Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• photochemical reactions, including photoisomerization, photocyclodimerization, and H2 evolution [7][23]. Chirality induction in a prochiral guest via photochemical reactions is a delightful approach. This can not only transfer the chirality of the host cavity to the molecular photoproduct via excited-state

• supramolecular chiral interactions but can also improve the photoenantiodifferentiating proficiency of the host. To prove this concept, Inoue et al. investigated the photoisomerization of (Z)-cyclooctene ((Z)-6) to the chiral E-isomer (E)-6 in an aqueous methanol solution through host–guest interactions between

• . Cibulka et al., Catalytic Photooxidation of 4‐Methoxybenzyl Alcohol with a Flavin–Zinc(II)‐Cyclen Complex, Chemistry – A European Journal, John Wiley and Sons. Enantiodifferentiating Z–E photoisomerization of cyclooctene sensitized by a chiral sensitizer as the host. Adapted with permission from [24

Vicinal difluorination as a C=C surrogate: an analog of piperine with enhanced solubility, photostability, and acetylcholinesterase inhibitory activity

• Yuvixza Lizarme-Salas,
• Alexandra Daryl Ariawan,
• Ranjala Ratnayake,
• Hendrik Luesch,
• Angela Finch and
• Luke Hunter

Beilstein J. Org. Chem. 2020, 16, 2663–2670, doi:10.3762/bjoc.16.216

• dual mechanism-of-action treatment for Alzheimer’s disease [4][10][11][12][13]. However, piperine (1) has some limitations as a drug lead. For example, it has poor solubility, and it is susceptible to photoisomerization of the conjugated system [15][16][17]. This prompted us to consider whether there

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• . Photoisomerization of the azo unit between cis and trans is achieved upon irradiation with 505 nm (trans→cis) and 435 nm (cis→trans). Concurrently with the isomerization and coordination/decoordination, the spin state of the Ni ion switches between singlet (low-spin) and triplet (high-spin). Previous studies have

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• primarily engaged in synthesizing various types of such multichromophoric systems to compare their photochemistry in detail [9][10][11][12][13][14][15]. Since in acyclic enones like C, E/Z-photoisomerization becomes one of the major energy dissipation pathways, we selected rigid bicyclic multichromophoric

• in acetonitrile at rt. Quantitative photoisomerization of 1 to 2 in all types of solvents. Accepted mechanistic pathway for the photochemical transformations of 1. Photochemical reactions of 3a–g. Irradiation using a Hanovia medium pressure 450 W lamp with a pyrex filter; a) conditions and yields are

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• -epoxypropane to propylene carbonate using an aluminum porphyrin and a photoresponsive ligand. The catalytic activity of the metal porphyrin depended on the axial coordination of an azostilbene and coordination of the latter ligand was controlled by photoisomerization of the stilbene unit [9]. Hecht et al

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• obtained in earlier studies [5][6][14][15][16]. Moreover, the occurrence of the Z/E-photoisomerization concomitant of the first stage of the rearrangement can be traced at small irradiation times (less than 1–2 min) of fulgide 3Z in acetonitrile solution with light of 436 nm. As shown in Figure 4 a slight

• ) (2.5 × 10−5 M, T = 293 K). Electronic absorption spectra of fulgimide 8E in acetonitrile solution before (1) and after irradiation with light of 365 nm for 10 (2), 20 (3), 30 (4), 60 (5), 90 (6), 120 (7), 180 (8), 260 (9) and 320 s (10) (2.5 × 10−5 M, T = 293 K). Photoisomerization of 2-benzo[b]thienyl

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes

• Dragana Vuk,
• Irena Škorić,
• Valentina Milašinović,
• Krešimir Molčanov and
• Željko Marinić

Beilstein J. Org. Chem. 2020, 16, 1092–1099, doi:10.3762/bjoc.16.96

• . Further, the separated isomers of 3–7 were irradiated and the reaction course followed by UV spectroscopy. In all cases, the longest wavelength absorption band gradually disappeared upon irradiation. Based on previous research, it was assumed, that the preliminary process could be a photoisomerization

