Bipyridinium Dication Research Articles

Two novel multifunctional chromic compounds: Synthesis, photochromism, ammonia sensing, and anion sensing

Two new Zn (II)-viologen chromic compounds, named {[(4-BCBPY)0.5(HIPA)]·H2O}n (1) and {[Zn3(IPA)4(4-BCBPY)]·2H2O}n (2) (4-BCBPY2+ = 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium dication, H2IPA = isophthalic acid) have been synthesized through varying reaction conditions. Structural analysis reveals that compound 1 possesses a supramolecular compound, while compound 2 exhibits a metal-organic framework (MOF) structure built from trinuclear metal building units. Under the irradiation of a 300 W Xe lamp, compound 1 undergoes a color change from orange to brown, while compound 2 transitions from yellow to green. The introduction of metal ions in compound 2 enhances its light response rate compared to compound 1. Additionally, compound 2 displays a visible color change in the presence of ammonia, whereas compound 1 does not exhibit this capability. Meanwhile, the stable product 2P of 2 was obtained through irradiation, and the structural differences between 2 and 2P were analyzed. Furthermore, the study of time-dependent density functional theory (TDDFT) provides theoretical support for understanding the properties of 1 and 2. Both compounds exhibit intriguing photomodulated luminescence properties and demonstrate remarkable sensing abilities toward Cr2O72−. Notably, the introduction of metal ions was found to modulate the photochromic behavior as well as the ammonia/anion sensing properties of these compounds.

Spin-Frustrated Trisradical Trication of PrismCage.

Organic trisradicals featuring threefold symmetry have attracted significant interest because of their unique magnetic properties associated with spin frustration. Herein, we describe the synthesis and characterization of a triangular prism-shaped organic cage for which we have coined the name PrismCage6+ and its trisradical trication─TR3(•+). PrismCage6+ is composed of three 4,4'-bipyridinium dications and two 1,3,5-phenylene units bridged by six methylene groups. In the solid state, PrismCage6+ adopts a highly twisted conformation with close to C3 symmetry as a result of encapsulating one PF6- anion as a guest. PrismCage6+ undergoes stepwise reduction to its mono-, di-, and trisradical cations in MeCN on account of strong electronic communication between its 4,4'-bipyridinium units. TR3(•+), which is obtained by the reduction of PrismCage6+ employing CoCp2, adopts a triangular prism-shaped conformation with close to C2v symmetry in the solid state. Temperature-dependent continuous-wave and nutation-frequency-selective electron paramagnetic resonance spectra of TR3(•+) in frozen N,N-dimethylformamide indicate its doublet ground state. The doublet-quartet energy gap of TR3(•+) is estimated to be -0.08 kcal mol-1, and the critical temperature of spin-state conversion is found to be ca. 50 K, suggesting that it displays pronounced spin frustration at the molecular level. To the best of our knowledge, this example is the first organic radical cage to exhibit spin frustration. The trisradical trication of PrismCage6+ opens up new possibilities for fundamental investigations and potential applications in the fields of both organic cages and spin chemistry.

Giant Conductance Enhancement of Intramolecular Circuits through Interchannel Gating

Summary For neutral intramolecular circuits with two constitutionally identical branches, a maximum 4-fold increase in total conductance can be obtained according to constructive quantum interference (CQI). For charged intramolecular circuits, however, the strong electrostatic interactions entangle the quantum states of these two parallel pathways, thus introducing complicated transport behavior that warrants experimental investigation of the intramolecular circuit rules. Here, we report that a tetracationic cyclophane with parallel channels exhibits a 50-fold conductance enhancement compared with that of a single-channel control, an observation that supplements intramolecular circuit law in systems with strong Coulombic interactions. Flicker noise measurements and theoretical calculations show that strong electrostatic interactions between charged parallel channels—serving as the chemical gate to promote the effective conductance of each channel—and CQI boosts the total conductance of the two-channel circuit. The molecular design presented herein constitutes a proof-of-principle approach to charged intramolecular circuits that are desirable for quantum circuits and devices.

Structural Diversity in Supramolecular Organization of Anionic Phosphate Monoesters: Role of Cations.

