Photoisomerizations

Seidner L, Stock G and Domcke W 1995 Nonperturbative approach to femtosecond spectroscopy - general theory and application to multidimensional nonadiabatic photoisomerization processes J. Chem. Phys. 103 4002... 

According to Kramers model, for flat barrier tops associated with predominantly small barriers, the transition from the low- to the high-damping regime is expected to occur in low-density fluids. This expectation is home out by an extensively studied model reaction, the photoisomerization of tran.s-stilbene and similar compounds [70, 71] involving a small energy barrier in the first excited singlet state whose decay after photoexcitation is directly related to the rate coefficient of tran.s-c/.s-photoisomerization and can be conveniently measured by ultrafast laser spectroscopic teclmiques. 

Figure A3.6.5. Photoisomerization rate constant of (ran.s -stilbene m n-pentane versus inverse of the self-diflfrision coefficient. Points represent experimental data, the dashed curve is a model calculation based on an...

Figure A3.6.8. Isothemis of k ) for tran.s-stilbene photoisomerization in n-hexane at temperatures between...

Figure A3.6.9. Viscosity dependence of photoisomerization rate constants of tran.s -stilbene (open circles) and E,E-diphenylbutadiene (fiill circles) in n-butanol. The broken line indicates a -dependence of k [96],...

Schroeder J, Tree J and Vdhringer P 1995 Photoisomerization of f/ a/rs-stilbene in compressed solvents Kramers turnover and solvent induced barrier shift Z. Phys. Chem. 188 287... 

Gehrke C, Schroeder J, Schwarzer D, Tree J and Voss F 1990 Photoisomerization of diphenylbutadiene in low-... 

Syage J A, Felker P M and Zewail A H 1984 Picosecond dynamics and photoisomerization of stilbene in supersonic beams. I. Spectra and mode assignments J. Chem. Phys. 81 4685-705... 

Nordhoim S 1989 Photoisomerization of stiibene—a theoreticai study of deuteration shifts and iimited internai vibrationai redistribution Chem. Phys. 137 109-20... 

Rothenberger G, Negus D K and Hochstrasser R M 1983 Solvent influence on photoisomerization dynamics J. Chem. Phys. 79 5360-7... 

Sundstrdm V and Gillbro T 1985 Dynamics of trans-cis photoisomerization of stiibene in hydrocarbon solutions Ber. Bunsenges Phys. Chem. 89 222-6... 

Park N S and Waldeck D FI 1989 Implications for multidimensional effects on isomerization dynamics photoisomerization study of 4,4 -dimethylstilbene in / -alkane solvents J. Chem. Phys. 91 943-52... 

Nikowa L, Schwarzer D, Troe J and Schroeder J 1992 Viscosity and solvent dependence of low barrier processes photoisomerization of c/s-stilbene in compressed liquid solvents J. Chem. Phys. 97 4827... 

Gehrke C, Mohrschladt R, Schroeder J, Troe J and Vdhringer P 1991 Photoisomerization dynamics of diphenylbutadiene in compressed liquid alkanes and in solid environment Chem. Phys. 152 45... 

Sun Y-P and Saltiel J 1989 Application of the Kramers equation to stiibene photoisomerization in / -alkanes using translational diffusion coefficients to define microviscosity J. Phys. Chem. 93 8310-16... 

Schroeder J, Schwarzer D, Troe J and Vbhringer P 1994 From barrier orossing to barrieriess reiaxation dynamios photoisomerization of f/ ans-stiibene in oompressed aikanois Chem. Phys. Lett. 218 43... 

Poliak E 1987 Transition state theory for photoisomerization rates of f/ a/rs-stilbene in the gas and liquid phases J. Chem. Phys. 86 3944... 

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... 

Nishiyama Kand Fujihira M 1988 Cis-trans reversible photoisomerization of an amphiphilio azobenzene derivative in its pure LB film prepared as polyion oomplexes with polyallylamine Chem. Lett. 1257-60... 

Nakahara H, Fukuda K, Shimomura M and Kunitake T 1988 Moleoular arrangements and photoisomerization of amphiphilio azobenzene derivatives in monolayers and multilayers Mppo/ Kagaku Ka/sh/1001-10... 

The easiest method for creating many vibrational excitations is to use convenient pulsed visible or near-UV lasers to pump electronic transitions of molecules which undergo fast nonradiative processes such as internal conversion (e.g. porjDhyrin [64, 65] or near-IR dyes [66, 62, 68 and 62]), photoisomerization (e.g. stilbene [12] or photodissociation (e.g. Hgl2 [8]). Creating a specific vibrational excitation D in a controlled way requires more finesse. The easiest method is to use visible or near-UV pulses to resonantly pump a vibronic transition (e.g. 

The vibronic coupling model has been applied to a number of molecular systems, and used to evaluate the behavior of wavepackets over coupled surfaces [191]. Recent examples are the radical cation of allene [192,193], and benzene [194] (for further examples see references cited therein). It has also been used to explain the lack of structure in the S2 band of the pyrazine absoiption spectrum [109,173,174,195], and recently to study the photoisomerization of retina] [196],... 

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

THE cvcLOBUTADENE-TETRAHEDRANE SYSTEM. A related reaction is the photoisomerization of cyclobutadiene (CBD). It was found that unsubstituted CBD does not react in an argon matrix upon irradiation, while the tri-butyl substituted derivative forms the corresponding tetrahedrane [86,87]. These results may be understood on the basis of a conical intersection enclosed by the loop shown in Figure 37. The analogy with the butadiene loop (Fig. 13) is obvious. The two CBDs and the biradical shown in the figure are the three anchors in this system. With small substituents, the two lobes containing the lone electrons can be far... 

In 1969 Lablache-Combi er et al. (110) found that in the presence of primary amines isothiazole photoisomerizes to thiazoie (Scheme 100). 

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