Bipyridinium Salts Research Articles

Ultrafast optical switching by photoinduced electrochromism in cast films of polymeric 4,4′-bipyridinium salts with di-iodides

Femtosecond dynamics of color changes due to photoinduced electron transfer and reverse reactions in polymeric 4,4′-bipyridinium di-iodides salts were studied with a fs laser pump–probe technique. The characteristic color change was shown to take place in less than 1 ps by fs-laser excitation of an ion-pair charge-transfer band, which may be applied to ultrafast THz all-optical switching devices using visible light.

Self-Assembly of Novel Polyrotaxanes: Main-Chain Pseudopolyrotaxanes with Poly(ester crown ether) Backbones.

Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temperature.

Controlling Polymeric Topology by Polymerization Conditions: Mechanically Linked Network and Branched Poly(urethane rotaxane)s with Controllable Polydispersity

Compared to that of model polyurethane 8 from the reaction of tetra(ethylene glycol) (6) and 4,4‘-methylenebis(p-phenyl isocyanate) (7) under the same polymerization conditions, polydispersities (PDI) of copolyurethanes 9−11 incorporating bis(5-(hydroxymethyl)-1,3-phenylene)-32-crown-10 (5) as comonomer were significantly higher; for these branched polymers, the PDI increased with feed ratio of 5 vs 6 up to Mw/Mn = 24 for 75% of 5. This constitutes an original method to control branching. The branching units in 9−11 are main chain rotaxanes formed with H-bonding between the ether moieties of macrocycle 5 and −OH groups as a driving force and thus are mechanically linked, as directly proven by 1H NMR spectra, NOESY, and complexation studies with a bipyridinium salt. The cavity of 5 acts as a “topological functionality”. Since solvent can either allow or disfavor such H-bonding, polymeric topology, branched or linear, can be controlled by the proper choice of solvent. Indeed, although homopolyurethanes were...

Novel polyimide ionene: synthesis and characterization of polyimides containing aromatic bipyridinium salt

A series of 4,4′-(1,4-phenylene)-bis(N-aminoaryl-2,6-diphenyl pyridinium perchlorate)s were synthesized by the reaction of 4,4′-(1,4-phenylene)-bis(2,6-diphenyl pyrylium) with aromatic diamines. They were used as monomers to react with various aromatic tetracarboxylic dianhydrides, to prepare polyimides via a two-stage procedure that included a ring-opening condensation in N,N-dimethylformamide (DMF) to give poly(amic acid)s, followed by thermal cyclodehydration to polyimides. The inherent viscosities of these poly(amic acid)s and polyimides were in a range of 1.03–0.07 dl g−1 (0.5% in DMF at 25°C). All polyimides had good solubilities in several polar aprotic solvents, such as DMF, N,N-dimethylacetamide (DMAc), etc. Polyimides derived from 4,4′-oxydiphthalic anhydride could form transparent flexible and tough films. They had a tensile strength range of 42–80 MPa, and an elongation around 5%. The glass transition temperatures of all polyimides were between 181 and 206°C (differential scanning calorimetry). Thermogravimetric analyses indicated that they were fairly stable up to 300°C, and 5% weight loss temperatures were recorded in the range of 337–367°C in nitrogen. These polyimides were semi-conductors with conductivities around 10−8 ohm−1 cm−1 and their conductivities could be further increased up to 10−7 ohm−1 cm−1 by I2-doping. These bipyridinium-based poly(amic acid)s and polyimides could reversibly develop colour by u.v. irradiation. © 1997 Elsevier Science Ltd.

Hydrogen Bonding in the 2,2'-Bipyridinium Salt of 1,2,4,5-Benzenetetracarboxylic Acid (Pyromellitic Acid)

