Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• switching speed of PIC opened up various potential applications, no photosensitivity to visible light limits its applications. In this study, we synthesized a visible-light sensitized PIC derivative conjugated with a benzil unit. Femtosecond transient absorption spectroscopy revealed that the benzil unit

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• (470 nm, 530 nm). The on-switching of fluorescence due to the ring-closure reaction was observed also with visible light of 470 nm (to an extent of 10% for compound SyOTh1) and attributed to the Urbach tail effect. Due to a high degree of fluorescence modulation (>270), good fatigue resistance and

• path, even at “one side” of the molecule (in asymmetric compounds) would enable switching with focusable light of 375 nm and above. To test this hypothesis, we designed a series of DAEs with mono- and bithiophene substituents attached to positions 6 and 6′ of an oxidized or a nonoxidized 2-alkylbenzo[b

• diluted solutions at a known concentration prior to irradiation. Solutions were irradiated in a home-made setup [5] with 355 nm light until the photostationary state (PSS365 nm). Figure 2 shows changes of absorption and emission spectra in the course of the switching process for compound SyTh2. Irradiated

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

• . In addition, it shows turn-off type fluorescence switching in an aprotic solvent and in crystals. The fluorescence is quenched as the content of closed-ring isomers increases upon UV light irradiation. Conclusions: A diarylethene containing an ESIPT functional group was prepared. It showed

• fluorescent turn-off behavior during photochromism in aprotic solvents as well as in crystalline state upon UV light irradiation. Furthermore, it showed AIE in THF/water mixtures with blue-shift of the emission. Keywords: AIE; diarylethene; ESIPT fluorescent switching; turn-off fluorescence; Introduction

• Diarylethenes are well-known photochromic molecules and are widely applied to molecular switches and systems [1][2]. Recently, the photo-switching of fluorescence signals by using diarylethene switches has attracted much attention because of the potential in various optoelectronic applications [3]. For example

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

• enzyme assay. The long irradiation periods that were necessary to obtain significant amounts of the (Z)-isomers did not permit switching of the inhibitors in the enzyme assay mixture, as the fluorescent substrate and the enzyme would be harmed by long-term UV radiation. We envisioned to replace the

• photoisomerization, but was not as effective as 452 nm radiation. 630 nm irradiation, in contrast, did not lead to an altered PSS composition obtained by UV irradiation of 365 nm. Switching between the two PSS could be repeated several times without any observable fatigue of the compound (Figure 5). The

• EtOH and 16 mL water) or vanillin/sulfuric acid (3.0 g vanillin and 0.5 mL H2SO4 in 100 mL EtOH) reagent. Synthesis was additionally monitored using high speed SFC/MS runs performed by a Nexera SFE-SFC/UHPLC switching system (Shimadzu Corporation, Kyoto, Japan) consisting of a pumping system (one LC

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• , indicating that the DN24C8 unit moved toward the N-methyl-1,2,3-triazolium station and was now close to the NDI moiety. This pH-controlled switching process is reversible (e.g., after addition of trifluoroacetic acid the original state is regained). On the other hand, there were no considerable changes in

• the 1H NMR spectra or color changes, upon addition of DIEA to the corresponding triazole analogue (precursor to 17a) because of only weak interaction between the crown ether and the triazole unit. This clearly proves the importance of the triazolium moiety for the switching process. Color changes with

• catenane 17b upon addition of base were less noticeable because of a weaker CT band in the case of a dibenzo-fused crown ether. Thus, the authors have proven that the movement of macrocyclic rings within catenanes can be controlled by switching the pH, and the bisnaphtho crown ethers can act either as

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

• supramolecular assemblies, the halogen donors need to bind both in the E- and Z-state. This is the case according to our computations, as isodensity values remain almost identical upon switching (Figure S14 in Supporting Information File 1). We therefore turned our attention to elucidate the change of

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• , the stabilization between the E and K forms is a result of the competition between the strength of the hydrogen bonding in the enol tautomer and the effect of simple alkyl substitution in the keto form skeleton. The calculations also suggest that the efficient switching towards the enol form can be

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• in our lab (Table 1) [49]. The synthesis of the triisopropylsilyl nitronate was initially attempted starting with 3-nitropropionic acid methyl ester but no desired product was observed. However, switching to 3-nitropropanol, protected as the THP ether, succeeded to prepare the required

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

• platform 2 (44%). The photophysical properties and the switching behaviour of 1, 2 and 3 were determined in solution (THF). The UV–vis spectra of the norbornadienes (NBD, black, 1a, 2a, 3a) and quadricylanes (QC, red, 1b, 2b, 3b) and the spectra of the QCs after irradiation with 311 nm for 1b and 2b or 254

