Synthesis and characterization of light‐emitting main‐chain metallo‐polymers containing bis‐terpyridyl ligands with various lateral substituents

A series of conjugated monomers ( 5a‐5d ) with various lateral substituents were symmetrically synthesized by the Sonogashira coupling reaction, in which central aromatic units (i.e. 9,9‐dipropylfluorenes) were linked to 2,2′:6′,2′‐terpyridyl (tpy) units via phenylene/ethynylene fragments. These light‐emitting monomers were further reacted with zinc(II) ions and subsequently anion exchanged to produce supramolecular main‐chain metallo‐polymers ( 6a‐6d ). The formation of polymers 6a‐6d was confirmed by the increased viscosities (up to 1.5–1.83 times) relative to those of their analogous monomers. The results of ¹H NMR titration and UV‐Vis spectral titration revealed a detailed complexation process of metallo‐polymers by varying the molar ratios of zinc(II) ions to monomers. After coordination with zinc(II) ions, the luminescent and thermal properties of the polymers were enhanced by the formation of metallo‐supramolecular structures in contrast to their monomer counterparts. PLED devices employing these metallo‐polymers as emitters gave yellow to orange electroluminescence (EL) emissions with turn‐on voltages around 6 V. The maximum power efficiency, external quantum yield, and brightness of the PLED device containing polymer 6c were 0.33 cd A^?1 (at 14 V), 1.02%, and 931 cd m^?2 (at 14 V), respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3243–3255, 2007     

Cover Picture: Angew. Chem. Int. Ed. 16/2002

The cover picture shows the molecular modeling of a star‐shaped metallo‐supramolecular polymer and the schematic drawing of a linear analogue. These molecules are of great interest because of their unique properties. Metallo‐supramolecular polymers emerge by the well‐directed combination of polymers, the properties of which have dominated the development of materials in recent years, with supramolecular ligands, which have the ability to organize spontaneously and form unique structures on a molecular level, and transition‐metal ions, which, through their physical properties bring characteristic functionalities. The well‐known properties of the individual components allow the use of established methods, such as UV/Vis spectroscopy, NMR spectroscopy, and gel permeation chromatography for characterization. However, the combination also requires the application of new methods, such as analytical ultracentrifugation or MALDI‐TOF mass spectrometry. More about metallo‐supramolecular polymers based on bipyridine and terpyridine complexes can be found in the review by U. S. Schubert and C. Eschbaumer on p. 2892 ff.     

Vom einfachen Komplex zum komplexen Gitter: Metallo‐supramolekulare Chemie

Supramolecular structures and metal‐complexes play a dominant role in the functionality of biomolecules. Taking nature as an example a major goal of metallo‐supramolecular chemistry is the extension of the traditional coordination chemistry towards supramolecular architectures, utilizing complex ligand systems. Herein we describe a wide range of different geometries such as helicates, linear rod‐like polymers, ladders, racks or grids, which are realized by the combination of supramolecular ligands and coordinating metal ions on the basis of self‐assembly and self‐recognition processes. Besides the pure beauty of the structures, the electro‐, photochemical and magnetic properties of the materials might open avenues to applications as smart coatings, catalysts or optical devices.     

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Higher efficiency in the end‐use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid‐state electroluminescent materials and belong to the general area of solid‐state lighting (SSL). The two main technologies being developed in SSL are light‐emitting diodes (LEDs) and organic light‐emitting diodes (OLEDs), but in recent years, light‐emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition‐metal complexes (iTMCs). Cyclometalated complexes of Ir^III are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn‐on time, stability, efficiency, and color is presented.     