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• -33501 Bielefeld, Germany Organic Chemistry II, Department Chemistry – Biology, Siegen University, Adolf-Reichwein-Str. 2, D-57068 Siegen, Germany 10.3762/bjoc.16.8 Abstract Azobenzenes are photoswitchable molecules capable of generating significant structural changes upon E-to-Z photoisomerization in

• peptides or small molecules, thereby controlling geometry and functionality. E-to-Z photoisomerization usually is achieved upon irradiation at 350 nm (π–π* transition), while the Z-to-E isomerization proceeds photochemically upon irradiation at >400 nm (n–π* transition) or thermally. Photoswitchable

• )phenyl)azophenylacetic acid, as the linker between two Im/Py polyamide strands. Only the (Z)-azobenzene-containing polyamides bound to the minor groove of double-stranded DNA hairpins. Photoisomerization was exemplarily evaluated by 1H NMR experiments, while minor groove binding of the (Z)-azobenzene

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• embryotoxicity of dithienylethene-modified peptides upon photoswitching, using 19 analogues based on the β-hairpin scaffold of the natural membranolytic peptide gramicidin S. We established an in vivo assay in two variations (with ex vivo and in situ photoisomerization), using larvae of the model organism Danio

• photoswitchable peptides explored in this study. (A) The reversible photoisomerization of the dithienylethene photoswitch core. (B) Photoconversion between ring-open and ring-closed photoforms of DAE-derived peptides. (C) Structures of the non-photoswitchable cytotoxic peptide GS (1), and one of our first

Starazo triple switches – synthesis of unsymmetrical 1,3,5-tris(arylazo)benzenes

• Andreas H. Heindl and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2020, 16, 22–31, doi:10.3762/bjoc.16.4

• at 365 nm with a high-power LED (see Supporting Information File 1 for specifications) to induce E-to-Z photoisomerization. For the cyano-substituted tris(arylazo)benzene species 3a, the π→π* absorption band decreased only to a relatively small extent, while for starazo 3b, the expected switching

• could be reached after only 20 and 7 s of irradiation, respectively, which was significantly faster than the E→Z photoisomerization. All in all, the irradiation experiments revealed that the methoxy-substituted derivative 3b shows reversible photoisomerization, while cyano-substituted tris(arylazo

• )benzene 3a could only be marginally isomerized. To get deeper insight into the photoisomerization, 1H NMR spectroscopy was applied to monitor the isomerization process. For both 3a and 3b, complex spectra were obtained after irradiation at 365 nm (see Figure S2 and Figure S3, Supporting Information File 1

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• conditions (pH < 1). While the low pKa makes the azonium form unsuitable, the neutral versions of these compounds undergo trans-to-cis photoisomerization with blue-green light and exhibit slow (τ1/2 ≈ 10 min) thermal reversion and so may find applications under physiological conditions. Keywords: azobenzene

• ; azonium; molecular switches; ortho substitution; photoisomerization; photoswitch; visible light; Introduction The application of photoswitches to control biological targets has been a driving force for the development of photoswitches that operate at wavelengths that are compatible with cells and tissues

• in an aqueous solution, it is useful as a photoswitch for the photocontrol of biomolecules [6]. It absorbs red light, undergoes trans-to-cis photoisomerization, and relaxes to the trans isomer in the dark on the timescale of seconds so that pulses of red light can be used to drive multiple

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• , the photoisomerization quantum yields as well as the half-lifes of the photoinduced forms appeared to be almost independent of the presence of the alkylamino substituent. Interestingly, a comparison with the data obtained for Z-2 in aqueous 10 mM Na-phosphate buffer containing 0.1 M NaCl, pH 7.0 [12

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• alternative approach to generate calcium release, where deforming an ion-binding site would render it less well-adapted to bind a guest. Photoisomerization of the azobenzene moiety has previously been successfully used to modulate the affinity of crown ethers [29], lariats [30], and foldamers [31] for various

