Single Molecule Conductance of Electroactive Helquats: Solvent Effect.

A series of helquat molecules with increasing number of rings n
was studied by electrochemical and break junction methods to
provide redox characteristics and single molecule conductance
properties. Even though selected species do not contain
anchoring groups the molecular junction conductance was
observed experimentally and depends strongly on the solvent
used. Single molecule conductance G is almost two orders of
magnitude higher in water environment compared to mesitylene, whereas the distribution of G values is narrow in water
and wide in mesitylene solvent. In the non-polar environment,
G increases with increasing n, contrary to generally accepted
notion of decreasing tunneling current with increasing molecular length. This behavior is, however, consistent with electrochemical properties, which showed that longer helquats are
reduced more easily than the shorter ones. Furthermore,
theoretical computations provided most probable molecular
junction configurations of helquats in water solvent with
excellent agreement between theoretical and experimental G
values.