Recent advances in ultrafast time-resolved chirality measurements: perspective and outlook

Abstract

Observing chirality changes as they occur is an important topic of research. It provides information that deepens the understanding of biomolecular configuration and conformation under environmental changes. Also, knowing the specific steps in chiral synthesis would simplify the production of specific chiral enantiomers that have a specific function. To gain better insight to the initial steps of conformational and configurational changes, the time‐resolution of chiral spectroscopy is continually pushed toward a shorter time‐scale. Recent advances have produced measurements of chirality changes with a femtosecond time‐resolution. These measurements are hindered by the inherently weak chirality signal, which can be overshadowed by different optical artefacts. This minireview will look at the so far successful techniques which measure chirality changes with femtosecond time‐resolution and discuss the advantages and disadvantages of these techniques. A short outlook will also look at new techniques that could improve the ability to measure chirality changes on an ultrafast time‐scale.

Time‐Resolved Pump–Probe Measurement of Optical Rotatory Dispersion in Chiral Metamaterial

“…The transient behavior of chirality can be characterized by measuring circular dichroism [8] or optical rotatory dispersion, which are related by Kramers-Kronig. To compare with the static ORP spectrum, the temporal behavior of ORP is directly measured using a time-resolved pump-probe setup.…”

“…Transient dynamics of handedness changes in natural chiral molecules have been studied via an ultrafast, time-resolved chirality measurement. [8] Metamaterial refers to an artificial structure composed of sub-wavelength inclusions. Artificial chirality is introduced by breaking the inversion symmetry of metallic inclusions to obtain a plasmonic chiral metamaterial (CMM), and its ORP spectral features are related to LSPRs of chiral metallic inclusions.…”

Ultrafast broadband circular dichroism in the deep ultraviolet

“…Most importantly, however, CD spectroscopy is a technique with structural sensitivity in the optical spectral range. With the use of pulsed ultrafast laser technology in a pump-probe scheme, it is now possible to measure transient chirality changes on time scales spanning from the nano- [2] to the femtosecond regime [3]. CD spectroscopy therefore offers a direct, nonempirical route to follow structural changes of molecular systems on the shortest time scales currently explored in molecular dynamics research.…”

“…Second, broadband detection is extremely difficult due to the polarization sensitivity of dispersive and reflective optics, which easily distorts static CD spectra [6,7]. This has limited commercial static CD spectropolarimeters and many TRCD setups to narrowband detection schemes [3,5,8], thus requiring probe wavelength scanning with increased DAQ times. Notable exceptions now exist in the visible spectral range [4,9,10].…”

Time-domain measurement of optical activity by an ultrastable common-path interferometer

“…Our time-domain approach has great potential for timeresolved OA measurements to study ultrafast stereochemical processes [30,31]. The device accepts broadband ultrashort pulses, whereas standard SP in the UV-visible allows only for monochromatic beams [19,32,33].…”