Redox-active Guest Research Articles

Para-Phenylenediamine Dimer as a Redox-Active Guest for Supramolecular Systems.

Redox-active components are highly valuable in the construction of molecular devices. We combined two p-phenylenediamines (p-PDA) with a biphenyl (BiPhe) unit to prepare a supramolecular guest 4 consisting of three binding sites for cucurbit[7/8]uril (CBn) and/or cyclodextrins (CD). Supramolecular properties of 4 were investigated using NMR, UV-vis, mass spectrometry and isothermal titration calorimetry. Our analysis revealed that 4 forms higher-order host-guest complexes, wherein a CD unit occupies the central BiPhe site, secured by two CBn units at the terminal p-PDA sites. Additionally, 1 : 1 complexes with α-CD and β-CD, a 1 : 2 complex with γ-CD and 2 : 1 complexes with CB7 and CB8 were identified. Through UV-vis and cyclic voltammetry, redox processes leading to the formation of a stable, deep blue dication diradical of 4 are elucidated. Furthermore, it is demonstrated that CB7 selectively protects oxidised 4 from reduction in the presence of a reducing agent. The supramolecular and redox properties of the structural motif represented by 4 render it an interesting candidate for the construction of supramolecular devices.

Tunable electrical conductivity in covalent organic frameworks by intercalation of electron acceptor molecules

Covalent organic frameworks (COFs) are crystalline organic materials with high porosity. The COFs are typically electrical insulators because of their wide bandgaps and closed-shell structures despite their π–π layer stacking motif suitable for carrier conduction. Here, we report a strategy for realizing tunable electrical conductivity in COFs by intercalating redox-active guest molecules. The approach is demonstrated using COF-5 with a boronate-ester-linked two-dimensional structure and one-dimensional nanopore channels infiltrated by 7,7,8,8-tetracyanoquinododimethane (TCNQ). Successful incorporation of guest TCNQ molecules into the cavities of the COF-5 host is confirmed by vibrational and optical spectroscopies and results in the appearance of guest–host charge-transfer transitions for TCNQ-intercalated COF-5. Overall electrical conductivities are enhanced by the carrier generation induced by the charge transfer between TCNQ and COF-5 with the retained layer-stacked structures in COF-5 also contributing to the conduction pathways. The tunable electronic properties of COFs realized by the host–guest strategies established here will further promote refinement of design principles of conductive COFs and deeper understanding of the conduction mechanism while simultaneously providing opportunities for using COFs in diverse applications.

Mechanochemical Impregnation of a Redox-Active Guest into a Metal–Organic Framework for Electrochemical Capture of CO2

Conventional adsorbents for CO2 capture typically utilize swings in temperature and/or pressure to adsorb and desorb CO2. These mechanisms can be energy-intensive, which has inspired further research on alternative capture mechanisms such as electro-swing CO2 capture. For this, metal–organic frameworks (MOFs) have been suggested as a potential adsorbent owing to their stability, ultrahigh surface areas, and ability to facilitate redox reactions. However, MOFs have not yet been utilized for the electrochemical capture of CO2. In this work, we demonstrate the facile synthesis of a redox-active MOF-based adsorbent for the electrochemical capture of CO2, and we employ spectroelectrochemistry to understand the adsorbent’s interaction with CO2. This represents an advancement toward the scalable production of electro-swing adsorbents and signals that MOFs can be successfully employed for this process.

Catalytic electron drives host-guest recognition.

Electron injection is demonstrated to trigger electrocatalytic chain reactions capable of releasing a solvent molecule and forming a redox active guest molecule. One-electron reduction of a hydroxy anthrone derivative (AQH–CH2CN) results in the formation of an anthraquinone radical anion (AQ˙−) and acetonitrile (CH3CN). The resulting fragment of AQ˙− exhibits high stability under mild reducing conditions, and it has enough reducing power to reduce the reactant of AQH–CH2CN. Hence, subsequent electron transfer from AQ˙− to AQH–CH2CN yields the secondary AQ˙− and CH3CN, while the initial AQ˙− is subsequently oxidized to AQ. Overall, the reactants of AQH–CH2CN are completely converted into AQ and CH3CN in sustainable electrocatalytic chain reactions. These electrocatalytic chain reactions are mild and sustainable, successfully achieving catalytic electron-triggered charge-transfer (CT) complex formation. Reactant AQH–CH2CN is non-planar, making it unsuitable for CT interaction with an electron donor host compound (UHAnt2) bearing parallel anthracene tweezers. However, conversion of AQH–CH2CN to planar electron acceptor AQ by the electrocatalytic chain reactions turns on CT interaction, generating a host CT complex with UHAnt2 (AQ ⊂ UHAnt2). Therefore, sustainable electrocatalytic chain reactions can control CT interactions using only a catalytic amount of electrons, ultimately affording a one-electron switch associated with catalytic electron-triggered turn-on molecular recognition.

