| Autor: |
Freixas VM; Department of Chemistry and Physics and Astronomy, University of California, Irvine, California 92697-2025, United States., Rouxel JR; Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States., Nam Y; Department of Chemistry and Physics and Astronomy, University of California, Irvine, California 92697-2025, United States., Tretiak S; Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States., Govind N; Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.; Department of Chemistry, University of Washington, Seattle, Washington 98195, United States., Mukamel S; Department of Chemistry and Physics and Astronomy, University of California, Irvine, California 92697-2025, United States. |
| Abstrakt: |
Chirality is a fundamental molecular property that plays a crucial role in biophysics and drug design. Optical circular dichroism (OCD) is a well-established chiral spectroscopic probe in the UV-visible regime. Chirality is most commonly associated with a localized chiral center. However, some compounds such as helicenes (Figure 1) are chiral due to their screwlike global structure. In these highly conjugated systems, some electric and magnetic allowed transitions are distributed across the entire molecule, and OCD thus probes the global molecular chirality. Recent advances in X-ray sources, in particular the control of their polarization and spatial profiles, have enabled X-ray circular dichroism (XCD), which, in contrast to OCD, can exploit the localized and element-specific nature of X-ray electronic transitions. XCD therefore is more sensitive to local structures, and the chirality probed with it can be referred to as local. During the racemization of helicene, between opposite helical structures, the screw handedness can flip locally, making the molecule globally achiral while retaining a local handedness. Here, we use the racemization mechanism of [12]helicene as a model to demonstrate the capabilities of OCD and XCD as time-dependent probes for global and local chiralities, respectively. Our simulations demonstrate that XCD provides an excellent spectroscopic probe for the time-dependent local chirality of molecules. |
