Tuning Conductance in π-σ-π Single-Molecule Wires.
While the single-molecule conductance properties of π-conjugated and σ-conjugated systems have been well-studied, little is known regarding the conductance properties of mixed σ-π backbone wires and the factors that control their transport properties. Here we utilize a scanning tunneling microscope-based break-junction technique to study a series of molecular wires with π-σ-π backbone structures, where the π-moiety is an electrode-binding thioanisole ring and the σ-moiety is a triatomic α-β-α chain composed of C, Si, or Ge atoms. We find that the sequence and composition of group 14 atoms in the α-β-α chain dictates whether electronic communication between the aryl rings is enhanced or suppressed. Placing heavy atoms at the α-position decreases conductance, whereas placing them at the β-position increases conductance: for example, the C-Ge-C sequence is over 20 times more conductive than the Ge-C-Ge sequence. Density functional theory calculations reveal that these conductance trends arise from periodic trends (i.e., atomic size, polarizability, and electronegativity) that differ from C to Si to Ge. The periodic trends that control molecular conductance here are the same ones that give rise to the α and β silicon effects from physical organic chemistry. These findings outline a new molecular design concept for tuning conductance in single-molecule electrical devices.
Department of Chemistry, Columbia University , New York, New York 10027, United States.
Timothy A
TA
Su
Department of Physics and Applied Math, Columbia University , New York, New York 10027, United States.
Haixing
H
Li
Department of Chemistry, Columbia University , New York, New York 10027, United States.
Rebekka S
RS
Klausen
Department of Physics and Applied Math, Columbia University , New York, New York 10027, United States.
Jonathan R
JR
Widawsky
Department of Physics and Applied Math, Columbia University , New York, New York 10027, United States.
Arunabh
A
Batra
Department of Chemistry, Columbia University , New York, New York 10027, United States.
Michael L
ML
Steigerwald
Department of Chemistry, Columbia University , New York, New York 10027, United States.|Department of Physics and Applied Math, Columbia University , New York, New York 10027, United States.
Latha
L
Venkataraman
Department of Chemistry, Columbia University , New York, New York 10027, United States.
Colin
C
Nuckolls