Sensing near the liquid:liquid interface remotely via ultrafast pump probe study

Ultrafast pump-probe technique has been invoked to understand the liquid:liquid interface by using a cyanine dye dissolved in dimethyl sulfoxide (DMSO), interfaced with neat diethyl-ether (Et2O). We show that the dynamics of the dye gets slow down on moving from the bulk dye solution in DMSO towards the interface with neat-diethyl ether. Hence we get an alternate picture of interface by looking at the time constants. Four time constants were used for fitting the experimental data which are assigned to be coherent artifact, vibrational cooling, intermediate state time and finally ground state recovery time. The drastic change in signal was observed at a distance of 0.1 mm from the interface. The decreasing time constants from bulk to near interfaced solution strongly suggests involvement of heterogeneity in the system because of the penetration of diethyl ether through the interface into the DMSO layer where the dye is dissolved, which strongly affects the dynamics at near the interface of the DMSO with neat-diethyl ether layer (at 0.1 mm distance from the interface).