Self‐assembly of H‐bonded side‐chain and cross‐linking copolymers containing diblock‐copolymeric donors and single/double H‐bonded light‐emitting acceptors

A series of diblock‐copolymers were synthesized through anionic polymerization of styrene and tert‐butyl methacrylate (tBuA) with different monomer ratios, and analogous block‐copolymeric derivatives (PS‐b‐PAA)s with monofunctional carboxylic acid groups were obtained by further hydrolyzation as hydrogen‐bonded (H‐bonded) proton donors. Via H‐bonded interaction, these diblock‐coplymeric donors (PS‐b‐PAA)s were incorporated with luminescent mono‐pyridyl/bis‐pyridyl acceptors to form single/double H‐bonded supramolecules, that is, H‐bonded side‐chain/cross‐linking copolymers, respectively. The supramolecular architectures formed by donor polymers and light‐emitting acceptors were influenced by the ratio of acid blocks in the diblock copolymeric donors and the type of single/double H‐bonded light‐emitting acceptors. Their thermal and luminescent properties can be adjusted by H‐bonds, and more than 100 nm of red‐shifted photoluminescence (PL) emissions were observed, which depend on the degrees of the H‐bonding interactions. Self‐assembled phenomena of amphiphilic dibolck copolymers and their H‐bonded complexes were confirmed by TEM micrographs, and supramolecular microphase separation of spherical micelle‐like morphology was demonstrated to affect the photophysical properties. Polymer light‐emitting diode (PLED) devices containing H‐bonded complexes showed electroluminescence (EL) emissions of 503–560 nm under turn‐on voltages of 7.5–9.0 V, maximum power efficiencies of 0.23–0.37 cd/A (at 100 mA/cm²), and maximum luminances of 318–519 cd/m² (around 25 V). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4685–4702, 2009     

Hue‐ and Chromaticity‐Based Exploration of Surface Complexation‐Induced Tunable Emission from Non‐Luminescent Quantum Dots

Herein we report the use of a hue parameter of HSV (Hue, Saturation and Value) color space—in combination with chromaticity color coordinates—for exploring the complexation‐induced luminescence color changes, ranging from blue to green to yellow to white, from a non‐luminescent Fe‐doped ZnS quantum dot (QD). Importantly, the surface complexation reaction helped a presynthesized non‐luminescent Fe‐doped ZnS QD to glow with different luminescence colors (such as blue, cyan, green, greenish‐yellow, yellow) by virtue of the formation of various luminescent inorganic complexes (using different external organic ligands), while the simultaneous blue‐ and yellow‐emitting complex formation on the surface of non‐luminescent Fe‐doped ZnS QD led to the generation of white light emission, with a hue mean value of 85 and a chromaticity of (0.28,0.33). Furthermore, the surface complexation‐assisted incorporation of luminescence properties to a non‐luminescent QD not only overcomes their restricted luminescence‐based applications such as light‐emitting, biological and sensing applications but also bring newer avenues towards unravelling the surface chemistry between QDs and inorganic complexes and the advantage of having an inorganic complex with QD for their aforementioned useful applications.     

Light‐Powered Self‐Healable Metallosupramolecular Soft Actuators

Supramolecular functional materials able to respond to external stimuli have several advantages over their classical covalent counterparts. The preparation of soft actuators with the ability to respond to external stimuli in a spatiotemporal fashion, to self‐repair, and to show directional motion, is currently one of the most challenging research goals. Herein, we report a series of metallopolymers based on zinc(II)–terpyridine coordination nodes and bearing photoisomerizable diazobenzene units and/or solubilizing luminescent phenylene–ethynylene moieties. These supramolecular polymers act as powerful gelating agents at low critical gelation concentrations. The resulting multiresponsive organogels display light‐triggered mechanical actuation and luminescent properties. Furthermore, owing to the presence of dynamic coordinating bonds, they show self‐healing abilities.     

共轭聚合物发光和光伏材料研究进展

聚合物光电功能材料与器件因其广阔的应用前景,1990年以年来吸引了世界各国学术界的广泛关注和兴趣.聚合物光电子器件主要包括聚合物电致发光二极管、聚合物场效应晶体管和聚合物太阳能电池等,其使用的关键材料是共轭聚合物光电子材料,包括共轭聚合物发光材料、场效应晶体管材料和光伏材料等.本文主要对共轭聚合物电致发光材料和光伏材料的研究进展进行综述,介绍了这些聚合物材料的种类、结构和性质以及在聚合物电致发光器件和聚合物太阳能电池中的应用.并讨论了当前共轭聚合物光电子材料中的关键科学问题和今后的发展方向.     

