Photochemistry in organized and confining media: a model

Weiss, Richard G.; Ramamurthy, V.; Hammond, George S.

doi:10.1021/ar00034a003

Cited by 230 publications

(185 citation statements)

References 35 publications

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“…Particularly relevant are the many examples of medium directed regiospecific or stereospecific photochemical reactions in the solid state (37,38). In this regard, one might expect HT to be of slow rate but not necessarily a low quantum yield process.…”

mentioning

confidence: 99%

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

Liu

Hammond²

2000

Proc. Natl. Acad. Sci. U.S.A.

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164

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This paper critically reviews examples in the literature of photochemical cis-trans isomerization paying particular attention to the medium effect and accompanied conformational changes. A case is made that the Hula-Twist mechanism, postulated in 1985 as a photochemical reaction pathway for a polyene chromophore imbedded in a protein binding cavity such as those of rhodopsin and bacteriorhodopsin, is also a dominant reaction pathway for a diene, or a longer polyene confined in a rigid (relative to isomerization rate) medium. The conventional one-bond-flip process is the preferred reaction pathway in a fluid medium. While defining experiments are proposed, this dual mechanistic approach successfully accounts for all examples in the literature on photoisomerization reactions whether involving conformational changes or not.

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mentioning

confidence: 99%

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

Liu

Hammond²

2000

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

164

130

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“…Most solid-state reactions in Step I hold in Schmidt's topochemical postulate which states that "reaction in the solid state occurs with a minimum amount of atomic or molecular movement." 17 In general, if a reaction cavity 5,18 around the reaction center is large enough to allow molecules to move around in the cavity, reaction can occur. If not, reaction can be suppressed or a product can immediately return to the initial structure via recombination or annihilation.…”

Section: Diffractometermentioning

confidence: 99%

X-ray Direct Observation of Reactions and Labile Species on the Basis of Crystal Design

Kawano

2013

Bulletin of the Chemical Society of Japan

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This account reviews recent development of in situ crystallographic study of reactive intermediates using the cryotrapping method. Starting from the basic concept of a reaction cavity in a crystal, we succeeded in not only observing photoinduced reactive species such as radical, carbene, and nitrene but also establishing a unique approach, crystalline molecular flask, to observe labile species in chemical reactions in a crystal. On the basis of such a crystalline reaction field design, we successfully observed irreversible reactive intermediates in a crystal.

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“…The free volume requirement of the cis is larger than that of the trans , and it has been estimated that the minimum free volume pocket required to allow isomerization to proceed via the inversion pathway (Naito et al, 1991;Paik and Morawetz, 1972) is 0.12 nm 3 , and B0.38 nm 3 via the rotation pathway (Lamarre and Sung, 1983). The effects of matrix free volume constraints on photochemical reactions in general have been considered (Weiss et al, 1993). The geometrical changes in azobenzene are very large, by molecular standards, and it is thus no surprise that isomerization modifies a wide host of material properties.…”

Section: Molecular Motionmentioning

confidence: 99%