Dehalogenative Homocoupling of Terminal Alkynyl Bromides on Au(111): Incorporation of Acetylenic Scaffolding into Surface Nanostructures

On-surface C–C coupling reactions of molecular precursors with alkynyl functional groups demonstrate great potential for the controllable fabrication of low-dimensional carbon nanostructures/nanomaterials, such as carbyne, graphyne, and graphdiyne, which demand the incorporation of highly active sp-hybridized carbons. Recently, through a dehydrogenative homocoupling reaction of alkynes, the possibility was presented to fabricate surface nanostructures involving acetylenic linkages, while problems lie in the fact that different byproducts are inevitably formed when triggering the reactions at elevated temperatures. In this work, by delicately designing the molecular precursors with terminal alkynyl bromide, we introduce the dehalogenative homocoupling reactions on the surface. As a result, we successfully achieve the formation of dimer structures, one-dimensional molecular wires and two-dimensional molecular networks with acetylenic scaffoldings on an inert Au(111) surface, where the unexpected C–Au–C organometallic intermediates are also observed. This study further supplements the database of on-surface dehalogenative C–C coupling reactions, and more importantly, it provides us an alternative efficient way for incorporating the acetylenic scaffolding into low-dimensional surface nanostructures

A π‑Conjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence

We have designed and synthesized a π-conjugated system that consists of a flexible and nonplanar π joint and two emissive rigid and planar wings. This molecular system exhibits respectively red, green, and blue (RGB) emission from a single-component luminophore in different environments, namely in polymer matrix, in solution, and in crystals. The flexible unit gives rise to a dynamic conformational change in the excited state from a nonplanar V-shaped structure to a planar structure, leading to a dual fluorescence of blue and green colors. The rigid and planar moieties favor the formation of a two-fold π-stacked array of the V-shaped molecules in the crystalline state, which produces a red excimer-like emission. These RGB emissions are attained without changing the excitation energy

Selective On-Surface Reactions of the Alkenyl <i>gem</i>-Dibromide Group Directed by Substrate Lattices

On-surface synthesis has demonstrated great advantages for atomically precise fabrication of surface-supported nanostructures that could be promising for the next generation of semiconducting materials and molecular electronic devices. The challenging and key issue in this field is to steer surface reaction pathways achieving precise synthesis. The alkenyl gem-dibromide group has been shown to have versatile chemical reactivity. Herein, by introducing such a complicated functional group on surfaces, we demonstrate that selective on-surface reactions, that is, homocoupling and hydrogen migration, could be achieved on Ag(111) and Ag(110) surfaces, respectively. The underlying mechanism of lattice-directed selectivity is revealed by extensive density functional theory (DFT) calculations on the competitive reaction pathways. Such a lattice-directed strategy would be an important means for steering on-surface reaction pathways, aiming to achieve atomically precise synthesis with high efficiency and selectivity

A π‑Conjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence

We have designed and synthesized a π-conjugated system that consists of a flexible and nonplanar π joint and two emissive rigid and planar wings. This molecular system exhibits respectively red, green, and blue (RGB) emission from a single-component luminophore in different environments, namely in polymer matrix, in solution, and in crystals. The flexible unit gives rise to a dynamic conformational change in the excited state from a nonplanar V-shaped structure to a planar structure, leading to a dual fluorescence of blue and green colors. The rigid and planar moieties favor the formation of a two-fold π-stacked array of the V-shaped molecules in the crystalline state, which produces a red excimer-like emission. These RGB emissions are attained without changing the excitation energy

Direct Formation of C–C Double-Bonded Structural Motifs by On-Surface Dehalogenative Homocoupling of <i>gem</i>-Dibromomethyl Molecules

Conductive polymers are of great importance in a variety of chemistry-related disciplines and applications. The recently developed bottom-up on-surface synthesis strategy provides us with opportunities for the fabrication of various nanostructures in a flexible and facile manner, which could be investigated by high-resolution microscopic techniques in real space. Herein, we designed and synthesized molecular precursors functionalized with benzal <i>gem</i>-dibromomethyl groups. A combination of scanning tunneling microscopy, noncontact atomic force microscopy, high-resolution synchrotron radiation photoemission spectroscopy, and density functional theory calculations demonstrated that it is feasible to achieve the direct formation of C–C double-bonded structural motifs <i>via</i> on-surface dehalogenative homocoupling reactions on the Au(111) surface. Correspondingly, we convert the sp³-hybridized state to an sp²-hybridized state of carbon atoms, <i>i</i>.<i>e</i>., from an alkyl group to an alkenyl one. Moreover, by such a bottom-up strategy, we have successfully fabricated poly­(phenylenevinylene) chains on the surface, which is anticipated to inspire further studies toward understanding the nature of conductive polymers at the atomic scale