Recognition Properties and Self‐assembly of Planar [M(2‐pyridyl‐1,2,3‐triazole)2]2+ Metallo‐ligands

Molecular recognition continues to be an area of keen interest for supramolecular chemists. The investigated [M( L )₂]²⁺ metallo‐ligands (M=Pd^II, Pt^II, L =2‐(1‐(pyridine‐4‐methyl)‐1 H‐1,2,3‐triazol‐4‐yl)pyridine) form a planar cationic panel with vacant pyridyl binding sites. They interact with planar neutral aromatic guests through π–π and/or metallophilic interactions. In some cases, the metallo‐ligands also interacted in the solid state with Ag^I either through coordination to the pendant pyridyl arms, or through metal–metal interactions, forming coordination polymers. We have therefore developed a system that reliably recognises a planar electron‐rich guest in solution and in the solid state, and shows the potential to link the resultant host–guest adducts into extended solid‐state structures. The facile synthesis and ready functionalisation of 2‐pyridyl‐1,2,3‐triazole ligands through copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) “click” chemistry should allow for ready tuning of the electronic properties of adducts formed from these systems.     

Toward Main Chain Metallo‐Terpyridyl Supramolecular Polymers: “The Metal Does the Trick”

Metallo‐supramolecular chemistry offers possibilities for the construction of stimuli‐responsive polymeric materials where the environment can have a large impact on the reversibility and strength of interactions between the individual components. The potential of manipulating the strength of the intermolecular non‐covalent bonds can result in impressive modifications of the metallo‐supramolecular structure and, subsequently, produces changes in the properties of the designed material. The present feature article provides an overview on recent developments in the field of metallo‐polymerization of chelating terpyridyl and analogues ligands. Synthetic strategies are described followed by a discussion regarding the characterization and the application of the reviewed metallo‐supramolecular structures, mainly based on terpyridines.

     

Constructing High‐Generation Sierpiński Triangles by Molecular Puzzling

Three generations of metalated trigonal supramolecular architectures, so‐called metallo‐triangles, were assembled from terpyridine (tpy) complexes. The first generation (G1) metallo‐triangles were directly obtained by reacting a bis(terpyridinyl) ligand with a 60° bite angle and Zn^II ions. The direct self‐assembly of G2 and G3 triangles by mixing organic ligands and Zn^II, however, only generated a mixture of G1 and G2, as well as a trace amount of insoluble polymer‐like precipitate. Therefore, a modular strategy based on the connectivity of ⟨tpy−Ru²⁺−tpy⟩ was employed to construct two metallo‐organic ligands for the assembly of G2 and G3 Sierpiński triangles. The metallo‐organic ligands L^A and L^B with multiple free terpyridines were obtained through Suzuki cross‐coupling of the Ru^II complexes, and then assembled with Zn^II or Cd^II to obtain high‐generation metallo‐triangular architectures in nearly quantitative yield. The G1–G3 architectures were characterized by NOESY and DOSY NMR spectroscopy, ESI‐MS, TWIM‐MS, and transmission electron microscopy.     

The Assembly of Supramolecular Boxes and Coordination Polymers Based on Bis‐Zinc‐Salphen Building Blocks

We report the assembly of supramolecular boxes and coordination polymers based on a rigid bis‐zinc(II)‐salphen complex and various ditopic nitrogen ligands. The use of the bis‐zinc(II)‐salphen building block in combination with small ditopic nitrogen ligands gave organic coordination polymers both in solution as well as in the solid state. Molecular modeling shows that supramolecular boxes with small internal cavities can be formed. However, the inability to accommodate solvent molecules (such as toluene) in these cavities explains why coordination polymers are prevailing over well‐defined boxes, as it would lead to an energetically unfavorable vacuum. In contrast, for relatively longer ditopic nitrogen ligands, we observed the selective formation of supramolecular box assemblies in all cases studied. The approach can be easily extended to chiral analogues by using chiral ditopic nitrogen ligands.     

