Students' seminar

Luminescent and photoactive transition metal complexes play a key role in technologies like OLEDs or organic solar cells, sensing applications, photocatalysis, and biomedical applications. However, they typically rely on some of the most precious and expensive metals e.g. Ru or Ir, with high ligand field splitting and hence long-lived charge-transfer (CT) excited states. Recently, spin-flip (SF) emitters based on more abundant first and second row transition metals, like Cr^III, with d³ electron configuration are becoming increasingly significant in photochemistry and photophysics.^[2,3] They exhibit fundamentally different excited state properties compared to classical d⁶ charge-transfer (CT) emitters, resulting in advantageous characteristics, such as fast intersystem crossing, near infrared phosphorescence, sharp emission bands and long excited state lifetimes.^[3] However, clear design principles for efficient spin-flip emission are not yet well-established, and structural modifications can unexpectedly suppress luminescence. To better understand these effects, we combine spectroscopic methods with quantum chemical calculations to study the photophysical behavior of [Cr(bimca^Me)₂]⁺, where weak ligand-centered fluorescence can be observed. [1] C. Förster, K. Heinze, Chemical Society reviews 2020, 49, 1057–1070. [2] W. R. Kitzmann, J. Moll, K. Heinze, Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology 2022, 21, 1309–1331. [3] W. R. Kitzmann, K. Heinze, Angewandte Chemie (International ed. in English) 2023, 62, e202213207. [more]

The detection of low concentrations of biomarkers is crucial for early-stage medical diagnostics and intervention. Therefore, the development of biosensors with low LOD (Limit of Detection) is essential, as even the smallest quantities of biological markers can provide indications of disease progression. Organic electrochemical transistors (OECTs) have attracted great interest in the field of biosensors to be used as a transducer due to their unique properties, including low operating voltages, compatibility with aqueous environments, and intrinsic signal amplification. OECTs are three-terminal devices based on an organic mixed ionic-electronic semiconductor, such as PEDOT:PSS, which operate in contact with an electrolyte. During operation, the conductivity of the channel is electrochemically modulated by a gate voltage. For biosensing applications, the OECT is functionalized with biomolecules that specifically bind with the target analyte, this biorecognition event is translated into an amplified modulation of the channel current. Despite these advantages, lowering the LOD remains a key challenge for the reliable detection of analytes. [more]

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Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios are used for the reconstruction of past diet and environments. δ¹³C of herbivores can differentiate between browsers and grazers as well as indicate prey preference of carnivores. δ¹⁵N shows trophic level: carnivores are 3 – 6 ‰ enriched compared to herbivores. δ¹³C is measured on the inorganic portion of tooth enamel, as enamel is highly robust to alteration. δ¹⁵N is measured on the organic fraction of collagen, which only rarely preserves past 50 ka. In 2021, a method was established at the MPIC that allows for the measurement of the small fraction of organic nitrogen within the mineral structure of enamel. Sterkfontein is a cave site in the Cradle of Humankind, South Africa, where all three hominin genera have been found. My project focusses on three infills of the cave. The Jacovec Cavern (3.6 Ma) has yielded Australopithecus fossils. Member 5 Oldowan (2.1 – 1.7 Ma) contained Paranthropus fossils, and Member 5 Acheulean (1.7 – 1.4 Ma) yielded early Homo specimens. I sampled tooth enamel of herbivores, carnivores, and hominins from each infill and measured δ¹³C and δ¹⁵N to reconstruct dietary behavior and the potential onset of meat consumption. [more]

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