Submitted on August 23, 2006
Accepted on October 16, 2006
Probing the Chiroptical Response of a Single Molecule
Ruthanne Hassey 1,
Ellen J. Swain 1,
Nathan I. Hammer 1,
Dhandapani Venkataraman 1,
Michael D. Barnes 1*
1 Department of Chemistry, University of Massachusetts-Amherst, Amherst, MA 01003, USA.
* To whom correspondence should be addressed.
Michael D. Barnes , E-mail: mdbarnes{at}chem.umass.edu
Chirally sensitive measurement techniques have generally been restricted to bulk samples. Here, we report the observation of fluorescence-detected circular dichroism (FDCD) from single (bridged-triarylamine) helicene molecules 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 measure ensemble measurements of a randomly oriented bulk sample.
