The Experts below are selected from a list of 36048 Experts worldwide ranked by ideXlab platform
Anne Staubitz - One of the best experts on this subject based on the ideXlab platform.
-
Modification of Azobenzenes by Cross-Coupling Reactions
Synthesis, 2021Co-Authors: Anne Staubitz, Melanie Walther, Waldemar Kipke, Sven Schultzke, Souvik GhoshAbstract:AbstractAzobenzenes are among the most extensively used molecular switches for many different applications. The need to tailor them to the required task often requires further functionalization. Cross-coupling reactions are ideally suited for late-stage modifications. This review provides an overview of recent developments in the modification of azobenzene and its derivatives by cross-coupling reactions.1 Introduction2 Azobenzenes as Formally Electrophilic Components2.1 Palladium Catalysis2.2 Nickel Catalysis2.3 Copper Catalysis2.4 Cobalt Catalysis3 Azobenzenes as Formally Nucleophilic Components3.1 Palladium Catalysis3.2 Copper Catalysis3.3 C–H Activation Reactions4 Azobenzenes as Ligands in Catalysts5 Diazocines5.1 Synthesis5.2 Cross-Coupling Reactions6 Conclusion
-
efficient reversible photoisomerisation with large solvodynamic size switching of a main chain poly azobenzene alt trisiloxane
Journal of Materials Chemistry C, 2020Co-Authors: Jan Strueben, Frank D. Sönnichsen, Anne Staubitz, Mathias Dowds, Dennis Bank, David Presa Soto, Falk Renth, F TempsAbstract:A photo-responsive linear poly(azobenzene) with an alternating sequence of azobenzene switching units connected by trisiloxane linkers was synthesised via step-growth polycondensation. By its design, the polymer features a high chromophore load (45 wt%) and a large number (≈130) of photoswitching units per chain. The ensuing photoisomerisation upon UV irradiation with 365 nm light was studied in several solvents and compared to the corresponding free azobenzene siloxane congener. Efficient E → Z isomerisation with high conversion yields was observed for the polymeric and isolated Azobenzenes alike. In the slightly polar solvents tetrahydrofuran (THF) and chloroform, this resulted in a photo-induced decrease in solvodynamic volume of 22% (THF) and 32% (chloroform). In n-hexane, however, a light-triggered collapse of the solvated polymer coil lead to a globular non-solvated form with a 70% decrease in volume. Ultrafast transient electronic absorption measurements showed that the underlying excited-state reaction pathways for the azobenzene units in the polymer main chain are essentially similar to those of the analogous single azobenzene in solution. The data suggest a sequential deactivation via ultrafast internal conversion from the initially excited S2 state to the S1 state, followed by intramolecular vibrational redistribution in the S1 state, and subsequent E → Z isomerisation and deactivation to the electronic ground state. These processes are slowed down only moderately for the main chain azobenzene units compared to the free azobenzene in solution and conform to the accepted scenario for unsubstituted azobenzene. The results explain the efficient, nearly unconstrained isomerisation of the embedded molecular switching units that is highly unusual for a main chain azobenzene polymer. Due to the unique combination of a high chromophore load and large number of photo-switchable units in the main chain in a regular alternating architecture, coupled with a high conversion yield, the poly(azobenzene-alt-trisiloxane) should find applications as photo-responsive material, in particular when large switching amplitudes are essential.
-
Synthesis, Structure, Thermal Behavior and cis/trans Isomerization of 2,2'-(EMe₃)₂ (E = C, Si, Ge, Sn) Substituted Azobenzenes
Molecules, 2019Co-Authors: Jonas Hoffmann, Thomas Josef Kuczmera, Enno Lork, Anne StaubitzAbstract:The synthesis of a series of 2,2′-bis(trimethyltetrel) Azobenzenes is reported, evaluating the different synthetic approaches that different group 14 element substituents individually require. The synthetic access to the carbon substituted congener is very different from the heavier tetrels, in that the key step is the formation of the N=N bond in azobenzene, rather than the azobenzene-C bond. Sn could be introduced with a cross-coupling route, whereas the Si and Ge congeners were prepared by a stannylation-lithiation-electrophilic quenching sequence. Iodo-lithium exchange was also a possible route to obtain the dilithiated species, which can be attributed to the chelating effect of the nitrogen atoms. However, the organo-lead species could not be obtained via these routes. The resulting structures were fully characterized (NMR, FTIR, HRMS and XRD). Furthermore, their thermal properties (TGA and DSC) and their photoswitching behavior in solution (UV-VIS & NMR experiments) were investigated and compared for the different tetrels (C, Si, Ge, Sn)
-
Synthesis, Structure, Thermal Behavior and cis/trans Isomerization of 2,2′-(EMe3)2 (E = C, Si, Ge, Sn) Substituted Azobenzenes
MDPI AG, 2019Co-Authors: Jonas Hoffmann, Thomas Josef Kuczmera, Enno Lork, Anne StaubitzAbstract:The synthesis of a series of 2,2′-bis(trimethyltetrel) Azobenzenes is reported, evaluating the different synthetic approaches that different group 14 element substituents individually require. The synthetic access to the carbon substituted congener is very different from the heavier tetrels, in that the key step is the formation of the N=N bond in azobenzene, rather than the azobenzene-C bond. Sn could be introduced with a cross-coupling route, whereas the Si and Ge congeners were prepared by a stannylation-lithiation-electrophilic quenching sequence. Iodo-lithium exchange was also a possible route to obtain the dilithiated species, which can be attributed to the chelating effect of the nitrogen atoms. However, the organo-lead species could not be obtained via these routes. The resulting structures were fully characterized (NMR, FTIR, HRMS and XRD). Furthermore, their thermal properties (TGA and DSC) and their photoswitching behavior in solution (UV-VIS & NMR experiments) were investigated and compared for the different tetrels (C, Si, Ge, Sn)
-
High-yield lithiation of Azobenzenes by tin-lithium exchange.
