Spectroscopy

Every synthetic chemist uses spectroscopy in the characterization of newly prepared compounds. We go beyond this basic knowledge in laser spectroscopy. There we investigate which electronic states of a molecule or a material are reached after absorption of a photon: The excited singlet state is characterized by fluorescence, the excited triplet state by phosphorescence. In the Kay group, spin multiplicity is detected by EPR (electron paramagnetic resonance) spectroscopy, while the Jung group focuses in particular on ultrasensitive fluorescence spectroscopy up to the detection of single molecules. The transitions cannot always be unambiguously assigned to molecular or atomic species, which is why quantum chemical computational methods of the Stopkowicz working group are then indispensable for the interpretation of the experiments.

In this context, it is worthwhile to study the interaction of light with matter in more detail. Intense excitations lead to non-linear effects: in colored diamond crystals, the Kay group succeeded for the first time in constructing a continuously operating maser (microwave amplification by stimulated emission of radiation) by amplifying the emission already at room temperature. Furthermore, the Kay group uses laser radiation to prepare very short-lived excited states of dyes (e.g. see picture: pentacene).

In the Jung group, fluorescent dyes are synthesized that can be used to follow chemical reactions at the single-molecule level. The unique feature here is that the fluorescent color differs before and after the reaction. With the aid of single-molecule microscopy, the color change can then be followed and short-lived intermediates can be detected that elude classical chemical analysis.