Transient absorption spectroscopy polarizers

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

Irradiation of t-1 with fumaronitrile in polar solvents results in the formation of a nonfluorescent radical ion pair which decays via intersystem crossing to locally excited t with a quantum yield of 1.0 (88). The rate constant for nonradiative decay of the radical ion pair increased with increasing solvent polarity (89). Dissociation of the ion pair competes inefficiently with intersystem crossing and yields the cation radical of t-1, which has been observed and characterized by time resolved resonance Raman (TR ) (88) and transient absorption spectroscopy (89). The strongest feature in the TR ... 

In the case of compound 32, no change in the absorption spectrum compared with that of 33 could be observed, neither in cyclohexane nor in benzonitrile. This indicates that intramolecular CT interaction is negligible in the ground-state. Nevertheless, fluorescence and transient absorption spectroscopy show that processes after excitation strongly depends on solvent polarity. In cyclohexane the Si state... 

Chemically induced dynamic nuclear polarization (CIDNP) has been used to discriminate radical and nonradical processes in cycloadditions of electron-rich alkenes and electron-poor carbonyl components <1998MI9>. Spectroscopic observation of the fragmentation of an oxetane radical anion revealed the generation of the most stable alkene radical <2003JOC10103, 2006PPS51>. Transient absorption spectroscopy has been employed to monitor the Paterno-Biichi cycloaddition of benzophenone and furan <2004JA2838>. 

In this paper we investigate the time dependent ground state hole spectrum of cresyl violet in polar solvents by means of subpicosecond transient absorption spectroscopy. The time correlation function expressed by eq (7) showed large difference in time profiles compared with the reported one expressed by eq (6). Possible mechanisms will be discussed. 

The presence of speeies able to initiate polymerization as observed by other spectroscopic tools such as electron spin resonance spectroscopy (ESR), emission spectroscopy, transient absorption spectroscopy or chemically induced dynamic nuclear polarization (CIDNP). 

The photodissociation of bromobenzene in solution has been investigated with ultrafast transient absorption spectroscopy, following excitation at 266 nm. The main kinetic feature in acetonitrile was a 9 ps decay that was assigned to predissociation similar decays were observed in hexane, dichloromethane and tetrachloromethane. Laser-aligned iodobenzene have been photodissociated into phenyl radicals and iodine atoms with a 1.5 ps laser pulse at 266 nm, and the yield of iodine photoproducts detected by resonant multiphoton ionization." Significant yield enhancements were observed when the dissociation laser was polarized parallel instead of perpendicular to the alignment laser polarization. 

Non-polar solvents, such as hexane and benzene, produce high yields of excited states via ion recombination, and relatively low yields of radical ions. In contrast, polar solvents like methanol, acetonitrile and water support high yields of radical ions with low excited state yields, due to solvation and stabilisation of the initial ions, particularly the electrons, leading to a slow rate of ion recombination. In intermediate polarity solvents, such as acetone, approximately equal amounts of radicals and excited states are generated. Hence, generally it is better to study solute excited states with pulse radiolysis in non-polar solvents and solute radicals or radical ions in polar solvents. This is often not possible due to insolubility in the preferred solvent, but if the transients are being monitored via transient absorption spectroscopy and they have high molar absorption coefiicients then low yields need not be problematic. 

Ns laser photolysis measurements on (1-pyrenyl) - (CH2 ) (p-N,N-dimethylaminophenyl) (abbreviated as P-(CH2)n"D) were performed in some solvents (18). Their absorption spectra are reproduced by the superposition of bands of the donor cation and the acceptor anion. Only the bandwidth is dependent upon solvent polarity and the number of CH2 groups, which is reduced to the relative geometrical structure of the donor and the acceptor. Exciplex formation dynamics of these compounds has been established by ps transient absorption spectroscopy (19). The absorption spectrum of P-CH2-D in 2-propanol is almost independent of the delay time. On the other hand, P-(0112)3-0 gives a similar spectrum at about 1 ns after excitation, and its spectral shape broadens with a time-constant of 1.2 ns. 

The rotational reorientation times of the sample in several solvents at room temperature were measured by picosecond time-resolved fluorescence and absorption depolarization spectroscopy. Details of our experimental setups were described elsewhere. For the time-correlated single photon counting measurement of which the response time is a ut 40 ps, the sample solution was excited with a second harmonics of a femtosecond Ti sapphire laser (370 nm) and the fluorescence polarized parallel and perpendicular to the direction of the excitation pulse polarization as well as the magic angle one were monitored. The second harmonics of the rhodamine-640 dye laser (313 nm 10 ps FWHM) was used to raesisure the polarized transient absorption spectra. The synthesis of the sample is given elsewhere. All the solvents of spectro-grade were used without further purification. 

A transient absorption band, with a profile similar to that of the dimethylani-line radical cation, was observed in polar solvents by time-resolved picosecond absorption spectroscopy. 

Nickel, in a very useful paper, has discussed the elimination of polarization bias effects from the measurement of luminescence properties and transient absorption in isotropic solutions. The theoretical treatment is fully developed and recommendations are given for making reliable observations under a variety of experimental conditions are detailed. Determination of quantitative data from steady state luminescence spectroscopy is by no means as straightforward as many workers assume this work very convincingly demonstrates otherwise. 

With the objective to characterize the performance-limiting recombination process in photovoltaics with high open-circuit voltages, we have recently introduced polarization-resolved transient absorption (TA) spectroscopy to directly track the movement of... 

In order to study the viscosity effect on the quenching of triplet excited state of (53) by TEMPO, chemically induced dynamic electron polarization and transient absorption spectra have been measured in ethylene glycol, 1,2-propanol and their mixtures. The results indicate that the quenching rate constant is viscosity-dependent and decreases linearly with the increase in solvent viscosity. The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion have been studied using photoelectron imaging taken at 480 nm, which clearly indicates resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. ... 

Photo-induced Electron Transfer. Electron transfer is one of the most fundamental and widespread reactions in nature and has been extensively studied. In addition to the optical absorption spectroscopy widely used, TR EPR has become established as an appropriate method to study electron-transfer processes. In most of these investigations CIDEP effects are observed. The spin-polarization effects originate in the spin selectivity of chemical and physical processes involved in free-radical formation and decay, as well as in the spin-state evolution in transient paramagnetic precursors. For this reason, CIDEP constitutes a unique probe of the mechanistic details of electron-transfer processes. 

The 3.5- and 8-ntn nanoparticles show well-resolved peaks at 362 and 473 nm, respectively, as well as other features at higher energies. The 4.5-nm particles show a well-resolved peak at 400 nm and a shoulder at 450 nm. It is tempting to assume that in each case, the lowest energy absorption corresponds to the lowest allowed transition (the A exciton) in bulk M0S2. Polarization spectroscopy can be used to determine if this is the case. The lowest allowed transitions in bulk material, the A and B excitons, are polarized perpendicular to the crystallographic c axis. If the lowest allowed transition correlates to the A exciton, then it would be expected to also be a planar (xy polarized) oscillator. However, tire results of polarization studies reveal that the actual situation is more complicated. A combination of time-resolved polarized emission and one-color time-resolved polarized absorption (transient bleach) studies facillitate assignment of the polarizations of the observed nanoparticle transitions. The 3.5-nm particles are emissive and the polarization of the several of the lowest transitions may be determined... 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

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