Supramolecular Wires Research Articles

Cyclooctatetraene‐Embedded Carbon Nanorings

AbstractWith the prosperity of the development of carbon nanorings, certain topologically or functionally unique units‐embedded carbon nanorings have sprung up in the past decade. Herein, we report the facile and efficient synthesis of three cyclooctatetraene‐embedded carbon nanorings (COTCNRs) that contain three (COTCNR1 and COTCNR2) and four (COTCNR3) COT units in a one‐pot Yamamoto coupling. These nanorings feature hoop‐shaped segments of Gyroid (G‐), Diamond (D‐), and Primitive (P‐) type carbon schwarzites. The conformations of the trimeric nanorings COTCNR1 and COTCNR2 are shape‐persistent, whereas the tetrameric COTCNR3 possesses a flexible carbon skeleton which undergoes conformational changes upon forming host–guest complexes with fullerenes (C60 and C70), whose co‐crystals may potentially serve as fullerene‐based semiconducting supramolecular wires with electrical conductivities on the order of 10−7 S cm−1 (for C60⊂COTCNR3) and 10−8 S cm−1 (for C70⊂COTCNR3) under ambient conditions. This research not only describes highly efficient one‐step syntheses of three cyclooctatetraene‐embedded carbon nanorings which feature hoop‐shaped segments of distinctive topological carbon schwarzites, but also demonstrates the potential application in electronics of the one‐dimensional fullerene arrays secured by COTCNR3.

Cyclooctatetraene-Embedded Carbon Nanorings.

With the prosperity of the development of carbon nanorings, certain topologically or functionally unique units-embedded carbon nanorings have sprung up in the past decade. Herein, we report the facile and efficient synthesis of three cyclooctatetraene-embedded carbon nanorings (COTCNRs) that contain three (COTCNR1 and COTCNR2) and four (COTCNR3) COT units in a one-pot Yamamoto coupling. These nanorings feature hoop-shaped segments of Gyroid (G-), Diamond (D-), and Primitive (P-) type carbon schwarzites. The conformations of the trimeric nanorings COTCNR1 and COTCNR2 are shape-persistent, whereas the tetrameric COTCNR3 possesses a flexible carbon skeleton which undergoes conformational changes upon forming host-guest complexes with fullerenes (C60 and C70), whose co-crystals may potentially serve as fullerene-based semiconducting supramolecular wires with electrical conductivities on the order of 10-7 S cm-1 (for C60⊂COTCNR3) and 10-8 S cm-1 (for C70⊂COTCNR3) under ambient conditions. This research not only describes highly efficient one-step syntheses of three cyclooctatetraene-embedded carbon nanorings which feature hoop-shaped segments of distinctive topological carbon schwarzites, but also demonstrates the potential application in electronics of the one-dimensional fullerene arrays secured by COTCNR3.

Shallow conductance decay along the heme array of a single tetraheme protein wire.

Multiheme cytochromes (MHCs) are the building blocks of highly conductive micrometre-long supramolecular wires found in so-called electrical bacteria. Recent studies have revealed that these proteins possess a long supramolecular array of closely packed heme cofactors along the main molecular axis alternating between perpendicular and stacking configurations (TST = T-shaped, stacked, T-shaped). While TST arrays have been identified as the likely electron conduit, the mechanisms of outstanding long-range charge transport observed in these structures remain unknown. Here we study charge transport on individual small tetraheme cytochromes (STCs) containing a single TST heme array. Individual STCs are trapped in a controllable nanoscale tunnelling gap. By modulating the tunnelling gap separation, we are able to selectively probe four different electron pathways involving 1, 2, 3 and 4 heme cofactors, respectively, leading to the determination of the electron tunnelling decay constant along the TST heme motif. Conductance calculations of selected single-STC junctions are in excellent agreement with experiments and suggest a mechanism of electron tunnelling with shallow length decay constant through an individual STC. These results demonstrate that an individual TST motif supporting electron tunnelling might contribute to a tunnelling-assisted charge transport diffusion mechanism in larger TST associations.

Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes.

