We present our first studies of the femtosecond dynamics of reactions in confined nanocavities in water solutions. Intramolecular proton transfer and isomerization dynamics of a hydrogen-bonded molecule (HPMO) in liquid solutions and encapsulated in the cavity formed by β-cyclodextrin (diameter ∼8 Å) is studied using the technique of fluorescence up-conversion. Our results suggest that the proton transfer in aprotic solvents occurs in much less than 300 fs while upon encapsulation this initial step is slowed to the subpicosecond time scale. Furthermore, in these aprotic solvents, HPMO undergoes a picosecond twisting motion around the interaromatic single bond, which is noticeably inhibited when the molecule is inside the nanocavity. Such studies of condensed-phase femtochemistry in nanocavities offer several promising extensions.

In this contribution, we report on studies of rotational and diffusional dynamics of 7-hydroxyquinoline (7HQ) within a reverse micelle (RM) containing different amounts of water. Analyzed in terms of the wobbling-in-a-cone model, the data reveal structural and dynamical properties of the nanopool. We clearly observed three regions in the behavior of confined water molecules within the RM hosting a double proton-transfer reaction between the probe and water. This observation remarkably reproduces the change of calculated water density within this life-mimicking medium. The number of water molecules per AOT head in the transition regions changes from 2 to 5, the latter being very near to the full solvation number (6) of the RM heads. Moreover, the H-bonds breaking and making within the RM to give new structures of the probe strongly affect the environment fluidization in different extents, reflected in different relaxation times of these structures; however, they are of similar sizes. We discuss the role of RM confinement and the proton-transfer dynamics on the behavior of water and their relationships to the packing of water molecules in the studied range of concentrations.

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Encapsulation processes and picosecond time‐resolved transient absorption spectra of 2‐(2î‐hydroxyphenyl) imidazo[1,2‐a]pyridine have been used to elucidate the fluorescence band shift and the transient absorption dynamics (in the picosecond time scale) of the proton transfer phototautomer in cyclodextrins and in cyclohexane, respectively. Restriction of the internal motion of the phototautomer by cyclodextrins leads to a 70 nm blue shift of the proton transfer fluorescence band. A shaping time (14 ps) of the transient absorption spectrum has been observed and assigned to a combination of this internal rotational motion and a vibrational‐cooling process of the phototautomers in the excited state. Both studies suggest the involvement of rotational processes in the intramolecular proton‐transfer cycle.