A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• diamminetetrakis(thiocyanato)chromate(III)), photochromic dyes have been proposed for such a purpose, mainly from the azobenzene, fulgide or diarylethene families [22]. The latter two are particularly attractive for visible light wavelengths above 400 nm. However, their use is conditioned by their availability and

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• VUF16216, a compound we have previously communicated as a small-molecule efficacy photoswitch for the peptidergic chemokine GPCR CXCR3. A series of photoswitchable azobenzene ligands was prepared through various synthetic strategies and multistep syntheses. Photochemical and pharmacological properties were

• latter one. One of the main reasons is that an azobenzene has a relatively simple structure that can resemble various biaryl moieties of bioactive compounds: two aromatic rings linked with a bridge (e.g., amide, ether, alkane or alkyne) [8]. In the case of azobenzene the bridge is a diazene group (also

• called azo group) and depending on the wavelength of illumination, a linear trans-isomer or a bent cis-isomer can be obtained [9]. If certain biaryl moieties are replaced by an azobenzene (i.e., azologization approach), there is a relatively good chance that one of the resulting photoisomers will have a

In search of visible-light photoresponsive peptide nucleic acids (PNAs) for reversible control of DNA hybridization

• Lei Zhang,
• Greta Linden and
• Olalla Vázquez

Beilstein J. Org. Chem. 2019, 15, 2500–2508, doi:10.3762/bjoc.15.243

• first compounds here reported, may find applications in different fields such as chemical biology, nanotechnology and materials science. Keywords: azobenzene; hemithioindigo; peptide nucleic acid (PNA); photoswitch; visible-light irradiation; Introduction Light-driven control of oligonucleotide

• translation [24][25]. Except a handful of current examples [22][24][26], most of these photoresponsive oligonucleotides are canonical ones where the classical azobenzene is the prominently used photoswitch; although spiropyrans [27], stilbenes [28], diarylethanes [29] and overcrowded alkenes [30] have also

• these precedents use azobenzene-containing PNA to mainly regulate PNA/DNA triplex helix formation by illumination at low wavelengths (360 nm/425 nm) [35][36]. This effect was successfully exploited for the photocontrol of transcription by T7 RNA polymerase in vitro [36]. In fact, such a result opens new

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• an absorption band in the region where the E-isomer absorbs is indicative of the photoinduced Z/E isomerization event, which thus results to be an ultrafast process, as observed for other photoswitches – azobenzene in particular [32]. Upon this initial ultrafast evolution, the transient absorption

Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• revealed within densely packed monolayers of azobenzene on planar gold [16]. In contrast, placing azobenzene inside the cavity of an octahedral cage renders it photochemically inert, stabilizing the typically metastable Z isomer [17]. Similarly, a related cage has recently been shown to induce negative

• affected by their confinement to the surfaces of inorganic nanoparticles. Among other examples, the isomerization kinetics of azobenzene could be tuned by a factor of >5000 by the molecules with which it was co-adsorbed on gold nanoparticles [23], and donor–acceptor Stenhouse adduct (DASA) switches were

• complex of 2 and tetra-o-fluoroazobenzene yields a 1:1 mixture of Z2 and free Z-azobenzene, which is insoluble in water and precipitates from the solution [49]. The Z isomer of 1, however, has much higher water solubility and, following expulsion from the cage, can remain stable in solution. To verify

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• molecules through replacing certain core motives with an bioisosteric azobenzene moiety [57][58][59]. Recent examples have proven successful for receptor ligands by exchange of a linear alkinyl spacer for the zigzag shaped (E)-diazeno group [60][61]. In that instance, the geometry of the lead had to be

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• building blocks both in solution and in the solid state in combination with neutral halogen bonding acceptors, such as lutidines. Therefore, we investigate the photochemistry of a series of azobenzene photoswitches. Upon introduction of iodoethynyl groups, the halogen bonding donor properties are

• azobenzenes with different halogen bonding donor properties are discussed in relation to their changing photophysical properties, rationalized by DFT calculations. Keywords: azobenzene; DFT calculations; fluorine chemistry; halogen bonding; photochemistry; Introduction The halogen bond is an attractive

• ) and E-4,4’-di(iodoethynyl)perfluoroazobenzene (A3) halogen bond donors can be combined with rigid u-shaped anthracene building blocks, bearing two 3,5-lutidine acceptors in 1 and 8 positions, to form self-assembled boxes of 25–30 Å length in solution and in the solid state [35]. We chose azobenzene

Morphology-tunable and pH-responsive supramolecular self-assemblies based on AB₂-type host–guest-conjugated amphiphilic molecules for controlled drug delivery

• Yang Bai,
• Cai-ping Liu,
• Di Chen,
• Long-hai Zhuo,
• Huai-tian Bu and
• Wei Tian

Beilstein J. Org. Chem. 2019, 15, 1925–1932, doi:10.3762/bjoc.15.188

• utilized as host units to construct these stimuli-responsive supramolecular self-assemblies [21][22][23][24][25][26][27]. For example, β-CD can form inclusion complexes with guests such as azobenzene [28][29], ferrocene [30][31] and benzimidazole [32][33][34] to construct light-, redox-, and pH-responsive

