Executive Summary Final - the Center for Nanoscale Science - an ...

IRG2: Powered Motion at the Nanoscale
to overcome the problem of steric hindrance in the lattice. We have designed adamantanetrithiol
molecules functionalized with azobenzenes to create space around each azobenzene unit thereby
providing sufficient spatial freedom for switching of the entire monolayer. Also, the adamantyl
cage electronically decouples the azobenzene moiety from the substrate, thereby improving
switching efficiency. Synthesis of molecules is being done by the Tour group and measurements
by the Weiss group. The effects of the power of UV and visible lights on the rates of
isomerization will also be studied in order to establish the minimum power required for
triggering photo-switching.
Less constrained untethered motion is possible with molecular nanocars. The synthesis and ringopening
metathesis polymerization activity of two nanocars functionalized with an olefin
metathesis catalyst was completed in 2010. In an effort to elucidate the mechanism of movement
of nano-vehicles on nonconducting surfaces, the synthesis of five fluorescently tagged nanocars
was completed and their optical properties were determined. The synthesis and imaging by
scanning tunneling microscopy of a nano-dragster were completed. A new class of nano-vehicles
incorporating trans-alkynyl(dppe)2 ruthenium-based wheels were also synthesized. A
computationally non-demanding method for simultaneously determining multiple trajectories of
single molecules was developed. Single molecule fluorescence imaging of dye-labeled nanocars
at room temperature was also investigated.
Many of these motors – at both the micro and nano scales – produce enhanced functionality if
they can interact with external fields. The IRG has been developing a new type of field with
which to control motors of diverse types: a standing surface acoustic wave. This active
separation technique uses standing surface acoustic wave to separate and/or pattern a wide range
of nanomaterials, including catalytic, biological and molecular motors. The excellent energy
confinement of SAWs propagating on a piezoelectric substrate makes this particle separation
device highly energy efficient.
A final area of IRG
investigation in 2010
involves the active control
of plasmonics using
molecular machines: the
IRG has demonstrated a
molecular-level active
plasmonic device based on
the formation of plasmonexciton
states by assembling J-aggregate molecules on an array of gold nanodisks. By changing
the incident angle of incoming light, we observed plasmon-exciton coupling of variable
strengths. We have also demonstrated a frequency-addressed plasmonic switch by embedding
uniform gold nanodisk /holes into dual-frequency responsive liquid crystal molecules (DFLCs).
This DFLC-based active plasmonic system demonstrates an excellent, reversible, frequencydependent
switching behavior and could be used in future integrated nanophotonic circuits.
Owing to the significance of these works, they have been selected as cover images of several
journals (figure above). We have also developed a wide range of plasmonic devices and currently