An azobenzene container showing a definite folding – synthesis and structural investigation

• Abdulselam Adam,
• Saber Mehrparvar and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156

• . As expected, the connection of the two macrocycles 2a and 3a via two trans-azobenzenes (trans,trans-10) results in a longer distance between the macrocycles compared to a connection via two cis-azobenzenes (cis,cis-10). The distance between the centers of the two macrocycles in the trans,trans-isomer

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• Abstract Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a

• gold. To investigate this mechanism further and to examine scope and limitation of the “spin-switch catalysis” we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis-configuration. Upon irradiation with light of 405 nm the cis-configuration isomerizes

• coupling to a bulk gold surface via a conjugated linker over 11 bonds and 14 Å [11]. Thermal cis→trans isomerizations of azobenzenes are usually slow with half-lives of the trans-isomer within the range of hours to days at room temperature (parent azobenzene: 4–5 d at 25 °C) [12]. Rotation around the N=N

Reversible end-to-end assembly of selectively functionalized gold nanorods by light-responsive arylazopyrazole–cyclodextrin interaction

• Maximilian Niehues,
• Patricia Tegeder and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2019, 15, 1407–1415, doi:10.3762/bjoc.15.140

• cycles. By the introduction of AAP, previous disassembly limitations based on the photostationary states of azobenzenes could be solved. The combination photoresponsive interaction and selectively end-functionalized nanoparticles shows significant potential in the reversible self-assembly of inorganic

• azobenzenes that form inclusion complexes with α- or β-CD exclusively in the trans configuration, not in the cis configuration [26]. This light-responsive interaction has been recently applied by Ma et al. for the end-to-end assembly of AuNR [27]. However, the system showed some limitations as the assembly

• -functionalized with the CD, no assembly could be observed after addition of the divalent azobenzene linker. Moreover, the assemblies could only once be disassembled by the combination of UV irradiation and physical forces by sonication. The light-induced back-isomerization of azobenzenes did not form similar end

Azologization of serotonin 5-HT₃ receptor antagonists

• Karin Rustler,
• Galyna Maleeva,
• Piotr Bregestovski and
• Burkhard König

Beilstein J. Org. Chem. 2019, 15, 780–788, doi:10.3762/bjoc.15.74

• hybrid biomolecule. In this context, various photochromic scaffolds including dithienylethenes, fulgi(mi)des, and azobenzenes are investigated [31][42]. The latter ones were already discovered in 1834 by E. Mitscherlich [43] but it took around another 100 years till G. S. Hartley [44] revealed their

• photo-induced trans–cis isomerization representing the time of birth of the azobenzene photoswitch. Benefiting of their accessible synthesis, large change in polarity and geometry upon switching, excellent photochromic properties and tuneability, azobenzenes are amongst the most widely used photochromic

• trans-isomer as biologically active configuration whereas its bent cis-isomer should be inactive. Synthesis of the quinoxaline-based azobenzenes The synthesis of the unsubstituted quinoxaline-based azobenzene derivatives 5a and 5b is based on a Baeyer [62]–Mills [63] reaction (Scheme 2). Therefore

Synthesis of functionalized diazocines for application as building blocks in photo- and mechanoresponsive materials

• Widukind Moormann,
• Daniel Langbehn and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 727–732, doi:10.3762/bjoc.15.68

• mechanophores such as azobenzene [4][5][6][7][8], diarylethene [9][10][11][12][13] and spiropyrans [14][15][16][17][18] have been investigated as photoswitchable building blocks. Bridged azobenzenes also known as diazocines exhibit excellent photochemical properties but applications are limited and suitably

• functionalized compounds are rare [19][20][21][22][23]. In contrary to azobenzenes, diazocines 1 are stable in their cis configuration. The bent cis isomer is less prone to π–π stacking which is known to reduce the switching efficiency (Figure 1a) [19][24]. The reverse stability of the cis and trans isomers in

• azobenzenes and diazocines should allow reciprocal applications in mechanoresponsive materials and in photopharmacology [25]. Another advantage of diazocines over azobenzenes is their switchability in the visible range (400 nm cis → trans, 530 nm trans → cis) preventing deterioration of the material or tissue

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• 10.3762/bjoc.14.257 Abstract Herein we report a reliable method to synthesize mono-functionalized S-diazocines in reproducible yields via intramolecular Baeyer–Mills reactions. Diazocines exhibit excellent photoswitchable properties. As opposed to azobenzenes they are more stable in their cis

• configuration. Particularly in photopharmacology mono-functionalized diazocines should be potentially useful and superior to the frequently used azobenzenes because the sterically more demanding cis configuration should be inactive, and the slender trans configuration should fit in a tight binding pocket of a

