Picosecond dynamics of Eosin B at the air/water interface by time-resolved second harmonic generation: orientational randomization and rotational relaxation

Time-resolved surface second harmonic generation has been used to study the picosecond dynamics of the dianion Eosin B dye molecule at the air/water interface. It is found that the induced second harmonic signal depolarization obtained with the perturbation of the distribution of Eosin B molecules at the interface can be attributed to an out-of-plane rotational diffusion motion of the molecules. The data also suggest that the high Fox er densities of the laser pulses randomize the orientation distribution of the molecules at the interface. A rotational diffusion time of 90 +/- 20 ps is measured, a value significantly faster than the one obtained in bulk aqueous phases. (C) 1998 Elsevier Science B.V. All rights reserved.