Synthesis and characterization of metallo-supramolecular polymers

Control of the light-response in supramolecular metallopolymeric gels by tuning the coordination metal

Two novel supramolecular metallo-heteropolymers bearing a photo-isomerizable telechelic bis-terpyridine ligand and either Fe(ii) or Co(ii) coordination metal were synthesized. Both polymers induced gelation of organic solvents at a concentration as low as 0.12 wt% yielding thixotropic gels. Judicious choice of the electronic and photophysical properties of both ditopic ligand and metal ion enabled to achieve control over photomechanical response in supramolecular organogels upon UV light irradiation through molecular design.

Metallacyclopentadienes: synthesis, structure and reactivity

Metallacyclopentadienes, which possess two M-C(sp²) bonds and feature the structure of M(C[upper bond 1 start]R¹[double bond, length as m-dash]CR²-CR³[double bond, length as m-dash]C[upper bond 1 end]R⁴), are an important class of five-membered metallacycles. They are considered as both reactive intermediates in the stoichiometric and catalytic transformations of organic molecules and useful precursors to main group element compounds, and have received considerable attention in organometallic chemistry, coordination chemistry and synthetic organic chemistry over the past six decades because of their unique metallacyclic structure. This review comprehensively presents the synthesis, structure and reactivity of the s-, p-, d- and f-block metallacyclopentadienes distributed in the whole periodic table. In addition, their application in synthetic organic chemistry and polymer chemistry is summarized. This review aims to be beneficial for the design and synthesis of novel metallacyclopentadienes, and for promoting the rapid development of metallacyclic chemistry.

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Dynamic metal-ligand coordination for multicolour and water-jet rewritable paper

Rewritable paper has recently become prevalent in both academic research and marketplace due to the potential environmental advantages, including forest conservation, pollution reduction, energy saving and resource sustainability. However, its real-life applications are limited by a lack of effective strategy to realize multicolour and water-jet printing on rewritable paper with long legible image-lasting times. Herein, we report an effective strategy to construct rewritable paper based on colour or luminescence switching induced by dynamic metal–ligand coordination. This type of rewritable paper can be conveniently utilized for multicolour water-jet printing by using aqueous solutions containing different metal salts as ink. In addition, the printed images on the water-jet rewritable paper can be retained for a long time (> 6 months), which shows great progress compared to previous work. We believe that this type of rewritable paper could be considered as a prototype for multicolour water-jet printing to meet the practical needs.

Rewritable paper is environmentally favourable, but its practical realization is stifled by limited ink colour versatility and poor image retention times. Here, the authors exploit the relatively stable but reversible nature of metal–organic coordination bonds to produce long-lasting and multicoloured inks for rewritable paper.

Synthesis and photochemical response of Ru(ii)-coordinated double-decker silsesquioxane

A double-decker silsesquioxane based bis(terpyridine) ruthenium(ii) complex (2Tpy/Ru-DDSQ), a member of the polyhedral oligomeric silsesquioxane (POSS) class, has been synthesized. Its structure has been characterized using comprehensive techniques such as nuclear magnetic resonance (1H NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. This work not only deals with the synthesis of 2Tpy/Ru-DDSQ but also provides the first comprehensive investigation based on the photoluminescence and electrochemical features of a POSS member. With this structure, an efficient anodic photocurrent response has been obtained. This result has been attributed to the perfect arrangement of ruthenium(ii)-bis(terpyridine) (tpy) ([Ru(Tpy)2]2+) moieties in the DDSQ nano building blocks. Therefore, 2Tpy/Ru-DDSQ can be considered as a promising candidate for the development of new generation photosensitizers.

Neutral two-dimensional organometallic–organic hybrid polymers based on pentaphosphaferrocene, bipyridyl linkers and CuCl

The reaction of the P_n ligand complex [Cp*Fe(η⁵-P₅)] (1: Cp* = η⁵-C₅Me₅) with CuCl in the presence of 4,4′-bipyridine or 1,2-di(4-pyridyl)ethylene leads to the formation of three unprecedented neutral 2D organometallic–organic hybrid networks.

Terpyridine-based metallosupramolecular constructs: tailored monomers to precise 2D-motifs and 3D-metallocages

Comprehensive summary of the recent developments in the growing field of terpyridine-based, discrete metallosupramolecular architectures.

Photothermal Möbius aromatic metallapentalenofuran and its NIR-responsive copolymer

A novel thermally and NIR-light responsive metallopolymer was copolymerized from a photothermal aromatic metallapentalenofuran and a glycol methyl ether methacrylate.