• field in medicine aiming at the development of drugs whose biological activity can be controlled with light [1][2][3][4]. There are several reported pharmacologically active compounds containing azobenzenes as photoswitchable units [5][6][7]. In most cases these drugs are active in the more stable trans

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• alkynes with azobenzenes 1 to synthesize dialkenated products 2 (Scheme 4) [32]. The reaction resulted in an anti-addition of the C–H bond with alkynes using the cobalt(I) catalysts CoH(N2)(PPh3)3 or CoH3(PPh3)3 under neat reaction conditions. After fifteen years, Yoshikai and co-workers developed a low

• , Prabhu and co-workers also reported a Co-catalyzed hydroarylation reaction of maleimides with indoles [86]. The hydroarylation of maleimides was further demonstrated with different arenes (Scheme 31). Thus, azobenzenes 1 were subjected to alkylation reaction with maleimides to form a variety of

• C–H carbonylation. Hydroarylation by C–H activation. Pathways for cobalt-catalyzed hydroarylations. Co-catalyzed hydroarylation of alkynes with azobenzenes. Co-catalyzed hydroarylation of alkynes with 2-arylpyridines. Co-catalyzed addition of azoles to alkynes. Co-catalyzed addition of indoles to

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

• Andreas H. Heindl,
• Raffael C. Wende and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

• Andreas H. Heindl Raffael C. Wende Hermann A. Wegner Institut für Organische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392 Gießen, Germany 10.3762/bjoc.14.106 Abstract The understanding and control of the light-induced isomerization of azobenzenes as one of the most

• important classes of molecular switches is crucial for the design of light-responsive materials using this entity. Herein, we present the stabilization of metastable (Z)-azobenzenes by London dispersion interactions, even in the presence of comparably stronger hydrogen bonds in various solvents. The Z→E

• isomerization rates of several N-substituted 4,4′-bis(4-aminobenzyl)azobenzenes were measured. An intramolecular stabilization was observed and explained by the interplay of intramolecular amide and carbamate hydrogen bonds as well as London dispersion interactions. Whereas in toluene, 1,4-dioxane and tert

Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

• Reji Thomas and
• Nobuyuki Tamaoki

Beilstein J. Org. Chem. 2016, 12, 2211–2215, doi:10.3762/bjoc.12.212

• solvent etc. [45][46][47][48][49][50]. Although we could separate the enantiomers of all these chiral cyclic azobenzenes, the experimental determination of the absolute stereostructure by X-ray diffraction was difficult due to the lack of heavy elements. In the present study, we demonstrate the

The role of alkyl substituents in deazaadenine-based diarylethene photoswitches

• Christopher Sarter,
• Michael Heimes and
• Andres Jäschke

Beilstein J. Org. Chem. 2016, 12, 1103–1110, doi:10.3762/bjoc.12.106

• ][18][19][20][21]. Most reported applications use azobenzenes, while diarylethenes, spiropyrans, fulgides and hemithioindigos are applied less frequently [18][19][20][21][22][23][24][25][26][27][28][29][30]. Diarylethenes are an important class of photoswitches. Originally developed for optical

Azobenzene-based inhibitors of human carbonic anhydrase II

• Leander Simon Runtsch,
• David Michael Barber,
• Peter Mayer,
• Michael Groll,
• Dirk Trauner and
• Johannes Broichhagen

Beilstein J. Org. Chem. 2015, 11, 1129–1135, doi:10.3762/bjoc.11.127

• of the synthesized azobenzenes, we found that the electronic structure does not strongly affect inhibition. Taken together, all compounds are strong blockers of hCAII with Ki = 25–65 nM that are potentially photochromic and thus combine studies from chemical synthesis, crystallography and enzyme

• (Figure 1b) [5]. Furthermore, sulfonamide-containing azobenzenes exhibit affinity and blocking ability for hCAII (Figure 1c) [6]. With our knowledge in azobenzene chemistry and photopharmacology, we aimed to further understand how electronic substitution patterns on azobenzenes correlate to changes in

• enzyme affinity. Results and Discussion Azobenzenes can be synthesized by a variety of known chemical transformations [8]. Among them the most widely used is the diazotization of aniline, followed by trapping of the diazonium salt with an electron-rich aromatic compound (such as anilines and phenols

Synthesis of photoresponsive cholesterol-based azobenzene organogels: dependence on different spacer lengths

• Yuchun Ren,
• Bin Wang and
• Xiuqing Zhang

Beilstein J. Org. Chem. 2015, 11, 1089–1095, doi:10.3762/bjoc.11.122

• have been utilized in supramolecular systems [19]. Examples of several cholesterol-linked azobenzenes with gel–sol reversible changes also have been studied [20][21][22][23]. R. Zentel found that the photoinduced reversible gel–sol changes between isotropic and anisotropic gels of a class of