Syntheses and structures of anionic arylphosphate monoesters [ArOP(O)2(OH)]− (Ar = 2,6-CHPh2-4-R-C6H2; R = Me/Et/iPr/tBu) with different counter cations are reported. The counter cations were varied systematically: imidazolium cation, 2-methyl imidazolium cation, N-methyl imidazolium cation, N,N′-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, 4,4′-bipyridinium dication, and magnesium(II) dication. The objective was to examine if the supramolecular structure of anionic arylphosphate monoesters could be modulated by varying the cation. It was found that an eight-membered P2O4H2-hydrogen-bonded dimeric motif involving intermolecular H-bonding between the [P(O)(OH)] unit of the anionic phosphate monoester along with the counter cation is formed with 2-methyl imidazolium cation, N-methyl imidazolium cation, N,N′-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, and magnesium(II) dication; both discrete and polymeric H-bonded structures are observed. In the case of imidazolium cations and 1,4-diazabicyclo[2.2.2]octan-1-ium cation, the formation of one-dimensional polymers (single lane/double lane) was observed. On the other hand, two types of phosphate motifs, intermolecular H-bonded dimer and an open-form, were observed in the case of 4,4′-bipyridinium dication.

Photochromism of three supramolecular assemblies derived from benzenecarboxylate donors and viologen acceptors

Based on 1,2,4,5-benzenetetracarboxylic acid (H4BTEC) and different viologen cations (MQ+ = 1-methyl-4,4′-bipyridinium cation; MV2+ = 1,1′-bis(methyl)-4,4′-bipyridinium dication; EV2+ = 1,1′-bis(ethyl)-4,4′-bipyridinium dication), three novel supramolecular assemblies [(H3O)(MQ)(H4BTEC)(H2BTEC)]·H2O (1), (H3O)(MV)0.5(BTEC)0.5 (2), (H3O)(EV)0.5(H2BTEC) (3), have been synthesized and structurally characterized with viologen cations as the guest and acid moieties acting as the host. The crystal structures and photochromic properties of three compounds have been explored. Similar to other viologen-based materials, compounds 2 and 3 are found to exhibit electron-transfer (ET) photochromism, while compound 1 has no photochromism observed. The photosensitivity of the compounds should be due to the rational modulation of electron acceptors and donors. Controllably fabricating appropriate donor and acceptor units at the molecular level in photosensitive materials is critical to the development of new photochromic host–guest materials.

Multi-responsive host-guest MOFs derived from ethyl viologen cations

The self-assembly reaction of TM2+ (TM = Zn, Cd), 1,3-benzenedicarboxylic acid (m-H2BDC), and ethyl viologen cation (EV2+ = 1,1′-bis(ethyl)-4,4′-bipyridinium dication) leads to two new host-guest MOFs {(EV)0.5[TM1.5(m-BDC)2]}n (1, Zn; 2, Cd), of which TM1.5(m-BDC)2]2- acts as host anion and EV2+ acts as guest cation. The two compounds have different chromic properties. Compound 1 exhibits both electron-transfer (ET) photochromism under indoor light, sunlight and UV light irradiation and ET thermochromism, while compound 2 only exhibits ET photochromism under sunlight and UV light irradiation. Compounds 1 and 2 have the same structure except for different coordination metal ions, the effects of metal ions on the chromic behaviors of two compounds have been explored.

Studies of bipyridinium ionic liquids and deep eutectic solvents as electrolytes for electrochromic devices

In this work, two bipyridinium di-cations based on [(allyl)2bpy]2+ and [(C10)2bpy]2+ combined with halogenate (I or Br), bistriflimide ([NTf2]) and dicyanamide [DCA] anions have been prepared and electrochemical characterized. These salts were studied using a conventional electrolyte (TBAP in acetonitrile) and alternative electrolyte based DES (LiTfO:6EG) for 3- and 2- electrodes configuration devices.In the 2-configuration device, [(allyl)2bpy][DCA]2 and [(C10)2bpy][DCA]2 showed different radical cation colorations particularly green and blue colors with different recovery times to original ones. In the case of [(C10)2bpy]I2 a blue and a red-violet colorations attributed to the electrogenerated radical cation and the dimer respectively was obtained in agreement with previous literature. In parallel, bipyridinium based DES by suitable combination between [(C10)2bpy]X2 and [(allyl)2bpy]X2 (X = Br, NTf2, DCA) with several hydrogen bond donors in 2-electrode configuration devices have been also studied. DES based on [(allyl)2bpy][NTf2]2:PEG200 and [(allyl)2bpy][DCA]2:PEG200 presented different coloration grades from pale brown to green taking longer times to recover the original color.The selected DES as alternative electrolytes or based bipyridinium derivatives can be promissory materials for efficient electrochromic devices.

Multi-mode supermolecular polymerization driven by host-guest interactions.