Modulation of a coordination structure in a europium(iii)-based metallo-supramolecular polymer for high proton conduction

Developing high proton conducting solid materials is significant in the field of fuel cells. A europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H) was successfully synthesized by modifying the synthesis conditions. The proton conductivity was enhanced with increasing the relative humidity (RH) from 30 to 95% RH. PolyEu-H showed about 10⁴ times higher proton conductivity than the polymer with coordinated carboxylic acids (PolyEu) and about 400 times higher than the polymer without carboxylic acids (PolyEu-2). The proton conductivity of PolyEu-H reached 4.45 × 10⁻² S cm⁻¹ at 95% RH and 25 °C and 5.6 × 10⁻² S cm⁻¹ at 75 °C. The activation energy, E_a was ultralow (0.04 eV), which indicates proton conduction based on the Grotthuss mechanism. The results indicate that efficient proton conduction occurs through proton channels formed by moisture in PolyEu-H.

Developing high proton conducting solid materials is significant in the field of fuel cells. We firstly synthesized europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H), for high proton conduction.

Metallo-Supramolecular Gels that are Photocleavable with Visible and Near-Infrared Irradiation

A photolabile ruthenium-based complex, [Ru(bpy)2 (4AMP)2 ](PF6 )2 , (4AMP=4-(aminomethyl)pyridine) is incorporated into polyurea organo- and hydrogels via the reactive amine moieties on the photocleavable 4AMP ligands. While showing long-term stability in the dark, cleavage of the pyridine-ruthenium bond upon irradiation with visible or near-infrared irradiation (in a two-photon process) leads to rapid de-gelation of the supramolecular gels, thus enabling spatiotemporal micropatterning by photomasking or pulsed NIR-laser irradiation.

Cooperative loading of multisite receptors with lanthanide containers: an approach for organized luminescent metallopolymers

Metal loading of multi-terdentate receptors with [Eu(pbta)₃] provides the first anti-cooperative factors large enough for programming metal alternation in lanthanidopolymers at room temperature.

Metal-containing (bio)organic polymers are materials of continuously increasing importance for applications in energy storage and conversion, drug delivery, shape-memory items, supported catalysts, organic conductors and smart photonic devices. The embodiment of luminescent components provides a revolution in lighting and signaling with the ever-increasing development of polymeric light-emitting devices. Despite the unique properties expected from the introduction of optically and magnetically active lanthanides into organic polymers, the deficient control of the metal loading currently limits their design to empirical and poorly reproducible materials. We show here that the synthetic efforts required for producing soluble multi-site host systems Lk are largely overcome by the virtue of reversible thermodynamics for mastering the metal loading with the help of only two parameters: (1) the affinity of the luminescent lanthanide container for a single binding site and (2) the cooperative effect which modulates the successive fixation of metallic units to adjacent sites. When unsymmetrical perfluorobenzene-trifluoroacetylacetonate co-ligands (pbta^–) are selected for balancing the charge of the trivalent lanthanide cations, Ln³⁺, in six-coordinate [Ln(pbta)₃] containers, the explored anti-cooperative complexation processes induce nearest-neighbor intermetallic interactions twice as large as thermal energy at room temperature (RT = 2.5 kJ mol^–1). These values have no precedent when using standard symmetrical containers and they pave the way for programming metal alternation in luminescent lanthanidopolymers.

Novel multi-analyte responsive ionic supramolecular gels based on pyridinium functionalized-naphthalimide

A novel ionic supramolecular gel (is-G) is synthesized using N-(pyridinium-4-yl)-naphthalimide (G1) and n-pentanoic acid. By rationally introducing competitive coordination into is-G, two ion coordinated ionic supramolecular gels is-IG and is-FeG (coordinated with I^- and Fe³⁺, respectively) are obtained. is-IG could fluorescently "turn-on" detect Hg²⁺ and l-Arg with specific selectivity, whereas, is-FeG could accurately identify l-Ser via fluorescence in water. Moreover, ion or amino acid responsive films based on these ionic supramolecular gels are prepared. These ionic supramolecular gels and films could act as multi-analyte detection materials as well as fluorescent display materials.

Thermoresponsive Memory Behavior in Metallosupramolecular Polymer-Based Ternary Memory Devices

Thermal-sensitive materials, such as metallosupramolecular polymers, have been integrated into devices for a broad range of applications. However, the role of these materials is limited to temperature sensing and the lack of a memory function. Herein, we present novel [PolyCo-L1_xL2_y-PF₆]-based organic resistive memories (ORMs) possessing both a thermal response and ternary memory behavior with three electrical resistance states [high (HRS), intermediate (IRS), and low (LRS)]. Furthermore, the thermal behavior can be memorized by the Al/[PolyCoL1_xL2_y-PF₆]/indium-tin oxide devices. Heating and cooling the devices at a LRS results in a switch from the LRS to a HRS and further to a LRS, indicating that the thermal behavior can be efficiently memorized. Following the heating and cooling process, devices at a HRS retain their ternary memory behavior, while an unstable resistance variation behavior is observed at the IRS. We propose a possible mechanism for the thermoresponsive memory behavior, and this finding provides a guide for the design of future thermoresponsive ORMs.