The performance of nanoelectronic and molecular electronic devices relies strongly on the employed functional units and their addressability, which is often a matter of appropriate interfaces and device design. Here, we compare two promising designs to build solid-state electronic devices utilizing the same functional unit. Optically addressable Ru-terpyridine complexes were incorporated in supramolecular wires or employed as ligands of gold nanoparticles and contacted by nanoelectrodes. The resulting small-area nanodevices were thoroughly electrically characterized as a function of temperature and light exposure. Differences in the resulting device conductance could be attributed to the device design and the respective transport mechanism, that is, thermally activated hopping conduction in the case of Ru-terpyridine wire devices or sequential tunneling in nanoparticle-based devices. Furthermore, the conductance switching of nanoparticle-based devices upon 530 nm irradiation was attributed to plasmon-induced metal-to-ligand charge transfer in the Ru-terpyridine complexes used as switching ligands. Finally, our results reveal a superior device performance of nanoparticle-based devices compared to molecular wire devices based on Ru-terpyridine complexes as functional units.

Construction of cluster-based supramolecular wire and rectangle.

Reactions of [Et4N][Tp*WS3(CuCl)3] (1) (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) with 2 equiv. of AgOTf (OTf- = trifluoromethanesulfonate) and 1 equiv. of several bidentate pyridine ligands including 2,5-bis(pyridine-4-yl)thiazolo[5,4-d]thiazole (L1), 2,7-di(pyridin-4-yl)-9H-fluorene (L2), 2,7-di(pyridin-4-yl)-9H-carbazole (L3), and 2,7-di(pyridin-4-yl)-9H-fluoren-9-one (L4) afforded four W/Cu/S cluster-based supramolecular compounds [(Tp*WS3Cu2Cl)2(L1)] (2), {[(Tp*WS3Cu3)2(μ-Cl)2(μ4-Cl)]2(L2)2}(OTf)2 (3), {[(Tp*WS3Cu3)2(μ-Cl)2(μ4-Cl)]2(L3)2}(OTf)2 (4) and {[(Tp*WS3Cu3)2(μ-Cl)2(μ4-Cl)]2(L4)2}(OTf)2 (5). Compounds 2-5 were characterized by elemental analysis, IR, UV-vis, 1H NMR, and single-crystal X-ray diffraction analysis. The neutral cluster 2 behaves as a supramolecular wire constructed by L1 bridging two butterfly-shaped [Tp*WS3Cu2Cl] cores. The cluster cations of 3-5 contain two [(Tp*WS3Cu3)2(μ-Cl)2(μ4-Cl)]+ cores linked by two L2, L3, or L4 ligands, which finally formed a cationic supramolecular rectangle. The third-order nonlinear-optical (NLO) properties of 3-5 in DMF were also investigated by Z-scan techniques and their NLO responses were enhanced compared to those of their precursor 1.

Fullerene Wires Assembled Inside Carbon Nanohoops.

Carbon‐nanohoop structures featuring one or more round‐shaped cavities represent ideal supramolecular hosts for spherical fullerenes, with potential to form host‐guest complexes that perform as organic semiconductors in the solid state. Due to the tight complexation between the shape‐complementary hosts and guests, carbon nanohoops have the potential to shield fullerenes from water and oxygen, known to perturb the electron‐transport process. Many nanohoop receptors have been found to form host‐guest complexes with fullerenes. However, there is only a little or no control over the long‐range order of encapsulated fullerenes in the solid state. Consequently, the potential of these complexes to perform as organic semiconductors is rarely evaluated. Herein, we present a survey of all known nanohoop‐fullerene complexes, for which the solid‐state structures were obtained. We discuss and propose instances where the inclusion fullerene guests form discrete supramolecular wires, which might open up possibilities for their use in electronic devices.

Emerged Metallicity in Molecular Ferromagnetic Wires.

Supramolecular engineering bridges molecular assembly with macromolecular charge-transfer salts, promising the design to construct supramolecular architectures that integrate cooperative properties difficult or impossible to find in conventional lattices. Here, we report the crystal engineering design and kinetic growth of one-dimensional supramolecular wires composed of bis(ethylenedithio)tetrathiafulvalene (ET+) cation and polymeric Cu[N(CN)2]2- anion. A bulk ferromagnetic order is discovered for filling up the gap where strong ferromagnetism is missing in such ET molecule-based charge-transfer salts. Metallicity is induced by electric current from the semiconducting wire, which is attributed to strain effect by tuning its close molecular contact. This structural feature is evidenced through the combination of various mechanistic spectroscopic studies. Electric dipole is established from the close molecular contacts and is suggestive to stabilize ferromagnetic spin interaction through anions bridging spin sites. The breakthrough shown here provides a pathway to explore low-dimensional supramolecular materials exhibiting strong electron correlation, metallicity, and ferromagnetism.

