Preparation, Supramolecular Organization, and On-Surface Reactivity of Enantiopure Subphthalocyanines: From Bulk to 2D-Polymerization.

The development of chiral materials is severely limited by the challenge to achieve enantiopure derivatives with both configurational stability and good optoelectronic properties. Herein we demonstrate that enantiopure subphthalocyanines (SubPcs) fulfill such demanding requirements and bear the prospect of becoming components of chiral technologies. Particularly, we describe the synthesis of enantiopure SubPcs and assess the impact of chirality on aspects as fundamental as the supramolecular organization, the behavior in contact with metallic surfaces, and the on-surface reactivity and polymerization. We find that enantiopure SubPcs remarkably tend to organize in columnar polar assemblies at the solid state and highly ordered chiral superstructures on Au(111) surfaces. At the metal interface, such SubPcs are singled out by scanning tunneling microscopy. DFT calculations suggest that SubPcs undergo a bowl-to-bowl inversion that was shown to be dependent on the axial substituent. Finally, we polymerize by means of on-surface synthesis a highly regular 2D, porous and chiral, π-extended polymer that paves the way to future nanodevice fabrication.

Discarding metal incorporation in pyrazole macrocycles and the role of the substrate on single-layer assemblies.

Pyrazole derivatives are key in crystal engineering and liquid crystal fields and thrive in agriculture, pharmaceutical, or biomedicine industries. Such versatility relies in their supramolecular bond adaptability when forming hydrogen bonds or metal-pyrazole complexes. Interestingly, the precise structure of pyrazole-based macrocycles forming widespread porous structures is still unsolved. We bring insight into such fundamental question by studying the self-assembled structures of a bis-pyrazole derivative sublimed in ultra-high-vacuum conditions (without solvents) onto the three (111) noble metal surfaces. By means of high-resolution scanning tunneling microscopy that is validated by gas phase density functional theory calculations, we find a common hexagonal nanoporous network condensed by triple hydrogen bonds at the molecule-metal interface. Such assembly is disrupted and divergent after annealing: (i) on copper, the molecular integrity is compromised leading to structural chaos, (ii) on silver, an incommensurate new oblique structure requiring molecular deprotonation is found and, (iii) on gold, metal-organic complexes are promoted yielding irregular chain structures. Our findings confirm the critical role of these metals on the different pyrazole nanoporous structure formation, discarding their preference for metal incorporation into the connecting nodes whenever there is no solvent involved.

Ferromagnetism on an atom-thick & extended 2D metal-organic coordination network.

Ferromagnetism is the collective alignment of atomic spins that retain a net magnetic moment below the Curie temperature, even in the absence of external magnetic fields. Reducing this fundamental property into strictly two-dimensions was proposed in metal-organic coordination networks, but thus far has eluded experimental realization. In this work, we demonstrate that extended, cooperative ferromagnetism is feasible in an atomically thin two-dimensional metal-organic coordination network, despite only ≈ 5% of the monolayer being composed of Fe atoms. The resulting ferromagnetic state exhibits an out-of-plane easy-axis square-like hysteresis loop with large coercive fields over 2 Tesla, significant magnetic anisotropy, and persists up to TC ≈ 35 K. These properties are driven by exchange interactions mainly mediated by the molecular linkers. Our findings resolve a two decade search for ferromagnetism in two-dimensional metal-organic coordination networks.

Searching for kagome multi-bands and edge states in a predicted organic topological insulator.

Recently, mixed honeycomb-kagome lattices featuring metal-organic networks have been theoretically proposed as topological insulator materials capable of hosting nontrivial edge states. This new family of so-called "organic topological insulators" are purely two-dimensional and combine polyaromatic-flat molecules with metal adatoms. However, their experimental validation is still pending given the generalized absence of edge states. Here, we generate one such proposed network on a Cu(111) substrate and study its morphology and electronic structure with the purpose of confirming its topological properties. The structural techniques reveal a practically flawless network that results in a kagome network multi-band observed by angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy. However, at the network island borders we notice the absence of edge states. Bond-resolved imaging of the network exhibits an unexpected structural symmetry alteration that explains such disappearance. This collective lifting of the network symmetry could be more general than initially expected and provide a simple explanation for the recurrent experimental absence of edge states in predicted organic topological insulators.