The solid-state architecture of a metallosupramolecular polyelectrolyte

Going against the flow: Os(ii)-to-Ru(ii) energy transfer in rod-like polypyridyl chromophore

The judicious design of a unique mixed-metal Ru-Os molecular rod led to the first photoinduced energy transfer from osmium-to-ruthenium in a polypyridyl complex. The absorbed light is directed from the osmium metal center to the peripheral ruthenium moieties, where only the low energy luminescence from the heteroleptic ruthenium phen-hpp complex was observed.

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.

Kinetic Studies of the Coordination of Mono- and Ditopic Ligands with First Row Transition Metal Ions

The reactions of the ditopic ligand 1,4-bis(2,2':6',2″-terpyridin-4'-yl)benzene (1) as well as the monotopic ligands 4'-phenyl-2,2':6',2″-terpyridine (2) and 2,2':6',2″-terpyridine (3) with Fe(2+), Co(2+), and Ni(2+) in solution are studied. While the reaction of 1 with Fe(2+), Co(2+), and Ni(2+) results in metallo-supramolecular coordination polyelectrolytes (MEPEs), ligands 2 and 3 give mononuclear complexes. All compounds are analyzed by UV/vis and fluorescence spectroscopy. Fluorescence spectroscopy indicates that protonation as well as coordination to Zn(2+) leads to an enhanced fluorescence of the terpyridine ligands. In contrast, Fe(2+), Co(2+), or Ni(2+) quench the fluorescence of the ligands. The kinetics of the reactions are studied by stopped-flow fluorescence spectroscopy. Analysis of the measured data is presented and the full kinetic rate laws for the coordination of the terpyridine ligands 1, 2, and 3 to Fe(2+), Co(2+), and Ni(2+) are presented. The coordination occurs within a few seconds, and the rate constant increases in the order Ni(2+) < Co(2+) < Fe(2+). With the rate constants at hand, the polymer growth of Ni-MEPE is computed.

Tailoring length and viscosity of dynamic metallo-supramolecular polymers in solution

We present a detailed study of metallo-supramolecular coordination polymers (MEPEs) and how to adjust their chain-length and viscosity. A model is established, which can easily be used to prepare MEPEs of desired average molecular weight.

Metallo/clusto hybridized supramolecular polymers

The introduction of metal centers to a supramolecular polymer system is an important approach to fabricate hybrid supramolecular polymers with synergistic properties between their inorganic and organic components, which is mainly realized through two strategies: one is the embedment of metal ions through metal-ligand coordination to form metallo-supramolecular polymers (MSPs); the other is using metal-containing clusters as hybrid building blocks to prepare clusto-supramolecular polymers (CSPs). The available paradigms of MSPs and CSPs not only exhibit the unique functions of metal centers but also hold the good processing ability and the stimuli-responsibility of dynamically bonded polymeric structures, thus representing a new class of hybrid soft materials. In this review, the development and recent progress of MSPs and CSPs are discussed in detail, including their structure design, synthetic procedures and related properties. Finally, challenges and potential areas in metal-containing supramolecular polymers are outlooked.

From terpyridine-based assemblies to metallo-supramolecular polyelectrolytes (MEPEs)

Introducing metal ion coordination as bonding motive into polymer architectures provides new structures and properties for polymeric materials. The metal ions can be part of the backbone or of the side-chains. In the case of linear metallo-polymers the repeat unit bears at least two metal ion receptors in order to facilitate metal-ion induced self-assembly. If the binding constants are sufficiently high, macromolecular assemblies will form in a solution. Likewise, polymeric networks can be formed by metal ion induced crosslinking. The metal ion coordination sites introduce dynamic features, e.g. for self-healing or responsive materials, as well as additional functional properties including spin-crossover, electro-chromism, and reactivity. Terpyridines have attracted attention as receptors in metallo-polymers due to their favorable properties. It is well suited to assemble linear rigid-rod like metallo-polymers in case of rigid ditopic ligands. Terpyridine binds a large number of metal ions and are readily functionalized giving rise to a plethora of available ligands as components in metallo-polymers. By the judicious choice of the metal ions, the design of the ligands, the counter ions and the boundary conditions of self-assembly, the final structure and properties of the resulting metallo-polymers can be tailored at all length scales. Here, we review recent activities in the area of metallo-polymers based on terpyridines as central metal ion receptors.

