Photoelectron circular dichroism of anionic chiral metal complexes and deprotonated molecules

Photoelectron circular dichroism (PECD) emerges as an asymmetry in the spatial distribution (regarding the light direction) of electrons detached from chiral molecules with left or right circular polarized light. In the past two decades PECD spectroscopy has manifested as a potential method for enantiomeric discrimination, with a chiral sensitivity that can surpass conventional methods, such as absorption circular dichroism. Conventionally, photoemitted electrons from neutral chiral molecules are studied, which can lead to PECD values of up to 20% [1]. Here, a modified version of PECD is implemented where photodetached electrons from chiral anions are considered. It can be called PECD in photodetachment or anion PECD. This approach simplifies the experiment since photodetachment requires in general less energy than ionization. Therefore, single photoelectron emission is achievable using common table-top lasers. Furthermore, mass selection before photodetachment is possible such that electrons can clearly be assigned to a species of specific mass. Apart from experimental advantages, the impact of short-range interactions (e.g. dipole moment, scattering potential) between molecule and electron on the PECD will be revealed since no cation but a neutral core is left behind after electron removal. Hence, this eliminates the need for considering long-range Coulombic interactions. Furthermore, the idea of a photodetached electron as a plane wave is challenged. At the start of this work, no experimental or theoretical work had reported on anion PECD. This effect in anions was even doubted to exist since photodetached electrons are usually considered to be plane waves, which cannot carry an asymmetry. Only a few years ago, the first successful experiments and calculations on anion PECD were published [2–4]. The here investigated chiral anions are either chiral gold complexes, consisting of a neutral chiral molecule (fenchone, menthone, 3-hydroxytetrahydrofuran or alaninol) and an atomic gold anion, or deprotonated chiral molecules (alaninol, 1-indanol), which are (in most cases) deprotonated at the hydroxyl group. These chiral systems are massselected and subsequently photodetached by a tunable laser with either linear or circular polarized light. Using velocity map imaging (VMI) photoelectron spectroscopy, the kinetic energy of the detached electron and its spatial distribution are recorded, providing insight into the energy-resolved PECD. Unfortunately, gold complexes do not reveal any PECD but photoelectron spectra measured with linear polarized light combined with density functional theory calculations yield intriguing results toward nonconventional hydrogen bonding. The photoelectron spectra show that the hydrogen bonds are strong enough for an interaction between gold and the chiral molecule. However, it does not lead to a measurable PECD effect. Anion PECD is successfully measured for the deprotonated molecules from which the deprotonated 1-indanol shows a particularly clear PECD. The strongest PECD is found for detachment from HOMO-2 with around 11%, which is comparable to PECD values of neutral molecules. Considering this asymmetry strength and the kinetic energy range the PECD asymmetry is recorded, this work emphasizes the importance of short-range interactions. [1] V. Ulrich, S. Barth, S. Joshi, U. Hergenhahn, E. Mikajlo, C. J. Harding, I. Powis, The Journal of Physical Chemistry A 2008, 112, 3544–3549. [2] P. Krüger, K.-M. Weitzel, Angewandte Chemie 2021, DOI 10 . 1002 / anie . 202107150. [3] P. Krüger, J. H. Both, U. Linne, F. Chirot, K.-M.Weitzel, The Journal of Physical Chemistry Letters 2022, 13, 6110–6116. [4] A. N. Artemyev, E. Kutscher, P. V. Demekhin, The Journal of Chemical Physics 2022, 156, 031101.

Author dc:creator

• Triptow, Jenny

Advisors dc:contributor.advisor

• Dopfer, Otto
• Fielicke, André

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Identifier URI

https://doi.org/10.14279/depositonce-20046

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/21246