- Effect of β-cyclodextrin on the thermal Cis-trans isomerization of azobenzenes
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The cis-trans thermal isomerization of p-methyl red (1), o-methyl red (2), and methyl orange (3) was inhibited by β-cyclodextrin (β-CD) at constant pH. Their isomerization rate decreased 4, 8, and 1.67 times, respectively, in a solution containing 0.01 M β-CD. This effect can be attributed to the formation of an inclusion complex between the substrate and β-CD which hinders the rotation of the N=N bond. The isomerization rate of methyl yellow (4), 4-(dimethylamino)-4′-methoxy-azobenzene (5), and naphthalene-1-azo[4′-(dimethylamino)benzene] (6) was not affected by β-CD due to the presence of an organic cosolvent in the solution which displaces the azobenzene from the cavity, and the complex formed is probably equatorial. In addition, the transition state for the isomerization of compounds 1-3 involves rotation and that of 4-6, which have only electron-donating groups, inversion. This latter process brings about less volume change than rotation so it is less hindered by the complexation with β-CD.
- Sanchez, Ana M.,De Rossi, Rita H.
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- Photoinduced, Direct C(sp2)?H Bond Azo Coupling of Imidazoheteroarenes and Imidazoanilines with Aryl Diazonium Salts Catalyzed by Eosin Y
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Herein, a greener approach to the eosin Y-Na2 catalyzed, C(sp2)?H bond azo coupling of imidazoheteroarene with aryl diazonium salts is described, under acid free conditions. This direct photoredox process resulted in the corresponding azo products in good to excellent yields. Besides, this new approach could also be applicable to anilines, which is a poorly reactive substrate by other methods. The main features of this reaction are that it provides high yields and is gram-scalable and applicable to biologically relevant imidazoheteroarenes and -anilines.
- Saba, Sumbal,Dos Santos, Caio R.,Zavarise, Bruno R.,Naujorks, Aline A. S.,Franco, Marcelo S.,Schneider, Alex R.,Scheide, Marcos R.,Affeldt, Ricardo F.,Rafique, Jamal,Braga, Antonio L.
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supporting information
p. 4461 - 4466
(2020/02/25)
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- Method for highly stereoselective preparation of trans-aromatic tertiary amine azo compound
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The invention provides a method for efficient and highly stereoselective preparation of an azo compound through para C-H bond selective activity of an organic aromatic tertiary amine. According to themethod, a Bronsted acid is adopted as a catalyst, an aromatic diazonium tetrafluoroboric acid compound and an organic aromatic tertiary amine compound are adopted as reaction substrates, and an organic solvent is put into a reaction system. The method has the advantages that the catalyst is cheap and easy to obtain, high in substrate applicability, gentle in reaction condition and safe and reliable; the selectivity of a target product is approximate to 100%, the E/Z selectivity of the target product is greater than 99:1, and relatively high yield is achieved; and by adopting the method, the defects that a conventional method for synthesizing different aromatic functional groups to replace organic aromatic tertiary amine azo compounds is harsh in reaction condition, poor in reaction selectivity, tedious in experiment step, low in yield, harmful to the environment since reagents harmful to the environment are used, and the like, can be overcome, and good industrial application prospectscan be achieved. The invention further provides an organic aromatic tertiary amine azo compound with different aryl substituted functional groups.
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Paragraph 0035
(2018/07/30)
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- Hole Catalysis as a General Mechanism for Efficient and Wavelength-Independent Z → E Azobenzene Isomerization
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Whereas the reversible reduction of azobenzenes has been known for decades, their oxidation is destructive and as a result has been notoriously overlooked. Here, we show that a chain reaction leading to quantitative Z → E isomerization can be initiated before reaching the destructive anodic peak potential. This hole-catalyzed pathway is accessible to all azobenzenes, without exception, and offers tremendous advantages over the recently reported reductive, radical-anionic pathway because it allows for convenient chemical initiation without the need for electrochemical setups and in the presence of air. In addition, catalytic amounts of metal-free sensitizers, such as methylene blue, can be used as excited-state electron acceptors, enabling a shift of the excitation wavelength to the far red of the azobenzene absorption (up to 660 nm) and providing quantum yields exceeding unity (up to 200%). Our approach will boost the efficiency and sensitivity of optically dense liquid-crystalline and solid photoswitchable materials. Video Abstract: [Figure presented] Molecular switches are a key ingredient in stimulus-responsive and adaptive materials and devices. Light is among the most attractive stimuli, yet photoswitches often require intense irradiation with high-energy UV light and suffer from inefficient switching as well as fatigue. Thus, the design of robust and efficient photoswitches constitutes an important challenge to boost the sensitivity and energy efficiency of the respective materials and devices. Here, we describe that the isomerization of azobenzene switches from their less stable Z isomer back to the more stable E isomer can be triggered by tiny, i.e., catalytic, amounts of holes caused by chemical, electrochemical, or photochemical oxidation. Our method is generally applicable to the entire family of azobenzene switches, does not require expensive equipment, and allows the reliable and efficient operation of these photoswitches by using red light with quantum efficiencies up to 200%. An efficient and generally applicable method is developed for operating azobenzene molecular switches by using catalytic amounts of holes (via an oxidant) or photons (via a photosensitizer). The pathway allows for indirect Z → E photoisomerization using lower-energy light than required for direct azobenzene excitation and with high quantum yields exceeding unity. The method should help to enhance the sensitivity of photoresponsive materials and devices with high optical density.
- Goulet-Hanssens, Alexis,Rietze, Clemens,Titov, Evgenii,Abdullahu, Leonora,Grubert, Lutz,Saalfrank, Peter,Hecht, Stefan
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supporting information
p. 1740 - 1755
(2018/06/29)
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- Effect of Hydroxide Ion on the Cis-Trans Thermal Isomerization of Azobenzene Derivatives
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Azobenzenes can be photochemically transformed from the trans (E) form, which is thermodynamically more stable, to the cis (Z) form.In the dark, the latter reverts to the former.We report here a kinetic study of the thermal isomerization of methyl orange (1), 4-(dimethylamino)-4'-methoxyazobenzene (2), and naphthalene-1-azo-(4'-(dimethylamino)benzene) (3) in water or in water/cosolvent solution measured at different hydroxide ion concentrations.It was found that the reaction is strongly dependent on the hydroxide ion concentration.The observed rate constant for 2 changes from 1.43E-2 s-1 at NaOH (1.0E-3 M) to 7.7E-4 s-1 at NaOH (0.10 M).These results can be interpreted in terms of the isomerization rate constant of the protonated substrates which is at least 1E8 times faster than that of the neutral compound.
- Sanchez, Ana M.,Rossi, Rita H. de
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p. 2974 - 2976
(2007/10/02)
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