Time resolved 3D orientation spectroscopy: experimental realization and simulation

Confocal microscopy is a powerful tool for single molecule investigation of fluorescent macromolecules. Besides the commonly studied features in single molecule detection, the 3D orientation determination of the emission dipole enables the analysis of different conformational states. These conformational states can be represented as state depending dipole orientations intrinsic to the fluorescent molecule and/or in relation to the molecular frame. They might be subject to intramolecular dynamics, which may lead to spectral diffusion, fluorescence intensity and/or lifetime fluctuations and changes in the orientation of the emission dipole. We demonstrate a detection scheme that allows for simultaneous determination of the full 3D emission dipole orientation, the fluorescence intensity, the fluorescence lifetime and the emission spectra of single fluorescent molecules. We evaluate the feasibility of our approach using pyridyl functionalized perylene bisimide (PBI) as a model system exhibiting conformational changes. Moreover, MC simulations demonstrate the full potential of our detection scheme to distinguish between intensity fluctuations due to conformational changes and changes in the out-of-plane orientation or changes in both of them.