CONFINED MOLECULAR SYSTEMS: THE NEW GENERATION OF MATERIALS
NATIONAL RESEARCH PROJECT GRANT NUMBER: PID2020-117605GB-I00
(September 2021 - August 2025)
PUBLICATIONS:
2021:
1) María Pilar de Lara-Castells*. "First-principles modelling of the new generation of subnanometric metal clusters: Recent case studies". Invited Feature Article. Journal of Colloid And Interface Science (2022)
Abstract: The very recent development of highly selective techniques making possible the synthesis and experimental characterization of subnanometric (subnanometer-sized) metal clusters (even single atoms) is pushing our understanding far beyond the present knowledge in materials science, driving these clusters as a new generation of quantum materials at the lower bounds of nanotechnology. When the size of the metalcluster is reduced to a small number of atoms, the d-band of the metal splits into a subnanometric d-type molecular orbitals network in which all metal atoms are interconnected, with the inter-connections having the length of a chemical bond (1-2 Å). These molecular characteristics are at the very core of the high stability and novel properties of the smallest metal clusters, with their integration into colloidal materials interacting with the environment having the potential to further boost their performance in applications such as luminescence, sensing, bioimaging, theranostics, energy conversion, catalysis, and photocatalysis. Through the presentation of very recent case studies, this Feature Article is aimed to illustrate how first-principles modelling, including methods beyond the state-of-the-art and an interplay with cutting-edge experiments, is helping to understand the special properties of these clusters. Moreover, it will be discussed how superfluid helium droplets can act both as nanoreactors and carriers to achieve the synthesis and surface deposition of metal clusters. This concept will be illustrated through the quantum simulation of the helium dropletassisted soft-landing of a single Au atom onto a titanium dioxide (TiO2) surface. Next, it will be shown how the application of first-principles methods has disclosed the fundamental reasons why subnanometric Cu5 clusters are resistant to irreversible oxidation, and capable of increasing and extending into the visible region the solar absorption of TiO2 and augmenting its efficiency for photo-catalysis beyond a factor of four, also considering the decomposition and photo-activation of CO2 as a prototypical (photo-)catalytic reaction. Finally, I will discuss how the modification of the same material with subnanometric Ag5 clusters has converted it into a ``reporter" of a surface polaron property as well as a novel two-dimensional polaronic material.
2) Alexander O. Mitrushckenkov, Alexandre Zanchet, Andreas W. Hauser*, María Pilar de Lara-Castells*. Nonadiabatic Effects in the Molecular Oxidation of Subnanometric Cu5 Clusters. Journal of Physical Chemistry A 2021, 125, 41, 9143–9150
Abstract: The electronic structure of subnanometric clusters, far off the bulk regime, is still dominated by molecular characteristics. The spatial arrangement of the notoriously undercoordinated metal atoms is strongly coupled to the electronic properties of the system, which makes this class of materials particularly interesting for applications including luminescence, sensing, bioimaging, theranostics, energy conversion, catalysis, and photocatalysis. Opposing a common rule of thumb that assumes an increasing chemical reactivity with smaller cluster size, Cu5 clusters have proven to be exceptionally resistant to irreversible oxidation, i.e., the dissociative chemisorption of molecular oxygen. Besides providing reasons for this behavior in the case of heavy loading with molecular oxygen, we investigate the competition between physisorption and molecular chemisorption from the perspective of nonadiabatic effects. Landau–Zener theory is applied to the Cu5(O2)3 complex to estimate the probability for a switching between the electronic states correlating the neutral O2 + Cu5(O2)2 and the ionic O2– + (Cu5(O2)2)+ fragments in a diabatic representation. Our work demonstrates the involvement of strong nonadiabatic effects in the associated charge transfer process, which might be a common motive in reactions involving subnanometric metal structures.
3) María Pilar de Lara-Castells* and Salvador Miret-Artés. "A subnanometric material reveals new quantum insights into surface polarons". Europhysics News. Under revision.
Abstract: The recent advent of cutting-edge experimental techniques allows for a precise synthesis of monodisperse subnanometric metal clusters composed by just a few atoms, and opens new possibilities for subnanometer science. The decoration of titanium dioxide surfaces with Ag5 atomic clusters has enabled the stabilization of surface polarons and provided new quantum insights into an electron polarization phenomenon accompanying their formation.
