10.1021/acs.jpcc.7b02246.s001 Alberto Milani Alberto Milani Matteo Tommasini Matteo Tommasini Valentino Barbieri Valentino Barbieri Andrea Lucotti Andrea Lucotti Valeria Russo Valeria Russo Franco Cataldo Franco Cataldo Carlo S. Casari Carlo S. Casari Semiconductor-to-Metal Transition in Carbon-Atom Wires Driven by sp<sup>2</sup> Conjugated End Groups American Chemical Society 2017 sp-hybridized carbon-atom wires equalized charge transfer cumulene-like Raman spectroscopy experiments sp 2 end groups polyyne-like polyyne bond future all-carbon-based science DFT calculation CAW modulation 2017-04-24 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Semiconductor-to-Metal_Transition_in_Carbon-Atom_Wires_Driven_by_sp_sup_2_sup_Conjugated_End_Groups/4982942 Bis­(biphenyl)-capped polyynes are investigated to unveil the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with π-conjugated sp<sup>2</sup> end groups. Raman and surface enhanced Raman spectroscopy experiments and density functional theory (DFT) calculations reveal structural changes from polyyne-like with alternating single–triple bonds toward 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 effect of different sp<sup>2</sup> end groups in driving a semiconductor-to-metal transition is investigated by DFT calculations on a series of CAWs capped with different terminations. We discuss how the modulation of the structural, electronic, and vibrational properties of the sp-carbon chain toward the metallic wire is not trivial and requires a suitable chemical design of the end group and control of charge transfer. These results provide a guideline for the design of novel sp–sp<sup>2</sup> 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–sp<sup>2</sup> systems appealing for a future all-carbon-based science and technology.