Probing the ultrafast solution dynamics of a cyanine dye in an organic solvent interfaced with water.

Dependence of ultrafast dynamics on the excited state evolution and ground state recovery of a cyanine dye (IR125) in dichloromethane (DCM) solvent interfaced with neat water is presented. We use degenerate pump-probe transient absorption spectroscopy to show that the excited-state dynamics of the dye molecule is strongly dependent on the position of the measurements from bulk DCM solution to the solution near the water layer. The decay component of the transient corresponding to the excited state lifetime increases from bulk DCM solution to its interface with water. Such results show that the effect of the presence of water layer over the dye solution in DCM extends several micrometers, indicating the surfactant nature of the IR125 molecules, and provides us a measure of the penetration of water into the DCM layer. The initial ultrafast decay component (coherent spike) directly correlates to the pulse-width of our near-transform limited pulses used in these experiments. This approach of measuring the excited state decay of a dye across an immiscible liquid interface can provide important characteristics of microtransport across such interfaces.