• observed in the 1H NMR spectra of the azobenzene-containing macrocycles 1f and 1 at 25 °C (Supporting Information File 1, Figures S13 and S14). Next, in the absence of Ca2+ ions, 1E was subjected to irradiation into the π–π* band (λmax = 362 nm) and photoisomerization of 1E to 1Z took place, as evidenced

• state (PSS) for the E→Z photoisomerization at 365 nm was 88:12 in favor of the cis-form (Figure 4). The reversibility of the photoswitching of the supramolecular host was tested over several isomerization cycles with little evidence of fatigue (Figure 5). Thermal isomerization Z→E resulted in the

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• dynamically control the shape and function of SCCs is a very promising strategy as it is a noninvasive stimulus that can be easily applied with high spatiotemporal control, without producing any waste. Systems have been reported where photoisomerization of azobenzene-derived anions encapsulated in

• metal centers has been used to control host–guest interactions [25][26][27][28], structural composition [29], and sol–gel transition [30]. However, dithienylethene undergoes a limited structural change upon photoisomerization and, up to now, photoswitchable ligands based on other types of photochromic

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• –Z photoisomerization is achieved by irradiating in the region of the high-energy π–π* band for the E-isomer, whereas Z–E photoisomerization occurs through irradiation in the low-energy n–π* band of the Z-isomer. However, an overlap in the absorbances between E/Z isomers causes incomplete

• in Supporting Information File 1). Compared to 4pzMe, photoswitches 4pzMe-Cl2 and 4pzMe-OMe2 show smaller π–π* band separations, which supports the reduced E–Z photoisomerization efficiency (80 and 81%, respectively) upon E–Z switching (Table 3). In contrast, 4pzMe-F2 and 4pzH-F2 still provide

• excellent E–Z photoisomerization of 93% and 92%, respectively, despite the relatively small π–π* band separation (30 and 33 nm, respectively). Conversely, the experimental n–π* band separation is very small (near complete band overlap) for the 4pzMe-X family (Figure 8), in contrast to the theoretical

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

• spatial disposition similar to the original biaryl unit and, therefore, a similar biological activity that might change upon isomerization of the azobenzene [8]. The second reason for the success of azobenzene in the photopharmacology field is the robust photoisomerization. It provides typically high

• yields of photoisomerization with relatively low intensity of light and minimal photobleaching even over hundreds of cycles. A third reason is the relatively high synthetic accessibility to azobenzenes. All these properties make azobenzene compounds ideal molecular photoswitches to control protein

• , Supporting Information File 1) and the photoisomerization are observed. When the substituent Y is a halogen atom, we observe a slight bathochromic shift of the π–π* band to higher wavelengths with increasing size of the heteroatom, from 323 nm for Y = H (3e) to 339 nm for Y = I (6e) (Table 3, Figure 4A

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

• even upon excitation at 350 nm, because of the induced E/Z photoisomerization process occurring within the experiment. Finally, the kinetics of the fluorescence decay of the Z-isomer has also been determined in acetonitrile, upon excitation at 400 nm, resulting in a lifetime of 479 ps (Figure S2

• photodegradation and limit the photoisomerization processes, the pump energy on the sample was reduced to 0.8 μJ/pulse at 400 nm and 4 μJ/pulse at 350 nm. Emission from the sample, collected at right angle with a 1 mm slit, was focused by means of a system of lenses into the spectrograph slit. Streak images were

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• have been studied to investigate the possible impact of the macrocycle ring size on their photodynamic properties. The results show that reducing the ring size counteracts the photoisomerization ability of the macrocycles. However, even the smallest macrocycle studied (stiff stilbene subunits linked by

• tweezer that binds ditopically to guest molecules [21][22]. This kind of complex would behave like a macrocycle upon photoisomerization, arising the question whether it might be possible to predict such photoisomerizability and to relate it to the length of a ditopically bound guest molecule connecting

• the two metalloporphyrin units. To investigate the photoisomerization ability of the stiff stilbene as a macrocycle segment a series of model compounds were chosen (Figure 1). To keep the system as simple as possible the SS was attached to an aliphatic carbon chain via ether groups. Four different

