In this project in the Physical Chemistry Program of the Chemistry Division, Prof. Bryan E. Kohler of the University of California at Riverside will engage in a study of electric fields in organic solids using the technique of hole burning spectroscopy. Previous successes for measuring and interpreting the effects of external electric fields on transition energies are the bases for the proposed research to map out the internal electric fields at a molecular site in a molecular system. Specifically, the effets of electric fields on linear polyene excitation energy, and the effect of external pressure on the effect of electric field on linear polyene excitation energy, will be determined for a number of different guest-host systems where the geometry can be calculated by standard molecular dynamics techniques. More complex systems will become available for investigation with the refinement of the interpretative model through a combination of measurement and theoretical simulation. Most theoretical models used for the determination of internal electric fields assume the point dipole approximation, which is found to be only qualitatively successful. The proposed investigations are designed to experimentally measure the fields using polyene doped alkane crystals. Much of our understanding of electronic structure of organic solid solutions is derived from optical spectroscopy. The amount of unambiguous information that can be extracted from a given optical spectrum is increased if the ensemble under investigation is made more homogeneous. This may be done by one of several methods of high resolution site selective spectroscopy, e.g., hole burning spectroscopy. With this technique resolution enhancements by a factor of up to one hundred thousand have been achieved. This in turn has allowed the investigations of relaxation processes such as, for example, optical dephasing, and spectral diffusion; energy transfer in organic solids; the characterization of photophysical processes in biological systems; applications of organic polymers to optical data storage and holography; and others. The research to be conducted in this project will contribute to a better understanding of optical processes in diverse solid organic systems and may lead to improved materials used in optical and electronic devices.
