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Time-resolved vibrational spectroscopy (Raman and IR) provides insight into energy relaxation processes and information about structural dynamics of molecules in solution. An extremely sensitive pump-probe laser-spectrometer has been built for time-resolved IR-spectroscopy in the coursework of this thesis. It allows one to initiate photochemical processes in the visible spectral region and to observe the changes in the mid-infrared. The achieved time resolution (delta tau_(FWHM) < 100 fs) makes it possible to follow extremely fast structural changes. With this setup dynamical processes can be resolved covering 4 orders of magnitude (from 100 fs to 4 ns). The setup is tunable in the range of 3-10 micrometer (1000-3300 cm^-1) and covers the whole relevant spectral range of vibrational structure analysis. \nIt is known from chemical synthesis, that reaction rates can depend on the chosen solvent. This might be due to partially solvent dependent energy redistribution processes. Such processes are important for chemical reactions, e.g. in stabilizing product states. The molecule para-Nitroaniline (pNA) is especially suitable to investigate such processes. pNA returns via fast (< 400 fs) internal conversion to a hot electronic ground state after excitation by a laser pulse (lambda = 400 nm). The vibrational energy relaxation can be followed subsequently. This relaxation has been observed by the symmetrical NO_2 stretch mode. Due to anharmonic coupling this low frequency mode has been an exceptionally sensitive sensor for the energy relaxation to a solvent. The observed relaxation time constants for pNA are 3,4 ps in deuterated dimethylsulfoxide, 1,9 ps in methanol and 1,5 ps in water. Cooling behavior correlates well with macroscopic thermal conduction and heat capacity of the used solvent. In the microscopic picture we assume a connection to the forming of hydrogen bonds. As chemical reaction rates depend strongly on the internal temperature of a molecule, these results improve the understanding of solvent effects. \nWith the same method the question of how fast structural changes can occur in a peptide of 8 amino acids has been explored by a collaboration with the group of prof. Hamm in Zurich. Due to the addition of an azobenzene switch in this peptide, which subsequently closes the cycle of the peptide chain, an ultrafast conformational change has been triggered by a light pulse. In a driven phase the peptide backbone reacts within the first 20 ps to the fast (< 2 ps) change in length of the switch. Weakly directed diffuse processes occur on a wide range of time scales, which lead to the final structure change. The results of the measurements gave new insights into the complexity of fast protein folding. A hierarchy of time scales is a typical signature, which can be observed when moving on a rough energy landscape.