Chemistry (Weinheim an der Bergstrasse Germany), 2015Co-Authors: Jan Strueben, Matthias Lipfert, Jan‐ole Springer, Colin A. Gould, Paul J. Gates, Frank D. Sönnichsen, Anne StaubitzAbstract:The lithiation of halogenated Azobenzenes by halogen-lithium exchange commonly leads to substantial degradation of the azo group to give hydrazine derivatives besides the desired aryl lithium species. Yields of quenching reactions with electrophiles are therefore low. This work shows that a transmetalation reaction of easily accessible stannylated Azobenzenes with methyllithium leads to a near-quantitative lithiation of Azobenzenes in para, meta, and ortho positions. To investigate the scope of the reaction, various lithiated Azobenzenes were quenched with a variety of electrophiles. Furthermore, mechanistic (119) Sn NMR spectroscopic studies on the formation of lithiated Azobenzenes are presented. A tin ate complex of the azobenzene was detected and characterized at low temperature.
Peter Saalfrank - One of the best experts on this subject based on the ideXlab platform.
-
electrocatalytic z e isomerization of Azobenzenes
Journal of the American Chemical Society, 2017Co-Authors: Alexis Goulethanssens, David Bléger, Jutta Schwarz, Peter Saalfrank, Manuel Utecht, Dragos Mutruc, Evgenii Titov, Lutz Grubert, Stefan HechtAbstract:A variety of Azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization...
-
quantum chemical investigation of thermal cis to trans isomerization of azobenzene derivatives substituent effects solvent effects and comparison to experimental data
Journal of Physical Chemistry A, 2009Co-Authors: Jadranka Dokic, Stefan Hecht, Marcel Gothe, Jonas Wirth, Maike V Peters, Jutta Schwarz, Peter SaalfrankAbstract:Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis → trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis → trans isomerization of Azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push−pull Azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined valu...
-
on the electronic structure of neutral and ionic Azobenzenes and their possible role as surface mounted molecular switches
Journal of Physical Chemistry B, 2006Co-Authors: Gernot Fuchsel, Jadranka Dokic, Tillmann Klamroth, Peter SaalfrankAbstract:We report quantum chemical calculations, mostly based on density functional theory, on azobenzene and substituted Azobenzenes as neutral molecules or ions, in ground and excited states. Both the cis and trans configurations are computed as well as the activation energies to transform one isomer into the other and the possible reaction paths and reaction surfaces along the torsion and inversion modes. All calculations are done for the isolated species, but results are discussed in light of recent experiments aiming at the switching of surface mounted Azobenzenes by scanning tunneling microscopes.
Maria Ribagorda - One of the best experts on this subject based on the ideXlab platform.
-
control over molecular motion using the cis trans photoisomerization of the azo group
Beilstein Journal of Organic Chemistry, 2012Co-Authors: Estibaliz Merino, Maria RibagordaAbstract:Control over molecular motion represents an important objective in modern chemistry. Aromatic Azobenzenes are excellent candidates as molecular switches since they can exist in two forms, namely the cis (Z) and trans (E) isomers, which can interconvert both photochemically and thermally. This transformation induces a molecular movement and a significant geometric change, therefore the azobenzene unit is an excellent candidate to build dynamic molecular devices. We describe selected examples of systems containing an azobenzene moiety and their motions and geometrical changes caused by external stimuli.
