Supramolecular surface-confined architectures created by self-assembly of triangular phenylene-ethynylene macrocycles via van der Waals interaction

At the liquid/graphite interface triangular and rhombic phenylene-ethynylene macrocycles substituted by alkyl chains self-assemble to form porous two-dimensional (2D) molecular networks of honeycomb and Kagomé types, respectively, or close-packed non-porous structures via alkyl chain interdigitation as the directional intermolecular linkages. Factors that affect the formation of the 2D molecular networks, such as alkyl chain length, solvent, solute concentration, and co-adsorption of guest molecules, were elucidated through a systematic study. For the porous networks, various molecules and molecular clusters were adsorbed in the pores reflecting the size and shape complementarity, exploring a new field of 2D host-guest chemistry.     

Two-dimensional porous molecular networks of dehydrobenzo[12]annulene derivatives via alkyl chain interdigitation

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been scrutinized by scanning tunneling microscopy (STM) at the liquid-solid interface. First, the influence of core symmetry on the network structure was investigated by comparing the two-dimensional (2D) ordering of rhombic bisDBA 1a and triangular DBA 2a (Figure 1). BisDBA 1a forms a Kagomé network upon physisorption from 1,2,4-trichlorobenzene (TCB) onto highly oriented pyrolytic graphite (HOPG). Under similar experimental conditions, DBA 2a shows the formation of a honeycomb network. The core symmetry and location of alkyl substituents determine the network structure. The most remarkable feature of the DBA networks is the interdigitation of the nonpolar alkyl chains: they connect the pi-conjugated cores and direct their orientation. As a result, 2D open networks with voids are formed. Second, the effect of alkyl chain length on the structure of DBA patterns was investigated. Upon increasing the length of the alkyl chains (DBAs 3c-e) a transition from honeycomb networks to linear networks was observed in TCB, an observation attributed to stronger molecule-substrate interactions. Third, the effect of solvent on the structure of the nonpolar DBA networks was investigated in four different solvents: TCB as a polar aromatic solvent, 1-phenyloctane as a solvent having both aromatic and aliphatic moieties, n-tetradecane as an aliphatic solvent, and octanoic acid as a polar alkylated solvent. The solvent dramatically changes the structure of the DBA networks. The solvent effects are discussed in terms of factors that influence the mobility of molecules at the liquid-solid interface such as solvation.     

Unconventional electronic and magnetic functions of nanographene-based host-guest systems

Nanographene has a unique electronic structure which critically depends on the shape of its edge. A zigzag-edged nanographene sheet has a non-bonding pi-electron state (edge state), yielding a strong spin magnetism for edge-state localized spins, in spite of the absence of such a state in an armchair-edged nanographene sheet. Nanographite (stacked nanographene sheets)-network-based nanoporous carbon is employed as the host material to build unconventional magnetic systems based on the host-guest interaction. The physisorption of various guest materials can cause a reversible low-spin/high-spin magnetic switching phenomenon, whose feature varies depending on the type of guest species. The edge-state spins are utilized as a probe to detect a huge condensation of helium atoms in the nanopores. The giant magnetoresistance of the nanographite network is controlled by the physisorption of magnetic oxygen molecules. The confinement of potassium clusters in the nanopores surrounded by nanographite domains yields an interesting nanomagnetic state. Nanographene/nanographite is an intriguing pi-electron-based nanocarbon material with the potential of producing unconventional magnetic structures that cannot be obtained using bulk graphite. The processability of nanographene/nanographite is expected to give a variety of magnetic functions for spintronic applications.     

Synthesis,Properties, and Remarkable 2 D Self‐Assembly at the Liquid/Solid Interface of a Series of Triskele‐Shaped 5,11,17‐Triazatrinaphthylenes (TrisK)

A series of 5,11,17‐triazatrinaphthylene (TrisK) derivatives, large disk‐like π‐conjugated molecules with C_3h symmetry, has been synthesised by following an optimised synthetic pathway. The synthesis was performed by a four‐step protocol based on the N‐arylation of 1,3,5‐tribromobenzene with appropriate anthranilate derivatives. This strategy permits the generation of either chlorinated ( TrisK‐Cl‐OCn ) or non‐chlorinated ( TrisK‐H‐OCn ) alkoxy‐substituted derivatives (OC_nH_2n+1 with n=3, 10, 12 and 16), thus providing additional versatility in the control of the structure–property relationships. The electronic properties of the various TrisK compounds have been characterised in solution by absorption and emission spectroscopies as well as cyclic voltammetry. The crystal structure of 2,8,14‐propyloxy‐5,11,17‐triazatrinaphthylene TrisK‐H‐OC3 has been determined by X‐ray diffraction analysis, which revealed the presence of stabilising weak intermolecular H bonds. Scanning tunnelling microscopy (STM) at the liquid/solid interface has revealed the remarkable 2D self‐assembling properties of the TrisK compounds. In particular, it has shown that TrisK‐H‐OC12 forms three concomitant self‐organised 2D phases with different row‐packing arrangements. This 2D polymorphism arises from slow ordering due to the presence of three long dodecyloxy chains on the molecular backbone. Individual molecules can be imaged with spectacular intramolecular resolution, thus providing the possibility of correlating the STM features with the calculated charge density distribution.     

