title: Photoswitching mechanism of cyanine dyes.
abstract: Cyanine dyes have been shown to undergo reversible photoswitching, where the fluorophore can be switched between a fluorescent state and a dark state upon illumination at different wavelengths. The photochemical mechanism by which switching occurs has yet to be elucidated. In this study, we have determined the mechanism of photoswitching by characterizing the kinetics of dark state formation and the spectral and structural properties of the dark state. The rate of switching to the dark state depends on the concentration of the primary thiol in the solution and the solution pH in a manner quantitatively consistent with the formation of an encounter complex between the cyanine dye and ionized thiol prior to their conjugation. Mass spectrometry suggests that the photoconversion product is a thiol-cyanine adduct in which covalent attachment of the thiol to the polymethine bridge disrupts the original conjugated pi-electron system of the dye.
authors: Graduate Program in Biophysics, School of Engineering and Applied Sciences, Howard Hughes Medical Institute, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors: Graham T
authors: GT
authors: Dempsey
authors: Mark
authors: M
authors: Bates
authors: Walter E
authors: WE
authors: Kowtoniuk
authors: David R
authors: DR
authors: Liu
authors: Roger Y
authors: RY
authors: Tsien
authors: Xiaowei
authors: X
authors: Zhuang
mesh_terms: D001665:Binding Sites; D002232:Carbocyanines / Q000737:chemistry* / Q000528:radiation effects; D004583:Electrons; D005456:Fluorescent Dyes / Q000737:chemistry / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D013058:Mass Spectrometry; D055668:Photochemical Processes; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes; D013438:Sulfhydryl Compounds