Potential energy surfaces photoisomerization

AMI Calculations of the potential energy surface of the photoisomerization of the hypothetical (V-imide 6 (R1 = CHO R2 = H) have been reported.78... 

Figure 55. Two-dimensional coupled potential energy surfaces and the wavepacket motion, (a) Si — S2 surfaces and (b) Si — So surfaces. The black, gray, and white circles and dotted lines indicate the locations of the FC region. Si - S2 conical intersection minimum, 5MR Si — So conical intersection minimum, and seam lines, respectively. The solid arrows indicate the schematic wavepacket pathway in the case of natural photoisomerization starting from the vibrational ground state. Taken from Ref. [49].

J. Troe Professor Marcus, you were mentioning the 2D Sumi-Marcus model with two coordinates, an intra- and an intermolecu-lar coordinate, which can provide saddle-point avoidance. I would like to mention that we have proposed multidimensional intramolecular Kramers-Smoluchowski approaches that operate with highly nonparabolic saddles of potential-energy surface [Ch. Gehrke, J. Schroeder, D. Schwarzer, J. Troe, and F. Voss, J. Chem. Phys. 92, 4805 (1990)] these models also produce saddle-point avoidances, but of an intramolecular nature the consequence of this behavior is strongly non-Arrhenius temperature dependences of isomerization rates such as we have observed in the photoisomerization of diphenyl butadiene. 

The fluorenone-sensitized irradiation of the all rrawj-triene (140) gives a photostationary mixture composed of the trans-cis-trans, cis-trans-trans and cis-cis-trans isomers. The potential energy surfaces of the ground and excited state of the triene (140) have been mapped,and a study of the fluorescence from this triene in lipid bilayers and isotropic solvents has been carried out. The photophysical properties of the dithienylpolyenes (141) and (142) have been measured. The photoisomerism of all-tranj-retinal to the 11-m isomer brought about by honeybee retina enzyme photoisomerase has been described. ... 

In this chapter, computational studies investigating the mechanism of the Pr -> Pfr conversion will be presented. Specifically, focus will be on calculations designed to assess whether the view [31-39] that the primary photochemical event occurs at the CD methine bridge can be explained in terms of the intrinsic reactivity of the bilin chromophores. In our work, this question was addressed by computing the excited-state potential energy surfaces for Z photoisomerizations at the AB, BC and CD methine bridges, in the absence of the protein [13, 14], Clearly, a detailed assessment of what role intrinsic reactivity plays is a prerequisite for subsequently understanding the role of the protein in the primary event. 

The E Z photoisomerization of stilbene has been studied in considerable detail. We use the customary labels T (for trans) to designate structures near that of ( )-stilbene, c (for cis) for those near (Z)-stilbene and p (for perpendicular) for those near the transition-state geometry for E Zisomerization in the ground state. Figure 5.20 shows schematic potential energy surfaces (PESs) for S0, Si and Ti that are based largely on the experimental data discussed below. 

Figure 11 Potential energy surafes of cis-trans isomerization of 8b. (Reprinted from ref. 114 Potential energy surfaces of a one-way photoisomerizing olefin studied by photoacoustic calorimetry and X-ray crystallography, T, Aral, H. Okamoto, K. Tokumaru, T. Ni, R. A. Caldwell, and K. Ueno, J. Photochem. Photobiol. A Chem. IS, 85-90 (1993) copyright (1998), with permission fiom Elsevier Science.)...

In the photoisomerization of 13-desmethylretinal it is shown that the hitherto unseen 13-cw-isomer is also present to an extent of 7% in addition to the 1-cis-, 9-cis-, and 1 l-cw-isomers. The photoisomerization processes of polyenes have been investigated using a theoretical approach and results of calculations for the potential energy surfaces with particular references to radiationless transitions presented. ... 

Syage J A, Felker P M and Zewail A H 1984 Picosecond dynamics and photoisomerization of stilbene in supersonic beams. II. Reaction rates and potential energy surface J. Chem. Phys. 81 4706-23... 

