Imaging Photoelectron Circular Dichroism in the Detachment of Mass‐Selected Chiral Anions

Abstract

Photoelectron Circular Dichroism (PECD) is a forward‐backward asymmetry in the photoemission from a non‐racemic sample induced by circularly polarized light. PECD spectroscopy has potential analytical advantages for chiral discrimination over other chiroptical methods due to its increased sensitivity to the chiral potential of the molecule. The use of anions for PECD spectroscopy allows for mass‐selectivity and provides a path to simple experimental schemes that employ table‐top light sources. Evidence of PECD for anions is limited, and insight into the forces that govern PECD electron dynamics in photodetachment is absent. Here, we demonstrate a PECD effect in the photodetachment of mass‐selected deprotonated 1‐indanol anions. By utilizing velocity map imaging photoelectron spectroscopy with a tunable light source, we determine the energy‐resolved PECD over a wide range of photon energies. The observed PECD reaches up to 11 %, similar to what has been measured for neutral species.

Investigation of photoelectron elliptical dichroism for chiral analysis

“…This powerful technique has allowed PECD to be examined in exquisite detail. 20,33,39,57,60,66,69 Alternatively, with a time-resolved spectrometer the 3D angular distribution can be retrieved directly as long as no more than one electron is emitted per laser pulse. 29,32,40,46,48,70…”

“…These include microwave three wave mixing, 1–4 Coulomb explosion imaging, 5–7 along with photoion circular dichroism (PICD) 8–17 and photoelectron circular dichroism (PECD). 12,13,18–62…”

Velocity-map imaging of photoelectron circular dichroism in non-volatile molecules using a laser-based desorption source

“…The methods of electrospray ionization (ESI) and matrix-assisted laser desorption/ ionization (MALDI) are commonly used for gas phase studies of thermally labile, non-volatile molecules. [5][6][7][8][9] Although these techniques have provided significant progress in studies of biomolecular spectroscopy and photochemical dynamics, there are limitations to their scope: in ESI, a gas-phase sample is created using polar molecules that easily undergo ion (or proton) attachment (or detachment) and therefore often yield a modified form of the molecule of interest (with potentially different underlying electronic and nuclear structure than in the corresponding neutral species). In MALDI, the preparation conditions must be tailored to the desired target, with the resulting gas-phase sample containing matrix molecules and associated solvents.…”

“…In this report, we present the first use of an LBD source within a VMI experiment by recording and analysing the PECD of the highly non-volatile phenylalanine molecule. This approach is a complimentary strategy to recent studies using ESI sources [6][7][8] to investigate the PECD of non-volatile systems in anionic form. With the approach detailed here, however, the PECD imaged is that of the neutral molecule.…”

Fast and precise chiroptical spectroscopy by photoelectron elliptical dichroism

“…Electrosprays coupled to ion optics are routinely used to put large non-volatile molecules in the gas phase in ionic forms. 32 This technology was recently shown to be compatible with photoelectron circular dichroism measurements, 30,33,34 but the low density of the target requires long acquisition times. Using evaporated neutral molecules enables producing much higher densities, resulting in faster measurements, and is less expensive.…”