• the cycloreversion was determined by linear fit of ln (k) as a function of 1/T. The cycloreversion of QC 1b to NBD 1a has an activation energy of 111 kJ mol−1 (degassed deuterated benzene). The switching efficiency of NBD 2a to QC 2b is quantitative (≈100%) after irradiation with 385 nm, whereas the

• switching between the norbornadiene and quadricyclane isomers with two different wavelengths was investigated. Norbornadienes 1 and 2 are quantitatively converted to the corresponding quadricyclanes upon irradiation with light of 385 nm. Back-isomerization with 311 nm to the norbornadiene isomer 1a is less

Design, synthesis and biological evaluation of immunostimulating mannosylated desmuramyl peptides

• Rosana Ribić,
• Ranko Stojković,
• Lidija Milković,
• Mariastefania Antica,
• Marko Cigler and
• Srđanka Tomić

Beilstein J. Org. Chem. 2019, 15, 1805–1814, doi:10.3762/bjoc.15.174

• hindrance of the mannose and peptide part during the inclusion process of the adamantane [37][39]. It is well known that vaccine adjuvants can enhance or modulate the Th1/Th2-bias of an induced immune response. Interferon-γ (as a Th1 cytokine) and IL-4 (as a Th2 cytokine) induce isotype switching to IgG2a

Metal-free mechanochemical oxidations in Ertalyte^® jars

• Andrea Porcheddu,
• Francesco Delogu,
• Lidia De Luca,
• Claudia Fattuoni and
• Evelina Colacino

Beilstein J. Org. Chem. 2019, 15, 1786–1794, doi:10.3762/bjoc.15.172

• significantly by switching to an Ertalyte® jar (86%) [68] which could be further enhanced (93%) by slightly increasing the amount of the oxidant agent (1.5 equiv). Ertalyte® jars (Figure S1b, in Supporting Information File 1) are composed of polyethylene terephthalate (PET-P) and characterized by wear- and

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

• is the design of artificial Lissoclinum cyclopeptides which can be switched by the incorporation of a suitable switching unit into the scaffold. A switching process would allow to vary the orientation and the distance between the recognition units. Examples for such switching units are photochromic

• 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

• for dibenzoyl 7 (Scheme 1). Diazocine 13 was obtained by reduction and oxidation in moderate yields (22%). The reaction of diazocine 13 with the TATA ion 9 gave the target diazocine 2 (88%, Scheme 2). The photophysical properties and the switching behavior of 1 and 2 were determined in solution (THF

• different diazocines mounted on TATA platforms (1, 2). The photochemical switching between the stable cis and metastable trans-isomers was investigated. Upon irradiation with light of 405 nm diazocine-TATAs 1 and 2 convert to their trans-configurations in moderate to good yields. The metastable trans

• support by the Deutsche Forschungsgesellschaft within the Sonderforschungsbereich 677, “Function by Switching”.

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

• reversibility of the switching behavior. The dispersion of AuNR assemblies after visible light irradiation can also be verified by TEM bright field images (Figure 4d) showing that the disassembly is possible without the combination of irradiation and sonication. This can be attributed to the favorable

• reversibly be shifted back and forth ending at the original wavelength. Switching of the end-to-end assembly was possible over four cycles without fatigue appearance. Previously reported limited feasibilities of azobenzenes could be resolved by the implementation of arylazopyrazoles. This report shows a

Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter

• Indrajit Paul,
• Debabrata Samanta,
• Sudhakar Gaikwad and
• Michael Schmittel

Beilstein J. Org. Chem. 2019, 15, 1371–1378, doi:10.3762/bjoc.15.137

• -component rectangle [Cu4(1)2(2)2]4+ and the four-component sandwich complex [Cu2(1)(2)(4)]2+ is triggered by inclusion and release of DABCO (4). The fully reversible and clean switching between two multicomponent supramolecular architectures can be monitored by fluorescence changes at the zinc porphyrin

• [29][30][31] with high selectivity. Results and Discussion To realize the aspired switching protocol, we have tested metal-ion and guest-dependent completive and incomplete self-sorting scenarios [32] by mixing ligands 4, 8, 9, 10 and [Cu(CH3CN)4]PF6 in a ratio of 1:1:1:2:1 (Scheme 2). Ligand 8 was

• . Partial spectra (400 MHz, CD2Cl2, 298 K) showing the reversible switching between rectangle and sandwich complexes over 2.0 cycles; (a) after mixing of [Cu(CH3CN)4]PF6, 1, and 2 in 2:1:1 ratio, furnishing rectangle 5 (state I); (b) after adding 2.0 equiv of DABCO, furnishing sandwich complex 6 (state II

