Structural, chemical, and extrinsic modifications of graphene-based nanostructures enable bandgap tuning, optoelectronics, spintronics, and quantum materials design. A well-known approach to modify their electronic properties involves introducing nonbenzenoid ring topologies in their ideal sp2-hybridized hexagonal lattice, such as azulene or Stone-Wales (SW) defects. However, despite the unique structural and electronic characteristics that these nonalternant defects induce, their systematic incorporation in graphene-based nanostructures remains challenging. Here, we demonstrate the on-surface synthesis of one-dimensional SW-based polymers linked through cumulene bonds on the Au(111) surface via thermal and visible-light-induced reactions of a tailored molecular precursor. Scanning tunneling and noncontact atomic force microscopies reveal the nonplanar structure of SW-based units within the polymer chain, while the chemical structure of the polymer has been verified by Raman spectroscopy in combination with theoretical modeling. Additionally, scanning tunneling spectroscopy measurements show an experimental bandgap of 1.8 eV, which significantly differs from its isostructural cumulene-bridged bisanthene analogs. Our results highlight the critical role of SW defects in the structural and electronic properties of carbon-based conjugated polymers, advancing their design with prospects in next-generation optoelectronic devices.

• Keywords
• Carbon‐based polymers, Non‐contact atomic force microscopy, Scanning tunneling microscopy, Stone‐Wales defect, Surface chemistry,
• Publication type
• Journal Article MeSH

Here, we report a new on-surface synthetic strategy to precisely introduce five-membered units into conjugated polymers from specifically designed precursor molecules that give rise to low-bandgap fulvalene-bridged bisanthene polymers. The selective formation of non-benzenoid units is finely controlled by the annealing parameters, which govern the initiation of atomic rearrangements that efficiently transform previously formed diethynyl bridges into fulvalene moieties. The atomically precise structures and electronic properties have been unmistakably characterized by STM, nc-AFM, and STS and the results are supported by DFT theoretical calculations. Interestingly, the fulvalene-bridged bisanthene polymers exhibit experimental narrow frontier electronic gaps of 1.2 eV on Au(111) with fully conjugated units. This on-surface synthetic strategy can potentially be extended to other conjugated polymers to tune their optoelectronic properties by integrating five-membered rings at precise sites.

• Publication type
• Journal Article MeSH

The design of organometallic complexes is at the heart of modern organic chemistry and catalysis. Recently, on-surface synthesis has emerged as a disruptive paradigm to design previously precluded compounds and nanomaterials. Despite these advances, the field of organometallic chemistry on surfaces is still at its infancy. Here, we introduce a protocol to activate the inner diacetylene moieties of a molecular precursor by copper surface adatoms affording the formation of unprecedented organocopper metallacycles on Cu(111). The chemical structure of the resulting complexes is characterized by scanning probe microscopy and X-ray photoelectron spectroscopy, being complemented by density functional theory calculations and scanning probe microscopy simulations. Our results pave avenues to the engineering of organometallic compounds and steer the development of polyyne chemistry on surfaces.

• Publication type
• Journal Article MeSH

We report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet-triplet spin-flip inelastic excitations with an effective exchange coupling (Jeff ) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon-based optoelectronics and spintronics.

• Keywords
• cumulenes, diradical polymers, nc-AFM, scanning tunneling microscopy, surface chemistry,
• Publication type
• Journal Article MeSH

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. Here we introduce a synthetic protocol based on the search for specific vibrational modes through an appropriate tailoring of the π-conjugation of the precursors, in order to increase the attempt frequency of a chemical reaction. First, we design a 1D π-conjugated polymer on Au(111), which is based on bisanthene monomers linked by cumulene bridges that tune specific vibrational modes. In a second step, upon further annealing, such vibrational modes steer the twofold cyclization reaction between adjacent bisanthene moieties, which gives rise to a long pentalene-bridged conjugated ladder polymer featuring a low bandgap. In addition, high resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, thus confirming the validity of the Glidewell and Lloyd´s rules for aromaticity. This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards π-conjugated polymers with specific structures and properties.

• Publication type
• Journal Article MeSH