Metal-containing polymers via electropolymerization

Electropolymerization of Donor-Acceptor Conjugated Polymer for Efficient Dual-Ion Storage

Rationally designed organic redox-active materials have attracted numerous interests due to their excellent electrochemical performance and reasonable sustainability. However, they often suffer from poor cycling stability, intrinsic low operating potential, and poor rate performance. Herein, a novel Donor-Acceptor (D-A) bipolar polymer with n-type pyrene-4,5,9,10-tetraone unit storing Li cations and p-type carbazole unit which attracts anions and provides polymerization sites is employed as a cathode for lithium-ion batteries through in situ electropolymerization. The multiple redox reactions and boosted kinetics by the D-A structure lead to excellent electrochemical performance of a high discharge capacity of 202 mA h g-1 at 200 mA g-1, impressive working potential (2.87 and 4.15 V), an outstanding rate capability of 119 mA h g-1 at 10 A g-1 and a noteworthy energy density up to 554 Wh kg-1. This strategy has significant implications for the molecule design of bipolar organic cathode for high cycling stability and high energy density.

Electroactive Behavior of Adjustable Vinylferrocene Copolymers in Electrolyte Media

The redox-active properties of a series of ferrocene-containing vinyl polymers were investigated in aqueous and organic media. Each metallopolymer contained vinylferrocene (VFc) and a non-redox-active species (X), and was combined with carbon nanotubes (CNT) to generate P(VFcn-co-X1-n)-CNT composites for heterogeneous electrochemical analysis. Tunable pseudocapacitances spanning ca. 0.03-280 F/g VFc in aqueous solution were achieved by varying the copolymer composition, with P(VFc0.11-co-HEMA0.89) producing standardized values at ca. 160-180 F/g VFc even for differently hydrated anions. Additionally, the polymer-bound ferrocene/ferrocenium redox potential was seen to depend prominently on its electrolyte anion's Gibbs free energy of hydration. Although the hydrophilic chloride anion negatively influenced the electrochemical stability of the VFc units when in their PVFc homopolymer, copolymerizing them with 2-hydroxyethyl methacrylate (HEMA) and introducing perchlorate anions ameliorated their overall capacity retention by 64% and 38%, respectively. Lastly, the electrodes' responses in aprotic and protic solvents were examined for correlations with numerous solvent polarity metrics and solubility measures, with a notable observation being the stability and pseudocapacitive increase of the styrene (St)-containing P(VFc0.27-co-St0.73)-CNT from 5 to ca. 190 F/g VFc when in methanol instead of water. This study can help provide insight regarding material design considerations for redox moiety implementation in electrochemical applications.

Polyoxovanadate-Based Cyclomatrix Polyphosphazene Microspheres as Efficient Heterogeneous Catalysts for the Selective Oxidation and Desulfurization of Sulfides

The [V₆O₁₃]^2- cluster is successfully immobilized to the polymeric framework of cyclomatrix polyphosphazene via the facile precipitation polymerization between the phenol group symmetrically modified [V₆O₁₃]^2- and hexachlorocyclotriphosphazene. The structure of the as-prepared polyoxometalate-containing polyphosphazene (HCCP-V) was characterized by FT-IR, XPS, TGA, BET, as well as SEM and zeta potential. The presence of a rigid polyoxometalate cluster not only supports the porous structure of the polymeric framework but also provides an improved catalytic oxidation property. By using H₂O₂ as an oxidant, the as-prepared HCCP-V exhibited improved catalytic oxidation activity toward MPS, DBT, and CEES, which can achieve as high as 99% conversion. More importantly, the immobilization of POMs in the network of cyclomatrix polyphosphazene also provides better recyclability and stability of the heterogeneous catalyst.

