Chirality is often discussed in chemistry as if it were a matter of degree: molecules are described as ‘more’ or ‘less’ chiral depending on the number of stereogenic elements, the magnitude of helical twist, or the extent of structural distortion. From a mathematical perspective, however, chirality is strictly binary—a structure is either superimposable on its mirror image or it is not. This apparent contradiction reflects a deeper issue: the classifications commonly used in chemistry obscure a more fundamental distinction. In this Perspective, we revisit molecular chirality through the lens of geometry and topology. We demonstrate that the vast majority of familiar stereochemical motifs—classified as central, axial, planar, or helical chirality—are topologically trivial and belong to a single class in which enantiomers are interconvertible by continuous deformation of the molecular geometry, without bond breaking. But there exists a fundamentally distinct class: topologically chiral molecules, such as certain interlocked and knotted architectures, whose enantiomers cannot be interconverted by any continuous deformation, even under the assumption of complete conformational flexibility. Viewed from this perspective, while some classification remains useful, extensive classification risks adding unnecessary complexity without improving our understanding of how chirality functions in practice. What ultimately matters to chemists is identifying the conditions under which chirality can be observed, preserved, and used. This Perspective does not aim to provide a comprehensive, mathematically rigorous unification of stereochemical classes, but rather to illustrate, through selected model systems, the relationship between topological chirality and classical, rigidly chiral frameworks.
Halide perovskites (HPs) have developed into a promising material platform for investigating spin-optoelectronic applications. A key obstacle for real-world implementation, however, is achieving long electron spin lifetimes under ambient conditions. This review focuses on recent experimental insights into spin relaxation pathways in HP semiconductors. We begin by outlining the four major spin-relaxation mechanisms and highlight the characteristic magnetic-field and temperature dependencies associated with each. These mechanistic ‘fingerprints’ provide an experimental framework for identifying dominant relaxation channels in HPs. We then survey how different HP compositions, crystal structures, and dimensionalities influence which mechanisms prevail. Finally, we summarize key spectroscopic techniques capable of probing such spin depolarization dynamics and offer complementary information.
This account highlights recent contributions from the Lacour group at the interface of chirality and light-matter interactions. Cationic helicenes, ylide-derived macrocycles and heterocycles, and boramidines are presented as complementary chiral platforms for tuning photophysical and chiroptical properties, notably ECD and CPL. Resolution methods and chiral ion pairing further extend these studies to advanced regimes, from supramolecular assemblies to ultrafast and X-ray spectroscopy.
The rich variety of compounds containing the element fluorine, be it natural products, synthetic materials, or even minerals are well-suited for a critical discussion of the opposites ‘natural’ and ‘unnatural’.
The capability of generating attosecond (10-18s) pulses of light in the extreme-ultraviolet domain through high-harmonic generation (HHG) has opened a broad range of possibilities in studying the fastest dynamics in matter. Notably, the creation of light pulses with tailored, time-dependent polarization states has opened a new window into the most fundamental structural and electronic dynamics underlying molecular chirality. This article reviews the work of our group on three forms of chiroptical spectroscopy: (i) high-harmonic spectroscopy with tailored light fields, which has achieved a ~13% dichroism effect in discrimination of enantiomers and the chirality-sensitive observation of a dissociative reaction, (ii) femtosecond time-resolved photoelectron circular dichroism (PECD), applied to resolve the photodissociation dynamics of two chiral molecules and (iii) the development of circularly polarized attosecond pulse trains, applied to coherently control PECD on the attosecond timescale and measure chirality-sensitive attosecond photoionization delays. These methods advance chiroptical spectroscopy to the attosecond timescale and open new perspectives for probing and controlling molecular chirality on electronic timescales.
Monolayer-protected metal clusters in the size range between about 10 to 300 metal atoms are a special class of materials with strongly size-dependent behaviour, which is mainly ascribed to discrete electronic energy levels. It was observed that certain sizes of metal clusters show exceptional stability, whereas others are only formed under special conditions, as minor species or not at all. The field has made tremendous progress in the last two decades both in terms of the discovery of new clusters and the understanding of their properties. The focus of this article is on the chirality of these nano-objects and the use of chiroptical spectroscopy to probe their properties.
Raman Optical Activity (ROA) is emerging as a powerful analytical tool for the characterization of molecular chirality, offering complementary capabilities to established chiroptical and crystallographic methods. In particular, its ability to probe molecules in solution and across a wide range of chemical classes makes it increasingly relevant for modern chemical and pharmaceutical research. This perspective highlights recent developments, practical considerations, and future opportunities.
We briefly review the development of fundamental concepts in the current theory and experiments on molecular chirality, including the small effects arising from parity violating weak nuclear interaction. After a short summary of the history of theory and experiments in this field, we discuss the five basic hypotheses on the structure of chiral molecules. One of these introduces parity violation as the dominant effect in isolated molecules. We then provide a brief description of current experiments for measuring the parity violating energy difference ΔpvE between the ground states of enantiomers of chiral molecules by an approach which can also be used for the construction of a molecular quantum switch and for testing other hypotheses of molecular chirality. We finally introduce the long-standing open question of the origin of biomolecular homochirality. We stress the important distinction between hypotheses postulating a selection either by a ‘de facto’ (chance) or by a ‘de lege’ mechanism (necessity because of parity violation). This leads to the recent astrophysical detection of chiral molecules in the interstellar medium as a basis for a future possible spectroscopic detection of extra-terrestrial and exoplanetary homochirality as a signature of life.
Circularly Polarized Luminescence (CPL) is emerging as a central tool for chiral photonics, enabling applications ranging from sensing and security inks to circularly polarized organic light-emitting diodes (OLEDs). While most highly developed CPL emitters are organic chromophores, lanthanide complexes, or 4d/5d transition‑metal compounds, recent work has placed kinetically inert chromium(III) polypyridines at the forefront of the field. Their near‑infrared (NIR) metal‑centered ‘spin‑flip’ emissions produce long-lived and relatively large dissymmetry factors (|glum| ≈ 2·10-1) when chirality is encoded through helically wrapped di‑tridentate ligands. This mini‑review summarizes the physical origin of large CPL in Cr(III) and highlights recent advances in rational tuning of glum and CPL brightness through modifications of the metal–ligand covalency (nephelauxetic effect). Finally, we outline emerging directions including magnetically induced CPL (M-CPL) and the first proof‑of‑concept for Cr(III) complex‑based CP‑NIR‑OLEDs.
