www.ir.ETHz.CH
Molecular quantum dynamics, the primary processes of molecules in motion, provide the foundation of all chemical processes, covering combustion as an early and still today important use of chemistry by mankind, the chemistry of planetary atmospheres and of interstellar space, of large scale industrial syntheses, catalysis, and also of the microscopic biomolecular processes in...
Within a bottom/up approach of molecular complexity, the study of isolated, substrate- and solvent-free chiral species is crucial, but classical chiroptical probes such as Circular Dichroism (CD) in absorption are poorly adapted to dilute matter because of their very weak associated asymmetries.
At the opposite, two decades ago was introduced a new chiroptical effect called Photoelectron...
PhotoElectron Circular Dichroism (PECD) is an effect driven by electric dipole interactions between an ensemble of chiral molecules and ionizing circularly polarized light [1,2]. It results in a preferential emission direction of photoelectrons along the light propagation axis, leading to an asymmetry that can be observed by recording their angular distribution with an electron detector....
A molecule is chiral if it lacks both a plane and a center of symmetry, resulting in two non-superimposable mirror-image forms known as enantiomers. Chirality is crucial in the physical and biological sciences because enantiomers, despite having the same chemical structure, often exhibit different chemical and physical properties when interacting with other chiral entities. While chirality is...
Chirality-sensitive, large-cross section Photoelectron Circular Dichroism (PECD) — the forward-backward asymmetry in photoemission from chiral molecules photoionized by circularly polarized light — uniquely connects molecular electronic structure to chirality. In addition, core-level PECD is site-specific and sensitive to chemical environment and especially to the conformation of small...
Time-resolved circular dichroism (CD) is a powerful technique to investigate the dynamics of conformational changes in molecules and in biomolecules. Starting from a pump-probe configuration, it consists in measuring the CD of the pump-excited molecules to gain information on the relevant timescales. Complementary experiments on short (picoseconds) or longer (microseconds) timescales have been...
The incorporation of chiral structures into photochemical systems is a powerful strategy to control their functions [1]. For example, uni-directional molecular motors, chiral photocatalysts, and chiral metal nanostructures have achieved exceptional levels of stereocontrol over mechanical motion, energy transfer, and electric charge-carriers on the nanoscale. However, the direct...
Since the pioneering transient circular dichroism (CD) experiments of Xie and Simon$^1$ and Kliger$^2$ more than three decades ago, laser technology has developed enormously, and highly stable, ultrashort broad-band pulses for extremely sensitive differential absorption measurements at wavelengths from the mid-IR to the far UV have become routinely available. Yet, progress in time-resolved CD...
Selective absorption of light at specific frequencies determines the color of an object and results from the discrete energy levels of atoms or molecules in the material. This selective absorption also occurs when the handedness of polarized light interacts with the non-superimposable mirror image of a chiral object, as in circular dichroism (CD). Tunability of light absorption, it is...
We present here our recent work on the development of ab initio time-domain methods for studying the contribution of inner molecular orbitals to the HHG spectrum [1] of aligned or non-aligned molecules [2-4]. First, we show how, in the presence of a linearly polarised pulse, the selection rules for harmonic generation can be different depending on the molecular orbital considered: an example...
An object is said to be chiral if it cannot be superimposed on its mirror image by any rotation. The two mirror images of the same chiral molecule are called enantiomers and are often referred to as “left”- and “right”-handed. While the physical properties of the two enantiomers of the same chiral molecule are nearly identical, the geometric property of chirality leads to vastly different...
Since the pioneering work by French scientists in the early 1800s, optical activity and chiral light-matter interactions have been produced via the chirality of light stemming from a degree of ellipticity in its local polarisation state. The mechanism is well understood: the polarisation state can rotate in a left or right-handed fashion and leads to differential interactions with left and...
This presentation will give an overview about the generation and applications of X-ray beams that exhibit an orbital angular momentum (OAM) using helical zone plates, focusing particularly on their ability to probe chiral properties in matter. Helical (or spiral) zone plates represent an advanced class of diffractive optical lenses that can modulate the phase of light while focusing it at...
The growing interest in chirality represents a notable example of convergence between different areas of research within the realm of condensed matter. The observation of skyrmions in compounds of group B20 [1] represents only the first report of a wealth of magnetic ordering [2] and collective excitations [3] that can be realized only in the absence of inversion and mirror symmetry...