A novel supermolecular self-assembly based on ternary host–guest interaction between cucurbit[8]uril (CB[8]), 1,1′-dimethyl-4,4′-bipyridinium dication (MV) and coumarin derivative was applied for the construction of linear supramolecular polymer with high degree of polymerization in aqueous solution. Accompanied by the introduction of azobenzene on linear ABBA type monomer the supermolecular polymerization is different and the morphology changes from linear to dendritic polymer. The successful supramolecular polymerization of linear and dendritic supramolecular polymers by non-covalent host–guest molecular recognition was confirmed by various characterization methods, such as 1H NMR spectroscopy, ROESY, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Meanwhile, the supramolecular polymerization could promote the conversion of the azobenzene from cis to trans, which ultimately results in no isomerism upon UV irradiation.

Extent of protonation of 4,4′-bipyridinium cations and nature of host influences the amount of guest intake by cobalt(II) 2,6-pyridinedicarboxylate

4,4′-Bipyridinium cobalt(II) 2,6-pyridinedicarboxylate hexahydrate forms host–guest complexes with hydroxy-aromatic compounds 2,3- or 2,7-dihydroxynaphthalene and phloroglucinol. Impressive aspect of the complex is the modification of protonated species in different ways while forming host–guest complexes with hydroxyaromatics. Complex with 2,3-dihydroxynaphthalene has 4,4′-bipyridinium monocation and dication as counter-ions, whereas 2,7-dihydroxynaphthalene complex has only 4,4′-bipyridinium dication. Host-guest complex with phloroglucinol has two 4,4′-bipyridinium monocations. Guest dependent templates are formed in each case. In the case of 2,3-dihydroxynaphthalene, interactions among amine-water-naphthalenediol resulted in chain-like structures within the self-assembly; whereas host–guest complex having 2,7-dihydroxynaphthalene holds water clusters within self-assembly. Substrate dependent host–guest complexes with variations on amounts of guest intake per unit cell was observed; for example with 1, 3, 5-trihydroxybenzene as guest molar ratio of cobalt ion with respect to guest is unity, whereas three equivalents of 2, 3- or 2, 7-dihydroxynaphthalene molecules per cobalt complex were observed.

Search for Electron Delocalization from [Fe(CN)6]3– to the Dication of Viologen in (DNP)3[Fe(CN)6]2·10H2O

K3Fe(CN)6 reacts with the viologen 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium dication, (DNP)2+, to form a supramolecular complex, (DNP)3[Fe(CN)6]2·10H2O (1). The crystal structure of 1 reveals that there are two [Fe(CN)6]3- anions within an organic framework of three (DNP)2+ cations with the shortest Fe(III)···Fe(III) distances of ca. 9.8 Å, distances that minimize extensive long-range magnetic exchange coupling interactions between the [Fe(CN)6]3- anions, and, thus, 1 is paramagnetic above ca. 17 K and exhibits weak ferromagnetic coupling between 17 and 3 K and antiferromagnetic coupling between 3 and 1.8 K. The long Fe(III)···Fe(III) distances permit slow spin-spin and slow spin-lattice paramagnetic relaxation, relative to the iron-57 Larmor precession frequency, as is evidenced by the Mössbauer spectra measured between 3 and 60 K; between 85 and 295 K, rapid paramagnetic relaxation is observed. Both the slow spin-spin and slow spin-lattice relaxation are mediated by the organic, π-conjugated viologen cations. The Fe-C distances, the Mössbauer isomer shifts, the temperature dependence of the magnetic susceptibility, and the 3 K magnetization results all indicate the presence of low-spin Fe(III) ions in the [Fe(CN)6]3- anions in 1. There is no unequivocal indication of the presence of any formal electron delocalization or transfer from the [Fe(CN)6]3- anion to the (DNP)2+ cations in the results obtained from X-ray crystallography, magnetic measurements, and Mössbauer spectra. Because of enhancement of the spin-orbit coupling by the heavy-atom or -ion effect, the Fe(III) ions in the [Fe(CN)6]3- anions interact with the (DNP)2+ cations, causing them to fluoresce with increasing intensity upon cooling from 90 to 25 K when excited at 300 nm. The resulting luminescence of the viologen (DNP)2+ cation induced by the [Fe(CN)6]3- anions indicates the presence of significant mixing of the molecular orbitals derived from the [Fe(CN)6]3- anions and the molecular orbitals associated with the (DNP)2+ cations to yield bonding supramolecular orbitals in 1, a mixing that is also observed between 50 and 3 K in the temperature dependence of the isomer shift of 1.

