Solvation Dynamics in the Cybotactic Region of Gas-Expanded Liquids: A Decade Later

Although gas expanded liquids (GXLs) were introduced at the beginning of the twentieth century, it was nearly a century later that they received renewed attention as a possible reactant medium offering not only a mechanism for subsequent controlled separation of products but also the tunability of the reaction itself. Early work showed that one could also control the cybotactic structurethat is, the relative average orientation of the solvent in a local environment around the reacting solutesin GXLs with CO2 as a cosolvent and, thereby, preferentially favor desired product pathways. Such properties have been demonstrated in more general solvent mixtures and in confined environments since then. Here, we further demonstrate that the dynamics and relaxation of solutes in cybotactic regions of GXLs can exhibit a range of properties that include those that would be expected from a glassy environment. This extends the range of controllable (or tunable) properties available to GXLs for reaction control.