Semiconductor-to-metal transition in carbon-atom wires driven by sp2 conjugated endgroups

Abstract

Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with π-conjugated $s{p}^2$ endgroups. Raman and Surface Enhanced Raman spectroscopy (SERS) investigation of these systems and Density Functional Theory (DFT) calculations reveal structural changes from polyyne-like with alternating single-triple bonds towards cumulene-like with more equalized bonds as a consequence of the charge transfer occurring when wires interact with metallic nanoparticles. While polyynes have semiconducting electronic properties, a more equalized system tends to a cumulene-like structure characterized by a nearly metallic behavior. The possibility to drive a semiconductor-to-metal transition has been investigated by systematic DFT calculations on a series of CAWs capped with different conjugated endgroups revealing that the modulation of the structural, electronic and vibrational properties of the sp-carbon chain towards the metallic wire cannot be simply obtained by using extended π-conjugated $s{p}^2$ carbon endgroups, but require a suitable chemical design of the endgroup and control of charge transfer. These results provide useful guidelines for the design of novel $sp-s{p}^2$ hybrid carbon nanosystems with tunable properties, where graphene-like and polyyne-like domains are closely interconnected. The capability to tune the final electronic or optical response of the material makes these hybrid $sp-s{p}^2$ systems appealing for a future all-carbon-based science and technology.

23 pages, 6 figures

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• Carbon-atom wires produced by nanosecond pulsed laser deposition in a background gas
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• Synthesis And Characterization Of Polyynes End-Capped By Biphenyl Groups ({\Alpha},Ω-Biphenylpolyynes)
• Vibrational and nonlinear optical properties of amine-capped push-pull polyynes by infrared and Raman spectroscopy
• Size-selected polyynes synthesized by submerged arc discharge in water
• Disclosing Early Excited State Relaxation Events in Prototypical Linear Carbon Chains
• Odd-even phonon transport effects in strained carbon atomic chains bridging graphene nanoribbon electrodes
• Exploring the Growth Dynamics of Size-selected Carbon Atomic Wires with in situ UV Resonance Raman Spectroscopy
• Halogen-Terminated Carbon Atomic Wires by Laser Ablation in Halogenated Organic Solvents: Synthesis and Characterization