Cyclopropenylidenes as Strong Carbene Anchoring Groups on Au Surfaces.

The creation of stable molecular monolayers on metallic surfaces is a fundamental challenge of surface chemistry. N-Heterocyclic carbenes (NHCs) were recently shown to form self-assembled monolayers that are significantly more stable than the traditional thiols on Au system. Here we theoretically and experimentally demonstrate that the smallest cyclic carbene, cyclopropenylidene, binds even more strongly than NHCs to Au surfaces without altering the surface structure. We deposit bis(diisopropylamino)cyclopropenylidene (BAC) on Au(111) using the molecular adduct BAC-CO2 as a precursor and determine the structure, geometry, and behavior of the surface-bound molecules through high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Our experiments are supported by density functional theory calculations of the molecular binding energy of BAC on Au(111) and its electronic structure. Our work is the first demonstration of surface modification with a stable carbene other than NHC; more broadly, it drives further exploration of various carbenes on metal surfaces.

Multifunctional Vesicles from a Self-assembled Cluster-Containing Diblock Copolymer.

We describe a new diblock copolymer composed of two segments with complementary functionalities. One block contains pendent photo-cross-linkable cinnamoyl groups, and the other contains molecular clusters, Co6Se8, capable of multielectron redox processes. This multifunctional macromolecule is synthesized by sequential ring-opening metathesis polymerization of monomers constructed using norbornene moieties. Remarkably, the tethered molecular cluster gives access to three different charge states in N, N-dimethylformamide: neutral, +1, and +2. In tetrahydrofuran, by contrast, the charged copolymer self-assembles into vesicles that inhibit the redox reactions. The wall of these vesicles can be cross-linked by exploiting the photoinduced 2 + 2 cycloaddition of the cinnamoyls to form cyclobutane dimers. Moreover, these vesicles can be loaded with molecular cargo and used as cross-linkable containers; we demonstrate this feature by encapsulating the molecular dye methylene blue into the capsules. Our work is the first report of a well-defined block copolymer containing a metal chalcogenide molecular cluster; more generally, it opens the door to new applications of metal-containing polymers.

Two-Dimensional Hierarchical Semiconductor with Addressable Surfaces.

Surfaces play a key role in determining material properties, and their importance is further magnified in the two-dimensional (2D) limit. Though monolayers are entirely composed of surfaces, there is no chemical approach to covalently address them without breaking intralayer bond. Here, we describe a 2D semiconductor that offers two unique features among 2D materials: structural hierarchy within the monolayer and surface reactive sites that enable functionalization. The 2D semiconductor is composed of a single layer of strongly interconnected Re6Se8 clusters arranged in an oblique lattice capped by substitutionally labile Cl atoms. We show that a simple ligand substitution strategy borrowed from traditional coordination chemistry can be used to modify the surface of the 2D material while preserving its internal structure. The potential generality of this approach establishes a promising route toward multifunctional 2D materials with tunable physical and chemical properties and may also facilitate better electrical top contact to 2D semiconductors.

Dimerization of Endohedral Fullerene in a Superatomic Crystal.

We describe a solid state material created from the reaction of Ni9 Te6 (PEt3 )8 and Lu3 N@C80 . The resulting superatomic crystal, [Ni12 Te12 (PEt3 )8 ]2 [(Lu3 N@C80 )2 ], contains dimers of Lu3 N@C80 that form upon reduction of the fullerene through a single C-C bond at the triple hexagon junctions. The encapsulated Lu3 N cluster displays an unprecedented orientation that is collinear and coplanar with the intercage carbon bond. Density functional theory calculations rationalize this unique bonding and relative orientation of the Lu3 N clusters. Our structural and theoretical results provide new insights into the effect that the M3 N cluster species has on the dimerization process of endohedral fullerenes.