53721-12-3Relevant articles and documents
Photoelectrochemistry using Quinone Radical Anions
Eggins, Brian R.,Robertson, Peter K. J.
, p. 2249 - 2256 (1994)
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.
Encapsulation of ferrocene and peripheral electrostatic attachment of viologens to dimeric molecular capsules formed by an octaacid, deep-cavity cavitand
Podkoscielny, Dagmara,Philip, Ivy,Gibb, Corinne L. D.,Gibb, Bruce C.,Kaifer, Angel E.
, p. 4704 - 4710 (2008)
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.
Physicochemical analysis of mixed micelles of a viologen surfactant: Extended to water-in-oil (w/o) microemulsion and cucurbit[8]uril-assisted vesicle formation
Mondal, Julfikar Hassan,Ahmed, Sahnawaz,Das, Debapratim
, p. 8290 - 8299 (2014)
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.
Boosting activity of molecular oxygen by pyridinium-based photocatalysts for metal-free alcohol oxidation
Ma, Shuai,Cui, Jing-Wang,Rao, Cai-Hui,Jia, Meng-Ze,Chen, Yun-Rui,Zhang, Jie
supporting information, p. 1337 - 1343 (2021/02/26)
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.
