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Search for "quenching" in Full Text gives 420 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Naphthalene diimides with improved solubility for visible light photoredox catalysis
Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201
- catalysis is mainly [Ru(bpy)3]2+ [21], due to its strong MLCT (metal-to-ligand charge transfer) absorption, the excellent yield of its triplet state and the long lifetime, the versatile redox behavior (Ru3+ vs Ru+) in quenching processes and the chemical and photochemical robustness. Despite their positive
Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments
Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164
- enantiopure P5A-DPA and P5A-Py. It was found that the CD signals were enhanced by aggregation. P5A-DPA showed aggregation-induced emission enhancement, while P5A-Py showed aggregation-induced emission quenching, accompanied by excimer emission when aggregating in water and THF mixed solution. Keywords
- to aggregation-caused quenching (ACQ), as was demonstrated by UV–vis absorption and CD studies. For compound P5A-Py, however, the fluorescence intensity continuously decreased when adding water into the THF solutions, and at 70% water content, a new emission peak at 540 nm was observed which was
- the THF solution. P5A-DPA and P5A-Py showed an enhancement of the CD signals by adding water due to restriction of the conformers’ rotations by aggregation. P5A-DPA showed a fluorescence enhancement when less than 50% of water was added, while P5A-Py showed emission quenching and excimer emission when
Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates
Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151
- (Table 2, entry 4), we conducted reactions with the series of arenes (Table 3). An excess of methanol was used for quenching of reaction mixtures instead of water. This treatment produced dimethoxyphosphoryl groups [(MeO)2P=O] in the reaction products, rather than the acidic group [(HO)2P=O] in compounds
- complex mixtures of oligomeric compounds. In the same reaction with benzene, allene 1b afforded alkene Z-11n in high yield (Scheme 5). The use of morpholine for quenching of the superacidic reaction mixture gave amide Z-11o in the reaction of 1a with benzene (Scheme 6). We also conducted a large-scale one
- cations A, B, and F–H. Large-scale one-pot solvent-free synthesis of amides 6a,b from the corresponding propargylic alcohols. AlCl3-promoted hydroarylation of allene 1b by benzene leading to alkene Z-11n. Reaction of allene 1a with benzene under the action of AlCl3 followed by quenching of the reaction
2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes
Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146
- macrocycle, which make it conformationally adaptive to maximize the binding affinities. In addition, the macrocycle shows fluorescent quenching when adding the chloride metal complexes in its solution and may be used as a fluorescent sensor for the detection of these coordination complexes. Keywords: host
- maximum of 1 is located at 350 nm (Figure S22, Supporting Information File 1). It is known that the binding of metal ions could cause fluorescence quenching through photo-induced electron transfer [44]. Indeed, the fluorescence intensity of 1 is quenched gradually upon addition of TBA[AuCl4] (Figure 6a
Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response
Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139
- luminescent dyes. Fluorescein, eosin Y, rose bengal, tetraphenylporphine sulfonate and sulfonated aluminum phthalocyanine were employed as classical aggregation-induced quenching dyes. 2-(p-Toluidinyl)naphthalene-6-sulfonic acid and 1-anilinonaphthalene-8-sulfonic acid were selected as representatives of
- with carboxylated bipyridyl ligands (Ru(dcbpy)3), were screened as model guests on account of the desired strong host–guest binding affinity (Scheme 2). Fl, EY, RB, TPPS and AlPcS4 were employed as classical aggregation-caused quenching (ACQ) dyes; 2,6-TNS and 1,8-ANS were selected as intramolecular
- as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8][28][29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1
Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction
Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138
- dehydrocoupling with ZnCl2 and CuCl2. Selenophene precursor 10 itself was readily obtained in 68% yield from selenophene (9) in a one-pot procedure by successive lithiation with n-BuLi and quenching with trimethylsilyl chloride and iodine, respectively. We reacted biselenophene 11 with K2S as sulfur source and
Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy
Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135
- position. The analogues were obtained by hydroboration of proper open-chain terminal alkenes that, after quenching with water, spontaneously afforded cyclic boronic acids with hemiacetal-like structures. Keywords: antitumor agents; boron neutron capture therapy; boronic acid; hydroboration; sugar analogue
- the desired product 7 by the simple treatment of 6 with an excess of borane-THF complex (5 molar equiv) followed by quenching with water, while in the same conditions compound 5 again gave extensive decomposition. These conditions allowed the isolation of the cyclic anomeric boron analogue 7 in
