Chemistry Reference
In-Depth Information
gold-coated microcantilever - could be actuated in concert to bend the cantilever up
and down, which was detected with a laser beam (Fig.
31
). Although it was below
the macroscopic scale, the experiment was a powerful demonstration that energy
can be transduced and work can be done by molecular switches on their immediate
environment, converting chemical or electrochemical energy to mechanical energy.
Leigh and coworkers [
228
] devised an ingenious experiment in 2005 that also
utilized molecular switches, this time to transport a macroscopic object on
a surface. Bistable rotaxanes were physisorbed onto a surface and irradiated with
UV light, which photoisomerized an olefin in some rotaxanes and caused the
macrocyclic component to shuttle over a fluorinated recognition site, which in
turn changed the polarophobicity of the surface. Photoswitching the surface in
this manner moved a drop of diiodomethane several millimeters up a 12
incline
(Fig.
32
). Though the world is still waiting for MIMs to physically do the macro-
scopic work, these approaches represent noteworthy steps in that direction.
Now for a bit of science fiction: what if single molecules could be utilized to
store information like transistors? Joint efforts [
229
-
235
] between the Heath and
Stoddart groups, which addressed the organization of bistable donor-acceptor
MIMs at crossbar interfaces using the Langmuir-Blodgett technique and their
actuation in these two-dimensional devices, culminated [
236
] in 2007 after
a decade with a device (Fig.
33
) approaching that metric. A monolayer of bistable
rotaxanes was incorporated into a crossbar logic architecture in a size regime
a
O
O
OH
O
OH
OH
O
O
O
OH
OH
OH
S
S
S
S
S
S
Au 1
11
1 mm
b
O
OH
O
O
OH
OH
O
O
O
OH
OH
OH
S
S
S
S
S
S
Au
111
1 mm
Fig. 32 Transport of a diiodomethane droplet up a 12
incline on a surface with physisorbed,
photoswitchable bistable [2]rotaxanes [
228
]. (a) Cartoon and photograph of the surface in the
ground state. The macrocycle preferentially encircles an unfluorinated recognition site. (b) The
same surface in the photostationary state (after UV irradiation). Olefin isomerization in
the preferred recognition site causes some macrocycles to shuttle to the fluorinated site, changing
the polarophobicity of the surface and moving the droplet several millimeters uphill
