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Download filePermethylation Introduces Destructive Quantum Interference in Saturated Silanes
journal contribution
posted on 17.09.2019, 16:35 authored by Marc H. Garner, Haixing Li, Madhav Neupane, Qi Zou, Taifeng Liu, Timothy A. Su, Zhichun Shangguan, Daniel W. Paley, Fay Ng, Shengxiong Xiao, Colin Nuckolls, Latha Venkataraman, Gemma C. SolomonThe
single-molecule conductance of silanes is suppressed due to
destructive quantum interference in conformations with cisoid dihedral
angles along the molecular backbone. Yet, despite the structural similarity,
σ-interference effects have not been observed in alkanes. Here
we report that the methyl substituents used in silanes are a prerequisite
for σ-interference in these systems. Through density functional
theory calculations, we find that the destructive interference is
not evident to the same extent in nonmethylated silanes. We find the
same is true in alkanes as the transmission is significantly suppressed
in permethylated cyclic and bicyclic alkanes. Using scanning tunneling
microscope break-junction method we determine the single-molecule
conductance of functionalized cyclohexane and bicyclo[2.2.2]octane
that are found to be higher than that of equivalent permethylated
silanes. Rather than the difference between carbon and silicon atoms
in the molecular backbones, our calculations reveal that it is primarily
the difference between hydrogen and methyl substituents that result
in the different electron transport properties of nonmethylated alkanes
and permethylated silanes. Chemical substituents play an important
role in determining the single-molecule conductance of saturated molecules,
and this must be considered when we improve and expand the chemical
design of insulating organic molecules.