Metal-Terpyridine Assembled Functional Materials for Electrochromic, Catalytic and Environmental Applications

Molecular assembly induced by metal-terpyridine-based coordinative interactions has become an emergent research topic due to its ease of synthesis and diverse applications. This article highlights recent significant developments in the metal-terpyridine-based supramolecular architectures. At first, the design aspect of the molecular building blocks has been described, followed by elaboration on how the ligand backbone plays an important role for achieving different dimensionalities of the resulting assemblies which exhibit a wide range of potential applications. After that, we discussed different synthetic approaches for constructing these assemblies, and finally, we focused on their significant developments in three specific areas, viz., electrochromic materials, catalysis and a new application in wastewater treatment. In the field of electrochromic materials, these assemblies made important advancements in various aspects like sub-second switching time (<1 s), low switching voltage (<1 V), increased switching stability (>10000 cycles), tuning of multiple colors by using multimetallic systems, fabrication of charge storing electrochromic devices, utilizing and storing solar energy etc. Similarly, the catalysis field witnessed application of the metal-terpyridine assemblies in C-H monohalogenation, heterogeneous Suzuki-Miyaura coupling, photocatalysis, reduction of carbon dioxide, etc. Finally, the environmental application of these coordination assemblies includes capturing Cr(VI) from waste water efficiently with high capture capacity, good recyclability, wide pH independency etc.

Impact of Counteranion on Reversible Spin-State Switching in a Series of Cobalt(II) Complexes Containing a Redox-Active Ethylenedioxythiophene-Based Terpyridine Ligand

The self-assembly of a redox-active ethylenedioxythiophene (EDOT)-terpyridine-based tridentate ligand and cobalt(II) unit with different counteranions has led to a series of new cobalt(II) complexes [Co(L)₂](X)₂ (X = BF₄ (1), ClO₄ (2), and BPh₄ (3)) (L = 4'-(3,4-ethylenedioxythiophene)-2,2':6',2″-terpyridine). The impact of various counteranions on stabilization and spin-state switching of the cobalt(II) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical studies. All three complexes 1-3 consisted of an isostructural dicationic distorted octahedral CoN₆ coordination environment offered by the two L ligands in a bis-meridional fashion and BF₄^-, ClO₄^-, and BPh₄^- as a counteranion, respectively. Complex 2 with ClO₄^- counteranion showed a reversible, gradual, and nearly complete spin-state switching between low-spin (LS) (S = 1/2) and high-spin (HS) (S = 3/2) states, while an incomplete spin-state switching behavior was observed for complexes 1 (BF₄^-) and 3 (BPh₄^-) in the measured temperature range of 350-2 K. The non-covalent cation-anion interactions played a significant role in stabilizing the spin-state in 1-3. Additionally, complexes 1-3 also exhibited interesting redox-stimuli-based reversible paramagnetic HS cobalt(II) (S = 3/2) to diamagnetic LS cobalt(III) (S = 0) conversion, offering an alternate way to switch the magnetic properties.

Reductive Electropolymerization and Electrochromism of Iron(II) Complex with Styrene-Based Ligand

The benzimidazole-based ligand containing polymerizable styrene group has been prepared via condensation of picolinaldehyde derivative containing styrene moiety and benzimidazole-based hydrazine. The ligand reacted with iron(II) tetrafluoroborate and iron(II) trifluoromethanesulfonate giving red-brown complexes of Fe(II) ions of formula [FeL₂]X₂, where X = CF₃SO₃⁻ (1) or BF₄⁻ (2). Reductive electropolymerization was used to obtain a thin layer of the polymeric complex, poly-1. Further investigation of electrochemical properties of the compound by cyclic voltammetry showed two quasi-reversible redox processes assigned to electrooxidation and electroreduction of the polymer. Spectroelectrochemical measurements confirmed that the polymer undergoes the color changes during oxidation and reduction process. The polymer in its neutral state (Fe(II)) is yellow and it exhibits absorption band at 370 nm, after oxidation to Fe(III) state absorption band shifts to 350 nm and the polymer is almost colorless. While the metal ions are reduced to Fe(I) absorption band at around 410 nm has been observed and the polymer changed its color to intense yellow. The stability of the polymer during multiple oxidation/reduction cycles has also been investigated.

