- Photoelectrochemistry using Quinone Radical Anions
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The photoelectrochemistry of quinone radical anions has been demonstrated qualitatively by the photoassisted reduction of methyl viologen with benzoquinone and of neutral red with chloranil.Data were then collected for the estimation of quenching rate constants using Marcus-Weller theory.Reduction potentials of seven quinones were obtained in four solvents (and two aqueous mixtures) by cyclic voltammetry.The solvent effects on these potentials were studied by fitting them to the Taft relationship.The effects of proton donors were also noted.Absorption spectra of the radical anions were measured and the solvent effects noted and commented upon.From the molar absorption coefficients of the radical anions, the mean lifetimes of the excited states were estimated.Fluorescence spectra were obtained for anthraquinone and naphthaquinone radical anions and excitation energies were calculated.These values were estimated for the other quinones.Values of redox potentials for the excited radical anions were thence obtained.The Gibbs energies of the electron transfers between the excited quinone radical anions and the various substrates were obtained and hence the Gibbs energies of activation were calculated using the Marcus equation.The quenching rate constants were calculated using the Rehm-Weller equation and plotted vs. ΔG giving a characteristic Marcus plot including some data in the inverted region.The significance of the inverted region is discussed.
- Eggins, Brian R.,Robertson, Peter K. J.
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- Unique Hydration/Dehydration-Induced Vapochromic Behavior of a Charge-Transfer Salt Comprising Viologen and Hexacyanidoferrate(II)
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We successfully prepared and crystallographically characterized the first intermolecular charge-transfer (CT)-based vapochromic compound, (EV)(H3O)2[Fe(CN)6] (1-Wet, EV2+: 1,1′-diethyl-4,4′-bipyridine-1,1′-diium), an ethyl viologen-containing CT salt. 1-Wet, which is purple in color, is transformed into a brown powder (1-Dry) upon exposure to methanol vapor, drying over silica gel, or heating; 1-Dry returns to 1-Wet upon exposure to water vapor. These color changes are induced by hydration and dehydration, and gravimetric analyses suggest that 1-Dry is the dehydrated form of 1-Wet, namely, (EV)(H)2[Fe(CN)6]. Interestingly, desorption of water molecules from the oxonium ions in 1-Wet produces isolated protons (H+) that remain in 1-Dry as counter cations. Powder X-ray crystal structure analysis of 1-Dry reveals the presence of very short contacts between the nitrogen atoms of adjacent [Fe(CN)6]4- anions in the crystal. The isolated protons are trapped between the nitrogen atoms of cyanido ligands to form very short N···H···N hydrogen bonds. A detailed comparison of the crystal structures of 1-Wet and 1-Dry reveals that hydration and dehydration induce changes in crystal packing and intermolecular CT interactions, resulting in reversible color changes.
- Tanaka, Rikako,Okazawa, Atsushi,Konaka, Hisashi,Sasaki, Akito,Kojima, Norimichi,Matsushita, Nobuyuki
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- Encapsulation of ferrocene and peripheral electrostatic attachment of viologens to dimeric molecular capsules formed by an octaacid, deep-cavity cavitand
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In aqueous media the deepcavity cavitand octaacid 1 forms stable dimeric molecular capsules 12, which are stabilized by hydrophobic effects. In this work we investigate the binding interactions in aqueous solution between these capsules and the redox active guests, ferrocene (Fc) and three 4,4×-bipyridinium (viologen) dications: methyl viologen (MV2+), ethyl viologen (EV2+), and butyl viologen (BV2+). Using NMR spectroscopic and electrochemical techniques we clearly show that the hydrophobic Fc guest is encapsulated inside 12. An interesting effect of this encapsulation is that the reversible voltammetric response of Fc is completely eliminated when it resides inside the 12 capsular assembly, a finding that is attributed to very slow electrochemical kinetics for the oxidation of Fc@12. Diffusion coefficient measurements (PGSE NMR spectroscopy) reveal that all three viologen guests are strongly bound to the dimeric capsules. However, the 1H NMR spectroscopic data are not consistent with encapsulation and the measured diffusion coefficients indicate that two viologen guests can strongly associate with a single dimeric capsule. Furthermore, the (V2+)2. 12 complex is capable of encapsulating ferrocene, clearly suggesting that the viologen guests are bound externally, via coulombic interactions, to the anionic polar ends of the capsule. The electrochemical kinetic rate constants for the reduction of the viologen residue in the V2+·12 complexes were measured and found to be substantially lower than those for the free viologen guests.
- Podkoscielny, Dagmara,Philip, Ivy,Gibb, Corinne L. D.,Gibb, Bruce C.,Kaifer, Angel E.