Self-assembly of the tetrachlorido(oxalato)rhenate(iv) anion with protonated organic cations: X-ray structures and magnetic properties

Two novel ReIV compounds of formulae [H2bpy][ReIVCl4(ox)] (1) and [H3biim]2[ReIVCl4(ox)] (2) [H2bpy2+ = 4,4′-bipyridinium dication, H3biim+ = 2,2′-biimidazolium monocation, and ox2− = oxalate dianion] have been synthesised and magneto-structurally characterised. 1 crystallises in the monoclinic system with space group C2/c, and 2 crystallises in the triclinic system with space group P. The ReIV ion in 1 and 2 is six-coordinate, bonded to four chloride ions and two oxalate-oxygen atoms in a distorted octahedral geometry. Short intermolecular ReIV–Cl⋯Cl–ReIV contacts, Cl⋯π type interactions and hydrogen bonds are present in the crystal lattice of both compounds, generating novel supramolecular structures based on the highly anisotropic [ReIVCl4(ox)]2− species. Examination of the magnetic properties of 1 and 2 reveals significant antiferromagnetic coupling between ReIV ions propagated primarily through the ReIV–Cl⋯Cl–ReIV interactions, as evidenced by the occurrence of maxima in the magnetic susceptibility at ca. 12 (1) and 17 K (2).

Synthesis and chemical properties of polyphenylenes cross-linked by electron-accepting viologen moiety

Polyphenylene (PP) with NH2 side groups, namely, polymer-1, was synthesized by the Pd-complex-catalyzed reaction of 2,5-dibromoaniline with 9,9-dihexylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester. The reaction of polymer-1 with 1,1′-bis(2,4-dinitrophenyl)-4,4′-bipyridinium dichloride (salt-1) in 1:0.5, 1:1, and 1:2 molar ratios eliminated 2,4-dinitroaniline to yield PPs cross-linked by a viologen (1,1′-disubstituted 4,4′-bipyridinium dications) moiety, polymer-2a, polymer-2b, and polymer-2c, respectively. The UV–vis spectrum of polymer-2c showed absorptions due to the viologen radical cation formed by electron transfer from the polymer backbone to the viologen moiety. The p-doping state of polymer-2c was stable in air. The ESR spectrum of polymer-2c confirmed the generation of the viologen radical. In contrast to photoluminescent polymer-1, the polymers cross-linked by a viologen moiety showed no photoluminescence because the viologen contained within them acted as a quencher. The electrical conductivity of the pellet molded from polymer-2c was higher than that of polymer-1 due to the self-doping in polymer-2c.

Impact of the Extended 1,1′-Bipyridinium Structure on the Electron Transfer and π-Dimer Formation. Spectroelectrochemical and Computational Study

The electrochemical reduction of the extended 1,1′-bipyridinium dication was investigated in detail by means of semiquantitative in situ electron paramagnetic resonance (EPR), UV–vis–NIR spectroelectrochemistry, and density functional theory (DFT) calculations. It was found that in the extended 1,1′-bipyridinium cation radical the spin density is localized on one of the pyridinium centers, which is in contrast to charge delocalization within the 4,4′-bipyridinium radical cation reported in the literature. The charge and spin density separation in the extended 1,1′-bipyridinium cation radical leads to π-dimer formation in a triplet electronic configuration.

1,8‐Dioxyanthracene‐Derived Crown Ethers: Synthesis, Complexation with Paraquat and Assembly of a Tetracationic Cyclophane‐Crown Ether Based [2]Catenane