Unusual Photoelectrochemical Properties of Electropolymerized Films of a Triphenylamine-Containing Organic Small Molecule

The electropolymerized films of poly(L)_n on an indium-tin oxide (ITO) electrode was prepared by anodic electrooxidation of a dichloromethane solution of a triphenylamine-carrying organic molecule L and were characterized/studied by ultraviolet-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, electrochemical impedance spectroscopy, cyclic voltammetry, and photoelectrochemical measurements. Poly(L)_n films were found to show surface-controlled TPA^•+1/0 associated quasi-reversible redox and exceptionally high photocurrent generation properties. At a zero external bias potential and under 100 mW/cm² white light irradiation, a photoelectrochemical device composed of a poly(L)₁-modified ITO as the working electode, a platinum disk counter electrode, and saturated calomel electrode reference electrode in a 0.1 M Na₂SO₄ aqueous solution exhibited a significant cathode photocurrent density of 2.2 μA/cm², which could be switched to be anodic and outperform most previously reported molecule-based modified ITO electrodes under similar experimental conditions. The results indicate that poly(L)_n films offer a number of future perspectives ranging from organic photovoltaic to photoelectrochemical catalysis and sensing.

Synthesis and electropolymerization of N-heterocyclic carbene complexes of Pd(ii) and Pt(ii) from an emissive imidazolium salt with a terthiophene backbone

The synthesis of an emissive terthiophene-based imidazolium iodide: 1,3-dimethyl-4,6-di(thiophen-2-yl)-thienoimidazol-3-ium iodide (4), the corresponding N-heterocyclic carbene (NHC) preligand, and Pd and Pt-NHC complexes (5a, 5b) are reported. A related Pd-NHC complex (8) with a mono-thiophene backbone has also been synthesized. The solid-state structures were determined by single crystal X-ray diffraction studies. Compounds 4, 5a and 5b were characterized by absorption/emission spectroscopy and an emission-quench phenomenon of 5a was observed. The Pd complexes 5a and 8 were shown to catalyze Heck type C-C bond forming reactions. The compounds with terthiophene backbones (4, 5a, 5b) were electropolymerized onto indium tin oxide (ITO)-coated glass electrodes to yield thin films of conducting metallopolymers (CMPs) (P1-3). UV-vis-NIR spectroelectrochemistry data of P1-3 showed reversible color changes upon oxidation due to the generation of charge carrier species along the polythiophene backbones.

On-Surface Self-Assembly of Stimuli-Responsive Metallo-Organic Films: Automated Ultrasonic Spray-Coating and Electrochromic Devices

We demonstrate the on-surface formation of homogeneous and uniform electrochromic films via ultrasonic spray coating. This fully automated process is capable of fabricating metallo-organic films on transparent conducting oxides (TCOs) on glass or flexible poly(ethylene terephthalate) (PET) with surface areas of up to 36 cm² and film thicknesses of half a micron. The assembly process involves alternatingly spray-coating dilute solutions of structurally well-defined iron polypyridyl ([Fe(mbpy-py)₃]²⁺) complexes and bis(benzonitrile)palladium dichloride (Pd(PhCN)₂Cl₂) onto conductive substrates, where the latter palladium salt was used as the inorganic cross-linker. The on-surface self-assembled three-dimensional networks are intensely colored and were subsequently integrated into laminated electrochromic devices (ECDs) containing a lithium-based gel electrolyte. The ECDs retain their intense color in the ground state, having a Δ T_max of 40-49% at λ_max ≈ 600 nm, and can be operated for up to 1500 redox cycles. The fluorine-doped tin oxide counter electrode coated with poly(3,4-ethylene-dioxythiophene)polystyrene sulfonate (PEDOT:PSS) as a charge-storage layer resulted in these stable devices. A significant decrease in the potential window of Δ E ≈ 2.5 V was achieved by using a metal grid on PET as the counter electrode. The operation of the electrochromic films is diffusion-controlled, and the diffusion coefficients ( D_f) reflect their molecular densities. During these studies, we found that ClO₄^- is a suitable counterion of the lithium-based electrolytes for optimal ECD performance.