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- A Viologen–Perylenediimide Conjugate as an Efficient Base Sensor with Solvatochromic Property
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A viologen–perylenediimide conjugate, denoted PDEV, is prepared for efficient base sensing. The conjugate shows solvatochromic behavior as well. The base sensitivity of viologen is purposefully coupled with the emission property of perylenediimide (PDI) to lower the detection limit. PDEV shows base-sensing ability at the ppb level, which is at least three orders of magnitude lower than those of previously reported sensors. The probe is sensitive toward solvent polarity and generates different shades of colors according to the polarity of the medium (solvent). The photophysical properties show a linear correlation with the solvent polarity, and this makes it an efficient solvatochromic agent. On the other hand, the generation of viologen radical cations by bases affects the aggregation and consequently the absorption and emission behavior of the PDI core. The effect of bases can also be visualized, because the probe generates different colors in the presence of bases, both under normal and under UV light. Organic amines can be detected even in the crystalline state, since the dark red color of the PDEV crystals changes to purple in a reversible fashion on exposure to amine vapors. An easy and practical paper-based tool created by using the probe can efficiently be used to detect solvent polarity and presence of bases optically.
- Pramanik, Bapan,Mondal, Julfikar Hassan,Singha, Nilotpal,Ahmed, Sahnawaz,Mohanty, Jyotirmayee,Das, Debapratim
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- Physicochemical analysis of mixed micelles of a viologen surfactant: Extended to water-in-oil (w/o) microemulsion and cucurbit[8]uril-assisted vesicle formation
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A systematic study of the self-assembly process of a viologen-containing surfactant in aqueous medium is reported. Dodecyl-ethyl-viologendibromide (DDEV) is mixed in different proportions with dodecyltrimethylammonium bromide (DTAB), and the physicochemical properties of micellization are evaluated in order to find a suitable combination which does not interfere with the micellar properties of DTAB but introduces the characteristic properties of viologen. In this process, 1% doping of DDEV with DTAB was found to be the most appropriate, as negligible changes were observed in the physicochemical behavior of this system with respect to that of pure DTAB. The 1% DDEV-doped DTAB mixed micellar system showed the characteristic two-step reduction process for the viologen units at the interface as revealed by CV experiments. 1% mixing of DDEV with DTAB also allowed us to prepare stable w/o microemulsions containing viologen units at the interface which is otherwise unattainable with pure viologen surfactants. The charge-transfer capability of the viologen unit to the electron-rich 2,6-dihydroxynaphthalene (DHN) moiety inside the macrocyclic host, cucurbit[8]uril (CB[8]) is also evaluated for this system, and surprisingly even at this very low concentration, the ternary complex of DDEV-DHN@CB[8] transformed the micellar assembly to uniform vesicles. All of these properties have been further extended to other tetraalkylammonium surfactants, and similar effects were observed.
- Mondal, Julfikar Hassan,Ahmed, Sahnawaz,Das, Debapratim
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- A low-cost and high-loading viologen-based organic electrode for rechargeable lithium batteries
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Organic active materials are regarded as a very promising choice for lithium batteries because of several outstanding advantages such as low-cost, flexible tunability and pollution-free sources. Viologen compounds are attractive two-electron storage materials with low redox potentials, which are mainly used as anolytes in redox flow batteries (RFBs) considering their high solubility in electrolytes. However, due to their relatively large molecular weight and low density, it is difficult to prepare high-loading and stable-cycling electrodes for lithium battery application. In this research, by adopting 4,4′-bipyridine as the raw material and combining salification with a high-energy ball milling method, a low-solubility and high-stability viologen carbon-coated composite, ethyl viologen dihexafluorophosphate-Ketjen black (EV-KB), is synthesized. Then, by optimizing the electrode preparation process, a high-loading viologen-based electrode is successfully prepared. Salification effectively reduces the solubility of viologen compounds in the electrolyte so that the EV-KB composite can be used in lithium batteries. At the same time, it is pointed out that current collectors and slurry solvents play an important role in achieving the high-loading electrode. By deliberately selecting carbon paper as the current collector and ethanol as the solvent, the EV-KB composite organic electrode with a loading up to 1.5-9 mg cm?2can achieve a specific capacity of 106-79 mA h g?1for 400 stable cycles with a coulombic efficiency of 96% as well as a good rate capability. The synthesis method and electrode preparation optimization process introduced in this paper provide a reference for other types of organic active materials to be used in high-loading lithium batteries.
