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Single molecule chiroptical spectroscopy: Fluorescence excitation circular dichroism and circular polarized luminescence of bridged triarylamine helicenes
In this thesis, I describe the first exploratory experimental efforts probing light-matter interactions of chiral systems at the single molecule level. The dissymmetric single molecule chiroptical response in both excitation and emission polarization has been studied for different diastereomeric forms of bridged triarylamine helicenes. Fluorescence excitation circular dichroism (FECD), measuring the dissymmetric absorption with respect to excitation polarization, reports on the response to excitation polarization. The magnitude and distribution of chiroptical single molecule responses suggest both surface and orientation effects play a significant role. Computational modeling done to calculate the dissymmetry for specific orientations supports orientational dependence. Using a defocused imaging technique, which can be used to obtain orientation information for linear dipoles, emission patterns were obtained that lacked bilateral symmetry. These emission patterns were simulated using a semi-classical model that closely approximated the lack of bilateral symmetry. Refinement of the model and additional experiments using oriented molecules will allow for direct correlation of orientation and dissymmetry which is important for understanding the heterogeneities in the single molecule responses. In addition, dissymmetry in emission polarization has been studied using a novel imaging technique resolving polarization components on a frame-by-frame basis. The research into the intersection of single molecule spectroscopy and chiroptics has given new insight into the role of solvation and local environment in chiroptical interactions and may be useful for understand chiral-based photonics and advancing new technologies.
Paradise, Ruthanne Hassey, "Single molecule chiroptical spectroscopy: Fluorescence excitation circular dichroism and circular polarized luminescence of bridged triarylamine helicenes" (2009). Doctoral Dissertations Available from Proquest. AAI3380002.