Dynamic depolarization spectroscopy

The rapid decay of absorption of excited states on the ps time scale has been measured for pyrazolotriazole azomethine dyes. The molecular orientation dynamics of polar dye probes in t-butanol-water mixtures have been determined by ps fluorescence depolarization spectroscopy. Dyes studied in this investigation were the monocations nile blue and thionine, resorufin a monoanion, and nile red a polar but neutral molecule. A very detailed ps study of rotational diffusion of excited states of merocyanine-540 in polar solvents, has also been reported . 

R. E. Dale, Membrane structure and dynamics by fluorescence probe depolarization kinetics, in Time-Resolved Fluorescence Spectroscopy in Biochemistry and Biology (R. B. Cundall and R. E. Dale, eds.), pp. 555-612, Plenum, New York (1984). 

G. Signorelli, V. Mazzacurati, M. Nardone, and C. Pona. Depolarized Raman Scattering from Disordered Systems. In J. van Kranendonk (ed.), Intermolecular Spectroscopy and Dynamical Properties of Dense Systems—Proceedings of the International School of Physics "Enrico Fermi," Course LXXV, North-Holland, Amsterdam, 1980, pp. 294-306. 

Time dependent fluorescence depolarization is influenced by the exciton annihilation which occurs in confined molecular domains . Photoemission results from singlet exciton fusion as shown by the excitation intensity dependence which occurs in anthracene crystals. Reabsorption of excitonic luminescence is an effect which has been shown to occur in pyrene crystals. The dynamics of exciton trapping in p-methylnaphthalene doped naphthalene crystals involves phonon assisted detrapping of electronic energy. Ps time resolved spectroscopy was the experimental technique used in this work. 

Historically, hydrogen exchange experiments (i.e., the replacement of one isotope of hydrogen bound to an O, N, or S atom in the protein interior by another isotope from the solvent water) provided some of the earliest evidence for the existence of conformational fluctuations in proteins. More recently, a wide range of experimental methods (such as fluorescence quenching and depolarization, nuclear magnetic resonance relaxation, infrared and Raman spectroscopy, and X-ray and inelastic neutron scattering) have been used to study the motions in proteins. However, it is primarily the application of theoretical methods, particularly molecular dynamics simulations, that have... 

Various spectroscopic techniques and probes have been used to investigate solubilization of probe molecules, mostly using UV/visible spectroscopy, fluorescence spectroscopy, ESR spectroscopy [64, 74, 217, 287] and NMR-spectro-scopy [367-369]. Fluorescence spectroscopy is particularly versatile [370], as various static and dynamic aspects can be covered by studying excitation and emission spectra, excimer or exciplex formation, quantum yields, quenching, fluorescence life-times, fluorescence depolarization, energy transfer etc. 

Evidence for mobility within proteins comes from a variety of physical methods single crystal X-ray or neutron diffraction, electron microscopy, and spectroscopic techniques such as NMR, fluorescence depolarization, Mossbauer spectroscopy and H-exchange studies. Theoretical approaches such as potential-energy minimization and molecular-dynamics calculations may also be used to study flexibility. An illustration of the frequency range of the various thermal motions detected in proteins is given in Table 1. 

O Faurskov Nielsen, DH Christensen, P-A Lund, E Praestgaard. Short time molecular dynamics in molecular liquids studied by depolarized Raman and Rayleigh-wing, and infrared absorption. Proceedings of the 6th International Conference on Raman Spectroscopy, Bangalore, London Heyden and Sun Ltd., 1978, pp 208-209. 

At first, an overview of the experimental methods which are suitable to characterize the CNT aggregation state in general, and thus are suitable to monitor CNT debundling in aqueous medium and in presence of surfactant, will be reviewed. Three main streams will be presented (i) "direct imaging of the CNT dispersions by m icroscopic techniques (ii] spectroscopic techniques, such as Raman spectroscopy, which exploit the difference in electronic properties between bundled and individualized CNTs and (iii] depolarized dynamic light scattering which is commonly used to characterize colloidal systems. 

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