title: Ultrafast intramolecular relaxation dynamics of Mg- and Zn-bacteriochlorophyll a.
abstract: Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption∕fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Qx state, but has almost no effect on the Qy state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Qx or Qy state. By comparing the kinetic traces of transient absorption, ground-state beaching, and stimulated emission after excitation to the Qx or Qy state, we showed that the Qx state was substantially incorporated in the ultrafast excited-state dynamics of bacteriochlorophyll a. Based on these observations, the lifetime of the Qx state was determined to be 50 and 70 fs for Mg- and Zn-bacteriochlorophyll a, respectively, indicating that the lifetime was influenced by the central metal atom due to the change of the energy gap between the Qx and Qy states.
authors.affiliation: The Osaka City University Advanced Research Institute for Natural Science and Technology, 3-3-138 Sugimoto, Osaka 558-8585, Japan. kosumi@ocarina.osaka-cu.ac.jp
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kosumi
authors.forename: Katsunori
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Sakai
authors.forename: Yuya
authors.initials: Y
authors.lastname: Nagaoka
authors.forename: Satoshi
authors.initials: S
authors.lastname: Maruta
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Sugisaki
authors.forename: Takehisa
authors.initials: T
authors.lastname: Dewa
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nango
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
mesh_terms: D000042:Absorption; D025541:Bacteriochlorophyll A / Q000737:chemistry*; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D055620:Optical Phenomena; D055668:Photochemical Processes; D013050:Spectrometry, Fluorescence; D015032:Zinc / Q000737:chemistry*
chemical_list: D025541:Bacteriochlorophyll A; D008274:Magnesium; D015032:Zinc