Synthesis and characterization of a new photoinduced switchable β-cyclodextrin dimer

• Florian Hamon,
• Claire Blaszkiewicz,
• Marie Buchotte,
• Estelle Banaszak-Léonard,
• Hervé Bricout,
• Sébastien Tilloy,
• Eric Monflier,
• Christine Cézard,
• Laurent Bouteiller,
• Christophe Len and
• Florence Djedaini-Pilard

Beilstein J. Org. Chem. 2014, 10, 2874–2885, doi:10.3762/bjoc.10.304

• to the guest molecules [9][10]. These cyclodextrins linked by ester [11], thioether [12][13][14][15][16], urea [17][18][19], or triazole [20] moieties have been previously described. In addition, aromatic azobenzenes are excellent candidates as molecular switch linkers as they have two forms, namely

Photoswitchable precision glycooligomers and their lectin binding

• Daniela Ponader,
• Sinaida Igde,
• Marko Wehle,
• Katharina Märker,
• Mark Santer,
• David Bléger and
• Laura Hartmann

Beilstein J. Org. Chem. 2014, 10, 1603–1612, doi:10.3762/bjoc.10.166

• oligomer shape and concomitantly in the sugar ligands accessibility. Indeed, dramatic shrinking of rigid-rod polymers for example, occurs upon photoirradiation when several azobenzenes are introduced in the main-chain, the embedded photoswitches acting as hinges [17][18]. In the present study, an

• ), whereas 10% of E,E-isomer did not isomerize (see Supporting Information File 1 for more details). This values correspond to a total amount of 80% of Z-azobenzenes in the PSS mixture, in accordance to the 78% of Z-azobenzene found in the PSS solution of Azo-Gal(1,3)-3 upon irradiation at 360 nm, indicating

Amino-substituted diazocines as pincer-type photochromic switches

• Hanno Sell,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1–7, doi:10.3762/bjoc.9.1

• Abstract Azobenzenes are robust, reliable, and easy to synthesize photochromic switches. However, their high conformational flexibility is a disadvantage in machine-like applications. The almost free rotation of the phenyl groups can be restricted by bridging two ortho positions with a CH2CH2 group, as

• ; molecular pincer; molecular switches; photochromic compound; Introduction Azobenzenes probably are the most frequently used photochromic switches in chemistry. They are employed as molecular actuators to drive a number of dynamic machine-like functions [1]. To achieve sophisticated engineering tasks such

• or with other molecules. Therefore, we explore different approaches to prepare diazocine derivatives. Since the nomenclature is not unambiguous and, hence, potentially confusing, we refer to 5,6-dihydrodibenzo[c,g][1,2]diazocine derivatives as 2,2’-ethylene-bridged azobenzenes (EBABs). Results and

Design and synthesis of a photoswitchable guanidine catalyst

• Philipp Viehmann and
• Stefan Hecht

Beilstein J. Org. Chem. 2012, 8, 1825–1830, doi:10.3762/bjoc.8.209

• rac-lactide in order to explain the findings. Keywords: azobenzenes; guanidines; molecular switches; organocatalysis; photochromism; ring opening polymerization; Introduction The macroscopic properties of a given polymer, e.g., the glass-transition temperature, morphology, density and tensile

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• .8.119 Abstract 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

• external stimuli. Keywords: azobenzenes; molecular switches; nanomachines; photoisomerization; Review This review is based on an article published in 2009 in Anales de Química (Real Sociedad Española de Química) [1]. Azobenzene was described for the first time in 1834 [2] and one century later, in 1937

• switches described so far. The azobenzenes are organic molecules that present two aromatic rings linked by an azo group (N=N). They have properties that have led to some applications of great importance, mainly for the chemical industry. The azobenzenes are highly coloured compounds and belong to the group

The effect of the formyl group position upon asymmetric isomeric diarylethenes bearing a naphthalene moiety

• Renjie Wang,
• Shouzhi Pu,
• Gang Liu and
• Shiqiang Cui

Beilstein J. Org. Chem. 2012, 8, 1018–1026, doi:10.3762/bjoc.8.114

• molecules must possess the following properties: (1) low cytotoxicity, (2) high sensitivity, (3) easy chemical modification. In the past few decades, various types of photochromic molecules, such as fulgides, spiropyranes, azobenzenes, and diarylethenes, have been developed [2][23][24][25][26][27][28][29

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• devices. Many different organic photochromic molecules are known in photochemistry, such as azobenzenes, stilbenes, spiropyranes, fulgides, diarylethenes and chromenes among many others (Figure 1) [16]. The photochromic processes that take place when such compounds are illuminated can be divided in three