Fluorescent H‐Aggregates Hosted by a Charged Cyclodextrin Cavity

Most macrocyclic host molecules, including cyclodextrins, usually prevent self‐aggregation of the guest organic molecules, by exploiting inclusion complexation of the guest with the host. In this work, it was found that a negatively charged β‐cylcodextrin derivative induces aggregation of a well‐known amyloid sensing dye, Thioflavin‐T, and leads to an unprecedented formation of the rarely observed emissive H‐type aggregates of the dye.     

Restricted Conformational Flexibility of a Triphenylamine Derivative on the Formation of Host–Guest Complexes with Various Macrocyclic Hosts

Herein, we report the host–guest‐type complex formation between the host molecules cucurbit[7]uril (CB[7]), β‐cyclodextrin (β‐CD), and dibenzo[24]crown‐8 ether (DB24C8) and a newly synthesized triphenylamine (TPA) derivative 1 X₃ as the guest component. The host–guest complex formation was studied in detail by using ¹H NMR, 2D NOESY, UV/Vis fluorescence, and time‐resolved emission spectroscopy. The chloride salt of the TPA derivative was used for recognition studies with CB[7] and β‐CD in an aqueous medium. The restricted internal rotation of the guest molecule on complex formation with either of these two host molecules was reflected in the enhancement of the emission quantum yield and the average excited‐state lifetime for the triphenylamine‐based excited states. Studies with DB24C8 as the host molecule were performed in dichloromethane, a medium that maximizes the noncovalent interaction between the host and guest fragments. The Förster resonance energy transfer (FRET) process involving DB24C8 and 1 (PF₆)₃, as the donor and acceptor fragments, respectively, was established by electrochemical, steady‐state emission, and time‐correlated single‐photon counting studies.     

Luminescence and mesogenic properties in crown-ether-isocyanide or carbene gold(I) complexes: luminescence in solution, in the solid, in the mesophase, and in the isotropic liquid state

A crown ether isocyanide CNR (R = benzo-15-crown-5) has been synthesized by dehydration of the corresponding formamide. Substitution reactions with the appropriate gold(I) precursors afford the luminescent mononuclear derivatives [AuX(CNR)] (X = Cl, C 6F 5, Br, I), [Au(C 6F 4OCH 2C 6H 4OC nH 2 n+1 - p)(CNR)] ( n = 4, 8, 10, 12), and [Au(C 6F 4OCH 2C 6H 2-3,4,5-(OC n H 2 n+1 ) 3(CNR)] ( n = 4, 8, 12). X-ray diffraction studies of [AuCl(CNR)] show the molecules associated in a tetranuclear manner with an antiparallel orientation and gold-gold distances of 3.420 and 3.427 A (Au...Au...Au angles are 121.2 degrees ). These tetranuclear units generate infinite zigzag chains through longer Au...Au distances of 3.746 A and weak C-H...O nonclassic interactions. Nucleophilic attack to the coordinated isocyanide in [AuCl(CNR)] by methanol or a primary amine produces the carbene derivatives [AuCl{C((NHR)(OMe)}] and [AuCl{C(NHR')(NHR)}] (R' = Me, n-Bu). The ether crown in these complexes is able to coordinate sodium from NaClO 4, affording the corresponding bimetallic complexes (Na/Au = 1:1). The derivatives containing one alkoxy chain are liquid crystals, displaying a smectic C mesophase (for n > 4), whereas the trialkoxy derivatives display unidentified or smectic C mesophases, depending on the alkyl chain length. After complexation of sodium salts, the mesogenic behavior is lost. All of the derivatives are luminescent at room temperature in the solid state with emission maxima in the range 405-550 nm; they emit at 77 K from 410 to 572 nm. Only the ligand and the fluoroaryl complexes emit in solution at room temperature, but all of the compounds are luminescent at 77 K. Very interestingly, some fluoroaryl derivatives with alkoxy chains are luminescent not only in the solid, and in solution, but also in the mesophase, and in the isotropic liquid at moderate temperatures. These are the first metal complexes ever reported to show luminescence in the isotropic liquid state.     