The 2,2′-bipyridinium salt of pyromellitic acid (PMA) (1,2,4,5-benzenetetracarboxylic acid), 2,2′-bipyridinium hemi[1,2,4,5-benzenetetracarboxylate(2-)] hemi(1,2,4,5-benzenetetracarboxylic acid), C10H8N2H+.1/2[C6H2(COO)4H2O]2-.1/2[C6H2(COO)4H4], has been prepared and studied by X-ray diffraction and IR spectroscopy. 2,2′-Bipyridine acts as a proton sponge by accepting a proton from pyromellitic acid. The transfer of protons results in strong asymmetric intramolecular hydrogen bonds: H(N)⋯N 2.603 (2) A in the bipyridinium cation which has syn conformation and H(O)⋯O 2.396 (2) A in the pyromellitate anion. The N-H⋯N hydrogen bond is part of a three-centred hydrogen bond with a carbonyl group of the neutral pyromellitic acid: N—H⋯N,O with H(N)⋯O 2.805 (2) A. Each neutral PMA molecule is connected by hydrogen bonds with two cations and four anions forming a two-dimensional network with plane indices (112). The IR spectrum also suggests the presence of strong hydrogen bonds.

Time-resolved ion-pair charge transfer fluorescence of bipyridinium salts in various microenvironments

The temperature dependence of ion-pair charge transfer (IPCT) fluorescence was studied by time-resolved spectroscopy in 4,4′-bipyridinium and 2,2′-bipyridinium salts with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate in microcrystals and polymer films at 10–300 K. Time-resolved fluorescence, peaking at 400–460 nm and 500 nm, appeared on excitation of IPCT absorption. A shorter wavelength peak in microcrystals was observed at 440 nm for the 4,4′-bipyridinium salt and at 460 nm for the 2,2′-bipyridinium salt; this peak was independent of temperature. A shorter wavelength peak in polymer films containing the 4,4′-bipyridinium salt was observed to shift from 432 nm å 420 nm å 402 nm with decreasing temperature from 300 K to 10 K, corresponding to the molecular motion of polymer chains. Similarly, a shorter wavelength peak in polymer films containing the 2,2′-bipyridinium salt was observed to shift from 460 nm to 440 nm with decreasing temperature from 300 K to 10 K. The fluorescence decay curves were composed of two fast components ( τ = 0.3−7 ns) and a slow component ( τ = 12–34 ns). The former corresponds to the shorter wavelength peak and the latter to the longer wavelength peak in the IPCT fluorescence spectra of the 4,4′-bipyridinium and 2,2′-bipyridinium salts. A reaction mechanism is proposed on the basis of these results.

Ultrafast photon-mode recording and switching by photoinduced electron transfer

Abstract

A New System for Forming High-Contrast Direct-Positive Images

A very-high-contrast direct-positive image was obtained when a prefogged AgBr photographic emulsion containing certain bipyridinium salts, such as 1-n-butyl-4-(4′-pyridyl)pyridinium bromide hydrochloride (Compound 1), was processed with a developer that contains Metol and ascorbic acid as developing agents. Results of photographic and electrochemical studies suggested that Compound 1 has two functions, as an electron acceptor and as a precursor of a nucleator. A theory was developed that, during exposure, Compound 1 acts as an electron acceptor, which produces a direct-image,and that Compound 1 is neutralized during development to form 1-n-butyl-4-(4′-pyridyl)pyridinium bromide (Compound 2), which acts as a nucleator during development and produces very-high-contrast images.

Charge‐Transfer Complexes of Metal Dithiolenes, XXII. Bis(maleonitriledithiolato)oxomolybdate(IV) – Bipyridinium Ion Pairs

AbstractThe oxomolybdenum complex (NBu4)2[MoO(mnt)2] (mnt2− = maleonitriledithiolate) 2 was characterized by X‐ray structural analysis. By metathetic reaction with bipyridinium salts AX2 ion pair charge‐transfer complexes of composition {A2+[MoO(mnt)2]2−} were isolated. Although a plot of the energy of the ion pair charge‐transfer band vs. the driving force of electron transfer from the dianion to the dication afforded a straight line, the slope of 0.45 suggests significant deviations from the Hush‐Marcus model. When bis(2‐hy‐droxyethyl)viologen is the acceptor, in addition to the supra‐molecular charge‐transfer interaction, hydrogen bridges are introduced between the two components as indicated by IR and X‐ray diffraction analysis.

