Coherent Oscillations in the PC577 Cryptophyte Antenna Occur in the Excited Electronic State

Transient absorption spectroscopy is a useful measurement for investigating ultrafast dynamics in molecules. We have developed a transient absorption spectrometer that utilizes balanced and fast detection methods to suppress noise and maintain high temporal and spectral resolution. We use the spectrometer to investigate the ultrafast dynamics in a photosynthetic pigment-protein complex, the phycobiliprotein PC577 isolated from the cryptophyte alga Hemiselmis pacifica CCMP706. We analyze coherent oscillations in the transient absorption data and attribute them to vibrational coherences. Analysis of the dynamic Stokes shift and motion of the wave packet on the potential-energy surface indicate that the coherences arise from vibrational wave packets in the excited electronic state of the protein.