The Ge and Potma groups joined forces in
constructing a new type of sum-frequency generation (SFG) microscope.
SFG microscopy enables a detailed look at molecules based on
vibrational sensitivity. This laser scanning microscope has the
potential to reveal precise spectroscopic information about molecules
at interfaces with sub-micrometer spatial resolution.
Lighting Up the Interior of a Single Molecule
Chi Chen, Ping Chu, C. A. Bobisch, D. L. Mills, and W. Ho
In the past 20 years, optical experiments have reached single
molecule sensitivity and removed ensemble averaging associated with
variations in the molecular environment. However, each emitting
molecule appears as a beacon of light without internal structure due to
the limited spatial resolution. By using a scanning tunneling
microscope, it is shown that the interior of a single molecule is
optically heterogeneous, displaying a rich structure that reflects the
states of the molecule involved in the optical transition. The atomic
scale resolution in the optical emission is achieved by taking
advantage of using tunneling electrons as the excitation source that is
spatially confined to Ångström dimensions. In the case of
the magnesium porphine, the light absorbing part of chlorophyll, the
optical image is highlighted by light emission concentrated in four
lobes, but the center of the molecule appears dim. Such images give a
first look into the internal structure of a chromophore that has
previously been discussed but not visualized. These results provide a
new window to observe the coupling of electron and light in a molecule
that forms the basis for dye sensitized solar energy conversion,
organic light emission, and photocatalytic chemistry.
Publication
This work has been highlighted by a number of sources: American
Physical Society, Nature
Research Highlights and Optics and
Photonics News.
Chemistry
at the
Space-Time Limit
(CaSTL)
Chemistry at
the Space-Time Limit (CaSTL) is a Center
for Chemical Innovation (CCI) at
UCI,
which is funded through the National
Science Foundation, and
administered through ISIS. The center is
dedicated to the development of real-time experiments with atomistic
resolution to probe the inner workings of molecules that characterize
elementary events in chemistry and photophysics. These processes
include: the oxidation and reduction of a single molecule, making and
breaking of chemical bonds, charge transfer/transport, heterogeneous
catalysis and videography of chemistry on the nanoscale. The capability
to follow individual chemical events with atomistic resolution would
usher a new perspective and mode of inquiry into molecular science and
engineering. Indeed, for the purposes of instructing chemistry, it is
hard to imagine a more incisive tool than the time-lapsed images of
molecules undergoing chemical change, or responding to various external
perturbations.