Shape-Adaptability and Redox-Switching Properties of a Di-Gold Metallotweezer.

The use of a carbazolyl‐connected di‐gold(I) metallotweezer for the encapsulation of several electron‐poor organic substrates, and a planar Au(III) complex containing a CNC pincer ligand, is described. The binding affinity of the receptor depends on the electron‐deficient character of the planar guest, with larger association constants found for the more electron‐poor guests. The X‐ray diffraction molecular structures of two host:guest adducts show that the host approaches its arms in order to facilitate the optimum interaction with the surface of the planar guests, in a clear example of an guest‐induced fit conformational arrangement. The electrochemical studies of the encapsulation of N,N’‐dimethyl‐naphthalenetetracarboxy diimide (NTCDI) show that the redox active guest is released from the receptor upon one electron reduction, thus constituting an example of redox‐switchable binding.

A conductive anionic Co-MOF cage with zeolite framework for supercapacitors

Conductive MOFs could exhibit full potential as integrated electrode materials for supercapacitors without interference from additional conductive additives. Here we report an anionic Co-MOF cage with zeolite framework, which was balanced by the redox-active guest [Co(H2O)6]2+ and protonated [(CH3)2NH2]2+ ions. Benefit from the unique ion skeleton structure, Co-MOF exhibits a conductivity higher than most of reported MOFs with the value of 1.42 × 10-3 S/cm, which can be directly fabricated as electrode for supercapacitors. A maximum specific capacitance of 236.2 F/g can be achieved at a current density of 1 A/g of Co-MOF. Additionally, the electric performance and morphology of this Co-MOF can be modified by cetyltrimethylammonium bromide (CTAB) and the maximum specific capacitance could increase up to 334 F/g at 1 A/g when the ratio of ligand and CTAB is 1:6 (Co-MOF-6). Furthermore, the specific capacitance can retain at 64.04% and 77.92% of the initial value after 3000 cycles of Co-MOF and Co-CTAB-6, respectively. Obviously, the addition of CTAB further improves both capacitance and cycle stability.

Redox-Guest-Induced Multimode Photoluminescence Switch for Sequential Logic Gates in a Photoactive Coordination Cage.

Molecular or supramolecular level photoluminescence (PL) modulation combining chemical and photonic input/output signals together in an integrated system can provide potential high-density data memorizing and process functions intended for miniaturized devices and machines. Herein, a PL-responsive supramolecular coordination cage has been demonstrated for complex interactions with redox-active guests. PL signals of the cage can be switched and modulated by adding or retracting Fc derivatives or converting TTF into different oxidation states through chemical or photochemical pathways. As a result, reversible or stepwise PL responses are displayed by these host-guest systems because of the occurrence of photoinduced electron-transfer (PET) or fluorescence resonance energy transfer (FREnT) processes, providing unique nanodevice models bearing off/on logic gates or memristor-like sequential memory and Boolean operation functions.

Metal-Organic Frameworks with Open Metal Sites for Sensing, Catalysis, and Energy Storage

