Effect of Solute Orientation on Solvation Dynamics at the Air/Water Interface

The ultrafast solvation dynamics of courmarin 314 (C314) molecules at the air/water interface has been shown to depend on their orientation with respect to the plane of the interface. A pump/second harmonic probe method using femtosecond laser pulses were used to measure the interface solvation dynamics. The pump light was S polarized, i.e., in the interface plane, or P polarized, i.e., in the plane perpendicular to the plane of the interface. The S pumped C314 molecules yielded a solvation time of 820 ( 60 fs, whereas P pumped yielded a solvation time of 1215 ( 90 fs. The interface inhomogeneous broadening on the solvation time scale is due to the differing orientations of C314 at the air/water interface.