Using photoelectron elliptical dichroism (PEELD) to determine real‐time variation of enantiomeric excess

Abstract

In this work, the photoionization of chiral molecules by an elliptically polarized, high repetition rate, femtosecond laser is probed. The resulting 3D photoelectron angular distribution shows a strong forward–backward asymmetry, which is highly dependent not only on the molecular structure but also on the ellipticity of the laser pulse. By continuously varying the laser ellipticity, we can observe molecular and enantiomer changes in real time at a previously unseen speed and precision. The technique allows enantiomeric excess of a pure compound to be measured with a 5% precision within 3 s, and a 10‐min acquisition yields a precision of 0.4%. The isomers camphor and fenchone can be easily distinguished, unlike with conventional mass spectrometry. Preliminary results for the pharmaceutically interesting ibuprofen are also given, showing the capability of photoionization as a means of distinguishing larger molecular systems.

Trends in angle-resolved molecular photoelectron spectroscopy

“…The technique has been expanded as an analytical tool, capable of real time (∼1 s) determination of enantiomeric excesses of several chiral molecules at the same time by scanning the ellipticity of the light. 276,277…”

“…The technique has been expanded as an analytical tool, capable of real time (B1 s) determination of enantiomeric excesses of several chiral molecules at the same time by scanning the ellipticity of the light. 276,277 The possibility offered by MP-PECD as an analytic tool for chirality detection has been exploited to study surface desorption of fenchone on Ag (111). 278 It demonstrates the potential for enantiomer-specific detection of surface reaction products on heterogeneous catalysts in asymmetric synthesis.…”

Photoelectron elliptical dichroism spectroscopy of resonance-enhanced multiphoton ionization via the 3s, 3p and 3d Rydberg series in fenchone

“…As a consequence, while in single-photon ionization the forward/backward photoelectron asymmetry is known to scale linearly with |S 3 |, 4 in (2 + 1) REMPI, it can increase non-linearly with |S 3 | 8,14 and even evolve non-monotonically. 15,16 The sensitivity of this PhotoElectron Elliptical Dichroism (PEELD) to the anisotropy of excitation should make it very sensitive to the intermediate state, specifically revealing information about the excitation process.…”

Assignment-free chirality detection in unknown samples via microwave three-wave mixing

“…Spectroscopic methods such as vibrational, photoelectron circular dichroism 10 – 14 , and microwave spectroscopy 15 – 23 can be mixture compatible and provide highly accurate information on species identity. So far, these methods have been limited by spectral assignment; prior to any chirality experiment, the spectrum of the molecule had first to be collected and fully assigned.…”