Metal-Organic Frameworks (MOFs) are a class of coordination polymer in which metal ions and organic electron donors (“linkers”) assemble to form crystalline structures with stable nanoporosity. As a result of well-understood principles governing inorganic coordination chemistry and the rigidity and topology of the linkers, rational design principles have been established that allow MOFs to be designed and synthesized with properties selected for specific applications. Among the thousands of known MOFs, those with incomplete coordination shells around the metal ion (also known as open metal sites, or OMS) exhibit unique properties, including increased uptake of weakly interacting gases such as H2 and CH4, catalytic behavior resulting from substrate coordination to the OMS, and guest-dependent electrical conductivity that provides an avenue to electronic devices and sensors. This presentation will provide an introduction to MOFs and MOFs with OMS, then illustrate their possibilities using examples from our recent research: 1) catalytic cleavage of carbon-oxygen bonds found in lignin using activated H2; 2) colorimetric sensing; and 3) creation of electrically conducting MOFs using redox-active guest molecules such as TCNQ (7,7,8,8-tetracyanoquinodimethane). In each of these examples, guest molecules in the MOF pores interact directly with the OMS, resulting in bond polarization, modification of the electronic structure of the metal ion, and/or charge transfer between the metal ion and the guest. In the case of C-O bond cleavage, chemisorption of substrate ether molecules to Mg(II) ions in the IRMOF-74 series weakens the C-O bond. In addition, the MOF activates H2 molecules in solution with the substrate, as shown by isotope exchange experiments. Colorimetric sensing is enabled by guest binding to Cu(II) ions in the MOF known as HKUST-1, resulting in new charge-transfer transitions in the visible and near-UV. These perturbations of the electronic structure are relatively minor compared with the binding of TCNQ, a pi acid that bridges between two dimeric copper units in HKUST-1, creating a pathway for charge transport via a hopping mechanism. These results demonstrate that the novel features of MOFs with OMS provide the means to achieve completely new classes of catalysts and materials for chemical sensing and other electronic devices.

Molecular Clusters: Nanoscale Building Blocks for Solid-State Materials.

The programmed assembly of nanoscale building blocks into multicomponent hierarchical structures is a powerful strategy for the bottom-up construction of functional materials. To develop this concept, our team has explored the use of molecular clusters as superatomic building blocks to fabricate new classes of materials. The library of molecular clusters is rich with exciting properties, including diverse functionalization, redox activity, and magnetic ordering, so the resulting cluster-assembled solids, which we term superatomic crystals (SACs), hold the promise of high tunability, atomic precision, and robust architectures among a diverse range of other material properties. Molecular clusters have only seldom been used as precursors for functional materials. Our team has been at the forefront of new developments in this exciting research area, and this Account focuses on our progress toward designing materials from cluster-based precursors. In particular, this Account discusses (1) the design and synthesis of molecular cluster superatomic building blocks, (2) their self-assembly into SACs, and (3) their resulting collective properties. The set of molecular clusters discussed herein is diverse, with different cluster cores and ligand arrangements to create an impressive array of solids. The cluster cores include octahedral M6E8 and cubane M4E4 (M = metal; E = chalcogen), which are typically passivated by a shell of supporting ligands, a feature upon which we have expanded upon by designing and synthesizing more exotic ligands that can be used to direct solid-state assembly. Building from this library, we have designed whole families of binary SACs where the building blocks are held together through electrostatic, covalent, or van der Waals interactions. Using single-crystal X-ray diffraction (SCXRD) to determine the atomic structure, a remarkable range of compositional variability is accessible. We can also use this technique, in tandem with vibrational spectroscopy, to ascertain features about the constituent superatomic building blocks, such as the charge of the cluster cores, by analysis of bond distances from the SCXRD data. The combination of atomic precision and intercluster interactions in these SACs produces novel collective properties, including tunable electrical transport, crystalline thermal conductivity, and ferromagnetism. In addition, we have developed a synthetic strategy to insert redox-active guests into the superstructure of SACs via single-crystal-to-single-crystal intercalation. This intercalation process allows us to tune the optical and electrical transport properties of the superatomic crystal host. These properties are explored using a host of techniques, including Raman spectroscopy, SQUID magnetometry, electrical transport measurements, electronic absorption spectroscopy, differential scanning calorimetry, and frequency-domain thermoreflectance. Superatomic crystals have proven to be both robust and tunable, representing a new method of materials design and architecture. This Account demonstrates how precisely controlling the structure and properties of nanoscale building blocks is key in developing the next generation of functional materials; several examples are discussed and detailed herein.

A giant M2L3 metallo-organic helicate based on phthalocyanines as a host for electroactive molecules.

An unprecedented Fe2Pc3 metallo-organic helicate has been assembled using a bidentate phthalocyanine (Pc) ligand, 2-formylpyridine and Fe(OTf)2. This giant helicate has proved itself as a host for large redox-active guests such as fullerene and naphthalenediimide derivatives. Photoactivated electronic interactions between components occur in the host-guest complex.

