Xm. Shang et al., Ultrafast solvation dynamics at silica/liquid interfaces probed by time-resolved second harmonic generation, J PHYS CH B, 105(47), 2001, pp. 11578-11585
The static absorption and ultrafast solvation dynamics of a tricarbocyanine
dye IR144 at the silica/acetonitrile and the silica/butanol interfaces wer
e investigated by using steady-state second harmonic generation (SHG) spect
roscopy and pump-probe time-resolved SHG (TRSHG) experiments. At both inter
faces, the peak wavelength for the S-0 --> S-1 transition of adsorbed IR144
is significantly red-shifted with respect to the maximum absorption wavele
ngth in the corresponding bulk solvent. Because IR144 is negatively solvato
chromic, this shift is indicative of a smaller polarity at the interface. A
theoretical model of TRSHG is discussed which allows extraction of the sol
vation dynamics correlation function from the time dependence of the TRSHG
signal measured in the pump-probe experiment at a chosen probe wavelength.
The time constant for the diffusive component of solvation at the silica/ac
etonitrile interface was found to be 1.05 +/- 0.14 ps. It is somewhat short
er, although of the same order of magnitude, than the time constant for the
diffusive solvation in bulk acetonitrile, 2.23 ps. At the silica/butanol i
nterface, a time constant of 1.20 +/- 0.15 ps was extracted, whereas in the
bulk butanol, the corresponding diffusive solvation is biexponential with
times of 3.5 and 33 ps.