Nanopatterns of arylene–alkynylene squares on graphite: self-sorting and intercalation

• Tristan J. Keller,
• Joshua Bahr,
• Kristin Gratzfeld,
• Nina Schönfelder,
• Marcin A. Majewski,
• Marcin Stępień,
• Sigurd Höger and
• Stefan-S. Jester

Beilstein J. Org. Chem. 2019, 15, 1848–1855, doi:10.3762/bjoc.15.180

• solvent molecules are sometimes resolved as intercalation adducts in STM of self-assembled monolayers. On the other hand, reports on intercalated TCB molecules are rather rare. Two exceptions are the observations of TCB in monolayers of arylene–alkynylene pentagons as well as triphenylene/azobenzene-based

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• , cyanine and azobenzene have also been reported [18][19][20][21][22][23][24]. High order oligorotaxanes with a multiple number of α- or β-CDs threaded through polymer chains have also been prepared [25][26][27][28]. The interlocked CDs have been shown to provide an interesting insulating effect to π

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• , while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA’s are known to exhibit extremely fast cis→trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes

• rate of isomerization by three orders of magnitude [2][3][4]. To keep the reacting azobenzene molecule at a distance of about 14 Å from the surface, it is not directly absorbed onto the surface but mounted on a carefully designed molecular framework. This approach was named the platform approach [5

• parameter controlling the cis–trans rate acceleration of azobenzenes and not the length of the spacer [1]. A full conjugation path from the azobenzene on top through the ethynyl spacer and the platform to a bulk gold surface shortens the half-life of the metastable cis-isomer from days to seconds even

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

• chemistry. Here, we present the synthesis of a foldable container consisting of two different types of Lissoclinum macrocyclic peptides which are connected via two azobenzene units. The container is controllable by light: irradiation with UV light causes a switching process to the compact cis,cis-isomer

• the high dispersion energy in the compact cis,cis-isomer. Keywords: azobenzene; macrocycles; molecular switch; Introduction In supramolecular chemistry rigid scaffolds are required to arrange different recognition units in predefined distances and spatial orientation to each other [1]. One example

• molecules which can be reversibly changed between two isomers of different structures [26][27][28][29]. One prominent switching unit is azobenzene and its derivatives [30][31][32][33][34][35][36][37][38][39][40][41]. The trans-isomer features a stretched and the cis-isomer has a compact geometry. In general

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

• platform (triazatriangulenium (TATA)) which adsorbs on the gold surface, with an acetylene spacer standing upright, like a post in the middle of the platform and the azobenzene unit mounted on top. The rate acceleration is due to a very peculiar thermal singlet–triplet–singlet mechanism mediated by bulk

• 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

• ” (triazatriangulenium) platforms which adsorb on Au(111) surfaces. A spacer, such as an ethynyl group is connected to the central carbon atom like a post and the azobenzene is mounted on top of the spacer. After preparation of an ordered self-assembled monolayer on gold, the azobenzene units are freestanding upright on

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

• was only achieved when the CD ligand and the divalent azobenzene linker were premixed to generate the host–guest complex. This solution was then added to the AuNR leading to a ligand exchange preferentially at the ends and therefore to the linear arrangement of AuNR. If the AuNR were first end

• -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

• -to-end aggregates. Ma et al. suggested that the host–guest interaction is not strong enough to assemble the particles if not preformed. Yet, this is not consistent with publications that report photoswitchable azobenzene–CD interaction on surfaces [28], in hydrogels [29], the assembly of CD vesicles

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• azobenzene [58]. The cyclopalladation process was proved to be a highly regioselective process and the observed palladation rate was faster compared to the conventional solution-phase method. An equimolar amount of 4'-(N,N-dimethylamino)-4-nitroazobenzene and Pd(OAc)2 in the presence of 25 μL of glacial

• of unsymmetrically substituted azobenzene [58]. a) Schematic representation for the construction of a [2]rotaxane. b) Chiu’s ball-milling approach for the synthesis of [2]rotaxanes. Mechanochemical synthesis of the smallest [2]rotaxane. Solvent-free mechanochemical synthesis of pillar[5]arene

Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

• Jennifer Klose,
• Tobias Severin,
• Peter Hahn,
• Alexander Jeremies,
• Jens Bergmann,
• Daniel Fuhrmann,
• Jan Griebel,
• Bernd Abel and
• Berthold Kersting

Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81

• represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, L' is an azobenzene carboxylate co-ligand, and M = Cd(II), Ni(II) or Zn(II), is reported. A series of new complexes were synthesized, namely [M2L(μ-L')]+ (L' = azo-H, M = Cd (1), Ni (2); L' = azo-OH, M = Zn (3), Ni (4); L' = azo-NMe2, M

