Regioselective Hula-twist photoisomerization of cinnamate esters in organic glass

Schieffer, Stefan; Pescatore, John; Ulsh, Richard; Liu, Robert S. H.

doi:10.1039/b411306n

Cited by 14 publications

(7 citation statements)

References 6 publications

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“…In summary, based on the results reported above, we conclude that naphthylphenylethylenes undergo regioselective HT photoisomerization at the benzylic site when irradiated in low temperature glasses. This conclusion is in agreement with other reported examples of HT photoisomerization, in particular the regioselective HT isomerization of diphenylbutadienes (13) and cinnamates (21) and computational results (22,23). It questions the conclusion of “No HT” of cis ‐ 1 (14) and whether it is appropriate to apply the Occam razor principle in determining reaction mechanisms of concern (8).…”

Section: Resultssupporting

confidence: 93%

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

Yang

Liu²

2007

Photochem & Photobiology

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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.

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Section: Resultssupporting

confidence: 93%

“…The combined results of cis-1 and cis-2 revealed a high regioselectivity for HT photoisomerization favoring the benzylic site. Similar selectivity was, in fact, detected in low temperature photoisomerization of isomers of DPB (13) and a cinnamate ester (21).…”

Section: Resultssupporting

confidence: 65%

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

Yang

Liu²

2007

Photochem & Photobiology

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“…The isomerization degree increased to 0.011 with an increase in the irradiation time up to 100 min. These results suggested that the E – Z isomerization occurred in the solid state, whereas the solid circumstance restricted the isomerization accompanied by a free volume change according to the literature 8. The E – Z isomerization may be attributed to the mobility of the P3HCA chains at room temperature as seen in the local rotation of phenylester polymers 9.…”

Section: Resultssupporting

confidence: 60%

“…These results suggested that the E-Z isomerization occurred in the solid state, whereas the solid circumstance restricted the isomerization accompanied by a free volume change according to the literature. 8 The E-Z isomerization may be attributed to the mobility of the P3HCA chains at room temperature as seen in the local rotation of phenylester polymers. 9 Although the ratio of E-Z isomerization was very small, it is sufficient to make a change of stable polymer chain conformation from extended to bended one.…”

Section: Photoreactionmentioning

confidence: 99%

Effects of double photoreactions on polycoumarate photomechanics

Yasaki

Suzuki

Yazawa

et al. 2011

J. Polym. Sci. A Polym. Chem.

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We established a polymerization condition of 3‐hydroxycinnamic acid, 3HCA, having photoreactive units over all the main chains. The polymers showed two types of photoreaction, that is, intramolecular E–Z isomerization and interchain [2 + 2] cycloaddition. Spectroscopic studies showed that the rate of the isomerization was higher than that of the cycloaddition. Although the original fiber was very brittle, the short‐time UV‐irradiation made the fiber softer and more elastic because the chain bending by the isomerization preferentially occurred. On the other hand, the long‐time irradiation made the fiber harder because of the cross‐linking by the cycloaddition, and simultaneously enhanced the elasticity. Besides we found that the cast film of P3HCA showed a photo‐bending behavior with the convex surface facing the UV‐lamp by the initial E–Z isomerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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“…The result showed that fluorescence spectra of t-1 and t-4 were identical to those of c-1 and c-4, respectively, suggesting that the cis-trans photoisomerization could occur even in organic glass. 15 Emission of c-2 displays a blue shift compared to that of t-2 at 78 K. However, when the temperature was raised to 297 K, the emission from these two isomers became identical. This probably indicates photoisomerization at room temperature (see ESI, Fig.…”

Section: Temperature Dependencementioning

confidence: 93%

Photophysical characterization of cinnamates

Karpkird

Wanichweacharungruang

Albinsson

2009

Photochem Photobiol Sci

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The photophysical properties of five methoxy-substituted 2-ethylhexylcinnamates were studied with experimental and theoretical methods. It was found that the fluorescence quantum yields varied strongly with the substitution pattern of the phenyl ring. A methoxy substitution at the meta position gave strong fluorescence, whereas the para substituted compounds were strongly quenched. This observation could be correlated to corresponding changes in the UV absorption spectra; the two lowest pipi* states were split for the meta-methoxy substituted cinnamate but almost degenerate for the para compound. Semi-empirical quantum mechanical calculations confirmed both the observed state order and the difference in the experimentally determined activation energies for non-radiative decay. This "meta-effect" was also preserved in the trimethoxy-substituted compounds, 2-ethylhexyl-2,4,5- and 2,4,6-trimethoxycinnamate, resulting in strong fluorescence and relatively high barrier for non-radiative decay in the former and weak fluorescence and relatively low barrier for non-radiative decay in the latter. The obtained information shows how the performance of the commercial sunscreen agent, 2-ethylhexyl-para-methoxycinnamate (OMC) might be improved.

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Regioselective Hula-twist photoisomerization of cinnamate esters in organic glass

Abstract: Irradiation of ethyl cis-o-fluorocinnamate and related compounds in organic glass led to two HT-isomerization processes that exhibit a strong preference at C-beta than at C-alpha as shown by low temperature UV absorption spectroscopy and supported by ab initio calculations.

Cited by 14 publications

References 6 publications

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

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

Effects of double photoreactions on polycoumarate photomechanics

Photophysical characterization of cinnamates

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