HINDERED ROTATIONAL DIFFUSION AND ROTATIONAL JUMPS OF SINGLE MOLECULES

We extended the sensitivity of fluorescence polarization anisotropy me asurements to the single molecule level by studying the polarization r esponse of single fluorophores rapidly rotating in liquid. Comparison with a simple model calculation allows us to obtain information on the hindered motion as well as on the rotational diffusion in the presenc e of specific molecular interactions. We also observed rotational jump s between surface-bound and unbound states and show that they are, sim ilar to jumps to long dark states, photoactivated.