Stilbene analogs in Hula-twist photoisomerization

Photochem & Photobiology

Liu²

2007

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Photoisomerization reactions of cis isomers of 1-beta-naphthyl-2-phenylethylene, an o-methylated homolog and 1-alpha-naphthyl-2-phenylethylene in organic glasses at liquid nitrogen temperature were studied. Reactions were followed by changes in UV-absorption spectra of the irradiated samples. Formation of an unstable trans-photoproduct was detected only with the o-methylated homolog. The results are consistent with high regioselective Hula-twist photoisomerization at the benzylic sites of the three compounds examined. Calculated data on relative energies of the conformers of both the cis and the trans isomers are in agreement with the suspected conformational population of the starting materials and the photoproducts.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanism of Photoisomerization of 1‐Naphthyl‐2‐Phenylethylenes in Organic Glasses

Photochem & Photobiology

Liu²

2007

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“…Because of its symmetrically substituted rings, for stilbene, it is not possible to ascertain whether the low temperature isomerization of the cis isomer proceeds by way of the OBF process (torsional relaxation) or the volume-conserving HT process. However, if one infers from the results of o-substituted stilbenes (6,15), it seems safe to conclude that in a low temperature glass cis-stilbene also isomerizes by way of HT. Ramamurthy et al described results of photoisomerization of stilbene imbedded in the Na Y zeolite (16), prepared by the interaction of the vacuum heated zeolite with a hexane solution of t-stilbene.…”

Section: Photoisomerization Of Simple Organic Polyenesmentioning

confidence: 99%

“…Changes of absorbance at 305 nm during irradiation (>310 nm) of isomers of stilbene at 77 K in EPA glass: round dots, trans isomer; triangles, cis isomer. The slight rise in absorption during early stage of irradiation of the trans isomer was probably due to local thawing and re-freezing(15).…”

mentioning

confidence: 97%

Mechanisms of Photoisomerization of Polyenes in Confined Media: From Organic Glasses to Protein Binding Cavities^†

Liu

Photochem & Photobiology

Liu

2007

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Photochemical reactivities of model organic systems (stilbene and diphenylbutadiene) in organic glasses were first examined and compared with those in solution and in organized media. These observations were in turn compared with reactivities of polyene chromophores in protein binding cavities (specifically PYP, rhodopsin and bacteriorhodopsin). The obvious conclusion is that the preference for the most volume-conserving Hula-twist mechanism isomerization in organic glasses is because of the close interaction between the guest and the host molecules. In organized media (zeolites, crystals and protein binding cavities), the residual empty space coupled with any specific guest-host interactions that are characteristic of a given system, could lead to involvement of the more volume-demanding one-bond-flip (i.e. torsional relaxation) or bicycle-pedal or an extended HT process in photoisomerization.

“…Other reported examples of 1,2 -diarylethylenes included the following: substituted stilbene( 13 a,b )and other miscellaneous compounds (e.g., 14 ) 11,19,20. …”

mentioning

confidence: 99%

Supramolecular Effects on Mechanisms of Photoisomerization: Hula Twist, Bicycle Pedal, and One‐Bond‐Flip

Liu

Supramolecular Photochemistry

Zhao

et al. 2011

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Photoisomerization in the form of interconversion of the cis and trans isomers around a double bond is the key triggering process for many photosensitive biopigments. 1 They include the visual pigment rhodopsin, the proton pumping bacteriorhodopsin (bR), the phototaxis of photoactive yellow protein (PYP), the seed -germinating trigger protein phytochrome, and many other related pigments. Much spectroscopic and chemical effort has gone into elucidation of the primary processes and products associated with these important pigments. These efforts along with photochemical and theoretical work with simple organic systems 2 have led to improved understanding of mechanisms of photoisomerization, often controlled by host molecules in dictating the exact mechanism participating in a given system. In this chapter, an attempt is made to review medium -controlled photoisomerization processes and to provide an overview of different types of mechanisms that take place in nature and under laboratory conditions. Ever since the fi rst picosecond time -resolved spectroscopic study on events revealing the rapid isomerization following photoexcitation of the visual 547 547 Supramolecular Photochemistry: Controlling Photochemical Processes, First Edition. Edited by V. Ramamurthy and Yoshihisa Inoue.