Weak Interactions in Crystals: 4,4′‐Di(tert‐butyl)‐N‐N′‐bipyridinium Diperchlorate—A Biphenyl Analogue with Perpendicular Pyridine Rings

AbstractOxidation of substituted N‐aminopyridinium compounds yields bipyridinium salts. After anion exchange Br− → CIO, it was possible to grow single crystals from the 4,4′‐di(tert‐butyl) derivative. The structure determined at 100 K shows a dihedral angle of 84° between the molecular halves connected by a shortened NN bond of 143 pm in length. This result is contrary to that expected from the isoelectronic correspondence 〉CC〈↔〉NN〈, which would suggest planarity, as has been observed experimentally both in solid biphenyl, and in tetraalkylhydrazine dications and radical cations. Lattice packing analysis, however, reveals the presence of hydrogen bonds C(H)…O between the phenyl rings and the perchlorate anions. AM 1 enthalpy hypersurface calculations for the isoelectronic series H5C5X–YC5H5 (X–Y = CC, +NC, +NN+, −BN+, BC, and BB−) predict single‐minimum potentials for both the dication 〉NN〈 as well as the dianion 〉BB〈 with the molecular halves twisted perpendicular to each other. In detailed model calculations, counteracting effects of π electron density delocalization vs. H/H repulsion of the ortho ring hydrogens adjacent to the central bond seem to dictate the delicate balance of the biphenyl twisting. For further experimental confirmation, the structure of the isosteric molecule 4,4′‐di(tert‐butyl)biphenyl has been determined: in contrast to the unsubstituted π hydrocarbon with a latticeenforced dihedral angle of 0°, close to the calculated value, the two molecular halves are twisted by 40°—as in biphenyl in the gas phase.

A New Redox System: Trichloromethylarene - Pyridine Base. On the Mechanism of the Synthesis of N-(4-Pyridyl)pyridinium Dichloride

A redox reaction of trichloromethylarenes with pyridines results in respective N-(α-chloroarylmethyl)-substituted pyridinium chlorides which give on hydrolysis aromatic aldehydes and 4-chloropyridines or 1,4′-bipyridinium salts.

A new redox system: Trichloromethylarene — pyridine base. On the mechanism of the synthesis of N-(4-pyridyl)pyridinium dichloride

A redox reaction of trichloromethylarenes with pyridines results in respective N-(α-chloroarylmethyl)-substituted pyridinium chlorides which give on hydrolysis aromatic aldehydes and 4-chloropyridines or 1,4′-bipyridinium salts.

Role of Bipyridinium Salts in Generation of Photocurrent by Rhodospirillum rubrum Cells

Abstract An anodic photocurrent was generated when an SnO2 electrode, which was immersed in a culture medium of a photosynthetic bacterium, Rhodospirillum rubrum, or in a buffer suspending the cell body, was illuminated under potentiostatic conditions. The anodic photocurrent was enhanced about four times with addition of methyl viologen (MV) to the cell suspension, but was suppressed with addition of 1,1′-ethylene-2,2′-bipyridinium dibromide (EBP). On the other hand, it was observed spectrophotometrically that EBP was reduced by Rs. rubrum cells about ten times faster than MV. The disagreement in both data of photocurrent and of reduction rate suggests this to be due to the difference of penetrability of the salts through the cell wall and membrane. This suggestion was confirmed from cyclic voltammetric results of the reagents dissolved in the cell suspension.

Reversible control of emission from ion-pair charge-transfer complex of 4,4′-bipyridinium with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion by electron transfer reaction

4,4′-Bipyridinium salts with tetrakis[3,5-bis(trifluoromethylphenyl)]borate anion (TFPB−) showed a charge-transfer (CT) absorption above 350 nm and broad structureless CT fluorescence with a maximum at 525 nm in 1,2-dimethoxyethane (DME). The excitation of a CT band (λex = 475 nm) in an oxygen-free atmosphere resulted in the quenching of CT fluorescence accompanied by a remarkable colour change from pale yellow to blue owing to the accumulation of 4,4′-bipyridinium radical cations. After disappearance of blue colour in about an hour at 20°C, the CT absorbance and fluorescence intensity in DME recovered very gradually to the equilibrium values. The CT fluorescence and colour changes were repeated reversibly. These results demonstrated that 4,4′-bipyridium TFPB− salts can be applied to a photon-mode-type optical memory which can be read with either absorption or emission.

Microenvironmental effect on charge transfer fluorescnece in ion-pair ct complexes of 4,4'-bipyridinium salt.

