Photoreactions of cisoid 1,4-diphenyl-1,3-butadienes. Direct irradiation in solution and in low temperature organic glass

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

doi:10.1039/b412128g

Cited by 7 publications

(2 citation statements)

References 16 publications

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“…BP and HT mechanisms are expected to reduce volume requirements associated with torsional relaxation by confining most of the motion to the vicinity of the isomerizing double bonds while minimizing the motion of bulky substituents. The HT mechanism has been claimed to account for photoisomerization of several olefins in amorphous glassy media at low temperatures. , Theoretical calculations suggest that 1,3-bond formation in the 2 1 A g states of polyenes at a conical intersection for ultrafast radiationless decay to the ground state − may open a pathway to HT products. − We reported recently that the photoisomerization of cis -1-(2-naphthyl)-2-phenylethene in methylcyclohexane glass at 77 K is conformer specific, giving the one bond twist ( OBT ) product as in solution . Direct cc- DPB to tt- DPB conversion is the only example, thus far, of the BP mechanism under similar conditions…”

Section: Introductionmentioning

confidence: 99%

Photoisomerization of cis,cis-1,4-Diphenyl-1,3-butadiene in the Solid State: The Bicycle-Pedal Mechanism

2006

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The cis-trans photoisomerization of crystalline or powdered cis,cis-1,4-diphenyl-1,3-butadiene (cc-DPB) was studied at room temperature. The progress of the reaction was monitored by fluorescence spectroscopy, powder X-ray diffraction, 1H NMR and HPLC. High conversions (up to 90%) to the trans,trans isomer were observed in a crystal to crystal reaction. Formation of the cis,trans isomer, the sole product obtained in solution and in very viscous glassy media at 77 K is entirely suppressed in the solid state. The observed two-bond photoisomerization is explained by Warshel's bicycle-pedal photoisomerization mechanism (BP). The results are consistent with X-ray diffraction measurements, which have revealed that cc-DPB molecules exist in crystals in edge to face alternating arrays of two conformer structures whose phenyl rings deviate significantly from the plane of the central diene moiety ( approximately 40 degrees ). One of the conformers has the two phenyls in parallel planes and the other in roughly perpendicular planes. Least motion considerations suggest that the former should undergo the two-bond photoisomerization more easily, in agreement with observations that indicate that the reaction proceeds in discrete stages. Recently reported cis,cis- to trans,trans-muconate photoisomerizations in the solid state are proposed to also proceed via the BP mechanism. The reactions are consistent with the X-ray crystal structures of the cis,cis-muconate isomers.

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Section: Introductionmentioning

confidence: 99%

Photoisomerization of cis,cis-1,4-Diphenyl-1,3-butadiene in the Solid State: The Bicycle-Pedal Mechanism

2006

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“…A recent claim that the photoconversion of previtamin D to tachysterol at 92 K in a rigid glass (5/5/1 ether/isopentane/ethyl alcohol) is consistent with the HT mechanism may provide the first experimental demonstration of this process in an amorphous medium . It breathed new life into this concept and has motivated its revival . Experimental evidence appears to be strong for protein-bound chromophores, and the HT has captured the imagination of the photochemical community.…”

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confidence: 99%

Photoisomerization of cis-1-(2-Naphthyl)-2-phenylethene in Methylcyclohexane at 77 K: No Hula-Twist

2005

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The cis-trans photoisomerization of cis-1-(2-naphthyl)-2-phenylethene (c-NPEA and c-NPEB) was studied in methylcyclohexane glass at 77 K. The progress of the reaction was followed by fluorescence spectroscopy. Formation of the extended trans conformer (t-NPEB) is revealed by the growth of sharp vibronic bands on the broad structureless fluorescence spectrum of c-NPE. Principal component analysis with self-modeling of a matrix consisting of spectra generated by irradiation of c-NPE at different excitation wavelengths and spectra of t-NPE measured under the same conditions as a function of excitation wavelength reveals that the diabatic photoisomerization is a completely conformer-specific one-bond twist process: c-NPEB --> t-NPEB. These observations are consistent with observations in solution at ambient temperature. They demonstrate unequivocally that free volume restrictions imposed by the amorphous glassy environment do not open a hula-twist process.

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Beyond the Limits of Atropochirality: Design of Highly Conformationally Restrained Biaryls with Bridgehead Phosphine Oxide

Mele

Babouri

Pirat

et al. 2023

Chemistry A European J

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In the last three decades, reacting sterically congested ortho-substituted arenes to form atropochiral biaryls is an appealing venture and a challenging subject that has garnered significant attention. Therefore, there is interest in developing methods to prepare these compounds. In this study, an efficient approach to produce a new class 2,2' disubstituted biaryls bridgehead phosphine oxides with an unusual topology and exceptional conformational stability is presented. Our methodology demonstrates that depending on the substitution pattern on the aryl moieties, the methanophosphocine backbone could be rigid enough to observe a double atropochirality, resulting in an under covered class of molecules. Notably, our studies revealed that replacing only one hydrogen at the ortho position by a fluorine atom led to sufficiently restricted rotation at temperatures below 80 °C, extending "far away" the limits of atropostability. Finally, our investigations, which employed variable-temperature NMR spectroscopy and DFT calculations, yielded unique insights into the isomerisation mechanism, indicating that the two biaryl motifs are fully independent in spite of their proximity.

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Photoreactions of cisoid 1,4-diphenyl-1,3-butadienes. Direct irradiation in solution and in low temperature organic glass

Cited by 7 publications

References 16 publications

Photoisomerization of cis,cis-1,4-Diphenyl-1,3-butadiene in the Solid State: The Bicycle-Pedal Mechanism

Photoisomerization of cis,cis-1,4-Diphenyl-1,3-butadiene in the Solid State: The Bicycle-Pedal Mechanism

Photoisomerization of cis-1-(2-Naphthyl)-2-phenylethene in Methylcyclohexane at 77 K: No Hula-Twist

Beyond the Limits of Atropochirality: Design of Highly Conformationally Restrained Biaryls with Bridgehead Phosphine Oxide

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