- Chen, Hongning,Chen, Mao,Liu, Lei,Zhang, Peiyao
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- Boosting activity of molecular oxygen by pyridinium-based photocatalysts for metal-free alcohol oxidation
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An eco-friendly and economical approach for the photocatalytic oxidation of organic inter-mediates by air under mild conditions is highly desirable in green and sustainable chemistry, where the photogeneration of active oxygen species plays a key role in improving conversion efficiency and selectivity. By using pyridinium derivatives as molecular mediators for electron transfer and energy transfer, the simultaneous activation of O2from air into superoxide radicals and singlet oxygen species can be achieved, and a photoinduced electron transfer catalytic system for the oxidation of alcohols has been developed. Thus, we have successfully simplified the complicated catalytic system into a single molecular catalyst without any additional noble metals and co-catalysts/additives. The current photocatalytic system shows high catalytic efficiency not only for aromatic alcohols but also for aliphatic alcohols that are generally difficult to undergo aerobic oxidation at room temperature under air atmosphere, representing an ideal photocatalytic platform for green and economical organic syntheses.
- Ma, Shuai,Cui, Jing-Wang,Rao, Cai-Hui,Jia, Meng-Ze,Chen, Yun-Rui,Zhang, Jie
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supporting information
p. 1337 - 1343
(2021/02/26)
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- The Host-Guest Properties Observed between the Viologens and Cyclopentanocucurbit[6]uril
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The interactions between cyclopentanocucurbit[6]uril (abbreviated as CyP6Q[6]) and a series of dialkyl-4,4′-bipyridinium and diaryl-4,4′-bipyridinium dicationic guest molecules, where the alkyl group is CH3(CH2)n with n = 0-6 (expressed as G1 to G7) and the aryl group is phenylene (G8) and xylene (G9), have been investigated in aqueous solution using 1H NMR spectroscopy, isothermal titration calorimetry (ITC), and electronic absorption spectroscopy. Our results show that G1 and G2 form 1: 1 host-guest inclusion complexes with CyP6Q[6], in which the bipyridinium core is partially embedded in the cavity of CyP6Q[6]. G3-G9 form 2: 1 dumbbell-type host-guest inclusion complexes, in which the substituents are encapsulated by CyP6Q[6]. At the same time, CyP6Q[6] was compared with several other cucurbit[n]urils (Q[n]s) and their derivatives, such as Q[6], Q[7], and TMeQ[6], which have been reported to interact with this type of guest molecule. In its binding mode, CyP6Q[6] shows many interesting and different properties, and this difference was mainly reflected with G1 and G2.
- Cheng, Si-Yuan,Qu, Yun-Xia,Tao, Zhu,Zhou, Kai-Zhi,Wei, Lian-Tong,Wang, Cong,Zhao, Wei-Wei,Jiang, Dao-Fa,Ma, Pei-Hua
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p. 601 - 607
(2020/01/24)
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- A study of the interaction between inverted cucurbit[7]uril and symmetric viologens
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The interaction between inverted cucuribit[7]uril (iQ[7]) and a series of symmetric viologen derivatives bearing aliphatic substituents of variable length, namely dicationic dialkyl-4,4′-bipyridinium guests where the alkyl is CH3(CH2)n with n = 0 to 6, has been studied in aqueous solution by 1H NMR spectroscopy, electronic absorption spectroscopy, isothermal titration calorimetry and mass spectrometry. In the case of both n = 5 (HV2+) and 6 (SV2+), single crystal X-ray diffraction revealed the composition to be [(iQ[7])2(HV)2][CdCl3Br][H3O+]2[H2O]12.5 and (iQ[7])2(C7-SV)1.5[CdCl4]4(H3O+)5(H2O)8, respectively, with both adopting an external B-type structure (the alkyl chains of the viologen reside within the iQ[7]).
- Gao, Zhongzheng,Bai, Dong,Chen, Lixia,Tao, Zhu,Xiao, Xin,Prior, Timothy J.,Redshaw, Carl
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p. 461 - 467
(2017/01/13)
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- Substituent-Modulated Assembly Formation: An Approach to Enhancing the Photostability of Photoelectric-Sensitive Chalcogenide-Based Ion-Pair Hybrids
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A series of electronically active viologen dications (RV) with tunable substituent groups were utilized to hybridize with [Ge4S10]4- (T2 cluster) to form the hybrids of T2@RV. These hybrids exhibited variable supermolecula
- Lin, Jian,Fu, Zhixing,Zhang, Jiaxu,Zhu, Yujia,Hu, Dandan,Li, Dongsheng,Wu, Tao
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supporting information
p. 3119 - 3122
(2017/03/24)
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- Cathodic electrochromic compound used in electrochromic device, and preparation method thereof
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The structural formula of a cathodic electrochromic compound is shown in the description, a pyridine ring in the middle of the cathodic electrochromic compound is connected to any carbon atom in pyridine rings at two sides through a C-C bond; and in the formula, R1 is selected from C2-20 alkyl groups, R2 to R12 are substituent groups on carbon atoms and are respectively independently selected from H, C1-50 alkyl groups, cycloalkyl groups, polycycloalkyl groups, aryl groups, heterocycloalkyl groups, aralkyl groups and alkaryl groups which are free from or contain halogen, N, O, S, Si, P or an unsaturated bond, and X is selected from a methylbenzenesulfonate anion, a tetrafluoroborate anion, a hexafluoroborate anion, a perchlorate anion, a bisoxalatoborate anion, an oxalyldifluroborate anion, a bis(trifluoromethanesulphonyl)imide anion and a tris(trifluoromethanesulfonyl)methyl anion. An electrochromic device using the compound has a long service life and a deep color, and can greatly reduce the visible light transmittance in the power-up state.
