Chemical Physics — Laser Spectroscopy

• Frequency-domain spectroscopy: Here, the group mainly concentrates on Raman spectroscopy to investigate material properties. The technique allows for the analysis of practically all substances in gas, liquid and solid phases. The vibrational spectrum of the molecules helps to determine materials’ compositions and their interactions with the environment. This research is performed in an extensive collaboration with other researchers and with companies in diverse fields such as food analysis, investigation of cancer development, and quality control for different kinds of polymer-based materials.
• Time-domain spectroscopy: Investigations with an extremely high temporal resolution in the femtosecond range (10-15 seconds) are very demanding. The Materny group has developed a variety of techniques to access elementary dynamics in molecular systems. Presently, the group is studying the dynamics in organic semiconductors and ionic liquids, which are salts that remain in a liquid state even when at room temperature. For this, electronic and vibrational dynamics are accessed, for example using “femtosecond coherent anti-Stokes Raman scattering” excited and probe with up to four ultrashort laser pulses. The ionic liquids have potential applications in fields such as pharmaceuticals and green chemistry.

• To make Raman spectroscopy even more useful, the group has developed techniques, which increase the sensitivity by enhancing the signal in the so-called surface-enhanced Raman scattering (SERS) process and at the same time suppressing unwanted background signals.
• Organic semiconductors are highly attractive due to their variability and relatively simple and cheap production. However, stability and efficiency of electronic devices, such as solar cells, still needs to be improved. For this, a better understanding of the generation dynamics of charges has been reached in close collaboration with the research group of Prof. Veit Wagner.
• Using femtosecond time-resolved coherent anti-Stokes Raman scattering, the dynamics of inter-ion energy transfer in ionic liquids has been studied. The results helped to design ionic liquids with specific properties. Together with partners from India, the experimental results have been supplemented by “Density Functional Theory” (DFT) calculations.
• In a project involving several companies and research institutes, biofilms, which form on microplastic particles in water, have been investigated. These biofilms consist of, for example, algae and bacteria, and might influence the lifetime of the particles, but could also pose a threat to animals and human health if ingested through food.
• Together with an industry partner from Bremen, ethylene tetrafluoroethylene (ETFE) plastic foils used in roof construction have been studied using Micro-Raman spectroscopy. The results helped to improve the chemical stability and resistance of coatings against the environment. Similar experiments have been performed with Russian research partners, with whom there is a long-standing cooperation.

Three PhD students and four postdoctoral fellows carried out most of the group’s research. Funding came from the German Research Foundation (DFG; Individual Grants Program), the Federal Ministry for Economic Affairs and Climate Action (BMWi; ZIM Program), the Alexander von Humboldt Foundation (postdoc fellowships), and industry.

• Rana, D., Donfack, P., Jovanov, V., Wagner, V., Materny, A. Ultrafast polaron-pair dynamics in a poly(3-hexylthiophene-2,5-diyl) device influenced by a static electric field: Insights into electric-field-related charge loss. Physical Chemistry Chemical Physics 21(38), pp. 21236- 21248 (2019).
• Sanchora, P., Pandey, D.K., Kagdada, H.L., Materny, A., Singh, D.K. Impact of alkyl chain length and water on the structure and properties of 1-alkyl-3methylimidazolium chloride ionic liquids. Physical Chemistry Chemical Physics 22(31), pp. 1768717704 (2020).
• Ghosh, S., Pradhan, B., Zhang, Y., Hofkens, J., Karki, K.J., Materny, A. Nature of the different emissive states and strong exciton-phonon couplings in quasi-two-dimensional perovskites derived from phase-modulated two-photon micro-photoluminescence spectroscopy. Physical Chemistry Chemical Physics 23(6), pp. 3983-3992 (2021).
• Mohaghegh, F., Mazaheri Tehrani, A., Rana, D., Winterhalter, M., Materny, A. Detection and quantification of small concentrations of moxifloxacin using surface-enhanced Raman spectroscopy in a Kretschmann configuration. Journal of Raman Spectroscopy 52(9), pp. 1617-1629 (2021).
• Ghosh, S., Pradhan, B., Zhang, Y., Roeffaers, M.B.J., Hofkens, J., Karki, K.J., Materny, A. Spatial Heterogeneity of n-Phases Leads to Different Photophysical Properties in Quasi-Two-Dimensional Methylammonium Lead Bromide Perovskite. Journal of Physical Chemistry C 126(1), pp. 478-486 (2022).