Study of organized and biological systems using an ultrafast laser

In an aqueous solution, weak (‘soft’) molecular interactions lead to the formation of many supramolecular assemblies. In such an assembly, the reactive chemical species remain confined in a nanocavity. Confinement and the local interactions render chemistry in these assemblies markedly different from that in an ordinary solution. Very recently, ultrafast time resolved spectroscopy has been applied to unravel the dynamics in these systems. The new experiments and the computer simulations reveal many surprising and highly interesting features. First, in such a confined system there is almost invariably a new ultraslow component which is slower by 100–1000 times compared to bulk water. Second, in spite of the restrictions imposed inside a nanocavity, dynamics of several processes displays an ultrafast component (in <10 ps time scale). In this review, we discuss five ultrafast processes in many organized and biological systems. The ultrafast processes include solvation dynamics, proton transfer, energy transfer (FRET), electron transfer and anisotropy decay.