• to the initial isomer even at elevated temperatures (e.g., fulgides and diarylethenes). ● T-type (thermally reversible type); the photogenerated isomer thermally reverts to the initial form (e.g., azobenzenes, stilbenes or spiropyranes). One of the most used organic chromophores for optical switching

• applications are certainly azobenzenes. Azobenzene, a photochromic T-type system, exhibits a reversible isomerisation process between its trans and cis isomers of different stability. In this process, the photoreaction simply causes the rearrangement of the electronic and nuclear structure of the molecule

Diarylethene-modified nucleotides for switching optical properties in DNA

• Sebastian Barrois and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2012, 8, 905–914, doi:10.3762/bjoc.8.103

• [5][6][7][8], azobenzenes [9], spirobenzopyrans [10] and diarylethenes [11] represent the most promising candidates for introducing photoswitching functionality into biopolymers, and thereby for regulating biological activity [12][13]. Azobenzenes were designed and synthesized as artificial

• polymerase reaction [18], photocontrol DNA triplex formation [19], and drive photon-fueled DNA-based nanomachines [20][21]. Concerning the extent of structural change, the cis–trans isomerization of azobenzenes behaves much simpler than the ring opening of spiropyrans to merocyanines. In the latter case not

Building photoswitchable 3,4'-AMPB peptides: Probing chemical ligation methods with reducible azobenzene thioesters

• Gehad Zeyat and
• Karola Rück-Braun

Beilstein J. Org. Chem. 2012, 8, 890–896, doi:10.3762/bjoc.8.101

• 4,5,6-trimethoxy-2-mercaptobenzyl auxiliary as well as the Nα-2-mercaptoethyl auxiliary. Thus, 3,4'-AMPB derivatives/peptides proved to be significantly less prone to reduction by aliphatic and aromatic thiols than were the 4,4'-AMPB compounds. Keywords: acyl transfer auxiliary; azobenzenes; ligation

• ; molecular switches; peptides; redox chemistry; Introduction Optical switches not only offer the advantage to elucidate, but also to control biological processes with high spatial and temporal resolution by using light, either in vitro or in vivo [1]. In this context, azobenzenes remain a privileged class

• thiol molecule at the N-sulfenohydrazodiarene B, yielding the symmetric disulfide and the respective hydrazine thioester or hydrazine peptide (Scheme 3, reaction 2). The reduction of diazene units by thiols has been intensively studied in the past for electron-poor azobenzenes or azodicarboxylates, en

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• -azobenzenes did not show any photochromicity. Therefore, in recent examples in the literature the azo-units have been dissected by incorporation of biphenyl units. Hecht and co-workers investigated the effect of the electronic coupling in detail and showed that the incorporation of ortho-methyl groups on the

• . Isomerization studies Compounds 13, 15, 16 and 2 were analyzed by UV spectroscopy. All of them exhibit the typical behavior of azobenzenes, with a strong absorption at 330 nm for the π–π* transition and a weak absorption at 430 nm for the n–π* transition (Figure 3). For compounds 16 and 2 an increased

Molecular switches and cages

• Dirk Trauner

Beilstein J. Org. Chem. 2012, 8, 870–871, doi:10.3762/bjoc.8.97

• photoswitches continue to emerge and “old friends”, such as azobenzenes are constantly improved and optimized. This is not only true with respect to their photophysical properties but also with regard to their synthetic accessibility. Indeed, as molecular switches are applied in ever-increasing quantities, the

• features include their absorption spectra, conductivity, geometry and bistability, as well as their polarity, solubility, efficacy, or catalytic activity. Photoswitches are covered extensively, ranging from diarylethenes (Pu, Wagenknecht) to dihydroazulenes/vinylheptafulvenes (Nielsen) and azobenzenes

• (Rück-Braun, Hoppmann). Two reviews discuss cis-azobenzenes with rapid thermal isomerization kinetics (Velasco), and highlight the azobenzene moiety as one of the smallest light-driven molecular motors conceivable (Merino). Issues of bistability are also addressed in an account on shape-persistent

Azobenzene dye-coupled quadruply hydrogen-bonding modules as colorimetric indicators for supramolecular interactions

• Yagang Zhang and
• Steven C. Zimmerman

Beilstein J. Org. Chem. 2012, 8, 486–495, doi:10.3762/bjoc.8.55

• and exhibit a range of vivid colors. Furthermore, the application of azobenzenes in chemistry is quite broad and includes their use as switches [42], in nonlinear optics [43], sensing devices [44], and in nanostructured films for optical storage [45]. Although this work does not focus on switching

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• -electronic devices, e.g. as logic gates [1]. In the life sciences, functionalized azobenzenes [6], hemithioindigos [7][8] and fulgimides [9][10] among other classes of photoswitches, have already proven to be valuable tools for photo-controlling the structure and function of complex biomolecules [6][7][8][9