The goal of the proposed research is to develop photochemical probes of globular protein structural fluctuation dynamics in the subnanosecond time regime. Specific aims include the delineation of the dynamics of the light-induced configurational (cis trans) isomerization of protein-bound stilbene and stilbene derivatives and of dipyrromethenone derivatives. Because rotation (leading to isomerization) in the excited singlet states of these compounds is fast (10-100 ps) and intersystem crossing is relatively slow, rotational dynamics can be related to fluorescence intensities and fluorescence lifetimes in simple ways. Rotational barriers provided by the protein environment can then be detected with facility. Effects of substituent size on isomerization dynamics, reflective of the "space" requirements for rotation, should yield additional information about the flexibility of the protein binding site. Effects of solvent viscosity on isomerization dynamics should relate to solvent protein interactions. Interpretation of dynamical data will require knowledge about the sites of binding of the probes to the protein and choice of proteins is critical. Proteins with "known" structures will be utilized. Apomyoglobin is planned for the first studies. A variety of approaches including high resolution nmr should reveal the binding sites. In more mature studies, derivatives of stilbene and dipyrromethenone that bind to active sites of enzymes (e.g., lysozyme) will be prepared to probe fast structural fluctuations in those sites and possible relations with enzymic function.