Synthesis, characterization, and OFET properties of amphiphilic heteroleptic tris(phthalocyaninato) europium(III) complexes with hydrophilic poly(oxyethylene) substituents

A series of amphiphilic heteroleptic tris(phthalocyaninato) europium complexes with hydrophilic poly(oxyethylene) heads and hydrophobic alkoxy tails {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8}Eu[Pc(OCnH2n + 1)8] (n = 6, 8, 10,12) (1-4) were designed and prepared from the reaction between homoleptic bis(phthalocyaninato) europium compound {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8} and metal-free 2,3,9,10,16,17,23,24-octakis(alkoxy)phthalocyanine H2Pc(OCnH2n + 1)8 (n = 6, 8, 10,12) in the presence of Eu(acac)3.H2O (Hacac = acetylacetone) in boiling 1,2,4-trichlorobenzene (TCB). These novel sandwich triple-decker complexes have been characterized by a wide range of spectroscopic methods and have been electrochemically studied. With the help of the Langmuir-Blodgett (LB) technique, these typical amphiphilic triple-decker complexes have been fabricated into organic field effect transistors (OFET) with an unusual bottom contact configuration. The devices display good OFET performance with the carrier mobility for holes in the direction parallel to the aromatic phthalocyanine rings, which shows dependence on the length of the hydrophobic alkoxy side chains, decreasing from 0.46 for 1 to 0.014 cm2 V(-1) s(-1) for 4 along with the increase in the carbon number in the hydrophobic alkoxy side chains.     

A porous framework polymer based on a zinc(II) 4,4'-bipyridine-2,6,2',6'-tetracarboxylate: synthesis, structure, and "zeolite-like" behaviors

The robust metal-organic framework compound {[Zn(2)(L)] x 4H(2)O}(infinity) I has been synthesized by hydrothermal reaction of ZnCl(2) and 4,4'-bipyridine-2,6,2',6'-tetracarboxylic acid (H(4)L). Compound I crystallizes in a chiral space group, P4(2)2(1)2, with the chirality generated by the helical chains of hydrogen-bonded guest water molecules rather than by the coordination framework. Removal of guest water molecules from the crystal affords the porous material, [Zn(2)(L)](infinity) (II), which has very high thermal stability and is chemically inert. The N(2) isotherm of II at 77 K suggests a uniform porous structure with a BET surface area of 312.7 m(2)/g and a remarkably strong interaction with N(2) molecules (betaE(0) = 29.6 kJ mol(-)(1)). II also exhibits significant gas storage capacities of 1.08 wt % for H(2) at 4 bar and 77 K and 3.14 wt % (44.0 cm(3)/g, 67 v/v) for methane at 9 Bar at 298 K. The adsorption behavior of II toward organic solvent vapors has also been studied, and isotherms reveal that for different solvent vapors adsorption is dominated by two types of processes, absorbate-absorbate or absorbate-absorbent interactions. The adsorption and desorption kinetic processes in II are determined mainly by the molecular size of the guest species and their interaction with the host.     

Locking the free-rotation of a prochiral star-shaped guest molecule inside a two-dimensional nanoporous network by introduction of chlorine atoms

Two star-shaped triazatrinaphthylene (TrisK) derivatives form highly-organized nanoporous honeycomb networks when adsorbed at the n-tetradecane/HOPG interface. STM reveals that replacing three H-atoms by three Cl-atoms in the chemical structure of the TrisK skeleton results in locking the free-rotation of the guest molecules inside the pore of the host network as a result of symmetry breaking.     

Control of release properties of guest molecules by the type of benzoheterocyclic ring in supramolecular host complexes

Three types of supramolecular benzoheterocyclic host complexes were successfully prepared using (1R,2S)-2-amino-1,2-diphenylethanol and three types of benzoheterocyclic (benzothiophene, benzofuran, and benzopyrrole) acid derivatives. The host complexes had one-dimensional (1D) channel-like cavities that were formed by the assembly of two-component 2₁-helical columnar network structures, which included guest alcohol molecules. The release behavior of the guest molecules could be tuned by the type of heterocyclic ring in the supramolecular host complex.     

Tunable Phosphorescence/Fluorescence Dual Emissions of Organic Isoquinoline-Benzophenone Doped Systems by Alkoxy Engineering

Dual/multi-component organic doped systems with room-temperature phosphorescence (RTP) properties have been developed. However, the unknown luminescence mechanism still greatly limits the development of the doped materials. Herein, a new doped system exhibiting phosphorescence/fluorescence dual emission (Φ_phos=4–24 % and τ_phos=101–343 ms) is successfully constructed through prediction and design. A series of isoquinoline derivatives with different alkoxy chains were selected as the guests. Benzophenone was chosen as the host owing to the characteristics of low melting point and good crystallinity. The alkoxy chain lengths of the guests are first reported to be used to control the fluorescence and phosphorescence intensities of the doped materials, which results in different prompt emission colors. Additionally, the doped ratio of the guest and host can also control the luminous intensities of the materials. In particular, the doped materials still exhibit phosphorescent properties even if the ratio of the guest/host is as low as 1:100 000.     