Temperature dependence of charge transfer (CT) fluorescence were studied by time-resolved spectroscopies in thin polymer films containing 4, 4′-bipyridinium tetrakis[3, 5-bis(trifluoromethyl)phenyl]borate salts as part of the main chain at 10-300°K. The time-resolved fluorescence with peaks at 432nm and 500nm appeared upon excitation of ion-pair charge-transfer absorption at room temperature at about 360 and 390nm, respectively. A shorter wavelength peak shifted from 432nm to 402nm with decreasing temperature from 300°K to 10°K. The fluorescence decay curve was analyzed by a fast (τ=3-6ns) and a slow (τ=15ns) component. The former corresponded to a shorter wavelength peak and the latter to that at ca. 500nm for CT fluorescence spectra of 4, 4′-bipyridinium salt. A reaction mechanism is proposed based on these results.

Application of the Solid Polymer Electrolyte Method to Organic Electrochemistry: XVII . Indirect Electrochemical Debromination Using Viologens as Microscopic Phase‐Transfer Mediators

Solid polymer electrolyte (SPE®) composite electrodes using a perfluorinated ion‐exchange membrane (Nafion®), which is known to be microscopically separated into hydrophilic and hydrophobic domains, were prepared. VariousN,N′‐dialkyl‐4‐4′‐bipyridinium salts (viologens) were incorporated in the SPE composite electrodes as phase transfer mediators. Electrochemical debromination of meso‐1,2‐dibromo‐1,2‐diphenylethane was carried out on the SPE composite electrodes. The results were compared with those obtained in an emulsion system consisting of water and dichloromethane. Of the viologen compounds tested, propyl viologen was the most effective mediator for the SPE composite electrode, while octyl viologen dibromide was the most effective mediator in the emulsion system. The active species for the debromination in the emulsion system was shown to be a doubly reduced neutral form of viologen that was generated by the disproportionation of cation radicals. The disproportionation constant, , of octyl viologen cation radical in a two‐phase system consisting of water and dichloromethane was estimated to be 809. The reaction mechanism on the SPE composite electrode was discussed, and it was considered that the active species was generated by disproportionation at the microscopically heterogeneous interface between the hydrophilic and hydrophobic domains of the Nafion.

Effect of α- and β-cyclodextrin on the electrochemistry of methylheptylviologen and dibenzylviologen

The electrochemistry of N-methyl- N′-heptyl-4,4′-bipyridinium (C 1C 7V 2+) and N, N′-dibenzyl-4, 4′-bipyridinium (BBV 2+) salts with α-cyclodextrin and β-cyclodextrin (CD) was studied. The cyclic voltammetric behavior of both viologens revealed a cyclodextrin-induced conproportionation reaction between the electrogenerated viologen neutral forms and viologen dications with β-CD, but not with the α form. Both α-CD and β-CD suppress dimerization of C 1C 7V 2+, whereas only β-CD is effective for disruption of the BBV .+ dimer. These results are interpreted in terms of the involvement of the bipyridine ring and benzyl group, depending on the oxidation state of viologen, in the inclusion complexation with β-CD, but not significantly with α-CD.

Photoinduced Electron Transfer in Supramolecular Assemblies Composed of Dialkoxybenzene-Tethered Ruthenium(II) Trisbipyridine and Bipyridinium Salts

Photoinduced Electron Transfer in Supramolecular Assemblies Composed of Dialkoxybenzene-Tethered Ruthenium(II) Trisbipyridine and Bipyridinium Salts

Effect of Temperature on the Color Developed by Near Ultraviolet Light for 4,4′-Bipyridinium Salts (Viologens) Embedded in Poly(1-vinyl-2-pyrrolidone) Matrix

Abstract Thermal stability of the colors developed by UV light for 4,4′-bipyridinium salts (viologens) embedded in the glass-sandwiched poly(1-vinyl-2-pyrrolidone) is dominated by the kind of counter anion. Temperature increase resulted in either no or slight changes of the colors developed for the major viologens, whereas it resulted in bleaching for some viologen sulfonates.

ChemInform Abstract: Photoinduced Electron Transfer Reactions: Nitrogen‐Oxygen Bond Cleavage in Reduced N‐(Aryloxy)pyridinium and N,N′‐Dialkoxy‐4,4′‐ bipyridinium Salts.

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