Room-Temperature Spin-Dependent Transport in Metalloporphyrin-Based Supramolecular Wires.

Here we present room‐temperature spin‐dependent charge transport measurements in single‐molecule junctions made of metalloporphyrin‐based supramolecular assemblies. They display large conductance switching for magnetoresistance in a single‐molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire: those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin‐dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis, and almost suppressed when it is perpendicular. The key ingredients for the above effect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule–electrode contact.

Room‐Temperature Spin‐Dependent Transport in Metalloporphyrin‐Based Supramolecular Wires

AbstractHere we present room‐temperature spin‐dependent charge transport measurements in single‐molecule junctions made of metalloporphyrin‐based supramolecular assemblies. They display large conductance switching for magnetoresistance in a single‐molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire: those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin‐dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis, and almost suppressed when it is perpendicular. The key ingredients for the above effect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule–electrode contact.

(Invited) Design and Fabrication of Organic Thin Film Transistors Using Solution-Processable Liquid Crystalline Phthalocyanine Derivatives

Phthalocyanines (Pcs) are an extremely non-toxic organic chromophores with a range of versatile range applications from industrial pigments to photodynamic agents in cancer therapy and photosensitizers in photocopiers and compact discs. The central atom is coordinated with four pyrrolic nitrogen atoms. The conjugated π-systems of eighteen electrons in the macrocyclic ring gives rise to unique semiconducting properties which can be tuned by substituents of alkyl, alkoxy, or alkoxymethyl chains at sixteen sites on the benzenoid rings and axial ligation sites at the central metal or metalloid. Unsubstituted Pcs are generally both thermally and chemically stable but ring substituents such as SO3H and aliphatic chains confer solubility in water and organic solvents, respectively. They can form liquid crystalline phases. The present talk will highlight the achievements in application of phthalocyanine layers in different electronic devices such as field effect transistors (OFET) and memory devices taking into account literature data and our experimental results. Special attention will be focused to liquid crystalline phthalocyanines. Disk-like molecules, typically comprising a flat rigid aromatic core and flexible peripheral substituents, self-organizes into one-dimensional "supramolecular wires". Due to high charge carrier mobility along the columns, discotic mesogens are considered as realistic candidates for application in organic electronic devices. The well-ordered films with controllable molecule alignment can be obtained by slow cooling from isotropic liquid temperature.

Organotellurium Chemistry: Synthesis and Properties of 2-Acylamino- and 2-Arylamino-1,3-benzotellurazoles

Synthetic methods have been developed to prepare novel 1,3-benzotellurazoles carrying acylamino and arylamino moieties in position 2, in order to investigate their propensity to self-assemble to supramolecular structures. The targeted compounds were obtained in yields ranging from 44% to 67%, by reacting bis(2-aminophenyl) ditelluride with acyl- and aryl isothiocyanates, respectively, and subsequent reductive cyclization of the resulting thiourea derivatives. Seven novel 1,3-benzotellurazole derivatives were prepared: 2-benzoylamino-1,3-benzotellurazole, 2-(4-chlorobenzoylamino)-1,3-benzotellurazole, 2-(2-bromobenzoylamino)-1,3-benzotellurazole, 2-(4-bromobenzoylamino)-1,3-benzotellurazole, 2-(4-methoxybenzoylamino)-1,3-benzotellurazole, 2-phenylamino-1,3-benzotellurazole, and 2-(4-chlorophenylamino-1,3-benzotellurazole. A simplified protocol was employed to synthesize all acyl isothiocyanates needed for their preparation from benzoyl halide derivatives and potassium thiocyanate. The reductive cyclization of the intermediate thioureas was challenging, only the use of hydroxymethanesulfinate in the presence of elemental mercury provided synthetically useful product yields. A mechanism was proposed, consisting of the insertion of mercury into the Te-Te bond, followed by intramolecular nucleophilic attack of the thiocarbonyl moiety by the resulting insertion product. All 2-acylamino-1,3-benzotellurazoles are crystalline solids, which are stable to ambient light, air and moderate heat. A characterization of selected samples by X-ray crystallography indicated that they form dimers in solid state, resulting from hydrogen bonding between the exocyclic and endocyclic nitrogen atoms of two adjacent molecules. This sets them apart from 2-alkyl- and 2-aryl-1,3-benzotellurazoles, which are known to self-assemble into supramolecular wires.