This presentation will review our recent progress studying chiral media with Mueller matrix polarimetry. A comprehensive presentation of our polarimetric method will be provided, detailing the instrumentation used, a few remarks about data analysis as well as some basic concepts about light propagation in chiral anisotropic media. We will discuss how optical characterization methods based...
Photoelectron Circular Dichroism (PECD), the forward/backward asymmetry in the angular distribution of the electrons resulting from the ionization of a chiral molecule by a circularly polarized light [1], is a very sensitive probe of molecular structure [2, 3, 4]. While it was historically studied using synchrotron facilities, recent developments show PECD using laser setups, both in the...
Traditional chiroptical methods rely on the chirality of circularly polarised light (CPL) to determine molecular handedness. However, due to the large disparity between the pitch of the light’s helix and the tiny size of the molecules, the interaction of CPL with chiral molecules is weakly enantiosensitive.[1] Synthetic chiral light has recently been proposed as an efficient alternative to...
During the 1980s, the study of laser-induced damage (LID) gained prominence in biophysics and bioengineering, leading to innovative clinical applications centered around laser-tissue interactions. Despite extensive investigations into the origins of LID in biological tissues and the nature of the laser-induced breakdown (LIB) process, key aspects of the underlying mechanisms remain elusive....
Ultrafast few-cycle lasers provide a versatile platform for probing and controlling the chirality of molecular and crystalline systems. Utilizing such pulses, high-harmonic generation (HHG) measurements grant valuable insights into ultrafast chiral dynamics. In these, the carrier-envelope phase (CEP) of the laser pulse plays a pivotal role. Precise CEP control allows manipulation of...
Quantum control methods exploit quantum mechanical effects in order to manipulate quantum systems towards a desired final state - in particular when several final states are energetically allowed - in most cases by applying external electromagnetic fields. In this way, quantum control methods can be used as the underlying mechanism of novel sensing methods at the nanoscale when...
Collective dynamics at the nanoscale in condensed matter is important for advancing both fundamental science and modern technology. The study of heat transport processes, vibrational modes or magnetization dynamics in the sub-100 nm length-scales can greatly benefit from the development of experimental tools for probing such dynamics and on the relevant timescale (i.e. ps and sub-ps) without...
Vibrationally resolved picosecond laser (2+1) multiphoton ionization of fenchone, pumped via a partially resolved manifold of Rydberg states, indicates strong vibronic branching in the decay channels with extensive vibrational redistribution. Associated to the vibronic structures are dramatically fluctuating photoelectron circular dichroism (PECD) chiral asymmetries.
The strong...
I will present fundamental insights on pure electron dynamics captured by pump–probe attosecond transient spectroscopic techniques, within the realms of real–time time-dependent density functional theory [1-4]. The method incorporates both scalar and spin-orbit relativistic effects variationally using modern atomic mean-field eXact two-component (amfX2C) Hamiltonian [4], necessary for X-ray...
In this talk, I will present real-time time-dependent density functional theory (RT-TDDFT) methods for simulating ground- and transient-state chiroptical properties [1,2]. For studies focused on high energy X-ray regions and systems containing heavy elements, incorporating relativistic effects is essential. Full four-component relativistic methods, while accurate, are often computationally...
Chiral molecules exist in pairs of mirror-reflected versions: the left and right enantiomers, which behave identically unless they interact with another chiral entity. Since most biomolecules are chiral, opposite enantiomers behave differently in biochemical and pharmaceutical contexts, making chiral recognition vital. However, traditional chiroptical methods are not efficient because the rely...
We investigate functional properties and collective responses in self-assembled ligand-coated nanoparticle (NP) supracrystals triggered by external light excitation [1]. Focusing on determining how changes in core-ligand, core-core, and ligand-ligand interactions influence the mesoscale photoinduced responses, our study aims to understand the role of heterogeneity and order/disorder...
Chirality is a fundamental concept that pertains to the property of molecules that cannot be superimposed onto their mirror images, existing in two non-superimposable forms called enantiomers. Like our left and right hands, opposite enantiomers have identical properties unless they are in the presence of another chiral entity, such as another chiral molecule or field. Since many biologically...
