title: Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations.
abstract: The ultrafast mechanisms underlying the initial photoisomerization (Pr→ Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces. Excited-state equilibrium was not observed, as shown via the absence of a dump-induced excited-state "Le Châtelier redistribution" of excited-state populations. The importance of incorporating the inhomogeneous dynamics of Cph1 in interpreting measured transient data is discussed.
authors.affiliation: Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Kim
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Rockwell
authors.forename: Lucy H
authors.initials: LH
authors.lastname: Freer
authors.forename: Che-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Shelley S
authors.initials: SS
authors.lastname: Martin
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
keywords: excited-state dynamic; photoreceptors; phytochromes; pump-dump-probe; transient absorption