Abstract
AbstractCumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on‐surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well‐controlled ultrahigh‐vacuum conditions. Here we report the on‐surface synthesis of a polymer linked by cumulene‐like bonds on a Au(111) surface via sequential thermally activated dehalogenative C−C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene‐like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X‐ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on‐surface synthesis of cumulene‐containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces.
Highlights
Over the last century, the well-known carbon allotropes with sp2- and sp3- hybridization have been extensively investigated due to their relevance, ranging from drugs to synthetic materials of interest in many applications because of their high surface area and physicochemical properties.[1,2,3] Only in 1985, fullerenes were observed for the first time,[4] opening a new era for synthetic carbon allotropes
We report on a comprehensive scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), non-contact atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) study of the surface-confined formation of a one-dimensional polymer linked by cumulene-like bonds
We have demonstrated the on-surface synthesis of a polymer linked via cumulene-like bonds on a coinage metal surface by a combination of high-resolution STM and non-contact atomic force microscopy (ncAFM) imaging together with DFT calculations, STS, and XPS
Summary
The well-known carbon allotropes with sp2- (graphite) and sp3- (diamond) hybridization have been extensively investigated due to their relevance, ranging from drugs to synthetic materials of interest in many applications because of their high surface area and physicochemical properties.[1,2,3] Only in 1985, fullerenes were observed for the first time,[4] opening a new era for synthetic carbon allotropes. The formation of cumulene-containing dimers and polymers by dehalogenative homocoupling reactions of gem-dibromides[20,21] and by enediyne coupling,[22] together with the generation of several intermediates on different surfaces via scanning tunneling microscopy (STM)based manipulation has been reported.[23,24] detailed studies of the on-surface synthesis of cumulenecontaining compounds and their in-depth structural and electronic characterization have remained elusive. We report on a comprehensive STM, scanning tunneling spectroscopy (STS), non-contact atomic force microscopy (ncAFM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) study of the surface-confined formation of a one-dimensional polymer linked by cumulene-like bonds. The specific adsorption geometry of the molecular precursor 1,5-bis(dibromomethylene)1,5-dihydrobenzo[5,6]cyclohepta[1,2,3,4-def]fluorene (1) on Au(111) leads to two coupling steps separated in temperature that result in a selective head-to-head/tail-to-tail monomer sequence in the polymer
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