Unusual Length Dependence of the Conductance in Cumulene Molecular Wires

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.

Single-molecule junctions of multinuclear organometallic wires: long-range carrier transport brought about by metal–metal interaction

“…Thus far, extensive single-molecule conductance studies have unveiled general strategies for organic and inorganic molecular wires with small b values such as (1) narrowing the HOMO-LUMO gap, [8][9][10] (2) extending p-conjugated systems (e.g. less bond alternation), 11,12 and making use of (3) p-stacking interactions [13][14][15] and (4) metal-metal bonded systems ( Fig. 1).…”

Next‐generation QTAIM for scoring molecular wires in E‐fields for molecular electronic devices

“…The desirable properties of conjugated carbon "linkages," for example, ─C C─, as wires between building blocks have prompted a huge and diverse body of research in polyenes, cumulenes, and related molecular motifs. [20][21][22][23][24][25] In this investigation we will use next-generation QTAIM that includes a 3-D, non-minimal three-stranded directional interpretation of bonding, incorporating the most preferred direction of electronic charge density accumulation using ethene as the molecular wire. [26] This directional approach can be used in a variety of circumstances where conventional QTAIM, [27] that only provides scalar measures such as bond ellipticity ε, is not useful.…”

“…In addition to building blocks, “wires” must also be considered in the design of molecular electronic devices. The desirable properties of conjugated carbon “linkages,” for example, ─CC─, as wires between building blocks have prompted a huge and diverse body of research in polyenes, cumulenes, and related molecular motifs …”

A review of functional linear carbon chains (oligoynes, polyynes, cumulenes) and their applications as molecular wires in molecular electronics and optoelectronics

“…The lack of length dependence in the conductance of 32 and 33 was attributed to the strong decrease in the HOMO-LUMO gap with increasing cumulene length. 129 An independent STM-BJ study included the [7]cumulene homologue 34. An incremental increase in conductance with increasing length, i.e.…”