• 5–8 display an isostructural series of compounds with bridging azobenzene carboxylates in the trans form. The paramagnetic Ni complexes 2, 4 and 7 reveal a weak ferromagnetic exchange interaction with magnetic exchange coupling constant values between 21 and 23 cm−1 (H = −2JS1S2). Irradiation of 1

• with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form. Keywords: azobenzene carboxylates; cadmium; complexes; macrocyclic ligands; nickel; zinc; Introduction The macrocyclic N6S2 donor ligand H2L is an effective dinucleating ligand that supports a large number

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

• detailed receptor examination. In the presented work, we summarize the synthesis, photochromic properties and in vitro characterization of azobenzene-based photochromic derivatives of published 5-HT3R antagonists. Despite reported proof of principle of direct azologization, only one of the investigated

• derivatives showed antagonistic activity lacking isomer specificity. Keywords: azobenzene; 5-HT3R; ion currents; photopharmacology; serotonin; Introduction 5-Hydroxytryptamine (5-HT), commonly known as serotonin [1][2] or enteramine [3][4], is a monoamine neurotransmitter and hormone which is produced in

• 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

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

• molecular switches in photo and mechanoresponsive macromolecules and other smart materials. Keywords: bridged azobenzene; diazocine; mechanophor; oxidative C–C coupling; photochrome; reductive azo cyclization; Introduction The field of photoresponsive materials is of growing interest [1][2][3]. Several

• 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

• photostationary states (PSS (385 nm): 25–30% trans). The electronic decoupling of the azobenzene unit and the oxygen and nitrogen containing functional groups (OH, OR, N3, NH2) was achieved by insertion of one or two CH2 groups. Thereby, the switching efficiencies were increased by about a factor of two (PSS (385

Olefin metathesis in multiblock copolymer synthesis

• Maria L. Gringolts,
• Yulia I. Denisova,
• Eugene Sh. Finkelshtein and
• Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2019, 15, 218–235, doi:10.3762/bjoc.15.21

• multiple click reactions of the diazido-telechelic PBD with a dialkynyl-containing azobenzene chromophore. The newly formed triazole moieties can tune and improve the photoresponsive properties of PBD. α,ω-Functional telechelic polymers also can be synthesized by acyclic diene metathesis (ADMET

Fabrication of supramolecular cyclodextrin–fullerene nonwovens by electrospinning

• Hiroaki Yoshida,
• Ken Kikuta and
• Toshiyuki Kida

Beilstein J. Org. Chem. 2019, 15, 89–95, doi:10.3762/bjoc.15.10

• functionalize such fibers is to use host–guest inclusion complexes in CD electrospinning. To date, Uyar and Celebioglu have reported electrospinning of two different inclusion complexes: hydroxypropyl-β-CD (HP-β-CD)–tricosan [16] and HP-β-CD–azobenzene inclusion complexes [17]. Although such complexes are

Lectins of Mycobacterium tuberculosis – rarely studied proteins

• Katharina Kolbe,
• Sri Kumar Veleti,
• Norbert Reiling and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2019, 15, 1–15, doi:10.3762/bjoc.15.1

• was originally published in the thesis of K. Kolbe [12] and has been slightly modified for this article). Structure of FimH CRD with a docked azobenzene mannobioside showing the aromatic aglycon and the tyrosine residues, Y48 and Y137, of the protein in close proximity. The figure is a slightly

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• ), a phenomenon that we have recently also observed for reductively and oxidatively induced azobenzene Z→E isomerization [44][45]. Mechanism of the electrochemical isomerization In the literature, either mono- [7][18][22][23][46] or bis-oxidized [9][10][11] open DAEs have been reported and discussed [8

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

• synthesis of diazocines opens a novel and convenient access to unsymmetrically substituted diazocines. Keywords: Baeyer–Mills reaction; bridged azobenzene; diazocine; reductive azo condensation; unsymmetrically functionalized S-diazocines; Introduction Photopharmacology is a promising, rapidly evolving

• derivatives [18][19]. Towards the synthesis of S-diazocines (Figure 1), two general approaches could be derived from the well investigated azobenzene preparation methods: a) Reductive coupling of two nitro groups or b) oxidative coupling of two amino groups [20]. To cleanly form N=N bonds by reduction of

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

• activation. In 1941, Kharasch and Fields applied a cobalt salt as the catalyst for the homocoupling of Grignard reagents [28]. After 15 years, Murahashi discovered a cobalt-catalyzed chelation-assisted ortho C–H carbonylation of azobenzene and imines as the preliminary example of directing group assisted C–H

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• reported (Figure 16) [85]. However, the axle bears a central azobenzene photoswitch, who’s E/Z-transitions can be controlled by light. The redox-switchable shuttle works as previously described and the position of the wheel can be controlled by oxidation or reduction. However, the configuration of the

• azobenzene strongly influences the life time of each redox-switching state. In the (E)-form, the wheel can easily move between the TTF and dihydroxynaphthalene station. In the Z-form, this movement is sterically hindered and slowed down. The wheel cannot shuttle to its energetically preferred station. This