Robust Circular Polarized Emission from Nanoscopic Single-Molecule Sources: Application to Solid State Devices

Controlling the polarization state of fluorescence emission in solid state devices is an important goal in optical display technologies. High-purity (right or left) circular polarized emission is particularly desirable because an arbitrary linearly polarized state can be generated with much higher efficiency (lower loss) as compared with a non-polarized fluorescence input. Here we discuss observation of resonant chiroptical effects (fluorescence detected circular dichroism (FDCD), and circular polarized luminescence (CPL)) from single (bridged-triarylamine) helicene molecules in a solid-film format. In the FDCD experiment using 457-nm excitation – an excitation wavelength where the bulk circular dichroism is negligible – single-molecule fluorescence from enantiomerically pure helicene samples show surprising distribution of dissymmetry (g) parameters centered near zero but with a significant contribution from molecules showing an almost perfectly pure response to either right or left circularly polarized light. Experiments combining a well-defined circularly polarized excitation (either right or left) with decomposition of the fluorescence into left- and right-circular polarization component show only a weak correlation between the dissymmetry (sign and magnitude) of the CPL with the polarization state of the input. Current efforts are directed at wavelength resolved CPL, FDCD at wavelengths that are more closely match to bulk circular dichroism features, and orientational dependence of FDCD and CPL. These results provide new insight into chiroptical properties of chiral fluorophores at the single molecule level and suggests new optical device possibilities with chiral fluorophores.