Supramolecular Networks and Wires Dominated by Intermolecular BiEDOT Interactions

The ditopic ligand bpy-PE2P-bpy self-assembles on surfaces and has been investigated by high resolution scanning tunneling microscopy. The molecule shows a cis-to-trans isomerization from its bipyridine terminal units, whereas the biEDOT central bridge is always locked in its trans conformation thanks to the intramolecular sulfur–oxygen interactions. The cis-bpy-PE2P-bpy conformers form linear supramolecular stripe and herringbone structures. Upon protonation, they are transformed to the trans conformers which form both a zigzag structure and different supramolecular wires of variable width. Long single molecular wires can be easily obtained. In the various supramolecular organizations, the intermolecular hydrogen bonds between the bipyridine units vary. On the contrary, the biEDOT moieties are always aligned in a similar way as that observed in crystallized PEDOT nanofibrils and the intermolecular biEDOT interactions remain identical. Our work contributes to the understanding of the impact of EDOT–EDOT interactions on the properties of organic and molecular devices.

Making Coaxial Wires Out of Janus Dendrimers for Efficient Charge Transport.

Highly conductive coaxial supramolecular wires are prepared by using a new family of Janus dendrimers that combines two rigid aromatic parts and two flexible aliphatic parts. The two external regions consist of a promesogenic block based on a third generation Percec-type dendron with four terminal dodecyloxy alkyl chains, whereas the two internal regions are formed by one, two, or three carbazole units bearing flexible spacers. These functional Janus dendrimers self-organize in columnar liquid crystal phases with a strong coaxial segregation within each column. Interestingly, the charge mobility studies revealed that these Janus dendrimers display semiconductor properties with hole mobility values up to 0.5 cm2 V-1 s-1, depending on the packing within the columns which can be tuned by the number of carbazole functional units. The high hole mobility values measured in these materials are among the highest values reported for columnar liquid crystals.

Dual‐Input Regulation and Positional Control in Hybrid Oligonucleotide/Discotic Supramolecular Wires

AbstractThe combination of oligonucleotides and synthetic supramolecular systems allows for novel and long‐needed modes of regulation of the self‐assembly of both molecular elements. Discotic molecules were conjugated with short oligonucleotides and their assembly into responsive supramolecular wires studied. The self‐assembly of the discotic molecules provides additional stability for DNA‐duplex formation owing to a cooperative effect. The appended oligonucleotides allow for positional control of the discotic elements within the supramolecular wire. The programmed assembly of these hybrid architectures can be modulated through the DNA, for example, by changing the number of base pairs or salt concentration, and through the discotic platform by the addition of discotic elements without oligonucleotide handles. These hybrid supramolecular‐DNA structures allow for advanced levels of control over 1D dynamic platforms with responsive regulatory elements at the interface with biological systems.

Dual-Input Regulation and Positional Control in Hybrid Oligonucleotide/Discotic Supramolecular Wires.

The combination of oligonucleotides and synthetic supramolecular systems allows for novel and long‐needed modes of regulation of the self‐assembly of both molecular elements. Discotic molecules were conjugated with short oligonucleotides and their assembly into responsive supramolecular wires studied. The self‐assembly of the discotic molecules provides additional stability for DNA‐duplex formation owing to a cooperative effect. The appended oligonucleotides allow for positional control of the discotic elements within the supramolecular wire. The programmed assembly of these hybrid architectures can be modulated through the DNA, for example, by changing the number of base pairs or salt concentration, and through the discotic platform by the addition of discotic elements without oligonucleotide handles. These hybrid supramolecular‐DNA structures allow for advanced levels of control over 1D dynamic platforms with responsive regulatory elements at the interface with biological systems.

Induced Aggregation of AIE-Active Mono-Cyclometalated Ir(III) Complex into Supramolecular Branched Wires for Light-Emitting Diodes.

