Photoisomerization dynamics, time-resolved

Many of the fiindamental physical and chemical processes at surfaces and interfaces occur on extremely fast time scales. For example, atomic and molecular motions take place on time scales as short as 100 fs, while surface electronic states may have lifetimes as short as 10 fs. With the dramatic recent advances in laser tecluiology, however, such time scales have become increasingly accessible. Surface nonlinear optics provides an attractive approach to capture such events directly in the time domain. Some examples of application of the method include probing the dynamics of melting on the time scale of phonon vibrations [82], photoisomerization of molecules [88], molecular dynamics of adsorbates [89, 90], interfacial solvent dynamics [91], transient band-flattening in semiconductors [92] and laser-induced desorption [93]. A review article discussing such time-resolved studies in metals can be found in... 

H. Hamaguchi I would like to comment on the stilbene photoisomerization in solution. We recently found an interesting linear relationship between the dephasing time of the central double-bond stretch vibration of Si franj-stilbene, which was measured by time-resolved Raman spectroscopy, and the rate of isomerization in various solutions. Although the linear relationship has not been established in an extensive range of the isomerization rate, I can point out that the vibrational dephasing time measured by Raman spectroscopy is an important source of information on the solvent-induced vibrational dynamics relevant to the reaction dynamics in solution. 

Solvent reorientation and isomerization of trans-stilbene in alkane solutions has been studied by ps time scale anisotropic absorption and polarization239 Coupling of solute and solvent decreases as the size of the solvent molecules increases. The applicability of currently favoured models for the activated barrier crossing in the photoisomerization of stilbene is discussed, A method for measuring quantum yields in the photoisomerization of trans-stilbene gives high accuracy without use of a chemical actinometer . Evidence has been found for dynamic solvent effects on the photoisomerization of 4,4 -dimethoxystilbene in which the effects of temperature and hydrostatic pressure were made in n-alkane and n-alkyl alcohol. A ps laser time-resolved study fits frequency dependent solvent shifts but gives results inconsistent with the free volume model. Photophysical and theoretical studies of trans and 9-... 

The primary photoreactions in the PYP have been experimentally studied both in the protein and in solution environments. The initial structural change of PYP was directly observed by time-resolved x-ray crystallography. Ultrafast fluorescence spectroscopy was performed on the initial process of the photoreaction of PYP. It was shown that the photoisomerization reaction of the PYP chromophore is completed within 1 ps. The initial photoreaction processes were analyzed by using time-resolved spectroscopic data. Although the reaction of the PYP chromophore in solution environments has been studied by several groups, the characterization of the dynamics in these environments is not fully understood. 

Time-resolved femtosecond absorption, fluorescence, IR, and Raman spectroscopy elucidate the molecular structure evolution during ultrafast chemical reactions [7-11]. The technique provides in real time direct insight into the structural dynamics of various systems including photoisomerization. In this chapter, we briefly describe modem methods of studying photochemical and photophysical processes that have been employed or can be employed in the stilbene photophysics and photochemistry. 

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