Abstract1,8‐Dioxyanthracene‐based bisarylene crown ethers, composed of ethylene glycol chains and aromatic moieties, have been synthesized. Complexation studies revealed that these crown ethers could form 1:1 complexes with methyl viologen dication (N,N′‐dimethyl‐4,4′‐bipyridinium dication; MV2+) in a mixed solvent of CDCl3 and CD3CN (1:1 v/v) with association constants in a range of (1.2 ± 0.1) × 103 M–1 to (1.6 ± 0.2) × 104 M–1. The structure of the complex and the strength of the π‐donor/π‐acceptor interactions between the 1,8‐dioxyanthracene planes and the pyridinium rings of MV2+ are highly dependent on the length of the polyether chains of the ethers. Structural analysis showed that the tetraethylene glycol‐derived bis‐1,8‐dioxyanthracene‐based crown ether 9 forms a U‐shaped host‐guest complex with MV2+ by inserting the coplanar pyridinium rings of MV2+ between the two parallel oriented 1,8‐dioxyanthracene units of 9, which is driven predominantly by π‐donor/π‐acceptor interactions. The pentaethylene glycol‐derived bis‐1,8‐dioxyanthracene‐based crown ether 10, however, adopts a crescent‐shaped conformation in complex 10⊃MV2+ with the MV2+ guest being encapsulated by the polyether chains, propelled mainly by the hydrogen‐bonding interactions between the hydrogen atoms of MV2+ and the oxygen atoms of the polyether chains of 10. Similarly, the hexaethylene glycol‐derived bis‐1,8‐dioxyanthracene‐based crown ether 11 forms a complex with MV2+. However, only weak π‐donor/π‐acceptor interactions between the aromatic groups of the mixed bisarylene crown ethers 12 and 13, and MV2+ were observed, and construction of tetracationic cyclophane [CBPQT4+] and crown ether 13 based [2]catenane 15 was achieved through supramolecular interactions between the [CBPQT4+] ring and naphtho unit in the crown ether.

Ion pair charge-transfer thiogermanate salts [MV]2Ge4S10·xSol: solvent induced crystal transformation and photocurrent responsive properties

As most of the chalcogenidometalate anions are well-known electron-rich systems, design and preparation of ion pair compounds, by integrating an organic acceptor (A) with an inorganic chalcogenidometalate donor (D), are an attractive strategy to obtain new functional materials. We report herein the single-crystal structures and properties of three new ion pair charge-transfer (IPCT) compounds by incorporating thiogermanates with methylviologen (MV(2+), N,N'-dimethyl-4,4'-bipyridinium dication), [MV]2Ge4S10·xSol (Sol = solvent). Sharp and fast solvent-induced color changes and switchable fluorescence emission are observed for the compounds. The weak interactions that relate to the solvent and ions in the structures are likely the key points to modulate the cation-anion charge-transfer. A photocurrent response is observed for the photoelectric system of the IPCT compound upon repetitive switching of light on and off.

Pillar[5]arene as a Co-Factor in Templating Rotaxane Formation

After the manner in which coenzymes often participate in the binding of substrates in the active sites of enzymes, pillar[5]arene, a macrocycle containing five hydroquinone rings linked through their para positions by methylene bridges, modifies the binding properties of cucurbit[6]uril, such that the latter templates azide-alkyne cycloadditions that do not occur in the presence of only the cucurbit[6]uril, a macrocycle composed of six glycoluril residues doubly linked through their nitrogen atoms to each other by methylene groups. Here, we describe how a combination of pillar[5]arene and cucurbit[6]uril interacts cooperatively with bipyridinium dications substituted on their nitrogen atoms with 2-azidoethyl- to 5-azidopentyl moieties to afford, as a result of orthogonal templation, two [4]rotaxanes and one [5]rotaxane in >90% yields inside 2 h at 55 °C in acetonitrile. Since the hydroxyl groups on pillar[5]arene and the carbonyl groups on cucurbit[6]uril form hydrogen bonds readily, these two macrocycles work together in a cooperative fashion to the extent that the four conformational isomers of pillar[5]arene can be trapped on the dumbbell components of the [4]rotaxanes. In the case of the [5]rotaxane, it is possible to isolate a compound containing two pillar[5]arene rings with local C5 symmetries. In addition to fixing the stereochemistries of the pillar[5]arene rings, the regiochemistries associated with the 1,3-dipolar cycloadditions have been extended in their constitutional scope. Under mild conditions, orthogonal recognition motifs have been shown to lead to templation with positive cooperativity that is fast and all but quantitative, as well as being green and efficient.

Breaking Aggregation and Driving the Keto-to-gem-Diol Equilibrium of the N,N′-Dimethyl-2,6-diaza-9,10-anthraquinonediium Dication to the Keto Form by Intercalation in Cucurbit[7]uril

