Femtosecond studies

Pedersen S, Herek J L and Zewail A H 1994 The validity of the Diradical hypothesis direct femtosecond studies of the transition-state structures Science 266 1359-64... 

The closed cycle of interconversions occurs on an ultrafast time scale. Femtosecond studies (95CPL35) of the ESIPT rearrangement of 347 (R = Me) (commercial name Tinuvin-P) carried out over a wide spectral range... 

Frey W, Laermer F, Elsaesser T (1991) Femtosecond studies of excited-state proton and deuterium transfer in benzothiazole compounds. J Phys Chem 95 10391-10395... 

Femtosecond studies being performed intensely the world over, using not only molecular beams but studying also processes on surfaces and clusters and in polymers. In addition, femtochemistry has been applied to the study of many important biological systems. 

The nanosecond studies that have been performed on similar systens [48-51,104] are apparendy at odds with the previously mentioned femtosecond study. However, 532-nm nanosecond laser pulses have different characteristics compared to a 388-nm femtosecond pulse and this may explain the discrepancies. Again, different substiments can also affect the outcome, and certainly the 6,8-dinitro-BIPS system is not a standard to gauge all other spiropyran systems. In fact, no typical molecule or molecular system exists which can be used as an example for describing the behavior of all other nominally similar systems. 

Takeda et al. [104] found that the steady-state irradiation of A-octadecyl 6,8-dinitro-BlPS resulted in the formation of the closed form. This is in agreement with the femtosecond studies. However, the fade reaction showed three components when monitored at 500 nm in 1,2-dichloroethane. The first component was manifest as a bleach that occurred within the instrument response time of 25 nsec. This was followed by two longer components with 240-nsec and 3.4 psec lifetimes. The spiropyran ring-closed form evolved with two exponential components with lifetimes of 620 nsec and 4 p-sec. The Af-octadecyl group may affect the outcome compared to the A-methylated form. 

Kinetic Modeling. For all the synthetic heme complexes studied, the lifetime of the first intermediate AS was on the order of 250 fs in agreement with the femtosecond study of Martin et al. ( ). As the jitter in the pulse duration is on the order of 1 ps, the AS lifetime is very approximate and chosen to obtain the best fit to the experimental spectra. 

Evans JE, Springer KW, Zhang JZ (1994) Femtosecond studies of interparticle electron transfer in coupled CdS-Ti02 colloidal system. J Chem. Phys 101 6222-6225... 

The postulation of trimethylene and tetramethylene diradicals as reactive intermediates involved in many thermal isomerization and fragmentation reactions has a long history,but not until 1994 had they ever been detected in real time. The validity of the diradical hypothesis was tested through femtosecond studies, and the tests provided dramatic evidence confirming that these short-lives species are indeed real, directly experimentally accessible chemical entities. 

The mass spectrum of diazabicyclo[2.2.1]hept-2-ene shows only a weak molecular ion and a very strong fragment at 68 amu. The femtosecond studies found that the 68 amu easily ionized transient profile could be modeled with a rise time of 30 10 fs and decay time of 190 10 fs, a value comparable to the decay time of trimethylene. 

This femtosecond study confirmed the involvement of the oxytetramethylene diradical as a reactive intermediate, and found that the trimethylene formed from it had the same hfetime as the trimethylene generated through the photodecarbonyl-ation of cyclobutanone. For tetrahydropyran, the oxypentamethylene drradical (86 amu) is formed readUy and the 85 amu transient, from the p-cleavage of a C H bond, is the dominant fragmentation product. 

Solvation Ultrafast Dynamics of Reactions IX. Femtosecond Studies of Dissociation and Recombination of Iodine in Argon Clusters, J-K. Wang, Q. Liu, and A. H. Zewail, J. Phys. Chem. 99, 11309 (1995). 

The Validity of the Diradical Hypothesis Direct Femtosecond Studies of the Transition-State Structures, S. Pedersen, J. L. Herek, and A. H. Zewail, Science 266, 1359 (1994). 

