Electronic Circular Dichroism of Matrix-Isolated Molecules

• Applicant: Professor Dr. Christian Merten
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545240636

Chiral organic radicals are of high interest in many fields of applications. Yet, their high reactivity often prevents their complete characterization, especially with regards to their chiroptical properties. Interesting, despite the many interesting applications that can be envisioned for it, the combination of matrix isolation (MI) and electronic circular dichroism (ECD) spectroscopy has not been reported in literature. Building on our expertise in realizing MI vibrational circular dichroism (VCD) spectroscopy, we want to establish MI-ECD spectroscopy as novel tool for the characterization of the chiroptical properties of high-spin reactive intermediates. The central objective of this proposal is dedicated to method development. We will realize the core implementation, which involves the setup of an MI system, realization of a custom-build sample compartment to accommodate the MI cold-head, and to record the first spectra of well-known model compounds. Key experimental aspects optimized and benchmarked. We strive to reach highest spectral resolution and try to push the instruments performance towards the lowest possibly achievable wavelength. For this purpose, we evaluate samples showing pronounced signatures of vibronic progression, or Far-UV transitions. The second central objective of this proposal is dedicated to demonstrating the capabilities of the newly implemented MI-ECD instrument for the characterization of highly reactive chiral species. For this purpose, we study two chiral helicene-based nitrenes, which will be generated photochemically under MI conditions from their parent azido-precursors. The MI-ECD studies carried out in this project will be complemented with MI-VCD and MI-EPR measurements and DFT calculations in order to further characterize the conformational preferences and, in case of the nitrenes, the electronic configuration of the isolated species.

• DFG Programme: Research Grants
• Major Instrumentation: CD Spectrometer
• Instrumentation Group: 1820 Nah-Infrarot-Spektralphotometer