(1)H NMR, ESI-MS, and DFT calculations with the M062X/6-31G* method show that, in water, the bistetrafluoroborate salt of N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication (DAAQ·2BF4(-)) exists in equilibrium with both its gem-diol and several aggregates (from dimers to at least octamers). With high concentrations of HCl (e.g., 1.2-1.5 M), all aggregates break up and the keto-to-gem-diol equilibrium is shifted quantitatively toward the quinone form. The same effect is observed with 1.5 mol equiv of cucurbit[7]uril, CB[7], with which all equilibria are shifted toward the quinone form, which undergoes slow exchange with the CB[7] cavity as both the free and the CB[7]-intercalated quinone (DAAQ@CB[7]) are observed simultaneously by (1)H NMR. The affinity of DAAQ for the CB[7] cavity (Keq = 4 × 10(6) M(-1)) is in the range found for tricyclic dyes (0.4-5.4 × 10(6) M(-1)), and among the highest observed to date. A computational comparative study of the corresponding CB[7] complex of the N,N'-dimethyl-4,4'-bipyridinium dication (N,N'-dimethyl viologen, MeV) suggests that the higher binding constant for intercalation of DAAQ may be partially attributed to a lesser distortion of CB[7] (required to maximize favorable nonbonding interactions) as a result of the flat geometry of DAAQ.

Synthesis and chemical properties of electrochromic π‐conjugated polyphenylenes with pendant viologen‐TCNQ salts

AbstractPolyphenylene (PP) with NH2 side groups, namely, PFluNH2, was synthesized by the Pd‐catalyzed reaction of 2,5‐dibromoaniline with 9,9‐dihexylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol) ester. The reaction of PFluNH2 with 1‐hexyl‐1′‐(2,4‐dinitrophenyl)‐4,4′‐bipyridinium diiodide (SaltBPy(I−)) eliminated 2,4‐dinitroaniline to yield PPs with viologen (1,1′‐disubstituted 4,4′‐bipyridinium dications), PFluBPy(I−). The reaction of PFluBPy(I−) with Li+TCNQ− resulted in anion exchange between Cl− and TCNQ−, and yielded PFluBPy(TCNQ−). The reaction of PFluBPy(TCNQ−) with the neutral TCNQ0 resulted in an interaction between TCNQ− and TCNQ0, and yielded PFluBPy(TCNQ−‐TCNQ0). Cyclic voltammetry measurements suggested that an electrochemical reduction of the viologen moiety and oxidation of the polymer backbone within PFluBPy(TCNQ−) and PFluBPy(TCNQ−‐TCNQ0). Furthermore, this reaction was accompanied by electrochromism. The electric conductivities (σ) of the pellets molded from PFluBPy(TCNQ−) to PFluBPy(TCNQ−‐TCNQ0) were 2.7 × 10−4 and 4.2 × 10−4 Scm−1, respectively; these σ values were higher than that observed for PFluNH2 (σ < 10−8 Scm−1) due to the self‐doping in the polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis and properties of new fluorenonocrownophanes having a stilbene fragment and their reaction with paraquat

New crownophanes containing 2,7-dioxyfluorenone and 4,4′-dioxystilbene fragments linked through di-, three, tetra-, and pentaethylene glycol linkers were synthesized. The formation of pseudorotaxanetype host-guest complexes in reactions of these crownophanes with 1,1′-dimethyl-4,4′-bipyridinium dication was detected by fast atom bombardment mass spectrometry, 1H NMR, and electron spectroscopy.

Photoinduced Electron Transfer between Ruthenium-bipyridyl Complex and Methylviologen in Suspensions of Smectite Clays

We examined photoinduced electron transfer (PET) in multicomponent aqueous suspensions composed of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+, photocatalyst), methylviologen (1,1′-dimethyl-4,4′-bipyridinium dication, MV2+, electron acceptor), and ethylenediamine tetraacetate (EDTA, sacrificial electron donor) together with particles of smectite-type clays although previous studies indicated inhibition of the electron transfer from Ru(bpy)32+ to MV2+ in the presence of clay particles. Clays with different lateral particle sizes were compared: hectorite (Hect) and saponite (Sapo) with small particle sizes (∼30 nm) and fluorohectorite (FH) and montmorillonite (Mont) with large particle sizes (>0.1 μm). Clay particles were flocculated and were settled in many cases after the addition of Ru(bpy)32+, MV2+, and EDTA species, and the Ru(bpy)32+ and MV2+ cations were almost all adsorbed on the clay particles. When Hect and Sapo were used, reduction of MV2+ was observed on the aggregated clay particles upon visible light irradiation indicating the occurrence of PET from Ru(bpy)32+ to MV2+. However, the reaction was not observed for the samples where the clay particles were not settled. When FH and Mont were used, PET was not observed irrespective of the flocculation of clay particles. These results demonstrated that PET from Ru(bpy)32+ to MV2+ in the presence of clay particles is possible when the clay particles with small sizes are appropriately aggregated to allow interparticle electron hopping.