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

• . First of all, the azacrown nitrogen atom is linked directly to the dye and it is part of the chromophore system, responsible for the “push–pull” effect and the photophysical properties of the dye. This provides control over the “push–pull” effect in the chromophore by switching on and off states (i.e

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• no reaction in some cases. In addition to above mentioned benzene derivatives, heteroaromatic boronic acids also worked well under the reaction conditions and provided high yields of the corresponding oxindoles 131. Finally, switching the N-substituent in the starting propiolamide 128 by a H or a Bn

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

• 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

• absorption spectrum upon switching (= isosbestic points) indicate a clear two-component switching between trans and cis-species without any degradation or formation of a side-product (Figure 1, dotted black arrows). The UV–vis absorption spectra of all compounds are depicted in Supporting Information File 1

• switching is required. In case of thermally stable cis-isomers constant irradiation to maintain a substantial amount of the cis-isomer can be avoided. Patch-clamp studies The synthesized azo antagonist derivatives 5a, 5b, 12a, 16a–d, 23, and 28 were tested for their inhibitory activity using the patch-clamp

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

• , amine and vinyl groups, which are suitable for polymer synthesis. Upon irradiation at 385 and 530 nm the diazocines perform a reversible, pincer-type movement switching the 3,3’-distance between 6.1 Å (cis, stable isomer) and 8.2 Å (trans, metastable isomer). Key reactions in the synthesis are an

• to 3,3’- and 4,4’-diaminodiazocine, which have been implemented in macromolecules for conformation switching, our compounds exhibit improved photophysical properties (photostationary states, separation of absorption bands in the cis and trans configuration). Hence they are promising candidates as

• 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

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• Dimroth–Reichardt polarity parameter (ET(30)) [54] was observed (Figure 6) for both classes of compounds. For example, the fluorescence QY of 7-deazapurine 11c in THF were determined to be 0.76 and non-detectable in methanol. Similarly, QY of purine 8c dropped from 0.56 to <0.01 by switching between the

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

• Sibylle Frei,
• Andrei Istrate and
• Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

• characteristic parameters of a B- or A-type helix, respectively (Figures S5–S7, Supporting Information File 1) [69]. Furthermore, the examination of the minor groove distances [70] disclosed for the 6’F-bc4,3-DNA/RNA duplex a flexibility switching between values of an A- and B-helix (Figure S8, Supporting

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

• A. S. Antonov,
• A. F. Pozharskii,
• P. M. Tolstoy,
• A. Filarowski and
• O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

• (Figure S13 in Supporting Information File 1). The addition of a second OMe group in the case of 6 leads to the formation of 25% 6b’. Upon the insertion of a third OMe group in 7, the amount of 7b’ expectedly increases to 33%. Switching of the solvent to acetone-d6 facilitates the proton transfer away

• . Switching of protonation sites in imines 4b–7b. Protonation of the out-inverted dialkylamino group. Examples of proton sponges with stabilised in,out-conformation. Influence of the solvent on the proton transfer to imino nitrogen in 4b–7b solutions at 25 °C. Supporting Information Supporting Information

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

• Eloi P. Coutant,
• Vincent Hervin,
• Glwadys Gagnot,
• Candice Ford,
• Racha Baatallah and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

• ensuing reduction of 6u using sodium borohydride led to a somewhat better yield of compound 3u (as estimated by 1H NMR), side products resulting from over-reductions of the ester moieties were still observed. It is only when switching to tetramethylammonium borohydride that this was alleviated and the

• ester 2af were of (only) 56% and 54%, respectively. Later on, when using a 1:1 proportion of compounds 47 and 48af, a slightly improved yield of 50% was achieved when switching from ammonium bicarbonate to lithium carbonate (note d in Table 2) or in the case of the preparation of compound 2ag switching

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

• methylpyridinium group as a substituent on the photochromic unit [27][28][29]. However, by a combination of suitable substituents, a bidirectional system able to operate in both switching directions either electrochemically or photochemically has been reported [28]. We have recently developed a new subclass of

• family of photoswitches possessing three switching states (E/Z/C). The oxidation potentials of a series of compounds with either 5-, 6-, or 7-membered rings attached to the central exocyclic double bond as well as the electronic influence of substituents were compared. We found that in particular the

• irradiation. Experiments in MeCN with 0.1 M Bu4NPF6, c = 1∙10−3 M, dE/dt = 1 V s−1. Combining double bond isomerization (E/Z) and cyclization/cycloreversion (Z/C) in three-state switching sDTEs. Photochemically, both ring-open isomers are converted to the closed isomer C in high yield when irradiated with

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

• , spectral data and crystallographic data. Acknowledgements The authors gratefully acknowledge financial support by the Deutsche Forschungsgesellschaft (DFG) within the Sonderforschungsbereich 677, “Function by Switching”.