Study will continue on the effects of partial solvation on the photophysics of important intrinsic and extrinsic fluorescence probe molecules, including principally tryptophan and arylaminonaphthalene sulfonate (ANS) derivatives. Supersonic expansion techniques are used to produce cold, isolated molecule samples of these molecules as well as partially solvated complexes containing various numbers of solvent molecules. The basic rationale of the experiments is to study the photophysics of successively larger solvent complexes in order to learn what specific solvent site interactions or collective solvent structures are necessary to bring about the key photophysical changes observed in bulk solution. In tryptophan further attention must be given to molecular conformation and solvent effects on amino/carboxyl groups while in ANS specific size solvent clusters may be important. As has already been the case, measurement of specific fluorescence lifetimes will yield useful photophysical information. It will be important to measure absorbance spectra as well, by employing a suitable pulsed slit nozzle, and to compare these spectra with laser induced fluorescence spectra for identification of solvent complex bands with quenched emission. The most important now experimental extension is construction of a supersonic jet/molecular beam system, which makes possible the application of photoionization/mass detection methods. By this approach it will be possible first to develop the means of preparing additional biological molecule sample expansions and second to identify and characterize larger solvent complexes.