Incorporation of Redox-active Guest in Conductive and Redox-active Host: Hierarchically Structured Composite of a Conductive Polymer and Quinone Derivative

Hierarchically structured composite of polypyrrole (PPy) and 1,4-naphthoquinone (NQ) was prepared by incorporation of the guest redox-active organic molecule NQ in the host redox-active conductive polymer PPy. The composite and its hierarchical structure induced enhanced electrochemical performances as a redox capacitor in an aqueous electrolyte.

(Invited) Thin Film Thermoelectric Metal-Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity

Metal-organic frameworks (MOFs) are extended, crystalline compounds consisting of metal ions interconnected by organic ligands such as benzene carboxylates, forming a crystalline, nanoporous structure. The low atomic density and long, bridge-like bonding characteristic implies that MOFs should exhibit low thermal conductivity, which is an attractive feature for thermoelectric energy conversion. However, most MOFs are electrical insulators due to the non-conjugated character of the organic ligands and poor overlap between their pi orbitals and the valence orbitals of the metal ions. Recently, we discovered that infiltrating the pores of the copper-containing MOF Cu3(BTC)2 with redox-active guest molecules TCNQ (7,7,8,8-tetracyanoquinododimethane) increases the electrical conductivity of thin film devices by as much as seven orders of magnitude [1]. Density functional theory indicates that electrical conductivity results from a donor-bridge-acceptor geometry, in which TCNQ binds to two Cu(II) dimer units within the MOF pore. In this paper we report the first thermoelectric properties characterization of a MOF thin film which yield a positive Seebeck coefficient of ~400 uV/K, in qualitative agreement with DFT calculations which also indicate that holes should be the dominant charge carriers in TCNQ@Cu3(BTC)2. Finally, we present results of molecular dynamics simulations which indicate that the phonon thermal conductivity of Cu3(BTC)2 MOF is indeed low, thus further suggesting that conducting MOFs are promising materials for thermoelectric energy conversion [2]. [1] A. A. Talin, A. Centrone, M. E. Foster, V. Stavila, P. Haney, R. A. Kinney, V. Szalai, F. El Gabaly, H. P. Yoon, F. Léonard, M. D. Allendorf, Science 343, 66 (2014) [2] K. J. Erickson , F. Léonard , V. Stavila , M. E. Foster, C. D. Spataru , R. E. Jones , B. M. Foley, P. E. Hopkins, M. D. Allendorf, and A. A. Talin, Adv. Mater. DOI: 10.1002/adma.201501078 (2015).

Two distinct redox intercalation reactions of hydroquinone with porous vanadium benzenedicarboxylate MIL-47.

One of the enticing features of metal-organic frameworks (MOFs) is the potential to control the chemical and physical nature of the pores through postsynthetic modification. The incorporation of redox active guest molecules inside the pores of the framework represents one strategy toward improving the charge transport properties of MOFs. Herein, we report the vapor-phase redox intercalation of an electroactive organic compound, hydroquinone (H2Q) or benzene-1,4-diol, into the channels of the host [V(IV)O(bdc)], (bdc =1,4-benzenedicarboxylate) conventionally denoted as MIL-47. The temperatures and especially the atmosphere in which the reactions took place were found to determine the products. In ambient atmosphere, quinhydrone charge-transfer complexes are formed inside the channels. Under anhydrous conditions, the framework itself was functionalized by a radical anion species derived from the pyrolysis of hydroquinone. Both cases are accompanied by the reduction of V(4+) to V(3+) via single-crystal-to-single-crystal transformations. The products were characterized by single crystal X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and electron paramagnetic resonance spectroscopy.

ChemInform Abstract: Toward Reversible Control of Cucurbit[n]uril Complexes

AbstractReview: 39 refs.