-
control over molecular motion using the cis trans photoisomerization of the azo group
Beilstein Journal of Organic Chemistry, 2012Co-Authors: Estibaliz Merino, Maria RibagordaAbstract:Control over molecular motion represents an important objective in modern chemistry. Aromatic Azobenzenes are excellent candidates as molecular switches since they can exist in two forms, namely the cis (Z) and trans (E) isomers, which can interconvert both photochemically and thermally. This transformation induces a molecular movement and a significant geometric change, therefore the azobenzene unit is an excellent candidate to build dynamic molecular devices. We describe selected examples of systems containing an azobenzene moiety and their motions and geometrical changes caused by external stimuli.
Hiroyuki Asanuma - One of the best experts on this subject based on the ideXlab platform.
-
Construction of photoresponsive RNA for photoswitching RNA hybridization
Organic & biomolecular chemistry, 2010Co-Authors: Hiroshi Ito, Hidenori Nishioka, Xingguo Liang, Hiroyuki AsanumaAbstract:By introducing Azobenzenes into RNA using D-threoninol as a scaffold, a photoresponsive RNA was constructed for efficiently photoswitching the formation and dissociation of RNA/RNA duplexes. The difference in melting temperature (Tm) between the trans and cis forms was so large that efficient photoregulation of RNA hybridization became possible, irrespective of the sequence adjacent to the introduced azobenzene. Compared to the corresponding photoresponsive DNA, the photoregulatory efficiency of azobenzene-modified RNA was even higher due to the drastic destabilization by cis-azobenzene. Structural analysis by NMR and molecular modeling indicated that the planar trans-azobenzene could not stabilize the RNA/RNA duplex with a rigid A-form structure by base pair stacking. However, the large steric hindrance caused by nonplanar cis-azobenzene was quite effective at distorting and destabilizing the duplex structure. We also discuss the effect of methylation of azobenzene at the ortho positions on photoregulation of RNA/RNA duplex formation. This newly constructed photoresponsive RNA has promising applications such as photoswitching of RNA functions.
-
effect of the ortho modification of azobenzene on the photoregulatory efficiency of dna hybridization and the thermal stability of its cis form
Chemistry: A European Journal, 2010Co-Authors: Hidenori Nishioka, Xingguo Liang, Hiroyuki AsanumaAbstract:We synthesized various Azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T(m) (DeltaT(m)) induced by trans-cis isomerization, was significantly improved for all ortho-modified Azobenzenes compared with non-modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized Azobenzenes, 4-carboxy-2',6'-dimethylazobenzene (2',6'-Me-Azo), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest DeltaT(m), whereas the newly synthesized 2,6-Me-Azo (4-carboxy-2,6-dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of DeltaT(m). Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2',6'-Me-Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis-2',6'-Me-Azo was also greatly improved, but not that of cis-2,6-Me-Azo. Solvent effects on the half-life of the cis form demonstrated that cis-to-trans isomerization of all the modified Azobenzenes proceeded through an inversion route. Improved thermal stability of 2',6'-Me-Azo but not 2,6-Me-Azo in the cis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the pi orbital of the nitrogen atom and the methyl group on the distal benzene ring.
-
a supra photoswitch involving sandwiched dna base pairs and Azobenzenes for light driven nanostructures and nanodevices
Small, 2009Co-Authors: Xingguo Liang, Toshio Mochizuki, Hiroyuki AsanumaAbstract:A supra-photoswitch is designed for complete ON/OFF switching of DNA hybridization by light irradiation for the purpose of using DNA as a material for building nanostructures. Azobenzenes, attached to D-threoninols that function as scaffolds, are introduced into each DNA strand after every two natural nucleotides (in the form (NNX)n where N and X represent the natural nucleotide and the azobenzene moiety, respectively). Hybridization of these two modified strands forms a supra-photoswitch consisting of alternating natural base pairs and azobenzene moieties. In this newly designed sequence, each base pair is sandwiched between two azobenzene moieties and all the azobenzene moieties are separated by base pairs. When the duplex is irradiated by visible light, the azobenzene moieties take the trans form and this duplex is surprisingly stable compared to the corresponding native duplex composed of only natural oligonucleotides. On the other hand, when the azobenzene moieties are isomerized to the cis form by UV light irradiation, the duplex is completely dissociated. Based on this design, a DNA hairpin structure is synthesized that should be closed by visible light irradiation and opened by UV light irradiation at the level of a single molecule. Indeed, perfect ON/OFF photoregulation is attained. This is a promising strategy for the design of supra-photoswitches such as photoresponsive sticky ends on DNA nanodevices and other nanostructures.
