On-surface synthesis of poly(p-phenylene ethynylene) molecular wires via in situ formation of carbon-carbon triple bond

Abstract

The carbon–carbon triple bond (–C≡C–) is an elementary constituent for the construction of conjugated molecular wires and carbon allotropes such as carbyne and graphyne. Here we describe a general approach to in situ synthesize –C≡C– bond on Cu(111) surface via homo-coupling of the trichloromethyl groups, enabling the fabrication of individual and arrays of poly(p-phenylene ethynylene) molecular wires. Scanning tunneling spectroscopy reveals a delocalized electronic state extending along these molecular wires, whose structure is unraveled by atomically resolved images of scanning tunneling microscopy and noncontact atomic force microscopy. Combined with density functional theory calculations, we identify the intermediates formed in the sequential dechlorination process, including surface-bound benzyl, carbene, and carbyne radicals. Our method overcomes the limitation of previous on-surface syntheses of –C≡C– incorporated systems, which require the precursors containing alkyne group; it therefore allows for a more flexible design and fabrication of molecular architectures with tailored properties.

Reaction selectivity of homochiral versus heterochiral intermolecular reactions of prochiral terminal alkynes on surfaces

“…Figure 3e, f show the Br-tip STM image and nc-AFM frequency shift map of a same area. Similar to many previous reports 26,39–41 , ethynylenes are imaged as bright dots in the nc-AFM frequency shift map (yellow arrow). C 1 s SRPES shown in Fig.…”

Fingerprints of sp1 Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials

“…By means of scanning tunneling microscopy (STM) they demonstrated the surface-mediated dehalogenation of the precursor and the formation of long sp1-sp2 carbon wires and a new 2D sp1-sp2 system belonging to the family of graphdiynes. On-surface synthesis has been performed also with Cl-functionalized precursors on Cu(111) and even for the synthesis of cumulene-like systems (i.e., sp1-carbon wires with all equal double bonds) [30,31,32]. These works reported the images of single sp1-carbon wires with resolution at molecular-bond level, obtained by the combined use of STM and atomic force microscopy (AFM).…”

Cyclo[18]carbon: Insight into Electronic Structure, Aromaticity, and Surface Coupling

“…Nevertheless, carbon allotropes are still in focus of synthetic attempts and theoretical predictions. [9][10][11][12][13][14][15] One of the most impressive recent achievements in this field is the successful synthesis and characterization of the closed-circle polyyne containing 18 sp-hybridized carbon atoms, called cyclo [18]carbon. 16 It is notable that cyclo [18]carbon possesses the special "double" aromaticity 17 because of delocalization of two scaffolds of 18 -electrons oriented in the plane of C18 ring (18in) and perpendicular to it (18out, Figure 1) that was first mentioned by Diederich et al 18 and developed further by Fowler et al 19 .…”