Molecule@MOF: A New Class of Electronic Materials

Conducting organic polymers are highly attractive electronic materials, having the advantages of low-cost fabrication routes, tunable electronic properties, and mechanical flexibility. Unfortunately, their charge mobility relative to traditional inorganic semiconductors is poor due in part to microstructural disorder. A new class of synthetically flexible, crystalline materials known as Metal-Organic Frameworks (MOFs) could solve the disorder problem, providing within a single material the highly ordered structure of inorganic conductors with the tunable properties and low cost of organics. MOFs are inorganic-organic hybrids consisting of metal cations linked by organic groups such as carboxylates and amines, forming a crystalline, nanoporous structure. With record-setting surface areas (>7000 m2/g), they are ideal for applications such as CO2sequestration and catalysis. While efforts to develop MOFs for these applications made major strides over the past decade, electrically conducting frameworks would open up a host of other promising avenues, such as novel electronic devices, photovoltaics, supercapacitors, and electrocatalysts. Recently, we discovered that infiltrating the pores of the copper-containing MOF HKUST-1 with redox-active guest molecules, such as TCNQ (7,7,8,8-tetracyanoquinododimethane), increases the electrical conductivity of thin film devices by as much as seven orders of magnitude [1]. This emergent property results from a novel donor-bridge-acceptor geometry, in which TCNQ binds to two Cu(II) dimer units within the MOF pore. In this presentation I will describe the synthesis and characterization of Molecule@MOF materials. Coupling these results with first-principles electronic structure calculations demonstrates that conductivity occurs via a hopping mechanism facilitated by the bridging TCNQ. From these results it will be clear that Molecule@MOF represents a novel class of electronic materials with the potential to bridge the properties gap between inorganic and organic conductors, providing a high degree of electronic tailorability combined with long-range order for high charge mobility. Figure 1 Process for fabrication of conductive metal-organic framework thin film devices, and electrical characterization data. (A) A thin film of metal-organic framework is grown on an insulating wafer pre-patterned with electrodes. Molecules are then infiltrated by exposing the thin film device to a solution containing the molecules. (B) A TCNQ molecule shown above a Cu3(BTC)2 MOF with arrow pointing to the pore. Atom color code: white – hydrogen, blue – nitrogen, cyan – carbon, red – oxygen, ochre (light brown) – copper. (C) SEM image of MOF thin film device with optical images of devices before and after TCNQ infiltration (the rectangular features are Au electrodes overcoated with the MOF film (D) Current-voltage characteristics before and after TCNQ infiltration indicating an increase in conductivity of ×107 or larger. Trace colors represent different electrode gaps[1] A. A. Talin, A. Centrone, A. Ford, M. E. Foster, V. Stavila, P. Haney, R. A. Kinney, V. Szalai, F. El Gabaly, H. P. Yoon, F. Léonard, M. D. Allendorf, Science 343, 66 (2014)

Toward Reversible Control of Cucurbit[n]uril Complexes

CONSPECTUS: The cucurbit[n]uril (CBn) host family consists of a group of rigid macrocyclic hosts with barrel-like shapes and limited solubility in aqueous media. These hosts are capable of reaching high binding affinities with positively charged hydrophobic guests. In optimum cases, equilibrium association constant (K) values as high as 10(17) M(-1) have been reported, exceeding the binding affinity of the avidin-biotin host-guest pair. The synthetic CBn receptors have shattered the notion that highly stable noncovalent complexes can form only when one of the partners is a molecule of biological origin. The work described in this Account is concerned with the development of methods geared toward the reversible modulation of the binding affinity of CBn inclusion complexes under mild conditions. A good fraction of the research work has dealt with redox active guests, such as 4,4'-bipyridinium (viologen), ferrocene, and cobaltocenium derivatives. Our experimental results show that the thermodynamics and kinetics of the electron transfer reactions of these compounds can be substantially altered by complexation with CBn hosts, and therefore, electron transfer reactions can be used to exert a measure of control on the overall binding affinity of the CBn complexes. We have also developed systems in which proton transfer reactions have a strong effect on the binding affinity. With more structurally elaborate guests containing more than one adjacent binding sites, proton transfer reactions may affect the average location of the CBn host within the complexes. A series of guest compounds containing paramagnetic 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residues also exhibit interesting binding properties with CB7 and CB8. The latter host forms a very stable host-guest pair with TEMPO subunits, in which the nitroxide group resides inside the host cavity. Finally, with suitable ditopic guests, we have detected distinct microscopic complexes using experimental techniques with relatively slow time scales, such as NMR spectroscopy. These unusual findings are the result of the considerable thermodynamic and kinetic stability of CBn inclusion complexes.