Stabilization of a Cyclometalated Ruthenium Sensitizer on Nanocrystalline TiO2 by an Electrodeposited Covalent Layer

A cyclometalated ruthenium sensitizer 3 containing a triphenylamine unit was synthesized and immobilized on a nanocrystalline TiO₂ surface. By using oxidative electrochemical deposition, a covalent layer of a related cyclometalated ruthenium complex 2 was coupled to the top of dye 3. Electrochemical studies suggested that complex 2 was immobilized on the TiO₂/3 film surface by a tetraphenylbenzidine linker to form a dimer-like structure. The immobilization of 3 and 2 was further supported by absorption spectral analysis. The resulting electrodeposited TiO₂/(3+2) film displays significantly enhanced sensitizer stabilization toward basic aqueous NaOH solution with respect to the original TiO₂/3 film. The dye-sensitized solar cells with the TiO₂/(3+2) photoanode display a power conversion efficiency of 4.4%, which is slightly inferior to that with the TiO₂/3 film (5.1%) under the same measurement conditions.

Nanocrystalline Sb-doped SnO2 films modified with cyclometalated ruthenium complexes for two-step electrochromism

Sb-Doped nanocrystalline SnO2 (SnO2:Sb) thin films functionalized with cyclometalated ruthenium complexes 1 or 2 on FTO conductive glasses have been prepared and characterized. These complexes contain a redox-active amine unit separated from the ruthenium ion by a phenyl or biphenyl linker, respectively, to modify the absorption wavelengths at different redox states. Near-infrared electrochromism of both films has been examined by oxidative spectroelectrochemical measurements and double-potential-step chronoamperometry. A contrast ratio (ΔT%) of 33% at 1070 nm and 63% at 696 nm has been achieved for the SnO2:Sb/1 film in two stepwise oxidation processes, respectively. The other film with complex 2 shows two-step electrochromism at 1310 and 806 nm with ΔT% of 36% and 76%, respectively. The response time of electrochromic switching is around a few seconds. Taking advantage of the good contrast ratio, the rapid response, and the long retention time of each oxidation state, these films have been successfully used to demonstrate surface-confined flip-flop memory functions with a high ON/OFF ratio.

A 3D electropolymerized thin film based on a thiophene-functionalized Ru(ii) complex: electrochemical and photoelectrochemical insights

A 3D electropolymerized Ru(ii) complex film exhibited a rapid redox reaction and an oxygen reduction enhanced photocurrent which increased by 1.5 fold to 2.3 μA cm⁻².

Dynamics of a Complex Multilayer Polymer Network: Mechanical Relaxation and Energy Transfer

In this paper, we focus on the mechanical relaxation of a multilayer polymer network built by connecting identical layers that have, as underlying topologies, the dual Sierpinski gasket and the regular dendrimer. Additionally, we analyze the dynamics of dipolar energy transfer over a system of chromophores arranged in the form of a multilayer network. Both dynamical processes are studied in the framework of the generalized Gaussian structure (GSS) model. We develop a method whereby the whole eigenvalue spectrum of the connectivity matrix of the multilayer network can be determined iteratively, thereby rendering possible the analysis of the dynamics of networks consisting of a large number of layers. This fact allows us to study in detail the crossover from layer-like behavior to chain-like behavior. Remarkably, we highlight the existence of two bulk-like behaviors. The theoretical findings with respect to the decomposition of the intermediate domain of the relaxation quantities, as well as the chain-like behavior, are well supported by experimental results.

Synthesis and characterization of metal-rich phosphonium polyelectrolytes and their use as precursors to nanomaterials

Upon efficient quaternization and salt metathesis of stable triethyl ferrocene/ruthenocene phosphines, styrene-based phosphonium triflate monomers with four different stoichiometric ratios of Fe/Ru were synthesized. Free-radical polymerization of the monomers afforded four polyelectrolytes (M_n: 38 650-69 100 g mol^-1, Đ: 3.16-4.10) that retained many of the spectroscopic and electrochemical properties of the ferrocene/ruthenocene units. TGA studies demonstrated the thermal stability (onset of decomposition: ∼310 °C) and high char yields (33-54% at 1000 °C) of the polyelectrolytes. Pyrolysis in N₂/H₂ (95/5) (film thickness of ∼6 μm, 1000 °C, 3 h) yielded crystalline, mixed-phase nanomaterials containing iron, ruthenium, and phosphorus with compositions influenced by the structure of the parent polyelectrolytes.

