The propagation of symmetry across different hierarchies of the universe, from the smallest elementary particles that form atoms, and all the way to galaxies, has long fascinated scientists. One particularly intriguing question in chemistry and crystallography is how symmetry at the atomic and molecular level translates into the structures and shapes of crystals. A key concept in this context is chirality, a geometric property of objects that cannot be superimposed onto their mirror images, much like left and right hands.
In 1848, Louis Pasteur made what is now considered a monumental discovery: crystals made from chiral molecules can themselves form chiral shapes. This observation led to the intuitive idea that chiral molecular building blocks naturally produce chiral crystal shapes. However, despite many observations of chiral crystal morphologies since then, the mechanisms behind their formation have proven to be far more complex and elusive than initially imagined.
In this ERC project, nanocrystals serve as model systems to study how chiral shapes emerge during crystallization. Nanocrystals are particularly well suited for this purpose because they resemble the earliest, “embryonic” stages of crystal growth. At this scale, structural details can be observed with exceptionally high resolution—details that are often hidden in conventional, macroscopic crystals. Beyond their fundamental importance, chiral nanocrystals are also technologically promising, with potential applications in optics, sensing, biotechnology and even spintronics.
The project focuses on a potentially universal crystal growth mechanism that operates at low concentrations of building blocks and is mediated by a common type of imperfection known as a screw dislocation. These defects are inherently chiral, yet their role in the transfer and amplification of chirality in crystals has received surprisingly little attention. Moreover, systematic attempts to induce and control screw dislocations are extremely rare. Keeping in mind these open challenges, the project was set around three main objectives. The first objective is to develop a general and widely applicable synthetic approach for "enantioselective screw-dislocation-mediated growth" in materials whose crystal structures are themselves achiral. In simple terms, the goal is to grow crystals from non-chiral materials that nonetheless exhibit chiral shapes due to screw dislocations, and to control whether these dislocations (and the crystal shapes that result) are right- or left-handed. The second objective is to investigate this mechanism in materials composed of chiral crystal structures. Here, the project asks whether screw dislocations have been overlooked as intermediates between molecular-scale chirality and the overall shape of the crystal. The third objective is to understand how screw dislocations originate in the first place. While there have been observations of the outcome of crystal growth in the presence of screw dislocations, much less is known about the processes by which they initially form.
Together, these objectives aim to provide a deeper understanding of a crystal growth mechanism that has been largely overlooked in relation to chirality. The insights gained will be relevant both for fundamental science and for the development of new strategies to engineer chirality at the nanoscale.