A case of adaptive self-assembly

We report in this paper direct observation of redox-induced uptake of a charged species in micelles with a complex coacervate core, using a system consisting of negatively charged iron-coordination polymers and positively charged-b-neutral block co-polyelectrolytes. Neutral, charge-balanced micelles are first prepared by stoichiometric mixing of the oppositely charged components. Upon a redox stimulus, the micelles develop excess charges, which (as proposed in our previous work) most likely lead to sequestration of oppositely charged species, as the charge balance has to be restored. In this work we verify this prediction by using a rigid, rod-like iron coordination polymer, namely, the positively charged MEPE, as the species to be taken up. After uptake of this rigid cargo, the morphology of the micelles was found to transform from spheres to banana-shaped bundles and fibers, which clearly indicate the uptake of MEPE in the micellar core. Our result proves that the redox stimulus indeed induces excess charges in the core, which forces the self-assembled particles to change both composition and shape. As an interesting example of "adaptive self-assembly", our findings also pave the way to novel redox-triggered uptake and release systems.

Highly conductive approximately 40-nm-long molecular wires assembled by stepwise incorporation of metal centres

One of the main goals of molecular electronics is to achieve electronic functions from devices consisting of tailored organic molecules connecting two metal electrodes. The fabrication of nanometre-scale spaced electrodes still results in expensive, and often scarcely reproducible, devices. On the other hand, the 'conductance' of long organic molecules--generally dominated by the tunnelling mechanism--is very poor. Here, we show that by incorporating a large number of metal centres into rigid molecular backbones we can obtain very long (up to 40 nm) and highly 'conductive' molecular wires. The metal-centre molecular wires are assembled in situ on metal surfaces via a sequential stepwise coordination of metal ions by terpyridine-based ligands. They form highly ordered molecular films of elevated mechanical robustness. The electrical properties, characterized by a junction based on Hg electrodes, indicate that the 'conductance' of these metal-centre molecular wires does not decrease significantly even for very long molecular wires, and depends on the nature of the incorporated redox centre. The outstanding electrical and mechanical characteristics of these easy-to-assemble molecular systems open the door to a new generation of molecular wires, able to bridge large-gap electrodes, and to form robust films for organic electronics.

Metallosupramolecular polyelectrolytes self-assembled from various pyridine ring-substituted bisterpyridines and metal ions: photophysical, electrochemical, and electrochromic properties

This work presents several metallosupramolecular coordination polyelectrolytes (MEPEs) self-assembled from rigid, pi-conjugated, pyridine ring functionalized bisterpyridines and metal ions. The MEPEs are water-soluble and display different colors spanning the entire visible regions. Optical, electrochemical, and electrochromic properties of the obtained MEPEs are presented. The results show that the properties are profoundly affected by the nature of the substituents at the peripheral pyridine rings. Namely, MEPEs assembled from the electron-rich OMe group modified ligands exhibit high switching reversibility and stability and show a lower switching potential than the unsubstituted and electron-deficient Br-substituted analogues. The response times can be tuned either by the design of the ligands or by the choice of the metal ions to cover a broad time scale from under 1 s to several minutes. The optical memory is enhanced from 30 s to longer than 15 min as a comparison of unsubstituted and substituted MEPEs shows. Thus, the significantly enhanced stability and the ease of tuning the properties render this type of supramolecular assembly attractive as electrochromic materials for applications in a large variety of areas. Most importantly, we presented the structure-property relationships of MEPEs, which lays the groundwork for further design of new bisterpyridine-based metallosupramolecular functional materials.

Diverse Synthesis of Novel Bisterpyridines via Suzuki-Type Cross-Coupling

A new protocol is presented for the synthesis of novel bisterpyridine derivatives using palladium-catalyzed Miyaura- and Suzuki-type cross-couplings as the key reactions. This protocol is quick, efficient, mild, and broadly applicable for the construction of versatile bisterpyridines by symmetric and unsymmetric introduction of various substituents in the pyridine rings as well as by tuning the spacers for bridging the two terpyridine moieties. [reaction: see text].

Transition metal ions: weak links for strong polymers

Extending macromolecular chemistry beyond carbon-based polymers offers fascinating perspectives and an enormous potential to improve the capacity of macromolecular materials with new dynamic properties.