Synthesis, structures, electrochemical and quantum chemical investigations of Ni(ii) and Cu(ii) complexes with a tetradentate Schiff base derived from 1-(2-thienyl)-1,3-butanedione

Electrochemical oxidation of four-coordinate square planar Schiff-base Ni(ii) and Cu(ii) complexes leads to the formation of oligomers at the electrode.

Recent advances in triphenylamine-based electrochromic derivatives and polymers

Triphenylamine-containing electrochromic materials with great potential applications in low energy-consumption displays, light-adapting mirrors in vehicles, and smart windows have experienced an exponential growth of research interests. In this review, the newly developed triphenylamine-based derivatives and polymers are reviewed and elaborated.

Nitrogen-containing polymers as a platform for CO2 electroreduction

Heterogeneous electroreduction of CO₂ has received considerable attention in the past decade. However, none of the earlier reviews has been dedicated to nitrogen-containing polymers (N-polymers) as an emerging platform for conversion of CO₂ to industrially useful chemicals. The term 'platform' is used here to underscore that the role of N-polymers is not only to serve as direct catalysts (through loaded metals) but also as co-catalysts/promoters and stabilizing agents. This review covers the current state, advantages, challenges, and prospects of the application of N-polymer-metal composites, also referred as polymer functionalized, coated, or modified electrodes, as well as functional hybrid materials, for the electrocatalytic conversion of CO₂. It briefly surveys the efficiencies of the N-polymer-metal electrodes already used for this application, methods of their fabrication, and proposed mechanisms of their catalytic activities.

Effect of conjugation length and metal-backbone interactions on charge transport properties of conducting metallopolymers

Detailed studies on the effect of organic conjugation length, metal centers, and metal-backbone redox interactions on the charge transport properties of conducting metallopolymers (CMPs) are reported.

Metal-containing polymers bearing pendant nickel(ii) complexes of Goedken's macrocycle

The design, synthesis, and characterization of polymers bearing pendant nickel(ii) complexes of Goedken's macrocycle are described.

A Thiophene-Containing Conductive Metallopolymer Using an Fe(II) Bis(terpyridine) Core for Electrochromic Materials

Three Fe(II) bis(terpyridine)-based complexes with thiophene (Fe(L1)₂), bithiophene (Fe(L2)₂), and 3,4-ethylenedioxythiophene (Fe(L3)₂) side chains were designed and synthesized for the purpose of providing two terminal active sites for electrochemical polymerization. The corresponding metallopolymers (poly-Fe(Ln)₂, n = 2 or 3) were synthesized on indium tin oxide (ITO)-coated glass substrates via oxidative electropolymerization of the thiophene-substituted monomers and characterized using electrochemistry, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and atomic force microscopy. The film poly-Fe(L2)₂ was further studied for electrochromic (EC) color-switching properties and fabricated into a solid-state EC device. Poly-Fe(L2)₂ films exhibit an intense MLCT absorption band at 596 nm (ε = 4.7 × 10⁴ M^-1 cm^-1) in the UV-vis spectra without any applied voltage. Upon application of low potentials (between 1.1 and 0.4 V vs Fc⁺/Fc), the obtained electropolymerized film exhibited great contrast with a change of transmittance percentage (ΔT%) of 40% and a high coloration efficiency of 3823 cm² C^-1 with a switching time of 1 s. The film demonstrates commonplace stability and reversibility with a 10% loss in peak current intensity after 200 cyclic voltammetry cycles and almost no loss in change of transmittance (ΔT%) after 900 potential switches between 1.1 and 0.4 V (vs Fc⁺/Fc) with a time interval of 0.75 s. The electropolymerization of Fe(L2)₂ provides convenient and controllable film fabrication. Electrochromic behavior was also achieved in a solid-state device composed of a poly-Fe(L2)₂ film and a polymer-supported electrolyte sandwiched between two ITO-coated glass electrodes.

