Single-molecule chiroptical spectroscopy: Fluorescence excitation of individual helicene molecules in polymer-supported thin-films.

We present results of fluorescence excitation circular dichroism studies of the chiroptical response of single (bridged triarylamine) helicene molecules immobilized at a polymer interface. We extract directly dissymmetry parameters, and corresponding probability distributions, associated with the single-molecule fluorescence excitation associated with modulation of a circular polarized excitation field for three different excitation wavelengths (405, 440, 457 nm) showing circular dichroism in bulk films. The observed single molecule chiroptical response is anomalously large in comparison with the results of time-dependent density functional calculations, and the observed defocused emission patterns seem to indicate a higher multipole nature to the transition probed. Our results provide new insights into chiroptical properties of chiral fluorophores that are hidden under the extensive averaging associated with conventional chiroptical probes. Chirality, 2008. © 2008 Wiley-Liss, Inc.