Picosecond kinetics

Schroeder J 1997 Picosecond kinetics of trans-cis photoisomerisations from ]et-cooled molecules to compressed solutions Ber. Bunsenges Phys. Chem. 101 643... 

New metliods appear regularly. The principal challenges to the ingenuity of the spectroscopist are availability of appropriate radiation sources, absorption or distortion of the radiation by the windows and other components of the high-pressure cells, and small samples. Lasers and synchrotron radiation sources are especially valuable, and use of beryllium gaskets for diamond-anvil cells will open new applications. Impulse-stimulated Brillouin [75], coherent anti-Stokes Raman [76, 77], picosecond kinetics of shocked materials [78], visible circular and x-ray magnetic circular dicliroism [79, 80] and x-ray emission [72] are but a few recent spectroscopic developments in static and dynamic high-pressure research. 

Picosecond kinetics, 266 Pre-equilibria, 133-135 Pre-steady-state region, 116 Pressure, effect on rate constants, 166-167... 

Barbara PF, Walsh PK, Brus LE (1989) Picosecond kinetic and vibrationally resolved spectroscopic studies of intramolecular excited-state hydrogen atom transfer. J Phys Chem 93 29-34... 

Figure 10.8 Picosecond kinetic flash photolysis apparatus...

Woodbury, N. W., M. Becker, D. Middendorf, and W. W. Parson, Picosecond kinetics of the initial photochemical electron transfer reaction in bacterial photosynthetic reaction centers. Biochem. 24 7516, 1985. Fast spectrophotometric techniques are used to follow the initial steps in reaction centers purified from photosynthetic bacteria. 

Everybody knows of the spectacular success of unravelling the structure and kinetics of the photosynthetic bacteria, rhodopseudomonas sphaeroides and viridis the structure by Deisenhoffer, Huber and Michel (Deisenhofer et al., 1984) following the isolation and crystallisation by Michel (Michel, 1982) and the picosecond kinetics (which came first) by Rockley, Windsor, Cogdell and Parson (Rockley et al., 1975) and also by Dutton, Rentzepis, Netzel et al. (Netzel et al., 1977). 

Kaufmann, K. J., Dutton, P. L., Netzel, T. L., Leigh, J. S., and Rentzepis, P. M., 1975, Picosecond kinetics of events leading to reaction centers bacteriochlorophyll oxidation. Science, 188 1301nl304. 

Photoprocesses in biliverdin dimethyl ester in ethanol have been studied by laser-induced optoacoustic spectroscopy." The picosecond kinetics of excited-state relaxation of this ester have also been reported." " Isophorcarubin is a conformationally restricted and highly fluorescent bilirubin." " The phototherapy for neonatal jaundice has stimulated investigations of configurational isomers of bilirubin" and of stereospecific and regioselective photoisomerization of bilirubin." ... 

We observed (Fig. 3) that in the absence of surface quinones, the relaxation of QD absorption bleach band (A,ex=528 nm) corresponding to 1 lSelSh> state reflects the trapping excited charge carriers at the surface. The picosecond kinetic analysis shows that in the presence of tCl-l,2-BQ the short time component of the transient bleach formation at A.reg=530 nm is additionally shortened from 93 ps down to 27 ps. It reflects the appearance of the additional non-radiative relaxation channel for electrons from QD conduction band to the lowest unoccupied molecular orbitals of quinone (LUMO). These results are in an agreement with calculations presented in [4]. We believe that long component (r> 3 ns) may reflect the electron shuttling from LUMO of the quinone to the QD valence band. 

Figure 7 Picosecond kinetics of hydrated electron recombination in the ionization spurs as a function ofthe temperature [7], Hydrated electron Is produced In 15 ps pulse of 8 MeV electrons delivered by the electron accelerator ELYSE. The absorbance of 2 cm of pure water Is analyzed by a laser at 790 nm. Due to the red-shift of the hydrated electron spectrum with Increasing temperature, the absorbance maximum value at790nm decreases from 23°C to350 °C. In the time range of 3 ns, the recombination of hydrated electron appears less and less efficient with Increasing temperature.

