On-surface synthesis and characterization of polyynic carbon chains

Abstract

Carbyne, an elusive sp-hybridized linear carbon allotrope, has fascinated chemists and physicists for decades. Due to its high chemical reactivity and extreme instability, carbyne was much less explored in contrast to the sp2-hybridized carbon allotropes such as graphene. Herein, we report the on-surface synthesis of polyynic carbon chains by demetallization of organometallic polyynes on the Au(111) surface, and the longest one observed consists of ∼60 alkyne units (120 carbon atoms). The polyynic structure of carbon chains with alternating triple and single bonds was unambiguously revealed by bond-resolved atomic force microscopy. Moreover, an atomically precise polyyne, C14, was successfully produced via tip-induced dehalogenation and ring-opening of the decachloroanthracene molecule (C14Cl10) on a bilayer NaCl/Au(111) surface at 4.7 K, and a band gap of 5.8 eV was measured by scanning tunnelling spectroscopy, in a good agreement with the theoretical HOMO–LUMO gap (5.48 eV).

Encapsulation and Evolution of Polyynes Inside Single-Walled Carbon Nanotubes

“…However, cross-linking reactions between the polyyne molecules are unavoidable, making it difficult to synthesize long polyynes. The longest polyynes consisting of from 44 and 48 to recent 68 and 120 carbon atoms have been synthesized using different ending groups and synthesis strategies (e.g., Glaser coupling) [ 11 , 12 , 13 , 14 ]. However, the properties, e.g., optical absorption, of the long polyyne did not become saturated, suggesting that the synthesized longest polyyne is still not long enough to achieve carbyne, an infinite LCC, or a long LCC with its property independent of its length [ 3 , 15 , 16 , 17 ].…”

Kinetics of On-Surface Dechlorinated Aryl–Aryl Coupling

“…In this context, on-surface Ullmann-type or dehalogenative C–C coupling stands as the predominant type of reaction in on-surface synthesis due to its high effectiveness, reliability, and controllability, making it a fundamental approach for predictable and precise on-surface construction of carbon nanostructures. − Additional design can be made through the choice of different halogen atoms (I, Br, Cl), allowing for a wide window of excitation conditions. From the relatively weak C–I bond over the moderate C–Br bond to the more rigid C–Cl bond, the required heating condition on Au(111) ranges from below room temperature to 573 K. , Functionalization of molecular backbones with two distinct types of halogens has effectively realized the intended hierarchical steps at different activation temperatures …”