Electrochemistry of double-wall carbon nanotubes encapsulating C60 and their spectral characterization

Electrochemistry of double-wall carbon nanotubes (DWCNTs) encapsulating C60 (C60@DWCNT) have been studied by preparing a C60@DWCNT modified electrode, and three pairs of reversible electro-reduction waves corresponding to electron transfer reactions of C60 inside DWCNTs have been obtained in a mixed solvent of toluene and acetonitrile (4:1, v:v) containing tetrabutylammonium cation as supporting electrolyte, which indicates that DWCNTs act as molecular wires to allow electrical communication between the underlying electrode and the redox-active guest C60. The influencing factors on the electrochemistry of C60@DWCNT modified electrodes have been investigated. The results suggest that the voltammetric behavior of C60@DWCNT is dependent on the nature of the supporting electrolyte and the solvent system. In addition, spectral characterization of the C60@DWCNT modified electrodes before and after electrochemical scanning reveals interaction between C60 and DWCNT and verifies the reduction of C60 encapsulated in DWCNTs. C60 molecules inside DWCNTs retains their redox activity, and can also act as an electron-transfer mediator to electrocatalyze the reduction of halohydrocarbon.

Cucurbiturils as Versatile Receptors for Redox Active Substrates

AbstractResearch on the chemistry of cucurbit[n]uril (CBn) hosts has picked up and maintained an impressive pace in the last decade, primarily due to the isolation of hosts with relatively larger cavity sizes, such as CB7 and CB8. This review article summarizes our involvement in this research effort, with particular emphasis on the binding of redox active guests by the CB7 and CB8 hosts. The binding of 4,4′‐bipyridinium (viologen) derivatives was the starting point of our CB research. While methylviologen is encapsulated by CB7, forming a highly symmetric inclusion complex, more hydrophobic viologens are bound by inclusion of one of the terminal N‐substituents inside the host cavity. Cationic ferrocene derivatives reach extremely high binding affinities with CB7. Binding by CB8 offers additional possibilities, since this host may accommodate two aromatic units inside its cavity, which can be utilized to exert redox control on the assembly of suitably dendronized guests. From a purely electrochemical standpoint, CB7‐included viologens maintain their voltammetric reversibility, but CB7‐included ferrocene residues experience a pronounced attenuation of their electron transfer kinetics. We have also applied these binding and electrochemical properties to the design and preparation of switchable, CB‐based pseudorotaxanes.

Molecular Logic Gates Using Surface-Enhanced Raman-Scattered Light

A voltage-activated molecular-plasmonics device was created to demonstrate molecular logic based on resonant surface-enhanced Raman scattering (SERS). SERS output was achieved by a combination of chromophore-plasmon coupling and surface adsorption at the interface between a solution and a gold nanodisc array. The chromophore was created by the self-assembly of a supramolecular complex with a redox-active guest molecule. The guest was reversibly oxidized at the gold surface to the +1 and +2 oxidation states, revealing spectra that were reproduced by calculations. State-specific SERS features enabled the demonstration of a multigate logic device with electronic input and optical output.

Cucurbituril Complexes of Redox Active Guests

This review summarizes recent work on the chemistry of inclusion complexes formed between redox active guests and cucurbit [n]uril hosts. The large majority of the surveyed research concerns the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8), while the guests are 4,4-bipyridinium (viologen) and ferrocene derivatives. The work includes dendronized guests, in which a guest residue is attached to a dendron in such a way that host-guest binding interactions are still possible. The main focus of the review is on the electrochemical behavior of the included guests. In general terms complexation by CB7 has a more pronounced effect on the ferrocene derivatives, giving rise to a measurable attenuation of the electrochemical kinetics. In contrast to this, the electrochemical kinetics of the viologen derivatives remains fast (in the voltammetric time scale, with scan rates up to 2 V s-1) upon inclusion complexation by CB7. The larger cavity host CB8 is extremely effective at mediating the redox-driven self-assembly of dendronized viologens. Keywords: Host-guest complexes, electrochemistry, cucurbituril hosts, ferrocene, cobaltocenium, viologen, cucurbit[n]uril (CBn), glycoluril, cyclodextrin, spectroscopic methods, stoichiometry, aromatic protons, pseudorotaxane complex, electrochemical techniques, dialkoxybenzene, voltammograms, cobaltocenium (Cb), ferrocenemethanol, half-wave, dendrimers, metallocene binding