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Paragraph 0083; 0084
(2017/08/30)
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- Ionic self-assembly affords mesoporous ionic networks by crosslinking linear polyviologens with polyoxometalate clusters
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Ionic-bonded mesoporous ionic networks were prepared by the ionic self-assembly of polyoxometalate (POM) clusters with linear cationic polyviologens in water. The POM-enriched PMIN-2(V) possesses a high surface area up to 120 m2 g-1, exhibiting superior non-noble metal heterogeneous catalytic performance in the ambient aerobic selective oxidation of 5-hydroxymethylfurfural.
- Chen, Guojian,Hou, Wei,Li, Jing,Wang, Xiaochen,Zhou, Yu,Wang, Jun
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supporting information
p. 4504 - 4508
(2016/03/19)
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- Three novel cation-templated metal thiocyanates with 1-2D polypseudorotaxane frameworks
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Three novel cation-templated complexes, {(BPE)3[Ag 4Br4(SCN)6]}n (1), {(DEBP) [Cu 2(SCN)4]}n (2) and {(DIBP) [Cu 2(SCN)4]}n (3) [BPE = 1, 2-bis (pyridinium) ethane; DEBP = 1, 1′-diethyl-4, 4′-bipyridinium dibromide; DIBP = 1, 1′-diisopentyl-4, 4′-bipyridinium], have been synthesized via self-assembly reaction in solution. Complex 1 possesses a one-dimensional polyrotaxane architecture with the organic cation BPE trapped in it, whereas both compounds 2 and 3 are infinite 2D supramolecular polypseudorotaxane, linked by bridging thiocyanate groups. All compounds were further characterized with IR spectra, thermal analysis, ultraviolet and fluorescence properties. The Royal Society of Chemistry 2011.
- Qiao, Yong-Zhen,Yue, Jun-Ming,Liu, Xiu-Cun,Niu, Yun-Yin
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experimental part
p. 6885 - 6892
(2012/04/17)
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- Microwave-assisted synthesis of symmetric and asymmetric viologens
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Viologens are generally synthesized by N-alkylating 4,4′-bipyridine with alkyl halides. Under conventional heating conditions, however, their synthesis suffers from long reaction times and, often, low yields. In this work, symmetric and asymmetric viologe
- Lamberto, Massimiliano,Rastede, Elizabeth E.,Decker, Justyne,Raymo, Franisco M.
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scheme or table
p. 5618 - 5620
(2010/10/21)
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- Revisiting the IspH catalytic system in the deoxyxylulose phosphate pathway: Achieving high activity
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(Chemical Equation Presented) From two C5 isoprene building blocks, isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP), the more than 30000 members of the isoprenoid family are constructed in nature using two biosynthetic pathways, the mevalonate (MVA) pathway and the deoxyxylulose phosphate (DXP) pathway. IspH of the DXP pathway is a protein containing an iron-sulfur cluster and catalyzes a reductive dehydration reaction of the DXP pathway. In the literature, a wide range of Escherichia coli IspH activities have been reported (2.0 nmol min-1 mg-1 to 3.4 μmol min-1 mg-1). For such a broad range of activities, reaction assays were carried out under many different conditions, preventing direct comparison of the activities and determination of the key factor responsible for such a dramatic difference in IspH activities. In this work, we systematically examined the role of redox mediators in IspH catalysis using E. coli IspH as the enzyme and dithionite as the ultimate electron source. Our studies not only suggest the importance of the iron-sulfur cluster but also improve the E. coli IspH activity by nearly 97-fold relative to that from the E. coli NADPH-flavodoxin reductase-flavodoxin system.
- Xiao, Youli,Chu, Lisa,Sanakis, Yiannis,Liu, Pinghua
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supporting information; experimental part
p. 9931 - 9933
(2009/12/08)
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