Fluorescence anisotropy controlled by light quenching

We demonstrated that fluorescence anisotropy can be effectively decreased or increased in the presence of light quenching, depending on relative polarizations of excitation and quenching pulses. For parallel light quenching anisotropy decreases to 0.103 and z-axis symmetry is being preserved. In the presence of perpendicular light quenching, the steady-state anisotropy of pyridine 2 glycerol solution increases from 0.368 for unquenched sample to 0.484, for quenched one. We show that angular distribution of transition moments loses the z-axis symmetry in the presence of perpendicular light quenching. In these cases we used more general definitions of anisotropy. Induced by light quenching anisotropy can be applied in both, steady-state and time-resolved measurements. In particular, the systems with low or none anisotropy can be investigated with proposed technique.