3.1 Dynamics of Condensed Phase Molecular Systems

Our research activities on ultrafast hydrogen bond dynamics, initiated in 1998 within the collaborative research centre SFB450 "Analysis and control of ultrafast photoinduced reactions", has until now witnessed six distinct time periods. The first three periods have been funded through the SFB450-B2 project (1998-2010). Since 2010 third party funding comes through an ERC Advanced Grant (Ultradyne, Elsaesser, 2010-2015) and an ERC Starting Grant (Fingerhut, 2019-2021).

Phase 1 (1999-2002):

Our research initally focussed on the investigation of the structurally well-defined medium-strong intramolecular hydrogen bonds of phthalic acid monomethyl ester and 2-(2'-hydroxyphenyl)benzothiazole, where we investigated the anharmonic couplings with low-frequency hydrogen bond modes, as well as the rapidly fluctuating hydrogen bond networks of isotopically diluted water (HOD in D₂O).

1-1 Coherent wavepacket motions in medium-strong intramolecular hydrogen bonds
1-2 Ultrafast dephasing and spectral diffusion of isotopically diluted water

Phase 2 (2002-2006):

In the following period we investigated the vibrational couplings of a prototype medium-strong intermolecular hydrogen bonded system, acetic acid dimer, a model system that frequently appears in protein structures. Here the couplings of the O-H stretching vibration with the fingerprint O-H bending, and the C-O and C=O stretching modes, as well as with the low-frequency hydrogen bond modes have been explored. In addition we have been able to measure the dephasing, spectral diffusion and vibrational relaxation of the O-H stretching band of neat liquid water, the hydrogen bonded system with the fastest vibrational dynamics observed until now.

2-1 Coherent wavepacket motions in medium-strong intermolecular hydrogen bonds
2-2 Ultrafast dephasing, spectral diffusion and vibrational relaxation of neat liquid water

Phase 3 (2006-2010):

In the third period we investigated the vibrational couplings of hydrogen bonds in DNA oligomers as well as intermolecular hydrogen bonded biomimetic systems, such as 7-azaindole dimer. Here the couplings of the N-H stretching vibrations with the fingerprint modes, as well as with the low-frequency hydrogen bond modes play a key role in the vibrational dynamics. In addition we explore the couplings of the DNA oligomers with O-H stretching vibrations of solvation shell water molecules. A novel line of research is the investigation of the structural dynamics upon vibrational energy redistribution and relaxation of neat liquid water through inspection of the oxygen K-edge using ultrafast X-ray spectroscopy with high temporal resolution.

3-1 Vibrational dynamics in hydrated adenine-thymine DNA oligomers, and biomimetic hydrogen-bonded base-pair systems
3-2 Ultrafast response of the oxygen K-edge of neat liquid water upon a temperature jump

Phase 4 (2010-2013):

In the fourth period we expand our investigation on the vibrational couplings of hydrogen bonds in DNA oligomer films as well as intermolecular hydrogen bonded biomimetic systems, such as guanosine-cytidine or adenosine-thymidine base pairs in weakly polar solution. Hydration phenomena in DNA oligomers as well as in phospholipid self-assemblies are subject of this research. Implementation of 2D-IR photon echo techniques operating at different frequencies enables, together with two-colour IR-pump-IR-probe measurements, the in-depth exploration of ultrafast dynamics of local hydration interactions.

4-1 Vibrational dynamics in hydrated DNA oligomers, and biomimetic hydrogen-bonded base-pair systems
4-2 Ultrafast dynamics in hydrated phospholipid self-assemblies

Phase 5 (2014-2017):

In the fifth period we targeted our research on hydration phenomena of DNA and RNA oligomers as well as of phosphate ions. A close collaboration with the junior theory group of Dr. Benjamin Fingerhut has been established. A new research line involves the vibrational dynamics of hydrated proton species.

5-1 Vibrational dynamics in hydrated DNA
5-2 Ultrafast dynamics of hydrated phosphate ions
5-3 Ultrafast dynamics of hydrated excess protons

Phase 6 (2018-2024):

In the sixth period we aim to tackle with in-depth detail the dynamics and interactions of interfacial water around phosphate groups, as hydrated ions in solution or as key structural units in the sugar-phosphate backbones of DNA and RNA. We further explore the ultrafast dynamics of hydrated protons subject to various solution conditions.

6-1 Ultrafast dynamics of hydrated phosphate-counterion interactions
6-2 Ultrafast dynamics of hydrated excess protons