Electronic Property Modulation of One-Dimensional Extended Graphdiyne Nanowires from a First-Principle Crystal Orbital View

Impact of Halogen Termination and Chain Length on π-Electron Conjugation and Vibrational Properties of Halogen-Terminated Polyynes

We explored the optoelectronic and vibrational properties of a new class of halogen-terminated carbon atomic wires in the form of polyynes using UV-vis, infrared absorption, Raman spectroscopy, X-ray single-crystal diffraction, and DFT calculations. These polyynes terminate on one side with a cyanophenyl group and on the other side, with a halogen atom X (X = Cl, Br, I). We focus on the effect of different halogen terminations and increasing lengths (i.e., 4, 6, and 8 sp-carbon atoms) on the π-electron conjugation and the electronic structure of these systems. The variation in the sp-carbon chain length is more effective in tuning these features than changing the halogen end group, which instead leads to a variety of solid-state architectures. Shifts between the vibrational frequencies of samples in crystalline powders and in solution reflect intermolecular interactions. In particular, the presence of head-to-tail dimers in the crystals is responsible for the modulation of the charge density associated with the π-electron system, and this phenomenon is particularly important when strong I··· N halogen bonds occur.

Stable and Solution-Processable Cumulenic sp-Carbon Wires: A New Paradigm for Organic Electronics

Solution-processed, large-area, and flexible electronics largely relies on the excellent electronic properties of sp² -hybridized carbon molecules, either in the form of π-conjugated small molecules and polymers or graphene and carbon nanotubes. Carbon with sp-hybridization, the foundation of the elusive allotrope carbyne, offers vast opportunities for functionalized molecules in the form of linear carbon atomic wires (CAWs), with intriguing and even superior predicted electronic properties. While CAWs represent a vibrant field of research, to date, they have only been applied sparingly to molecular devices. The recent observation of the field-effect in microcrystalline cumulenes suggests their potential applications in solution-processed thin-film transistors but concerns surrounding the stability and electronic performance have precluded developments in this direction. In the present study, ideal field-effect characteristics are demonstrated for solution-processed thin films of tetraphenyl[3]cumulene, the shortest semiconducting CAW. Films are deposited through a scalable, large-area, meniscus-coating technique, providing transistors with hole mobilities in excess of 0.1 cm²  V^-1  s^-1 , as well as promising operational stability under dark conditions. These results offer a solid foundation for the exploitation of a vast class of molecular semiconductors for organic electronics based on sp-hybridized carbon systems and create a previously unexplored paradigm.

Scanning tunneling microscopy and Raman spectroscopy of polymeric sp-sp2 carbon atomic wires synthesized on the Au(111) surface

Long linear carbon nanostructures based on sp-hybridization can be synthesized by exploiting on-surface synthesis of halogenated precursors evaporated on Au(111), thus opening a way to investigations by surface-science techniques. By means of an experimental approach combining scanning tunneling microscopy and spectroscopy (STM and STS) with ex situ Raman spectroscopy we investigate the structural, electronic and vibrational properties of polymeric sp-sp2 carbon atomic wires composed by sp-carbon chains connected through phenyl groups. Density-functional-theory (DFT) calculations of the structure and the electronic density of states allow us to simulate STM images and to compute Raman spectra. The comparison of experimental data with DFT simulations unveil the properties and the formation stages as a function of the annealing temperature. Atomic-scale structural information from STM complement the Raman sensitivity to the single molecular bond to open the way to detailed understanding of these novel carbon nanostructures.

Functionalized Graphdiyne Nanowires: On-Surface Synthesis and Assessment of Band Structure, Flexibility, and Information Storage Potential

Carbon nanomaterials exhibit extraordinary mechanical and electronic properties desirable for future technologies. Beyond the popular sp² -scaffolds, there is growing interest in their graphdiyne-related counterparts incorporating both sp² and sp bonding in a regular scheme. Herein, we introduce carbonitrile-functionalized graphdiyne nanowires, as a novel conjugated, one-dimensional (1D) carbon nanomaterial systematically combining the virtues of covalent coupling and supramolecular concepts that are fabricated by on-surface synthesis. Specifically, a terphenylene backbone is extended with reactive terminal alkyne and polar carbonitrile (CN) moieties providing the required functionalities. It is demonstrated that the CN functionalization enables highly selective alkyne homocoupling forming polymer strands and gives rise to mutual lateral attraction entailing room-temperature stable double-stranded assemblies. By exploiting the templating effect of the vicinal Ag(455) surface, 40 nm long semiconducting nanowires are obtained and the first experimental assessment of their electronic band structure is achieved by angle-resolved photoemission spectroscopy indicating an effective mass below 0.1m₀ for the top of the highest occupied band. Via molecular manipulation it is showcased that the novel oligomer exhibits extreme mechanical flexibility and opens unexplored ways of information encoding in clearly distinguishable CN-phenyl trans-cis species. Thus, conformational data storage with density of 0.36 bit nm^-2 and temperature stability beyond 150 K comes in reach.

Electronic Property Modulation of One-Dimensional Extended Graphdiyne Nanowires from a First-Principle Crystal Orbital View

Graphdiyne and derivatives with delocalized π‐electron systems are of particular interest owing to their structural, electronic, and transport properties, which are important for potential applications in next‐generation electronics. Inspired by recently obtained extended graphdiyne nanowires, explorations of the modulation of the band gap and carrier mobility of this new species are still needed before application in device fabrication. To provide a deeper understanding of these issues, herein we present theoretical studies of one‐dimensional extended graphdiyne nanowires using first‐principle calculations. Modulation of the electronic properties of the extended graphdiyne nanowire was investigated systemically by considering several chemical and physical factors, including electric field, chemical functionalization, and carbo‐merization. The band gap was observed to increase upon application of an electric field parallel to the plane of the synthesized graphdiyne nanowire in a non‐periodic direction. Although chemical functionalization and carbo‐merization caused the band gaps to decrease, the semiconducting property of the nanowires was preserved. Band gap engineering of the extended graphdiyne nanowires was explored regarding the field strength and the number of −C≡C− units in the carbon chain fragments. The charge carrier mobility of chemically functionalized and carbo‐merized extended graphdiyne nanowires was also calculated to provide a comparison with pristine nanowire. Moreover, crystal orbital analysis was performed in order to discern the electronic and charge transport properties of the extended graphdiyne nanowires modified by the aforementioned chemical and physical factors.