Efficient resolution of racemic crown-shaped cyclotriveratrylene derivatives and isolation and characterization of the intermediate saddle isomer
Beilstein J. Org. Chem. 2019, 15, 1339–1346, doi:10.3762/bjoc.15.133
- belongs to the saddle isomer, its isolation and characterization was necessary. First, we tried to generate 1-S by heating a DMSO solution of (rac)-1 to 200 °C for 5 minutes and quenching the mixture by pouring it into ice water according to the procedure established by Luz for the methoxy-substituted CTV
- corresponds to the saddle conformer and is marked with 1-S. a) 1H NMR spectrum of the neat crown isomers of (rac)-1 in CD3OD (400 MHz, 298 K); b) 1H NMR spectrum in CD3OD (400 MHz, 298 K) of a sample of (rac)-1 after heating it to 200 °C in DMSO and quenching the solution by pouring it into an ice water
N-doped carbon dots covalently functionalized with pillar[5]arenes for Fe3+ sensing
Beilstein J. Org. Chem. 2019, 15, 1262–1267, doi:10.3762/bjoc.15.123
- a good linear correlation (R2 = 0.992) and the lowest detection limit (LOD) was determined to be 1.2 μM [16][24][25]. Subsequently, the quenching mechanism of Fe3+ toward CCDs was investigated. As demonstrated in Figure 3e, the UV–vis absorption of Fe3+ overlaid with the emission peak of CCDs, thus
- , quenching performance can be contributed to the energy transfer between ions and the materials [26]. Meanwhile, the UV–vis absorption peaks of CCDs exhibited no shift and regeneration before and after Fe3+ sensing, indicating that the fluorescence quenching is not resulted from the formation of new
- nm, Em. 5 nm. Fluorescence quenching degrees of a) CCDs and b) CN-dots in the presence of different metal ions. The concentrations of metal ions were 400 μМ. c) Fluorescence spectra of a CCDs system in the presence of different concentrations of Fe3+ ions (0–500 μM). d) Linear curve of the relative
Self-assembly behaviors of perylene- and naphthalene-crown macrocycle conjugates in aqueous medium
Beilstein J. Org. Chem. 2019, 15, 1203–1209, doi:10.3762/bjoc.15.117
- -assembly behavior in various solvents was investigated particularly in aqueous medium, due to the recently discovered hydrophilic properties of B21C7 crown macrocycle. An unexpected fluorescence quenching phenomenon was observed in the PDI-B21C7 macrocycle conjugate in chloroform. The detailed UV–vis
- quenching (ACQ) effect, the fluorescence of 1 in MeCN decreased dramatically, and was almost totally quenched in MeOH and H2O. It is surprising to us that the fluorescence of 1 in CHCl3 is also quenched even at such a low concentration (5.0 × 10−6 M), as only a faint blue fluorescent emission of 1 could be
- detected (Figure 1b inset). According to previous reports, such a fluorescent quenching indicated the formation of a dimeric structure [67][95], and the electron rich substituents at the imide nitrogen should play an important role [96][97]. For comparison, UV–vis absorption and fluorescence spectra of 2
Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids
Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116
- significantly (>90:10, 17:18) if the reaction was maintained at −78 °C for several hours before quenching at that temperature, giving isolated yields of 30–50% for 17. The absolute configuration of 17 was based on the chemical correlation studies of Seebach [17][18][19] and of Pan [26] for benzylations, and
- principally arose from alkylation (then protonation, by unreacted 7) [19] of the (achiral) dienolate 36 (Scheme 10) of 7. In the current work, where the major difference is prolonged reaction time at low temperature and no warming before quenching, the minor diastereomer is not observed – but dialkylated
- time at −78 °C, followed by quenching at that temperature; these conditions also avoid cogeneration of the (racemic) diastereomer side-product originally observed on warming. Essentially racemic dialkylated tartrate is observed as a minor side-product under our modified conditions. The reaction
Precious metal-free molecular machines for solar thermal energy storage
Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106
- other processes, quenching the photoisomerization; (v) the energy storing MOST materials have to utilize light in the visible range of the spectrum; (vi) it will be a crucial benefit for the MOST technology, if toxic and precious metals are avoided. Focusing on environmentally friendly MOST system is an
Synthesis of (macro)heterocycles by consecutive/repetitive isocyanide-based multicomponent reactions
Beilstein J. Org. Chem. 2019, 15, 906–930, doi:10.3762/bjoc.15.88
- macrocycles [40]. Synthesis of cholane-based hybrid macrolactams by MiBs [41]. Synthesis of macrocyclic oligoimine-based DCL using the Ugi-4CR-based quenching approach [42]. Dye-modified and photoswitchable macrocycles by MiBs [43]. Synthesis of nonsymmetric cryptands by two sequential double Ugi-4CR-based
Mechanochemistry of supramolecules
Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86
- hydrogen to control basicity of the amines [114]. a) Identified exothermic reactions. b) Successful reaction by quenching the heat intramolecularly. c) The plausible mechanism of acidic C–H functionalization intramolecularly. Acknowledgements A.B. thank CSIR (India) for fellowship.
Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells
Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84
- ultraviolet (355 nm) irradiation (Scheme 1) [33]. De-aerated conditions are necessary for the triplet-sensitized generation of TEMPO due to the triplet quenching ability of O2. The polymerization reactions were initiated via photochemical reaction [34][35][36]. For physiological studies, however, the
Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands
Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81
- physicochemical properties of the bound guest molecules are also greatly affected. Thus, complexation of naphthalene diimide carboxylato ligands leads to a substantial (>95%) quenching of the diimide fluorescence [5], and incorporation of a Fe(CpCO2H)2 unit leads to a significant anodic shift of the metallocene’s
Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines
Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41
- with a possible character of TICT [55], which could explain a dual-fluorescence and fluorescence quenching in the high polarity media. The charge transfer nature of the transitions for the compounds 8c and 11c, compared to reference compounds 8a and 11a, was confirmed by quantum chemical calculations
Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives
Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36
- group and – after quenching with water – to give NMN analogues with one alkoxy group at the phosphorus atom. The resulting compounds were purified by column chromatography on an aminopropyl-modified silica gel Quadrasil AP column to yield the pure NMN analogues in low to moderate yields (8–40%). The
Oxidative radical ring-opening/cyclization of cyclopropane derivatives
Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23
- (dtbbpy)PF4 as photocatalyst, and K2HPO4 as base in MeCN under the irradiation of 24 W blue LED light at room temperature for 12–36 h. A plausible mechanism is shown in Scheme 19. Firstly, the substrate 84a underwent oxidative quenching under the action of an iridium photoredox catalyst to afford the
Synthesis of nonracemic hydroxyglutamic acids
Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22
- . However, when the reaction mixture was warmed to 0 °C before quenching, an intramolecular cyclization occurred under basic conditions to give the oxazolidine (4S,5R)-25 as an almost (>20:1) pure diastereoisomer. The hydroxy group which acted as a nucleophile preferred to attack the re-face of the double
N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes
Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5
- insufficient reduction potential of the photoredox catalyst, the Markovnikov addition of alcohols through oxidative quenching is yet limited to highly activated, aromatic alkenes. To the best of our knowledge no methods are known today that allow the addition of alcohols to α-methyl-substituted styrenes
- , and N-phenylphenothiazine 1. Having this electron shuttle (ca. 1 M) in the reaction mixture efficiently leads to silent or non-silent quenching of the reactive species due to the following modes of quenching. While the back-electron transfer under generation of the triethylamine radical cation
Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands
Beilstein J. Org. Chem. 2019, 15, 44–51, doi:10.3762/bjoc.15.4
- monomer 9 (Scheme 4). Synthesis of unsymmetrical ladderphane 8 by sequential ROMPs catalyzed by 6 Polymerization of monomer 9 in the presence of 10 mol % of 6 was performed in THF at 0 °C for 4 h, followed by quenching with ethyl vinyl ether to give polymer 14 in 86% yield (Scheme 5). It is worth noting
A simple and effective preparation of quercetin pentamethyl ether from quercetin
Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291
- of TLC (2 h), and 1 was easily isolated in pure form in 85% yield simply by partition with ethyl acetate (EtOAc, run 2 in Table 2). QPE (1) was also obtained when NaOH was used in place of KOH (run 3 in Table 2); in this case the product was isolated by filtration after quenching the reaction mixture
Degenerative xanthate transfer to olefins under visible-light photocatalysis
Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283
- state of the photocatalyst is a key factor for the energy transfer mechanism. To obtain a detailed mechanistic insight, steady-state photoluminescence (PL) quenching of photocatalyst 8 was examined using xanthate 1a and 1-octene (2a) as potential quenchers (Figure 1). The intensity of the PL peak of
- xanthate 1a was gradually increased, a reduction in the PL intensity (I) of photocatalyst 8 was observed (Figure 1A). The Stern–Volmer plot of the ratio I0/I, where I0 is the initial PL intensity in the absence of quencher, versus concentration of 1a showed a linear relationship with a quenching rate kq
- = 1.25 × 107 M−1s−1 (see Supporting Information File 1). On the other hand, the addition of 1-octene (2a, 40 mM), in place of xanthate 1a, resulted in only a small PL quenching of photocatalyst 8 (<8%, Figure 1B). The time-resolved PL lifetime decay profiles of photocatalyst 8 (25 μM solution in degassed
Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region
Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282
- should be long enough to exhibit a high quenching efficiency with the additives, i.e., to have enough time to react with the additives. This is frequently referred as the Golden Rules of photoredox catalysis. Photoredox catalysis has been largely developed in organic chemistry in the last decades and
- complex as described in [68], i.e., nitro-functionalization and sulfino-functionalization decreased the photocatalytic activity of the complex. Moreover, this functionalization affects the oxidative quenching rate and the stability of the complex. Thus, as for other complexes described above, the choice
- . Thus, radicals are produced to initiate the polymerization. The polymerization can be controlled through oxidative or reductive pathways. An example is provided where the controlled photopolymerizations are based on an oxidative quenching mechanism. This means that the photoredox catalyst is irradiated
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