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Hydrogen bond dynamics and directional interactions in nanostructured condensed phases

The hydrogen bond is a key intermolecular interaction in chemistry, biology, geology, and materials science, with its energy tuned for a perfect balance between structural rigidity and rapid dynamic rearrangements around ambient conditions. Ultrafast infrared spectroscopic methods are described that can interrogate the dynamics and intermolecular interactions of the hydroxyl stretch mode, a sensitive reporter of hydrogen bonding environments, of water and alcohols in complex environments far removed from the bulk liquids. New methodology for conducting noncollinear two-dimensional infrared experiments in a rotating frame to accelerate data acquisition is described. Water confined in polyacrylamide hydrogels is found to slow as one population as the size of the water pool decreases. The lack of any water with bulk-like dynamics is surprising and attributed to the continuity of hydrogen bond network between the water pool and confining polymer. Room temperature ionic liquids, a family of tunable, non-volatile, and non-flammable solvents composed entirely of cations and anions, are structured at the nanoscale by charge ordering as well as the possibility of other motifs, such as segregation of polar and apolar groups. Water and alcohols isolated in ionic liquids, as representative solutes or cosolvents, experience hydrogen bond interactions with the solvating ions. A rich hierarchy of dynamical processes in the randomization of their orientations and intermolecular interactions is observed, ranging from less than 100 femtoseconds to sometimes over 100 picoseconds. The hydrogen bond interactions are highly directional, leading to distinct forms in the polarization dependence of ultrafast IR measurements of structural dynamics (spectral diffusion), particularly in ionic liquids. Theory is developed to characterize these directional interactions and dynamics quantitatively and separate the reorientation-induced spectral diffusion (RISD) processes, arising through rotation of the tracer, from spectral diffusion that is due to the randomization of the surroundings. Related theories of RISD are presented that are appropriate for carbon dioxide, a highly symmetrical vibrational probe, as well as fluorescent probe molecules undergoing time-dependent Stokes shift with highly directional interactions that determine the absorption and emission frequencies. Measurements of the dynamics of water confined in the nanoscale pores of amorphous silica are presented. Several techniques to overcome the inherent scatter from silica particles (sand) were combined, including phase cycling, polarization control, and spatial filtering, and their individual merits are discussed. The slowdown in dynamics of water in the silica pore are compared to previous measurements of the dynamics of selenocyanate, an anion that H-bonds to the surrounding water in the pore.