-
synthesis of azobenzene tethered dna for reversible photo regulation of dna functions hybridization and transcription
Nature Protocols, 2007Co-Authors: Hiroyuki Asanuma, Xingguo Liang, Hidenori Nishioka, Daijiro Matsunaga, Makoto KomiyamaAbstract:A phosphoramidite monomer bearing an azobenzene is synthesized from D-threoninol. Using this monomer, azobenzene moieties can be introduced into oligodeoxyribonucleotide (DNA) at any position on a conventional DNA synthesizer. With this azobenzene-tethered DNA, formation and dissociation of a DNA duplex can be reversibly photo-regulated by cis–trans isomerization of the azobenzene. When the azobenzene takes a trans-form, a stable duplex is formed. After isomerization of the trans-azobenzene to its cis-form by UV-light irradiation (300 nm 400 nm). The introduction of Azobenzenes into the T7 promoter at specific positions also efficiently and reversibly photo-regulates transcription by T7-RNA polymerase. The reversible regulation can be repeated many times without causing damage to the DNA or the azobenzene moiety. These procedures take approximately 10 d to complete. NOTE: In Figure 4 of the version of this article originally published online, the base sequence of the oligonucleotide was incorrect. The figure has been replaced in all versions of the article.
-
azobenzene tethered t7 promoter for efficient photoregulation of transcription
Journal of the American Chemical Society, 2006Co-Authors: Mingzhe Liu, Hiroyuki Asanuma, Makoto KomiyamaAbstract:Azobenzene was additionally introduced into side chain of T7 promoter for the photocontrol of transcription reaction by T7 RNA polymerase (T7 RNAP). When a single azobenzene molecule was introduced into the T7 promoter either at the loop-binding region of the RNAP (−7 to −11 position) or at the unwinding region (−1 to −4 position), transcription was suppressed in the trans-form but proceeded faster in the cis-form. The amount of transcripts after UV irradiation with respect to that in the dark was 1.5−2.0-fold. Kinetic analysis of the transcription reaction revealed that the photoregulatory mechanism was different in these positions. The photoisomerization of an azobenzene at the loop-binding region primarily affected Km. On the other hand, the isomerization of an azobenzene at the unwinding region mainly affected kcat. Still more clear-cut photoregulation was achieved when two Azobenzenes were introduced into both loop-binding and unwinding regions, respectively: transcription proceeded 7.6-fold faster ...
Sang Youl Kim - One of the best experts on this subject based on the ideXlab platform.
-
Rapid and Reversible Gel−Sol Transition of Self-Assembled Gels Induced by Photoisomerization of Dendritic Azobenzenes
Langmuir, 2009Co-Authors: Jung Hak Kim, Myungeun Seo, Yun Jun Kim, Sang Youl KimAbstract:An asymmetric bis-dendritic gelator (1) consisting of an azobenzene dendron and an aliphatic amide dendron was synthesized to achieve a photoresponsive self-assembly. The compound gelled in a wide range of organic solvents, even at concentrations as low as 0.02% (w/v) in cyclohexane. The self-assembled fibrillar network structure was confirmed by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses. The rapid and reversible gel−sol transition by irradiation with UV and visible light was investigated by UV−vis and Fourier transform infrared (FT-IR) spectroscopy, FE-SEM, and XRD analyses. Upon irradiation of the gel with UV, trans-to-cis isomerization of the azobenzene groups occurred, and the gel turned into a sol state. The gel was recovered immediately by the reverse cis-to-trans isomerization after the exposure to visible light. The trans-to-cis isomerization of the Azobenzenes disrupted the hydrogen bonding of azobenzene amide groups,...
-
rapid and reversible gel sol transition of self assembled gels induced by photoisomerization of dendritic Azobenzenes
Langmuir, 2009Co-Authors: Jung Hak Kim, Myungeun Seo, Yun Jun Kim, Sang Youl KimAbstract:An asymmetric bis-dendritic gelator (1) consisting of an azobenzene dendron and an aliphatic amide dendron was synthesized to achieve a photoresponsive self-assembly. The compound gelled in a wide range of organic solvents, even at concentrations as low as 0.02% (w/v) in cyclohexane. The self-assembled fibrillar network structure was confirmed by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses. The rapid and reversible gel−sol transition by irradiation with UV and visible light was investigated by UV−vis and Fourier transform infrared (FT-IR) spectroscopy, FE-SEM, and XRD analyses. Upon irradiation of the gel with UV, trans-to-cis isomerization of the azobenzene groups occurred, and the gel turned into a sol state. The gel was recovered immediately by the reverse cis-to-trans isomerization after the exposure to visible light. The trans-to-cis isomerization of the Azobenzenes disrupted the hydrogen bonding of azobenzene amide groups,...
