The environment surrounding a molecular junction affects
its charge-transport
properties and, therefore, must be chosen with care. In the case of
measurements in liquid media, the solvent must provide good solvation,
grant junction stability, and, in the case of electrolyte gating experiments,
allow efficient electrical coupling to the gate electrodes through
control of the electrical double layer. We evaluated in this study
the deep eutectic solvent mixture (DES) ethaline, which is a mixture
of choline chloride and ethylene glycol (1:2), for single-molecule
junction fabrication with break-junction techniques. In ethaline,
we were able to (i) measure challenging and poorly soluble molecular
wires, exploiting the improved solvation capabilities offered by DESs,
and (ii) efficiently apply an electrostatic gate able to modulate
the conductance of the junction by approximately an order of magnitude
within a ∼1 V potential window. The electrochemical gating
results on a Au–VDP–Au junction follow
exceptionally well the single-level modeling with strong gate coupling
(where VDP is 1,2-di(pyridine-4-yl)ethene). Ethaline is also an ideal
solvent for the measurement of very short molecular junctions, as
it grants a greatly reduced snapback distance of the metallic electrodes
upon point-contact rupture. Our work demonstrates that DESs are viable
alternatives to often relatively expensive ionic liquids, offering
good versatility for single-molecule electrical measurements.