Liquid‐crystalline and light‐emitting polyacetylenes

Rigid polymer backbones have often been considered to be detrimental to the packing of mesogenic pendants, and polyacetylenes have generally been regarded as unpromising materials for light‐emitting applications. Our group, however, has succeeded in creating a series of liquid‐crystalline polyacetylenes with rigid backbones and a variety of light‐emitting polyacetylenes with luminescent chromophores. Here we demonstrate that the rigid polyacetylene skeleton can play a constructive role in guiding the alignments of mesogenic pendants and prove that polyacetylenes can be highly emissive with photoluminescence quantum yields of up to 98% and electroluminescence performances comparable or superior to those of the best blue‐light‐emitting polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2607–2629, 2003     

Mechanically Induced Multicolor Change of Luminescent Materials

Mechanofluorochromic or piezochromic fluorescence chemistry involves the switching and tuning of the luminescent properties of solid‐state materials induced by exogenous forces, such as grinding, shearing, compression, tension, and so forth. Up until now, most reported mechanochromic systems, including liquid crystals, organic molecules, organometallic compounds, polymers, and dye‐doped polymers, have displayed reversible two‐color changes, which arise from either supramolecular or chemical structure transformations. However, fluorescent materials that undergo mechanically induced multicolor changes remain rare; this Minireview is focused on such materials. Topics are categorized according to the different applied forces that are required to induce the multicolor change, including mechanical control of either the supramolecular structures or the chemical structures, and mechanical control of both the supramolecular structures and chemical structures.     

Planar 2‐Pyridyl‐1,2,3‐triazole Derived Metallo‐ligands: Self‐assembly with PdCl2 and Photocatalysis

Self‐assembled metallosupramolecular architectures (MSAs) with built‐in functionalities such as light‐harvesting metal centers are a promising approach for developing emergent properties within discrete molecular systems. Herein we describe the synthesis of two new but simple “click” ligands featuring a bidentate 2‐pyridyl‐1,2,3‐triazole chelate pocket linked to a monodentate pyridyl (either 3‐ or 4‐substituted, L1 and L2 ) unit. The ligands and the corresponding four Pd^IIand Pt^IImetallo‐ligands ( Pd1 , Pd2 , Pt1 and Pt2 ) were synthesized and characterized using nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization mass spectrometry (ESI‐MS), and X‐ray crystallography. Solid‐state characterization of the series of ligands and metallo‐ligands revealed that these compounds display a co‐planar conformation of all the aryl units. The Pt^IIcontaining metallo‐ligands ( Pt1 and Pt2 ) were found to assemble into square ( Sqr ) and triangular ( Tri ) shaped architectures when combined with neutral PdCl₂ linker units. Additionally, the ability of the Pt^IImetallo‐ligands and Tri to photocatalyze the cycloaddition of singlet oxygen to anthracene was investigated.     

Metallosupramolecular approach toward functional coordination polymers

An appropriate definition of metallosupramolecular coordination polymer is offered, and the relationship between the polymer length, binding constant, and concentration is clarified. The possibility of influencing the binding constant with chelating ligands is discussed on the basis of examples of different Zn²⁺ complexes and their respective binding constants. In the main part, coordination polymers constructed by a supramolecular approach from different metal ions and pyridine–ligand systems are highlighted, and their applications as functional materials for artificial membrane and enzyme models, responsive gels, light‐harvesting systems, and organic light‐emitting diodes are discussed on the basis of individual examples. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4981–4995, 2005     

Photoresponsive Circular Supramolecular Polymers: A Topological Trap and Photoinduced Ring‐Opening Elongation

Topological features of one‐dimensional macromolecular chains govern the properties and functionality of natural and synthetic polymers. To address this issue in supramolecular polymers, we synthesized two topologically distinct supramolecular polymers with intrinsic curvature, circular and helically folded nanofibers, from azobenzene‐functionalized supramolecular rosettes. When a mixture of circular and helically folded nanofibers was exposed to UV light, selective unfolding of the latter open‐ended supramolecular polymers was observed as a result of the curvature‐impairing internal force produced by the trans‐to‐cis photoisomerization of the azobenzene. This distinct sensitivity suggests that the topological features of supramolecular polymers define their mechanical stability. Furthermore, the exposure of circular supramolecular polymers in more polar media to UV irradiation resulted in ring opening followed by chain elongation, thus demonstrating that the circular supramolecular polymer can function as a topological kinetic trap.     

