On-Surface Synthesis of Giant Conjugated Macrocycles.

We have achieved an on-surface synthesis of giant conjugated macrocycles having a diameter of ≈7 nm and consisting of up to 30 subunits. The synthesis started with a debrominative coupling of the molecular precursors on a hot Ag(111) surface, leading to the formation of arched oligomeric chains and macrocycles. These products were revealed by scanning tunneling microscopy in combination with density functional theory to be covalent oligomers. These intermediates also display C-Ag organometallic bonds between parallel molecular subunits due to site-selective debromination and the asymmetric molecular conformation. Subsequent cyclodehydrogenation at higher temperatures steered the final conjugation of the macrocycles. Our findings provide a novel design strategy toward π-conjugated macrocycles and open up new opportunities for the precise synthesis of organic nanostructures.

On-Surface Cascade Reaction Based on Successive Debromination via Metal-Organic Coordination Template.

Precise control over on-surface covalent reaction pathways is crucial for engineering organic nanostructures with the single-atom precision. Herein, we demonstrate a step-by-step control of an on-surface cascade covalent reaction based on a successive debromination templated by noncovalent metal-organic coordination motifs. The molecular precursor is predesigned with different reactive sites and functional ligands, allowing for both chemical and structural tuning during on-surface reactions. Through the Fe-terpyridine template effect, we are able to direct the reaction to proceed in a three-step cascade pathway and finally to achieve a porous polyarylene nanoribbon structure. The approach opens new opportunities for construction of on-surface organic nanostructures in a predictable manner.

Realigning the melon chains in carbon nitride by rubidium ions to promote photo-reductive activities for hydrogen evolution and environmental remediation.

The photocatalytic efficiency of polymeric carbon nitride (PCN) suffers from unsatisfactory charge separation because of its amorphous structure. Herein, we report a simple bottom-up method to synthesize a novel structure of rubidium ion inserted PCN (Rb-PCN), which involves the regular alignment of melon chains to endow a crystalline feature in PCN. The insertion of Rb+ decreased not only the N p electrons in the heptazine ring but also the plane angle of the heptazine motifs in the melon chain, which promoted the long-range periodicity and crystallinity of carbon nitride. This structurally rearranged crystalline Rb-PCN demonstrated considerably enhanced separation of charge carriers, resulting in six-fold higher photocatalytic hydrogen evolution activity than its amorphous counterpart. Furthermore, the photoexcited electrons can be efficiently trapped by O2 to generate H2O2, which facilitates the production of reactive oxygen species to inactivate bacteria and degrade organic pollutants, showing great potential for use in both energy and environmental applications.