Chemical Doping by Fluorination and Its Impact on All Energy Levels of π-Conjugated Systems – Publication by A2 (Witte) and A8 (Koert/Dürr)

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In their combined experimental and theoretical study published in the Journal of Physical Chemistry Letters, the groups of Holger Bettinger (Uni Tübingen), Ulrich Koert (A8) and Gregor Witte (A2) investigated the impact of fluorination on the C1s core level energies in fluorinated acene derivates.

Fluorination affects the inner potential and thus the energy levels, as symbolized by the water level. The electron binding energies are probed via X-ray photoelectron spectroscopy (XPS). (Image: Y. Radiev, Reprinted with permission from ACS J. Phys. Chem. Lett. 2023. Copyright 2023 American Chemical Society.).

Fluorination is commonly used to tailor the frontier energy levels. In the present study, the authors utilized the recent achievements in the synthesis of regio-selectively fluorinated acenes and systematically investigated the core level binding energies by means of X-ray photoelectron spectroscopy (XPS) complemented by density functional theory (DFT) calculations.

These investigations reveal that fluorination leads to core level shifts, which are not limited to directly fluorinated carbon atoms, but also affect more distant carbon atoms. These shifts depend on the degree of fluorination, indicating that local fluorination affects the electron density of the entire aromatic system similar to doping. Since commonly core level shifts are used as fingerprint signatures for the identification of molecular entities, the new results challenge this method for fluorinated π-conjugated molecules. Moreover, as these shifts do not only influence the core levels, but also the molecular valence orbital energies, transitions from the former into the latter are hardly affected by fluorination, as verified by X-ray absorption spectroscopy (NEXAFS) measurements.

Overall, the results show that not only the energies of frontier orbitals but also of all core levels in fully π-conjugated systems are affected by local fluorination, hence limiting a chemical identification based on supposedly characteristic core level energies since they instead depend also on the degree of fluorination.

Publication

D. Bischof, Y. Radiev, M.W. Tripp, P.E. Hofmann, T. Geiger, H.F. Bettinger, U. Koert, G. Witte
Chemical Doping by Fluorination and Its Impact on All Energy Levels of π-Conjugated Systems
J. Phys. Chem. Lett. (2023) DOI:10.1021/acs.jpclett.3c00287

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083 project A2
Tel.: 06421 28-21384
EMAIL

Poster Presentation Prize at DPT 2022 in Karlsruhe

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Marleen Axt (B6) was awarded for the best poster presentation at the 26th German Conference of Women in Physics („Deutsche Physikerinnentagung“, DPT) in Karlsruhe

Poster: „Time-resolved second-harmonic imaging microscopy: Ultrafast processes in ultrathin materials“ by M. Axt, J. E. Zimmermann, G. Mette, and U. Höfer (Philipps-Universität Marburg).

The German Conference of Women in Physics takes place annually since 1997. Supported by the German Physical Society (DPG), it offers female scientists of all areas of physics and at different carrier levels – from student to professor as well as physicists in industry – the possibility for networking and professional exchange. The 2022 conference had 250 participants and was hosted by the Karlsruhe Institute of Technology (KIT) from November 24-27, 2022.

In her contribution, Marleen Axt (project B6) reported on investigations of ultrafast charge-transfer processes between van-der-Waals monolayers of different twist angles by means of time-resolved second-harmonic imaging microsocopy, a technique developed by the Höfer group. The experiments provide insight into fundamental electronic properties at interfaces.

Dr. Philip Klement (B2 & B13) receives the dissertation prize of the Justus-Liebig-Universität Gießen

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We congratulate Dr. Philip Klement on receiving the 2021/22 dissertation prize of the Justus-Liebig-Universität Gießen in the category natural sciences for his excellent dissertation.

Prof. Martin Kramer (r.) and Prof. Volker Wissemann (m.) congratulate Dr. Philip Klement (l.). Photo: JLU / Roland Duss

Philip Klement advanced the understanding of interfaces by his studies on the influence between materials and their environment. Interfaces ‒ junctions between materials ‒ are crucial for the design and performance of modern electronic devices. The impact of interfaces on the materials properties increases continuously as structures become smaller.

In his dissertation “Interface Phenomena in Two-Dimensional Materials” Philip Klement combined the dynamic and highly competitive research areas of two-dimensional materials and organic-inorganic perovskites to gain innovative insights. In his central work, he discovered free-standing, single layers of an organic-inorganic mixed crystal ‒ something not deemed feasible before. Further, he discovered the thickness dependence of the emission wavelength of this material ‒ an effect which was to date unknown. These results may enable the facile color tuning in next-generation efficient and sustainable lighting and display technologies.

Philip Klement continues to explore these new developments and opportunities as a member of the SFB projects B2 (Chatterjee) & B13 (Chatterjee/Volz), and in close collaboration with A15 (Heine).

Please see the coverage of the award ceremony for more impressions and a recent audio interview of Dr. Klement and Prof. Chatterjee for more details of their research (both in German).