Figure 1. Potential energy surfaces of photoisomerization in the triplet state.

The foregoing methodology enables one to draw the potential energy surfaces of the photoisomerization of ethenes more precisely. 

The potential energy surface of the isomerization is discussed in terms of adiabatic and diabatic processes [1-4,12,18,71]. Two-way isomerization in the triplet manifold without a quencher takes place as a diabatic process by deactivation at p. However, as mentioned above, photochemical cis- trans one-way isomerization in the triplet state proceeds by an adiabatic process where the excited state of a starting material, c, undergoes adiabatic conversion to the excited state of the product, t, followed by either unimolecular deactivation to the, ground state of the product, t, or energy transfer to c to give t and c. The isomerization of 5b also proceeds partly by way of an adiabatic process. Deactivation from t occurs as an adiabatic process, but that from p proceeds as a diabatic process [25]. Therefore, two-way photoisomerization usually takes place as a diabatic process, whereas one-way photoisomerization and isomerization... 

Figure 6. Potential energy surfaces of one-way photoisomerization of 8b in the excited singlet and triplet states [71],...

Quantum mechanical study of the photoisomerization reaction of PYP began with calculations of the adiabatic potential energy surfaces of small model compounds of the chromophore (Yamada et al. 2001). However, to fully describe the protein-chromophore interaction, we had to include the entire protein molecule in the photoisomerization reaction. Recently, QM/MM (Hayashi and Ohmine 2000) and the ONIOM (Yamada et al. 2002 Vreven and Morokuma 2003), both of which are hybrid methods of high- and low-level calculations, have been used for large molecular systems. We performed the ONIOM (IMOMM) calculations on PYP to elucidate the role of the protein enviroiunent (Yamada etal. 2004a,b). We also investigated the origin of the force that drives photoisomerization. 

See, for example, D. L. Bunker, /. Chem. Phys., 40,1946 (1963). Monte Carlo Calculations. IV. Further Studies of Unimolecular Dissociation. D. L. Bunker and M. Pattengill,/. Chem. Phys., 48, 772 (1968). Monte Carlo Calculations. VI. A Re-evaluation erf Ae RRKM Theory of Unimolecular Reaction Rates. W. J. Hase and R. J. Wolf, /. Chem. Phys., 75,3809 (1981). Trajectory Studies of Model HCCH H -P HCC Dissociation. 11. Angular Momenta and Energy Partitioning and the Relation to Non-RRKM Dynamics. D. W. Chandler, W. E. Farneth, and R. N. Zare, J. Chem. Phys., 77, 4447 (1982). A Search for Mode-Selective Chemistry The Unimolecular Dissociation of t-Butyl Hydroperoxide Induced by Vibrational Overtone Excitation. J. A. Syage, P. M. Felker, and A. H. Zewail, /. Chem. Phys., 81, 2233 (1984). Picosecond Dynamics and Photoisomerization of Stilbene in Supersonic Beams. II. Reaction Rates and Potential Energy Surface. D. B. Borchardt and S. H. Bauer, /. Chem. Phys., 85, 4980 (1986). Intramolecular Conversions Over Low Barriers. VII. The Aziridine Inversion—Intrinsically Non-RRKM. A. H. Zewail and R. B. Bernstein,... 

We have used the AIMS method with ab initio QM/MM potential energy surfaces to investigate the role of environmental effects in the photoisomerization reaction of... 

A map of the singlet-singlet excitation and photoisomerization potential energy surface for tetraphenylethylene in alkane solvents were prepared using fluorescence and picosecond optical calorimetry (Figure 3.4) [4]. The line shapes of the vertical and relaxed exdted-state emissions at 294 K in methylcyclohexane were obtained from the steady-state emission spectrum, the wavelength dependence of the time-resolved fluorescence decays, and the temperature dependence of the vertical and relaxed state emission quantum yields and of the time-resolved fluorescence decays. 

Figure 3.4 A map of the photoisomerization potential energy surface for tetraphenylethylene in alkane solvents [4]. (Reproduced with permission.)...

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