Multistate Redox Switching and Near-Infrared Electrochromism Based on a Star-Shaped Triruthenium Complex with a Triarylamine Core

A star-shaped cyclometalated triruthenium complex 2(PF₆)_n (n = 3 and 4) with a triarylamine core was synthesized, which functions as a molecular switch with five well-separated redox states in both solution and film states. The single-crystal X-ray structure of 2(PF₆)₃ is presented. This complex displays four consecutive one-electron redox waves at +0.082, +0.31, +0.74, and +1.07 V vs Ag/AgCl. In each redox state, it shows significantly different NIR absorptions with λ_max of 1590 nm for 2⁴⁺, 1400 nm for 2⁵⁺, 1060 nm for 2⁶⁺, and 740 nm for 2⁷⁺, respectively. Complex 2⁴⁺ shows a single-line EPR signal at g = 2.060, while other redox states are all EPR inactive. The spin density distributions and NIR absorptions in different redox states were rationalized by DFT and TDDFT calculations. A vinyl-substituted triruthenium analogous 3(PF₆)₄ was prepared, which was successfully polymerized on ITO glass electrode surfaces by reductive electropolymerization. The obtained poly-3ⁿ⁺/ITO film was characterized by FTIR, AFM, and SEM analysis. It shows four well-defined redox couples and reversible multistate NIR electrochromism. In particular, a contrast ratio (ΔT%) up to 63% was achieved at the optic telecommunication wavelength (1550 nm).

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Phosphaalkene-oxazoline copolymers with styrene as chiral ligands for rhodium(I)

The radical-initiated copolymerization of phosphaalkene-oxazoline, MesP[double bond, length as m-dash]C(Ph)CMe2Ox [1, Ox = CNOCH(iPr)CH2] with different loadings of styrene affords poly(methylenephosphine-co-styrene)s [2a (1 : S = 1 : 2): Mw = 7400 g mol(-1), PDI = 1.1; 2b (1 : S = 1 : 5): Mw = 18 000 g mol(-1), PDI = 1.2; 2c (1 : S = 1 : 10): Mw = 16 000 g mol(-1), PDI = 1.3]. Copolymers 2a-2c are demonstrated as viable macromolecular ligands for rhodium(i). By comparison with the crystallographically characterized model P,N-bidentate complex, [Mes(Me)P-CH(Ph)CMe2Ox·Rh(cod)]BF4, the polymer complexes [2·Rh(cod)]BF4 were prepared. The macromolecular metal complexes were characterized by GPC {for [2a·Rh(cod)]BF4: Mw = 14 000 g mol(-1), PDI = 1.2}, UV/Vis spectroscopy, (1)H, (13)C and (31)P NMR spectroscopy. Integration of the (31)P NMR spectra of mixtures of 2 and [Rh(cod)2]BF4 permitted the determination of the mol% of incorporation of monomer 1 in copolymer 2 (2a: 17%; 2b: 5%; 2c: 4%). These results compared favorably with those determined by elemental analysis (2a: 17%; 2b: 6%).

Diblock metallocopolymers containing various iron sandwich complexes: living ROMP synthesis and selective reversible oxidation

New diblock copolymers containing two iron-sandwich complexes in the side chain have been synthesized and oxidized to obtain mixed-valent Fe^II–Fe^III copolymers.

Tunable luminescence of lanthanide (Ln = Sm, Eu, Tb) hydrophilic ionic polymers based on poly(N-methyl-4-vinylpyridinium-co-styrene) cations

Hydrophilic luminescent lanthanide-containing ionic polymers poly-[MVPS]₂[Ln(NO₃)₅] were prepared, which can be utilized as reversible colorimetric water-responsive sensors.