectra calculations and molecular dynamics simulations for the analysis of experimental data. Suitable organic model compounds are synthesized within the project.

Principal investigator: Christian Merten
2. Supervisor: Guido Clever
Co-advisor: Evan Williams

PhD student: Kevin Scholten

A3: Confinement-Controlled Structure-Dynamics-Property Relationships in Supramolecular Cages

The aim of the project is to obtain an atomic-level understanding of the structural dynamics of the guest-host interaction, the free energy landscape of host-guest binding, and the enthalpy and entropy contributions to the free energy of guests inside supramolecular cages. Chiral azacryptands and metallo-supramolecular cages serve as host molecules whereas small anorganic molecules are the guests. Classical molecular dynamics (MD) simulations, free energy simulations, quantum chemical calculations, and polarisable force field MD simulations are performed to decipher guest binding and light-induced release.


Principal investigator: Lars Schäfer
2. Supervisor: Christian Merten
Co-advisor: Teresa Head-Gordon

PhD student: Anna Selina Juber

A4: Exploring Photochemical Reaction Dynamics Modified by Confining Surroundings

The aim of the project is to determine how encapsulation influences photochemical processes, especially the dependence of photo-induced charge transfer on confining conditions, and the functionality and benefits of photo-switchable containers. The confining environments comprise photoswitchable cages and droplets in reverse micelles, investigated systems are organic compounds capable of taking up charges, cage components, and guest species. Processes like photoinduced charge transfer or light-induced guest release are investigated with UV-MIR femtosecond transient absorption spectroscopy and time-resolved fluorescence methods.

Principal investigator: Patrick Nürnberger
2. Supervisor: Wolfram Sander
Co-advisor: Dan Neumark

PhD student: Niklas Sülzner

A5: Ion Coordination and Precipitation Reactions in Reverse Micelles Studied by X-ray Analysis

The aim of the project is to determine the effect of spatial confinement on ion coordination in solution and its effect on nanoparticle precipitation reactions. The confinement is realized by reverse micelles with enclosed small ions. Metal ion coordination and nanoparticle precipitation induced by reducing agents and by electrochemical means are investigated by various spectroscopic methods. Among these are soft X-ray scattering (performed at storage ring beamlines) in a chamber with cryogenic samples environment and liquid jet technology, small angle X-ray scattering, and step-scan FTIR with stopped flow.


Principal investigator: Axel Rosenhahn
2. Supervisor: Kristina Tschulik
Co-advisor: Rich Saykally

PhD student: Patricia Palitza

A6: Can the Chiral Shape of a Confined Space Determine Stereoselectivity?

The aim of the project is to gain spectroscopic insights into conformational preferences of small guest molecules in macrocycles in order to elucidate how the chiral host molecules influence chiral reactions taking place in or at the guest molecule. Studies include chiral crown ethers and other macrocyclic compounds in solution and photochemical isomerization as model reactions. Vibrational circular dichroism experiments are performed in solution and are complemented by DFT-based spectra calculations and molecular dynamics simulations, as well as organic synthesis of the investigated model compounds.

Principal investigator: Christian Merten
2. Supervisor: Lars Schäfer
Co-advisor: Evan Williams

PhD student: Luisa Weirich

A7: Reactive Molecules in Confinement – from Matrix Cages to Surface Molecules

The aim of the project is to synthesize and isolate highly reactive carbenes and radicals in matrix cages, supramolecular host molecules, and on surfaces, and to investigate the bimolecular chemistry of these species. In combination with organic synthesis including isotopic labelling, laser-induced photochemical reactions are studied for carbene precursors and small molecules under cryogenic conditions, e.g. inert gas matrices, amorphous water ice, or parahydrogen matrices. The employed spectroscopic methods combine matrix isolation with IR and UV-VIS studies as well as with X- and Q-band EPR spectroscopy.

