A single-molecule study of polycrystalline microstructure by fluorescence polarization spectroscopy

The structure of n-hexadecane polycrystalline matrices is examined with single molecule fluorescence spectroscopy at a temperature of 1.7 K. Some single chromophores exhibit spectral dynamics during experiments: their resonances either jump between two frequencies or split into two components. By means of polarization measurements, we investigate the molecular spectra in order to distinguish between the case of two spatially unresolved molecules and the case of chromophore — two level system (TLS) pair. For closely spaced molecules two-dimensional Gaussian function fitting is applied to extract the spatial coordinates of the molecules. For TLS-chromophore systems, parameters of the TLSs are estimated.