RESUMEN
Magnetic molecules adsorbed on two-dimensional (2D) substrates have attracted broad attention because of their potential applications in quantum device applications. Experimental observations have demonstrated substantial alteration in the spin excitation energy of iron phthalocyanine (FePc) molecules when adsorbed on nitrogen-doped graphene substrates. However, the underlying mechanism responsible for this notable change remains unclear. To shed light on this, we employ an embedding method and ab initio quantum chemistry calculations to investigate the effects of surface doping on molecular properties. Our study unveils an unconventional chemical bonding at the interface between the FePc molecule and the N-doped graphene. This bonding interaction, stronger than non-covalent interactions, significantly modifies the magnetic anisotropy energy of the adsorbed molecule, consistent with experimental observations. These findings provide valuable insights into the electronic and magnetic properties of molecules on 2D substrates, offering a promising pathway for precise manipulation of molecular spin states.
RESUMEN
We realized a highly efficient formal [1,2]-sigmatropic rearrangement of ammonium ylides generated from 3-methylene-azetidines and α-diazo pyrazoamides. The employ of readily available chiral cobalt(II) complex of chiral N,N'-dioxide enabled the ring-expansion of azetidines, affording a variety of quaternary prolineamide derivatives with excellent yield (up to 99 %) and enantioselectivity (up to 99 %â ee) under mild reaction condition. For the rearrangement of ammonium ylides, the installation of a pyrazoamide group as a masked brick to build chiral scaffolds proved successful. The enantioselective ring expansion process was elucidated by DFT calculations.
RESUMEN
Circular dichroism (CD) is broadly employed for distinguishing molecular chiralities. However, its practical application is often limited by the weak magnitude of chiral signal. We propose to use azimuthally and radially polarized vector beams to probe CD spectra. By taking advantage of the strong longitudinal components of the vector beams, the transmitted light can be detected in the radial direction. The resulting CD signal is several orders of magnitude stronger than conventional CD signal with plane waves. Quantitative analysis and numerical simulations show that the enhancement factor is independent of molecular properties and can be increased by decreasing the path length of the sample cuvette and the interaction cross section between the light beam and molecular sample. The proposed novel CD spectroscopy is feasible with the current optical technology.
RESUMEN
Adsorption of magnetic transition metal atoms on a metal surface leads to the formation of Kondo states at the atom/metal interfaces. However, the significant influence of surrounding environment presents challenges for potential applications. In this work, we realize a novel strategy to regularize the Kondo states by moving a CoPc molecular mold on an Au(111) surface to capture the dispersed Co adatoms. The symmetric and ordered structures of the atom-mold complexes, as well as the strong dπ-π bonding between the Co adatoms and conjugated isoindole units, result in highly robust and uniform Kondo states at the Co/Au(111) interfaces. Even more remarkably, the CoPc further enables a fine tuning of Kondo states through the molecular-mold-mediated superexchange interactions between Co adatoms separated by more than 12 Å. Being highly precise, efficient and reproducible, the proposed molecular mold strategy may open a new horizon for the construction and control of nano-sized quantum devices.
RESUMEN
The precise tuning of local spin states in adsorbed organometallic molecules by a mechanically controlled scanning tunneling microscope (STM) tip has become a focus of recent experiments. However, the underlying mechanisms remain somewhat unclear. We investigate theoretically the STM tip control of local spin states in a single iron(II) porphyrin molecule adsorbed on the Pb(111) substrate. A combined density functional theory and hierarchical equations of motion approach is employed to simulate the tip tuning process in conjunction with the complete active space self-consistent field method for accurate computation of magnetic anisotropy. Our first-principles-based simulation accurately reproduces the tuning of magnetic anisotropy realized in experiment. Moreover, we elucidate the evolution of geometric and electronic structures of the composite junction and disclose the delicate competition between the Kondo resonance and local spin excitation. The understanding and insight provided by the first-principles-based simulation may help to realize more fascinating quantum state manipulations.