Principal investigator: Wolfram Sander
2. Supervisor: Karina Morgenstern
Co-advisor: Martin Head-Gordon

PhD student: Julien Rowen

B2: Altered Electrochemistry in 0D Confinement

The aim of the project is to determine the effects of geometric confinement in 0D on charge transfer at the solid/liquid interface. Using single micelle electrochemistry and ensemble studies, the reactivity changes of solution phase redox couples in 0D confinement are explored, and the effect of 0D confinement on electrochemical reaction rates and mechanism of multi-electron transfer reactions is investigated. Applied experimental techniques comprise cyclic voltammetry and chronoamperometry at micelle modified electrodes, single entity electrochemistry, and surface and micelle characterization (AFM, dark field microscopy & hyperspectral imaging).

Principal investigator: Kristina Tschulik
2. Supervisor: Axel Rosenhahn
Co-advisor: Miquel Salmeron

PhD student: Maximilian Jaugstetter

B3: Altered Electrochemistry in 1D Confinement

The aim of the project is to determine the effects of geometric confinement in one dimension on charge transfer at the solid/liquid interface. For this, membranes with adjustable pore size are studied: anodically oxidized aluminium (AAO, prepared within this project), ion track-etched polymer membranes, and unmodified and metal coated membrane pores. This is pursued by constant and pulsed high potential electrochemical etching, electrodeposition, cyclic voltammetry and chronoamperometry at porous membranes, surface and cross-sectional characterization (atomic force microscopy, scanning electron microscopy).

Principal investigator: Kristina Tschulik
2. Supervisor: Axel Rosenhahn
Co-advisor: Miquel Salmeron

PhD students: Niclas Blanc, Kevin Wonner

B4: Disentangling One- and Two-dimensional Confinement Effects from Wall Effects

The aim of the project is to determine the effect of the dimensionality of confinement onto elementary surface reactions and disentangle geometrical confinement effects from changes due to electronic alterations of the molecules on a fundamental level. Laser-induced photochemical reactions are studied on surfaces (ZnO and rare gas layers on a patterned surface) for azobenzene and carbene precursors with small inorganic molecules. Several scanning tunneling microscope techniques are applied, e.g. at low temperature in ultrahigh vacuum or with meV resolution, complemented by in-situ molecule deposition and laser activation as well as infrared spectroscopy under UHV conditions at 80 K with sub-meV resolution.

Principal investigator: Karina Morgenstern
2. Supervisor: Dominic Marx
Co-advisor: Miquel Salmeron

PhD students: Inga Langguth, Vladimir Lykov

B5: Nanoconfined Chemistry within Graphene Slit Pores

The aim of the project is to explain nanoconfinement effects on chemical reactivity by computationally studying archetypical chemical reactions in water within graphene slit pores via tuning interlayer distances. Confinement is achieved by graphene sheets with different interlayer distance down to the limit of allowing only a water monolayer in the confined space, while water self-dissociation plus other key reactions, e.g. nucleophilic substitutions and elimination reactions, are explored. The employed methods comprise ab initio molecular dynamics simulations (CP2K), DFT with dispersion corrections (RPBE-D3), a QM/MM hybrid scheme combining force fields with ab initio electronic structure calculations, and sampling of free energy landscapes.

Principal investigator: Dominik Marx
2. Supervisor: Lars Schäfer
Co-advisor: Teresa Head-Gordon

PhD student: Saskia Körning

B6: Chemistry in Confinement Characterized by THz Spectroscopy

The aim of the project is to study reactions in nanoconfinement and nanoenclosures by THz spectroscopy, identifying the low frequency fingerprints of pressure-induced spectral changes of trapped molecules and the changes of Thz dynamics of confined water. Stability and reactions under confinement are studied as a function of pore size and/or layer distance (e.g. pressure-assisted dissociation of salts into their hydroxides and oxides) for materials like graphene, silica structures, or organic sub-nanopores as nanoreactors. The applied experimental techniques are THz-FTIR spectroscopy for pressure- and temperature-dependent studies, non-linear THz spectroscopy, and nano-electrospraying for salts solutions in confinement.

Principal investigator: Martina Havenith
2. Supervisor: Patrick Nürnberger
Co-advisor: Evan Williams

PhD students: Sarah Funke, Thorsten Ockelmann