Synthesis of Air-Stable Cyclopentadienyl Fe(CO)2 (Fp) Polymers by a Host-Guest Interaction of Cyclodextrin with Air-Sensitive Fp Pendant Groups

Host-guest chemistry is used to address the challenge of the synthesis of air-stable polymers containing air-sensitive metal complexes. The complexation of the CpFe(CO)₂ (Fp) pendent group with cyclodextrin (CD) molecules created air-stable poly(Fp-methylstyrene) P(CD/FpMSt). This CD complexation resulted in dimerization of the adjacent Fp groups, which was characterized by NMR, FTIR, and cyclic voltammetry (CV) analyses. P(CD/FpMSt) was soluble in DMSO and remained stable even the solution was exposed to air for months. The host-guest chemistry accounted for the improved stability, because the Fp groups decomposed upon removal of the CD molecules using competing guest molecules. The CD-complexed polymer showed light-trigged properties, including CO release and antimicrobial activity. Host-guest chemistry of air-sensitive organometallic complexes is therefore a promising technique that can be used to broaden the scope of metal-containing polymers (MCPs) with processable novel functions.

Soluble PtII-Containing Polymers Based on a 2,6-Bis(1H-1,2,3-triazol-4-yl)-4-ethynylpyridine Ligand

A soluble Pt^II-acetylide polymer 6 was prepared in a supramolecular polymerization of a Pt^II-chloro precursor complex 5, which represents a self-complementary AB-type monomer. This new type of polymer combines the structural features of the common polyplatinynes and cationic Pt^II-acetylide complexes. Though the photophysical and electrochemical properties of the material still need to be advanced, a versatile and straightforward method for the preparation of soluble, cationic Pt^II-acetylide polymers with phosphorescent behavior is offered.

Importance of Compact Random Walks for the Rheology of Transient Networks

Controlling the mechanical behavior of novel supramolecular materials is of the utmost importance and requires a fundamental understanding of the underlying physical processes. We present a multimethods approach to the dynamics of entangled transient polyisoprene networks. Small-angle neutron scattering (SANS) on randomly functionalized chains shows homogeneous supramolecular melts with Gaussian chain conformations. The H-bond lifetimes (dielectric α*-process) and the rheological response in terms of the loss modulus G″ differ by 2 orders of magnitude in time. Within the concept of a compact random walk (RW), where the random walker (urazole group acting as a sticker) undergoes multiple returns to its starting point and following the concept of theoretical proposed renormalized sticky bond lifetimes, we quantitatively solve this longstanding and unexplained large discrepancy: While the bond opening gives rise to the dielectric response, for rheological relaxation the association with a new partner is relevant. This takes place only after multiple returns to the original binding partner.

Functional metallosupramolecular architectures using 1,2,3-triazole ligands: it's as easy as 1,2,3 “click”

Self-assembled metallosupramolecular architectures generated using “click” ligands have become an increasingly popular area of inorganic chemistry.

Ion-pair coordination driven stimuli-responsive one-dimensional supramolecular helicate

A new self-assembled ion-pair coordination driven one-dimensional (1D) smart supramolecular helical assembly is reported. Moreover, thermo- and chemo-responsive transformation/disassembly/reassembly of the helical superstructure was also demonstrated.

Amphipathic metal-containing macromolecules with photothermal properties

Metal-containing macromolecules with extraordinary properties have attracted a great deal of interest owing to their potential application in the development of functional materials.

Density functional theory modeling of C–Au chemical bond formation in gold implanted polyethylene

We have studied processes of gold ion implantation in polyethylene (PE) by theoretical chemistry methods.

CrIII as an alternative to RuII in metallo-supramolecular chemistry

Semi-labile [Cr(tpy)(CF₃SO₃)₃] precursors can be exploited for building rod-like dinuclear dyads, in which paramagnetic and luminescent trivalent Cr^III replace diamagnetic Ru^II for unravelling intermetallic communication in supramolecular architectures.

Neutral linear supramolecular polymers constructed by three different interactions

Neutral linear supramolecular polymers were constructed by the combination of quadruple hydrogen bonding, pillar[5]arene-based molecular recognition and π–π donor–acceptor interactions.

Amphiphilic Metallopolymers for Photoswitchable Supramolecular Hydrogels

A series of amphiphilic metallopolymers is described that features zinc(II) bis-terpyridine coordination nodes as well as a backbone with hydrophobic azoaryl moieties and hydrophilic phenylene-ethynylene units decorated with PEG brushes. Using such metallopolymers at very low concentration, stable, photo-responsive and self-healing hydrogels are obtained. UV irradiation of the gel allows modulation of the degree of hydrophobic π-π interactions between photoisomerizable azoaryl units and a polarity switch that overall induces a fast gel-to-sol transition. Finally, the material phase can be readily and fully restored to the thermodynamically stable state either thermally or photochemically by using visible light. The presented strategy can be further generalized towards modular supramolecular metallopolymers for injectable gels in drug delivery and bio-engineering applications.