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

• which natural systems employ confinement effects to control photoisomerization reactions [26]. Recently, much effort has been devoted to developing new families of heterocyclic azo switches [27][28][29][30][31], largely driven by the rapid growth of the emerging field of photopharmacology [32][33][34

• photoisomerization of encapsulated E-1. UV irradiation (365 nm light-emitting diode, LED) of the transparent yellow solution of (E-1)22 in water did not result in any pronounced visual changes. However, UV–vis absorption spectroscopy showed (Figure 4) a dramatic decrease in the intensity of E-1’s absorption at 336

• to UV light. Notably, all six resonances of 1’s protons have shifted, indicating a highly efficient photoisomerization to Z-1. The corresponding NOE spectra (Figures S18–S20, Supporting Information File 1) feature multiple correlations between the host’s and the guest’s protons. For example, the set

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• crystals are inherently capable of photo-reversible luminescence switching because the electronic structures of photochromic molecules reversibly change upon photoisomerization [13][14]. However, such a fluorescent system in condensed phase emits fluorescence often absorbed in adjacent molecules, therefore

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

• studies proposed a binding mode in which 2a mimics the nicotinamide residue of NAD+, whereas aromatic amino acid residues of the selectivity pocket stabilize the dimethylphenol ring [35]. As photoisomerization in stilbenes and azo dyes is accompanied by a perpendicular twist of the phenyl ring towards the

• unclear. Photochemistry of azastilbenes The photochemical behaviour of stilbenes has been subject to intense investigation in the past. It is reported that unsubstituted stilbene undergoes E→Z photoisomerization [47], as well as photocyclization to dihydrophenanthrene upon UV irradiation, which is

• oxidized to phenantrene in the presence of oxygen [48]. In high concentrations, (E)-stilbene furthermore undergoes photocyclodimerization to cyclobutane derivatives [49]. Photoisomerization and photocyclization are also reported for 3-styrylpyridines, forming two regioisomeric dihydroazaphenanthrenes that

Precious metal-free molecular machines for solar thermal energy storage

• Meglena I. Kandinska,
• Snejana M. Kitova,
• Vladimira S. Videva,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• Stanislav B. Baluschev,
• Silvia E. Angelova and
• Aleksey A. Vasilev

Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106

• photoisomerization and a longer life time of the higher energy forms in comparison with the known analogs. The chemical structures of all dyes in the series were characterized by NMR, UV–vis, IR spectroscopy and elemental analysis. The steady-state photophysical properties of the dyes were elucidated. The stability

• photoisomerization with lifetimes of the higher energy form longer than 500 seconds. Density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p) level were performed in order to predict the enthalpies (H) of the cis and trans isomers and the storage energies (ΔH) for the systems studied. Keywords: aza-15

• -crown-5 ether; benzothiazolium crown ether-containing styryl dyes; E/Z photoisomerization; molecular solar thermal system; Introduction Molecular photoswitches permanently attract considerable interest because they hold potential for application in molecular electronic and photonic devices [1][2][3][4

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

• 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

• , SQUID magnetometry and X-ray crystallography is reported herein. Preliminary results concerning the photoisomerization of compound 1 are reported as well. Results and Discussion Synthesis of ligands and metal complexes Scheme 1 shows the synthetic procedures. The yellow-orange colored zinc complexes (3

• -allowed 3A2g(F) → 3T2g(F) (ν3) transition is expected around 440 nm, but is obscured by the stronger RS → Ni2+ charge transfer and π→π* transitions in this region. We carried out orienting irradiation experiments with regard to a possible trans to cis photoisomerization of the bound azobenzene-carboxylate

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

• Diarylethenes (DAEs) are a rich family of organic photoswitches formally derived from stilbene [1][2]. Upon irradiation they are able to undergo reversible photoisomerization based on 6π-electrocyclization and -cycloreversion, respectively, between two thermally stable states, which make them interesting