Hindered rotational diffusion and rotational jumps of single molecules

We extended the sensitivity of fluorescence polarization anisotropy measurements to the single molecule level by studying the polarization response 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 presence of specific molecular interactions. We also observed rotational jumps between surface-bound and unbound states and show that they are, similar to jumps to long dark states, photoactivated.