Holographic Relaxation Spectroscopy of a Benzospiropyran in Mixtures of Water and Dioxane

Article abstract of DOI:10.1021/j150642a011

The photochromic spiropyran derivative 1-(β-carboxyethyl)-3,3-dimethyl-6'-nitrospiro permits the establishment of laser-induced gratings in aqueous solutions and thus is a potential label for biomolecules.Holographic relaxation experiments have been performed on this spiropyran in water/dioxane mixtures using UV radiation (330 nm) for χ(H2O) = 0-0.8 and visible light (514 nm) for 0.8-1.0.Also, the lifetimes of the photoexcited states were measured.The diffusion coefficients for the spiropyran were obtained by analysis of the time dependence of the laser-induced gratings.In phosphate buffer (pH 7.5, 20 deg C) the diffusion coefficient is (4.19 +/- 0.02) X 10^-6 cm²/s.Diffusion measurements were possible down to spiropyran concentrations of 0.01 mM, the lower limit being determined by the low repetition rates which were required in signal averaging by the long lifetimes of the photoexcited states.