title: Second-chance forward isomerization dynamics of the red/green cyanobacteriochrome NpR6012g4 from Nostoc punctiforme.
abstract: The primary ultrafast Z-to-E isomerization photodynamics of the phytochrome-related cyanobacteriochrome NpR6012g4 from Nostoc punctiforme was studied by transient absorption pump-dump-probe spectroscopy. A 2 ps dump pulse resonant with the stimulated emission band depleted 21% of the excited-state population, while the initial photoproduct Lumi-R was depleted by only 11%. We observed a red-shifted ground-state intermediate (GSI) that we assign to a metastable state that failed to isomerize fully. Multicomponent global analysis implicates the generation of additional Lumi-R from the GSI via crossing over the ground-state thermal barrier for full isomerization, explaining the discrepancy between excited-state and Lumi-R depletion by the dump pulse. This second-chance ground-state dynamics provides a plausible explanation for the unusually high quantum yield of 40% for the primary isomerization step in the forward reaction of NpR6012g4.
authors: Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
authors: Peter W
authors: PW
authors: Kim
authors: Lucy H
authors: LH
authors: Freer
authors: Nathan C
authors: NC
authors: Rockwell
authors: Shelley S
authors: SS
authors: Martin
authors: J Clark
authors: JC
authors: Lagarias
authors: Delmar S
authors: DS
authors: Larsen
mesh_terms: D007536:Isomerism; D007700:Kinetics; D046937:Nostoc; D055668:Photochemical Processes; D010860:Pigments, Biological / Q000737:chemistry*
chemical_list: D010860:Pigments, Biological