Spectral Hole Burning in Hyperquenched Glassy Films and Biomolecular Gels: Science and Applications

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Abstract 9630781 Small The proposed studies are inspired mainly by the development of a versatile thermospray based-hyperquenching apparatus for reproducible vitrification of liquids and its successful application, with nonphotochemical hole burning and other spectroscopies, to Al-phthalocyanine tetrasulphonate (APT) in hyperquenched glassy films of water (HGW). The ability to study films at a given temperature with different histories of preparation (deposition temperature, annealing procedure) opens the way for further detailed studies of thermodynamic continuity / kinetic accessibility between different states of a glass, disorder-induced and other mechanisms for optical dephasing, electron-phonon coupling and mechanistic aspects of nonphotochemical hole burning. To this end, sulphonated Al-phthalocyanines and resorufin in hyperquenched films of ethanol and methanol and the cyanine dye HITCI in ethylene glycol glasses will be used. The data will be used with theory to test the suggestion that the marriage of hole burning and photon echo techniques is a promising approach to understanding optical coherence loss in liquids. Construction of a novel hyperquenching apparatus compatible with pressure dependent ( 5 MPa) hole burning is proposed. It would be used to determine, for example, the relative compressibilities (5 K) of unannealed and annealed HGW films (APT as the chromophore). This is important because the density of intrinsic two level systems (TLSint), responsible for dephasing at low temperatures, is a factor of 5x higher in unannealed than in annealed films. Thus, it will be possible to test the hypothesis that TLSint are intimately associated with the excess free volume of glasses. Work completed under the current NSF grant has also shown that the hole burning properties of APT in HGW at low and high temperatures (- 77 K) are significantly superior to those of other molecular amorphous systems. The Principal Investigator proposes to study APT in high water content protein gels (e.g. "Jello") whose ease of preparation and high optical quality make them attractive for time domain optical memory/processing applications. The goal is to achieve a frequency storage density of 600 at 77 K, a factor of four higher than that for APT in buffered HGW. Additional studies of APT in HGW are proposed, the objectives being to understand the hydrogen-bond switching associated with the exceptionally efficient hole burning at both low and high temperatures and to test predictions of a notable resilience of APT/HGW (deuterated)'s optical memory against destructive readout due to hole burning and light-induced hole filling. Finally, infra-red hole burning experiments with annealed and unannealed HGW films will be performed in order to determine the contributions from inhomogeneous broadening and vibrational excitonic coupling to the underlying structure of the OH stretching band. The understanding of this structure is a fascinating problem of longstanding interest, one whose solution bears on the structure and intermolecular forces of liquid water. %%% Disorder and its effects on configurational relaxation, energy and charge transport, the dynamics of spectroscopic transitions and other properties in complex solids, such as glasses, polymers and proteins, are subjects of intense interest in the physics, biophysics and chemistry communities. This is understandable since to understand physical and biological phenomena which are strongly influenced by structural disorder is both important and very challenging. Furthermore, such research has and will continue to reveal new physics and chemistry. This project is concerned with configurational relaxation and dynamics in molecular glasses and the development of a new class of efficient, high temperature persistent spectral hole burning materials for optical memory/processing and other applications. These and other projects are designed to provide insights on the relationship between optical coherence loss in liquid and glasses, and destructive readout of optical memory at high temperature.