Probing the Chiroptical Response of a Single Molecule
Ruthanne Hassey,
Ellen J. Swain,
Nathan I. Hammer,
Dhandapani Venkataraman,
Michael D. Barnes*
Chirally sensitive measurement techniques have generally been
restricted to bulk samples. Here, we report the observation
of fluorescence-detected circular dichroism (FDCD) from single
(bridgedtriarylamine) helicene molecules by using an excitation
wavelength (457 nanometers) in the vicinity of an electronic
transition that shows circular dichroism in bulk samples. The
distributions of dissymmetry (
g) parameters by analysis of signals
from pure
M- and
P-type diastereomers are almost perfect mirror
images of one another, each spanning a range of both positive
and negative values. In addition, we observe a well-defined
structure in the histogram of dissymmetry parameters suggestive
of specific molecular orientations at the polymer interface.
These single-molecule results highlight strong intrinsic circular
dichroism responses that can be obscured by cancellation effects
in ensemble measurements of a randomly oriented bulk sample.
* To whom correspondence should be addressed. E-mail: mdbarnes{at}chem.umass.edu
