Unusual Length Dependence of the Conductance in Cumulene Molecular Wires. Issue 25 (17th May 2019)

• Record Type: Journal Article
• Authors: Xu, Wenjun; Leary, Edmund; Hou, Songjun; Sangtarash, Sara; González, M. Teresa; Rubio‐Bollinger, Gabino; Wu, Qingqing; Sadeghi, Hatef; Tejerina, Lara; Christensen, Kirsten E.; Agraït, Nicolás; Higgins, Simon J.; Lambert, Colin J.; Nichols, Richard J.; Anderson, Harry L.
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 25(2019)
• Page Start: 8378
• Page End: 8382
• Publication Date: 2019-05-17
• Subjects: break junctions -- conductance -- cumulenes -- molecular wires -- single-molecule studies; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201901228
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Cumulenes are sometimes described as "metallic" because an infinitely long cumulene would have the band structure of a metal. Herein, we report the single‐molecule conductance of a series of cumulenes and cumulene analogues, where the number of consecutive C=C bonds in the core is n =1, 2, 3, and 5. The [ n ]cumulenes with n =3 and 5 have almost the same conductance, and they are both more conductive than the alkene ( n =1). This is remarkable because molecular conductance normally falls exponentially with length. The conductance of the allene ( n =2) is much lower, because of its twisted geometry. Computational simulations predict a similar trend to the experimental results and indicate that the low conductance of the allene is a general feature of [ n ]cumulenes where n is even. The lack of length dependence in the conductance of [3] and [5]cumulenes is attributed to the strong decrease in the HOMO–LUMO gap with increasing length. Abstract : Cumulene wires, such as that shown above, with an odd number of double bonds are more conductive than expected for their length, as revealed by experimental single‐molecule break‐junction results and computational simulations. The conductance is almost independent of the length because the HOMO–LUMO gap decreases steeply as the molecules become longer.