Carotenoids are essential components of the photosynthetic apparatus of bacteria, algae and higher plants and serve critical roles in light-harvesting and protection against photosensitized oxidations. Although the roles of carotenoids in light-harvesting and photoprotection are clearly established, the details of the excited singlet and triplet energy transfer reactions required for these are poorly understood. Drs. Albrecht and Owens propose to investigate the in vivo photophysics of photosynthetic carotenoids in several bacterial and algal pigment-protein complexes. Primary emphasis will be placed on providing a mechanistic description of singlet energy transfer from carotenoids to chlorophylls. Ultrafast absorption spectroscopy will be used to study the dynamics of singlet and triplet transfer reactions and to identify heterogeneous carotenoid function. Resonance Raman techniques, including Raman excitation profiles, will be used to probe heterogeneous carotenoid functions in vivo.