If the basic center in the ESPT molecule is not suitably disposed to form a direct hydrogen bond with the dissociable proton, involvement of protons from the solvent medium becomes necessary and the processes is biprotonic (e.g., 5- and 6-aminoindazole [68,69], 7-azaindole monomer [70]). This type of ESPT has recently been called ESDPT. The dimer of 7-aminoindazole shows ESDPT between the two monomeric units that are suitably hydrogen-bonded [71]. Femtosecond studies by Douhal et al. [72] has suggested a mechanism in which the two protons are transferred in sequence. Some other molecules in which ESDPT has been observed are I-II-pyrrolo[3,2-//]quinoline [73], [2,2 -bipyridyl]-3,3 -diol [74,75],... 

Zhang, J. G. O Neil, R. H. Roberti, T. W. Femtosecond studies of photoinduced electron dynamics at the liquid-solid interface of aqueous CdS colloids, J. Phys. Chem. 1994, 98, 3859. 

Cavaleri, J. J. Skinner, D. E. Colombo, D. P. J. Bowman, R. M. Femtosecond study of the size-dependent charge carrier dynamics in ZnO nanocluster solutions, J. Phys. Chem. 1995, 103, 5378. 

Femtosecond spectroscopy has an ideal temporal resolution for the study of ultrafast water motions from femtosecond to picosecond time scales [33-36]. Femtosecond solvation dynamics is sensitive to both time and length scales and can be a good probe for protein hydration dynamics [16, 37-50]. Recent femtosecond studies by an extrinsic labeling of a protein with a dye molecule showed certain ultrafast water motions [37-42]. This kind of labeling usually relies on hydrophobic interactions, and the probe is typically located in the hydrophobic crevice. The resulting dynamics mostly reflects bound water behavior. The recent success of incorporating a synthetic fluorescent amino acid into the protein showed another way to probe protein electrostatic interactions [43, 48]. 

Kiwi J, Denisov N, Gak Y, et al. Catalytic Fe3+ clusters and complexes in nation active in photo-Fenton processes. High-resolution electron microscopy and femtosecond studies. Langmuir 2002 18 9054-66. 

Zhong, D., Douhal, A., and Zewail, A.H. (2000) Femtosecond studies of protein-ligand hydrophobic binding and dynamics human serum albumin Proc. Natl. Acad. Sci. 97, 14056-14061. 

Long FH, Lu H, Eisenthal KB (1990) Femtosecond studies of the presolvated electron An excited state of the solvated electron Phys Rev Lett 64 1469-1472. 

Femtosecond studies of solvation and intramolecular configurational dynamics of fluorophores containing heterocyclic fragments in liquid solution 04CRV1929. 

Colombo D. P. Jr, Roussel K. A., Saej J., Skinner D. E., Cavaleri J. J. and Bowman R. M. (1995), Femtosecond study of the intensity dependence of electron-hole dynamics in Ti02 nanoclusters , Chem. Phys. Lett. 232, 207-214. 

WZinth, MC Nuss, MA Franz, W Kaiser and H Michel (1985) Femtosecond studies of the reaction center of Rhodopseudomonas viridis. The very first dynamics of the electron-transfer processes. In ME Michel-Beyerle (ed) Antennas and Reaction Centers of Photosynthetic Bacteria, pp 286-291. Springer... 

DL Dexter (1953) A theory of sensitized luminescence in solids. J Chem Phys 21 836-860 T Gillbro and RJ Cogdell (1989) Carotenoid fluorescence. Chem Phys Lett 158 312-316 T Katoh, U Nagashima and M Mimuro (1991) Fluorescence properties of the allenic carotenoid fucoxanthin Implication for energy transfer in photosynthetic pigment systems. Photosynthesis Res 27 221-226 AP Shreve, JK Trautman, TG Owens and AC Albrecht (1991) A femtosecond study of electronic state dynamics of fucoxanthin and implication for photosynthetic carotenoid-to-chlorophyll energy transfer mechanisms. Chem Phys 154 171-178... 

Femtosecond Studies of Proton Transfer in Cyclodextrin Complexes... 

A Femtosecond Studies of Proton Tranter in Cyclodextrin Complexes 233... 

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