Sub-100fs Elementary Molecular Interactions in 2 Dimensions

One of the central issues in chemical physics is how the structures of complex molecular systems evolve, and how such dynamics are related to processes of chemical or biological relevance. For over two decades, multi- dimensional nuclear magnetic resonance (NMR) spectroscopy has been a valuable and well established technique to answer these questions. Manipulation of spins by appropriate pulse sequences allows to probe structure and dynamics of molecules in great detail, exploiting spin-spin interactions through chemical bonds or directly through space. Displaying the signal obtained by varying n parameters results in n-dimensional (nD) correlation plots, which form the basis of nD spectroscopies. The spreading of spectroscopic information in more than one dimension helps to resolve congested spectra, selectively eliminates static broadening mechanisms, and provides structural and dynamical information unavailable from one-dimensional measurements. However, although two- dimensional (2D) NMR can resolve the structure of complex molecules with atomic resolution, its millisecond timescale is too slow to follow the ultrafast dynamics (tens of femtoseconds to picoseconds), which is crucial for the elementary understanding of interactions between electronic (optical) excitations (excitons). Due to the much shorter timescales involved, requiring techniques of ultrafast pulsed laser instrumentation, optical spectroscopy has only recently reached a state where similar control over vibrational or electronic excitations becomes accessible, and this development was guided by considerable advances in the theoretical description of the underlying phenomena. The project being presented, in particular, aims at the implementation of a new generation of phase- locked, heterodyne detected three-pulse photon-echo experiments in the optical regime. This kind of optical spectroscopy has the unique potential to disentangle electronic molecular interactions, usually hidden in conventional linear spectra of complex many-bodies, by spreading the spectroscopic information into a second frequency-channel. Special emphasis will be placed on the application of this technique to study excitonic molecular systems of increasing complexity, such as specially designed dimers, dendrimers, supramolecular assemblies, aggregates, and polymers, both in solution and in the solid state. We expect that the combination of femtosecond optical spectroscopy with nD methods of magnetic resonance will open up exciting views on elementary molecular interactions and reveal dynamics of excitonic interaction with the highest possible time- resolution.

One of the central issues in chemical physics is how the structures of complex molecular systems evolve, and how such dynamics are related to processes of chemical or biological relevance. For over two decades, multi- dimensional nuclear magnetic resonance (NMR) spectroscopy has been a valuable and well established technique to answer these questions. Manipulation of spins by appropriate pulse sequences allows to probe structure and dynamics of molecules in great detail, exploiting spin-spin interactions through chemical bonds or directly through space. Displaying the signal obtained by varying n parameters results in n-dimensional (nD) correlation plots, which form the basis of nD spectroscopies. The spreading of spectroscopic information in more than one dimension helps to resolve congested spectra, selectively eliminates static broadening mechanisms, and provides structural and dynamical information unavailable from one-dimensional measurements. However, although two- dimensional (2D) NMR can resolve the structure of complex molecules with atomic resolution, its millisecond timescale is too slow to follow the ultrafast dynamics (tens of femtoseconds to picoseconds), which is crucial for the elementary understanding of interactions between electronic (optical) excitations (excitons). Due to the much shorter timescales involved, requiring techniques of ultrafast pulsed laser instrumentation, optical spectroscopy has only recently reached a state where similar control over vibrational or electronic excitations becomes accessible, and this development was guided by considerable advances in the theoretical description of the underlying phenomena. The project being presented, in particular, aims at the implementation of a new generation of phase- locked, heterodyne detected three-pulse photon-echo experiments in the optical regime. This kind of optical spectroscopy has the unique potential to disentangle electronic molecular interactions, usually hidden in conventional linear spectra of complex many-bodies, by spreading the spectroscopic information into a second frequency-channel. Special emphasis will be placed on the application of this technique to study excitonic molecular systems of increasing complexity, such as specially designed dimers, dendrimers, supramolecular assemblies, aggregates, and polymers, both in solution and in the solid state. We expect that the combination of femtosecond optical spectroscopy with nD methods of magnetic resonance will open up exciting views on elementary molecular interactions and reveal dynamics of excitonic interaction with the highest possible time- resolution.