Thiophene-based Tripodal Anchor Units for Hole Transport in Single-Molecule Junctions with Gold Electrodes

Molecule–metal junctions are
inevitable for the realization
of single-molecule electronics. In this study, we developed new tripodal
anchors with electron-rich aromatic rings to achieve robust contact
with gold electrodes, an effective hybridization of the π orbital
with gold electrodes (π channel), and hole transport through
π-channel hybridization. Cyclic voltammetry and X-ray photoelectron
spectroscopy measurements of the monolayers indicated that the thiophene-based
tripodal molecule exhibits anchoring characteristics as expected.
The electrical conductance of thiophene-anchored bistripodal molecules
using the scanning tunneling microscope (STM)-based break junction
technique confirmed the formation of molecular junctions. The Seebeck
coefficient of this compound estimated from thermoelectric voltage
measurements using a STM was determined to be a positive value, which
indicates that the charge carriers are holes. On the contrary, the
corresponding pyridine-anchored molecules showed electron transport.
These results reveal the versatility of π-channel tripodal anchors
for the control of charge-carrier type in single-molecule electronics.