Results from additional picosecond kinetic measurements of the photochemical and electron-transfer reactions in photosynthetic bacteria also gave support to the notion of the existence of an intermediary electron acceptor. This can best be illustrated with the kinetic studies of Kaufmann, Dutton, Netzel, Leigh and Rentzepis on the involvement of BO as a transient intermediary electron acceptor in photosynthetic bacteria. When Q is functional, i.e., Q is present in the oxidized state [see Fig. 1], flash illumination would be expected to produce first the [P BO"]-Q-state followed by the [P BO] Q -state. Examination of this reaction by picosecond spectroscopy revealed both the time it takes for electron donation from P to BO and the lifetime of BO , i.e., the time it takes for BO to transfer an electron to Q. 

Fig. 3 shows the picosecond kinetics reported by Kaufmann etal.. These workers used Rb. sphaeroides R-26 reaction-center complexes poised either at -1-200 mV to maintain Q in the oxidized state and functional [Fig. 3 (A)], or poised at 400 mV, so that Q is chemically reduced before the flash [Fig. 3 (B)]. Picosecond absorbance changes at 540 run were measured to directly monitor the redox changes of BO. In both cases, BO photoreduction represented by the initial absorbance decrease occurred in < 10 ps. In both cases, the risetime of the 1250-nm absorbance inaease (not shown), which can be assigned exclusively to the photooxidation of P870, also showed a risetime of <10. These results indicate that, independent of the redox state of Q, P870 is photooxidized and loses an electron to BO, by way of the [P BO]-t//v->[P BO ] reaction, in <10ps.

Fig. 3. Kinetics of picosecond iaser-induced absorbance changes at 540 nm in Rb. sphaeroides R-26 reaction centers. Sample (A) poised at +200 mV and (B) at -400 mV. Figure source Kaufmann, Dutton, Netzel. Leigh and Rentzepis (1975) Picosecond kinetics of events leading to reaction center bacteriochlorophyll oxidation. Science 188 1303.

MG Rockley, MW Windsor, RJ Cogdell and WW Parson (1975) Picosecond detection of an Intermediate In the photochemical reaction of bacterial photosynthesis. Proc Nat Acad Sci, USA 72 2251-2255 J Fajer, DC Brune, MS Davis, A Forman and LD Spaulding (1975) Primary charge separation In bacterial photosynthesis Oxidized chlorophylls and reduced pheophytin. Proc Nat Acad Sci, USA 72 4956 960 PL Dutton, KJ Kaufmann, B Chance and PM Rentzepis (1975) Picosecond kinetics of the 1250 nm band of the Rps. sphaeroldes reaction center. The nature of the primary photochemical Intermediary state. FEES Lett 60 275-280... 

KJ Kaufmann, PL Dutton, TL Netzel, JS Leigh and PM Rentzepis (1975) Picosecond kinetics of events iead-ing to reaction center bacteriochiorophyii oxidation. Science 188 1301-1304... 

V. Picosecond Kinetics of Photochemical Charge Separation and Electron Transport in Photosystem II..316... 

Fig. 7. Picosecond kinetics of flash-induced absorbance changes at 432 and 380-390 nm in PS-1 core complex [PTOO-AqA,] isolated from Synechocystis sp. PCC 6803. Figure source Brettel and Vos (1998) Spectroscopic resolution of the picosecond reduction kineticsofthe secondary electron acceptor in photosystem I. FEBS Lett 447 316.

The picosecond kinetics of tetracene dianions have been studied using a new extension of picosecond spectroscopy methods.100 The rise times of the Stokes-shifted fluorescence from rhodamine B, rhodamine 6G, and erythrosine dissolved in water have been investigated using picosecond techniques. Figure 4 schematically indicates the situation following excitation. The best fit to the data corresponds to a relaxation time within the vibronic manifold of S of <1 ps.101 Although these fast spectroscopic techniques provide direct means of examining the behaviour of short-lived species, indirect methods are more convenient and often quite successful. Such is the case for the determination of rf from calculated radiative rate constants and measured Of values for a series of cyanine dyes.102... 

Woodbury, N.W., Beeker, M., Middcmdmf, D., Parson, W.W. Picosecond kinetics of the initial photochcanical electron-transfcu reaction in bacterial photosynthetic reaction center. Biochemistry 24, 7516-7521 (1985)... 

Particular emphasis will be given to the problem of a possible heterogeneity in the kinetics of the primary processes and their possible origins. Among other results we present the first evidence for an energy transfer process occuring on the time-scale of several picoseconds in a bacterial reaction center. This finding bears considerable consequences for the interpretation of picosecond kinetic data on reaction centers. 

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