Ultrafast Time-Resolved Resonance

Ultrafast Time-Resolved Resonance Raman (TR ) Spectroscopy... 

Ultrafast time-resolved resonance Raman (TR ) spectroscopy experiments need to consider the relationship of the laser pulse bandwidth to its temporal pulse width since the bandwidth of the laser should not be broader than the bandwidth of the Raman bands of interest. The change in energy versus the change in time Heisenberg uncertainty principle relationship can be applied to ultrafast laser pulses and the relationship between the spectral and temporal widths of ultrafast transform-limited Gaussian laser pulse can be expressed as... 

Towrie, M., Grills, D.C., Dyer, L., Weinstein, J.A., Matousek, R, Barton, R., Bailey, R.D., Subramaniam, N., Kwok, W.M., Ma, C., Phillips, D., Parker, A.W. and George, M.W. (2003) Development of a broadband picosecond infrared spectrometer and its incorporation into an existing ultrafast time-resolved resonance Raman, UV/visible, and fluorescence spectroscopic apparatus. Appl. Spectrosc., 57, 367-380. 

Since there are a large number of different experimental laser and detection systems that can be used for time-resolved resonance Raman experiments, we shall only focus our attention here on two common types of methods that are typically used to investigate chemical reactions. We shall first describe typical nanosecond TR spectroscopy instrumentation that can obtain spectra of intermediates from several nanoseconds to millisecond time scales by employing electronic control of the pnmp and probe laser systems to vary the time-delay between the pnmp and probe pnlses. We then describe typical ultrafast TR spectroscopy instrumentation that can be used to examine intermediates from the picosecond to several nanosecond time scales by controlling the optical path length difference between the pump and probe laser pulses. In some reaction systems, it is useful to utilize both types of laser systems to study the chemical reaction and intermediates of interest from the picosecond to the microsecond or millisecond time-scales. 

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. 

Thus far, the only excited-state structural dynamics of oligonucleotides have come from time-resolved spectroscopy. Very recently, Schreier, et al. [182] have used ultrafast time-resolved infrared (IR) spectroscopy to directly measure the formation of the cyclobutyl photodimer in a (dT)18 oligonucleotide. They found that the formation of the photodimer occurs in 1 picosecond after ultraviolet excitation, consistent with the excited-state structural dynamics derived from the resonance Raman intensities. They conclude that the excited-state reaction is essentially barrierless, but only for those bases with the correct conformational alignment to form the photoproducts. They also conclude that the low quantum yields observed for the photodimer are simply the result of a ground-state population which consists of very few oligonucleotides in the correct alignment to form the photoproducts. 

Mizutani, Y Kitagawa, T., Ultrafast dynamics of myoglobin probed by time-resolved resonance Raman spectroscopy. Chem. Rec. 2001,1, 258-275. 

Kitagawa, T. Haruta, N. Mizutani, Y, Time-resolved resonance Raman study on ultrafast structural relaxation and vibrational cooling of photodissociated carhonmonoxy myoglobin. Biopolymers 2002, 61, 207-213. 

Negrerie, M. Cianetti, S. Vos, M. H. Martin, J.-L. Kruglik, S. G., Ultrafast heme dynamics in ferrous versus ferric cytochrome c studied by time-resolved resonance Raman and transient absorption spectroscopy. J. Phys. Chem. B 2006, 110, 12766-12780. 

Ultrafast time-resolved transient absorption and resonance Raman spectroscopy of the photodeprotection and rearrangement reactions of p-hydroxyphenacyl phosphates (72), via intermediate M, have been described (Scheme 13). ... 

Time-resolved resonance Raman spectrometry is a technique that allows collection of Raman spectra of excited state moleeules. It has been used to study intermediates in enzyme reactions, the spectra of carotenoid excited states, ultrafast electron transfer steps, and a variety of other biological and bioinorganic processes. Time-discrimination methods have been used to overcome a major limitation of resonance Raman spectroscopy, namely, fluorescence interference either by the analyte itself or by other species present in the sample. 

Picosecond TR of carbonmonoxy Coo A (a CO-sensing transcriptor activator) shows vFe-His at 211 cm" immediately after photolytic CO-loss. vFe-N(His) is at 231 cm" in cytochrome d from Alcaligentes xylosoxidansP Ultrafast time-resolved IR was used to probe myoglobin dynamics via vFe-His This mode was seen at 244 cm" in the resonance Raman spectrum of the ferrous form of flavohaemoglobin from E. coli and at 211 cm" for the SoxB-type cytochrome c oxidase from Bacillus stearothermophilusP ... 

Xanthene Compounds. Ghosh et al. have quantified the excited state(s) injection and direct molecule-to-particle dynamics of several xanthene compounds (fluorescein, eosin Y, erythrosine B and rose bengal) adsorbed to TiOa nanoparticles (Ramakrishna, 2001). The strong electronic coupling thought necessary for the ultrafast electron injection was previously observed by time-resolved resonance Raman spectroscopy, for eosin Y bonded to a Ti02 surface (Rossetti, 1984). A mechanistic scheme for interfacial electron transfer... 

Recently, Eisenthal and coworkers have developed time-resolved surface second harmonic techniques to probe dynamics of polar solvation and isomerization reactions occurring at liquid liquid, liquid air, and liquid solid interfaces [22]. As these experiments afford subpicosecond time resolution, they are analogous to ultrafast pump probe measurements. Specifically, they excite a dye molecule residing at the interface and follow its dynamics via the resonance enhance second harmonic signal. 

---