Aggregation-induced emission (AIE) is commonly observed in irregular bulk form. Herein, unique aggregation properties of an AIE-active complex into branched supramolecular wires are reported for the first time. Mono-cyclometalated Ir(III) complex shows in-plane J-aggregation at the air-water interface owing to the restriction of intramolecular vibration of bidentate phenylpyridinato and intramolecular rotations of monodentate triphenylphosphine ligands at air-water interface. As a consequence, a large enhancement of luminescence comparable to the solid state is obtained from the monolayers of supramolecular wires. This unique feature is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular wires as active layer. This study opens up the need of ordered assembly of AIE complexes to achieve optimal luminescence characteristics.

Massively parallel and linear-scaling algorithm for second-order Møller–Plesset perturbation theory applied to the study of supramolecular wires

We present a scalable cross-platform hybrid MPI/OpenMP/OpenACC implementation of the Divide–Expand–Consolidate (DEC) formalism with portable performance on heterogeneous HPC architectures. The Divide–Expand–Consolidate formalism is designed to reduce the steep computational scaling of conventional many-body methods employed in electronic structure theory to linear scaling, while providing a simple mechanism for controlling the error introduced by this approximation. Our massively parallel implementation of this general scheme has three levels of parallelism, being a hybrid of the loosely coupled task-based parallelization approach and the conventional MPI +X programming model, where X is either OpenMP or OpenACC. We demonstrate strong and weak scalability of this implementation on heterogeneous HPC systems, namely on the GPU-based Cray XK7 Titan supercomputer at the Oak Ridge National Laboratory. Using the “resolution of the identity second-order Møller–Plesset perturbation theory” (RI-MP2) as the physical model for simulating correlated electron motion, the linear-scaling DEC implementation is applied to 1-aza-adamantane-trione (AAT) supramolecular wires containing up to 40 monomers (2440 atoms, 6800 correlated electrons, 24440 basis functions and 91280 auxiliary functions). This represents the largest molecular system treated at the MP2 level of theory, demonstrating an efficient removal of the scaling wall pertinent to conventional quantum many-body methods.

Sorption Properties and Nitroaromatic Explosives Sensing Based on Two Isostructural Metal–Organic Frameworks

We first designed and synthesized a new semirigid tripodal ligand with tetrazole groups, 1,3,5-tri(4-(2H-tetrazol-5-yl)phenoxy)benzene (H3TTPB). Two isostructural microporous metal–organic frameworks (MOFs), namely [Cu3(TTPB)2(H2O)6]·5DMF (JUC-130) and [Cd3(TTPB)2(H2O)6]·6DMF (JUC-131) (JUC = Jilin University, China), were successfully synthesized under solvothermal reactions based on this ligand, which both possess two-dimensional (2D) frameworks based on similar trinuclear metal centers as secondary building units (SBUs). H3TTPB was designed as the organic building block, not only because it is suitable to construct functionalized microporous frameworks with numerous nitrogen atoms but also by reason for its blue luminescent emission. Gas sorption measurements indicated that they are both microporous frameworks. JUC-130 showed high stability in water and selective sorption capabilities for alcohol and water vapors, which may be further used for the separation of alcohol–water mixtures. In addition, JUC-131 exhibited interesting and important fluorescent properties, which can be used as one of the few known MOFs useful for the detection of nitroaromatics via “supramolecular wire effect”.

On-surface self-organization of a robust metal-organic cluster based on copper(I) with chloride and organosulphur ligands.

Direct sublimation of a Cu4Cl4 metal-organic cluster on Cu(110) under ultra-high vacuum allows the formation of ultra-large well-organized metal-organic supramolecular wires. Our results show that the large monomers assemble with each other by π-π interactions connecting dipyrimidine units and are stabilized by the surface.

Construction of Bis-pyrazole Based Co(II) Metal–Organic Frameworks and Exploration of Their Chirality and Magnetic Properties

In continuation of our interest in pyrazole based multifunctional metal–organic frameworks (MOFs), we report herein the construction of a series of Co(II) MOFs using a bis-pyrazole ligand and various benzene polycarboxylic acids. Employment of different acids has resulted in different architectures ranging from a two-dimensional grid network, porous nanochannels with interesting double helical features such as supramolecular chicken wire, to three-dimensional diamondoid networks. One of the distinguishing features of the network is their larger dimensions which can be directly linked to a relatively larger size of the ligand molecule. Conformational flexibility of the ligand also plays a decisive role in determining both the dimensionality and topology of the final structure. Furthermore, chirality associated with helical networks and magnetic properties of two MOFs have also been investigated.