The photophysics of arylaminonaphthalene sulfonate (ANS) and tryptophan molecules, in bare molecule and partially solvated forms, will be studied. Supersonic expansion techniques will be used to prepare the samples and laser spectroscopic techniques employed to study them. The principal methods of spectroscopy to be used are pulsed, tunable laser fluorescence excitiaton scans; dispersed fluoresecence of specific features excited; and fluorescence lifetime measurements of specific excited state features, the latter carried out using a synchronously pumped dye laser and time-correlated photon counting. In biological systems ANS derivatives can be used as extrinsic fluorescence probes and tryptophan as a intrinsic one. The photophysics of these molecules is not, however, fully understood. In both cases there have been experimental advances in recent years, primarily involving lifetime measurements in solution environments, and photophysical hypotheses have been refined for each class of molecules. In ANS-type molecules a charge transfer state, facilitated by solvents such as water, appears to be of primary importance; in tryptophan, important effects might arise from molecular conformation, energetically close excited states, and solvent effects on the amino and carboxyl groups. Supersonic expansions can address questions on a molecular scale of interaction; condensed phase experiments cannot offer this possibility. First, the photophysics of bare single molecules will be studied. In particular, control of rotameric conformation of bare tryptophan derivatives should be possible, a potentially powerful tool in studying tryptophan photophysics. Next, ANS and tryptophan derivatives will be complexed with selected solvent molecules, such as water. Spectroscopic bands from different sized complexes will be identified and selectively laser excited for studies of emission properties. In the process of carrying out this work, refinements will be attempted for resolving and characterizing spectroscopic bands from partially solvated complexes with larger numbers of addends. These advances will enable additional solvation studies to proceed on ANS and tryptophan, as well as on other biophysically interesting molecules. The long-term objective is to develop and confirm a complete picture of the photophysics of these systems. It is hoped that, with such an understanding, the influence of environment and bonding on the fluorescent probes' responses can be given a more detailed and correct interpretation.