Deep Eutectic Supramolecular Polymers: Bulk Supramolecular Materials

Application of new strategies for supramolecular self‐assembly can significantly impact the properties and/or functions of supramolecular polymers. To realize a facial strategy for the development of solvent‐free supramolecular polymers in bulk, “deep eutectic solvents” were employed. Cyclodextrins and natural acids were used to prepare deep eutectic supramolecular polymers ( DESP s). Deep eutectic solvents have special characteristics that endow DESP s with unique macroscopic properties and excellent processability. DESP s exhibit supramolecular adhesion and temperature‐dependent behavior originating from the combined effects of deep eutectic solvents and supramolecular polymerization. Because DESP s are solvent‐free and display interesting macroscopic properties, they have potential as new adaptive materials.     

PL and EL behavior of near‐red luminescent metallopolymer easily prepared from phosphine‐containing copolymer and chloro{bis(1‐phenylisoquinolinato‐N,C2′)}iridium(III), and its monomeric analog

We successfully developed phosphorescent cyclometallated iridium‐containing metallopolymers, which are near‐red luminescent iridium complexes bearing phosphine‐containing copolymers used as polymer ligands, and investigated their photoluminescence and electroluminescence behavior. The phosphine copolymer ligand made from methyl methacrylate and 4‐styryldiphenylphosphine can be used as an anchor, which coordinates luminescent iridium units to form the metallopolymer easily. Organic light‐emitting diodes were fabricated from the metallopolymer and its nonpolymer analog, [IrCl(piq)₂PPh₃]. These complexes exhibited quite similar luminescence behavior, except for emission from the free‐phosphine‐units in the polymer side chain and their energy‐transferring properties from host to guest materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4366–4378, 2009     

Design and Sensing Properties of a Self‐Assembled Supramolecular Oligomer

Supramolecular polymers are a class of macromolecules stabilized by weak non‐covalent interactions. These self‐assembled aggregates typically undergo stimuli‐induced reversible assembly and disassembly. They thus hold great promise as so‐called functional materials. In this work, we present the design, synthesis, and responsive behavior of a short supramolecular oligomeric system based on two hetero‐complementary subunits. These “monomers” consist of a tetrathiafulvalene‐functionalized calix[4]pyrrole (TTF‐C[4]P) and a glycol diester‐linked bis‐2,5,7‐trinitrodicyanomethylenefluorene‐4‐carboxylate (TNDCF), respectively. We show that when mixed in organic solvents, such as CHCl₃, CH₂ClCH₂Cl, and methylcyclohexane, supramolecular aggregation takes place to produce short oligomers stabilized by hydrogen bonding and donor–acceptor charge‐transfer (CT) interactions. The self‐associated materials were characterized by ¹H NMR and UV/Vis/NIR absorption spectroscopy, as well as by concentration‐ and temperature‐dependent absorption spectroscopy and dynamic light scattering (DLS) analyses of both the monomeric and oligomerized species. The self‐associated system produced from TTF‐C[4]P and TNDCF exhibits a concentration‐dependent aggregation behavior typical of supramolecular polymers. Further support for the proposed self‐assembly came from theoretical calculations. The fluorescence emitting properties of TNDCF are quenched under conditions that promote the formation of supramolecular aggregates containing TTF‐C[4]P and TNDCF. This quenching effect has been utilized as a probe for the detection of substrates in the form of anions (i.e., chloride) and nitroaromatic explosives (i.e., 1,3,5‐trinitrobenzene). Specifically, the addition of these substrates to mixtures of TTF‐C[4]P and TNDCF produced a fluorescence “turn‐on” response.