4) María Pilar de Lara-Castells* and Alexander O. Mitrushchenkov*. "Mini Review: Quantum Confinement of Atomic and Molecular Clusters in Carbon Nanotubes". Frontiers in Chemistry 2021, 9, 796890.
Abstract: We overview our recent developments on a computational approach addressing quantum confinement of light atomic and molecular clusters (made of atomic helium and molecular hydrogen) in carbon nanotubes. We outline a multi-scale first-principles approach, based on density functional theory (DFT)-based symmetry-adapted perturbation theory, allowing an accurate characterization of the dispersion-dominated particle–nanotube interaction. Next, we describe a wave-function-based method, allowing rigorous fully coupled quantum calculations of the pseudo-nuclear bound states. The approach is illustrated by showing the transition from molecular aggregation to quasi-one-dimensional condensed matter systems of molecular deuterium and hydrogen as well as atomic 4He, as case studies. Finally, we present a perspective on future-oriented mixed approaches combining, e.g., orbital-free helium density functional theory (He-DFT), machine-learning parameterizations, with wave-function-based descriptions.
5) Alvaro García-Castillo, Andreas W. Hauser, María Pilar de Lara-Castells*, and Pablo Villarreal*. "A Path Integral Molecular Dynamics Simulation of a Harpoon-Type Redox Reaction in a Helium Nanodroplet". Molecules 2021, 26 (19), 5783.
Abstract: We present path integral molecular dynamics (PIMD) calculations of an electron transfer from a heliophobic Cs2 dimer in its (3Σu) state, located on the surface of a He droplet, to a heliophilic, fully immersed C60 molecule. Supported by electron ionization mass spectroscopy measurements (Renzler et al., J. Chem. Phys.2016, 145, 181101), this spatially quenched reaction was characterized as a harpoon-type or long-range electron transfer in a previous high-level ab initio study (de Lara-Castells et al., J. Phys. Chem. Lett. 2017, 8, 4284). To go beyond the static approach, classical and quantum PIMD simulations are performed at 2 K, slightly below the critical temperature for helium superfluidity (2.172 K). Calculations are executed in the NVT ensemble as well as the NVE ensemble to provide insights into real-time dynamics. A droplet size of 2090 atoms is assumed to study the impact of spatial hindrance on reactivity. By changing the number of beads in the PIMD simulations, the impact of quantization can be studied in greater detail and without an implicit assumption of superfluidity. We find that the reaction probability increases with higher levels of quantization. Our findings confirm earlier, static predictions of a rotational motion of the Cs2 dimer upon reacting with the fullerene, involving a substantial displacement of helium. However, it also raises the new question of whether the interacting species are driven out-of-equilibrium after impurity uptake, since reactivity is strongly quenched if a full thermal equilibration is assumed. More generally, our work points towards a novel mechanism for long-range electron transfer through an interplay between nuclear quantum delocalization within the confining medium and delocalized electronic dispersion forces acting on the two reactants.
6) Zúlema Fernández, Berta Fernández, Emilio Quiñoá, and Félix Fréire*, "Merging Supramolecular and Covalent Helical Polymers: Four Helices Within a Single Scaffold". Journal of American Chemical Society 2021, 143, 49, 20962–20969
Abstract: Supramolecular and covalent polymers share multiple structural effects such as chiral amplification, helical inversion, sergeants and soldiers, or majority rules, among others. These features are related to the axial helical structure found in both types of materials, which are responsible for their properties. Herein a novel material combining information and characteristics from both fields of helical polymers, supramolecular (oligo(p-phenyleneethynylene) (OPE)) and covalent (poly(acetylene) (PA)), is presented. To achieve this goal, the poly(acetylene) must adopt a dihedral angle between conjugated double bonds (ω1) higher than 165°. In such cases, the tilting degree (Θ) between the OPE units used as pendant groups is close to 11°, like that observed in supramolecular helical arrays of these molecules. Polymerization of oligo[(p-phenyleneethynylene)n]phenylacetylene monomers (n = 1, 2) bearing L-decyl alaninate as the pendant group yielded the desired scaffolds. These polymers adopt a stretched and almost planar polyene helix, where the OPE units are arranged describing a helical structure. As a result, a novel multihelix material was prepared, the ECD spectra of which are dominated by the OPE axial array.
