Single Molecule Dynamics Studied by Polarization Modulation

We observed and made unambiguous distinctions between abrupt photophysical events of single molecules: a rotational jump of a single dipole, a transition to a dark state (reversible and irreversible photobleaching), and a spectral jump. The study was performed in the far field by modulating the excitation polarization and monitoring the fluorescence in time. This technique also allowed us to measure the in-plane dipole orientation of stationary single molecular dipoles with subdegree accuracy and to resolve desorption and readsorption of fluorophores from and onto a glass surface. In one case, clear evidence was obtained for rapid rotation of the dipole after a desorption process.