Guest-Controlled Formation of a Hydrogen-Bonded Molecular Capsule

The dimerization of the self-complementary resorcarene tetraesters is triggered by the entrapment of a tropylium cation in the π-basic cavity. Eight intermolecular OH⋅⋅⋅OC hydrogen bonds together with host–guest interactions such as charge transfer and C−H⋅⋅⋅π bonding are responsible for the high stability of this assembly (see picture). Hereby neither the host–guest interaction nor the interaction of two resorcarene molecules through hydrogen bonds is sufficient by itself to form the complex.     

Inclusion Compounds Formed from N,N-bis(2-hydroxybenzyl)alkylamine Derivatives and Transition Metal Ions via Molecular Assembly

A series of N,N-bis(2-hydroxybenzyl)alkylamine derivatives (1–5) have been found to form host–guest compounds with transition metal ions. The inclusion phenomena in solution are confirmed from the new peak at 415?nm observed by UV-Vis (ultraviolet-visible) spectroscopy and the aromatic and methylene peak shifts observed by ¹H NMR (proton nuclear magnetic resonance) spectroscopy. Comparative studies on 1–5 by liquid–liquid extraction studies suggest that the bulky group at the aza position of the derivatives obstructs the ion interaction resulting in the decrease in ion extraction ability. Inclusion depends on the interaction of the transition metal ions with the compounds 1–5 at the aza and hydroxyl groups as identified by the two-dimensional nuclear Overhauser enhancement technique (¹H–¹H NOESY). The results from Job's plot and electrospray ionization mass spectroscopy (ESIMS) imply molecular assembly of the host–guest system in a 2:1 ratio. Comparative studies among different ions, i.e., Cu²⁺, Zn²⁺ and Cd²⁺ suggest that the host–guest formation is effective when electron sharing is possible through the outer orbital of the transition metal ions. In the case of inclusion in the solid state, the FTIR (Fourier transform infrared) spectra show the changes in vibrational mode of the functional groups in host molecules whereas the X-ray diffraction (XRD) patterns suggest a change in the packing structure of the host molecules. After host–guest formation, the thermal stability of the host molecules decreases as a result of the change in the packing structure from a hydrogen-bonded network to one of ionic interaction with the guest.     

Crystalline-state guest-exchange and gas-adsorption phenomenon for a "soft" supramolecular porous framework stacking by a rigid linear coordination polymer

A 1D rigid, linear coordination polymer, (4,4'-bipyridine)(2-pyridylsulfonate)copper, has been applied for the controlled-assembly of a new porous host that generates 1D channels by an interdigitated packing through the recognition of hydrogen bonding and pi-pi stacking interactions. The porous structure is architecturally robust when it reversibly uptakes water molecules and exchanges guest small molecules (MeOH, i-PrOH) from solution as determined by single-crystal-to-single-crystal transformation studies. Moreover, the open-channel solid displays irreversible benzene and toluene vapor sorption behaviors attributed to a widening of the channel cross-section that fetters the larger guest molecules, resulting from the dynamic, "soft" supramolecular framework.     

Host/Guest Chemistry of Organic Onium Compounds—Clathrates,Crystalline Complexes,and Molecular Inclusion Compounds in Aqueous Solution

The importance of organic onium compounds for host/guest interactions in biological processes has been long recognized. In contrast, the versatility of synthetic onium compounds as host molecules in abiotic chemistry has only been investigated in detail for the last few years. Due to their inclusion ability and selectivities, organic ammonium, pyridinium, and phosphonium salts and other organic salts with specific structural features are interesting as clathrate-forming molecules. The crystal structures of the clathrates afford insight into the conformational adaptability of onium clathrands with limited flexibility to the geometric requirements of the guest molecules. Optically active onium hosts can be used for enantiomeric enrichment. In crystalline tetracyanoquinodimethane(TCNQ) complexes and radical anion salts, the structure of the organic heterocation has a marked effect on the electrical conductivity. Macrocyclic onium compounds of the phane type with “exohydrophilic” and “endolipophilic” cavities are suitable as models of enzymes and biological receptors. They can also be used to transfer aromatic and aliphatic guest molecules selectively into aqueous solution. Catalytic activity (including H/D exchange) has already been obtained with synthetic compounds having large cavities. The further development of such host/guest systems may contribute to the understanding of biological systems and the improvement of technical processes (catalysis in molecular cavities).     

Restricted conformational flexibility of a triphenylamine derivative on the formation of host-guest complexes with various macrocyclic hosts

Herein, we report the host-guest-type complex formation between the host molecules cucurbit[7]uril (CB[7]), β-cyclodextrin (β-CD), and dibenzo[24]crown-8 ether (DB24C8) and a newly synthesized triphenylamine (TPA) derivative 1X(3) as the guest component. The host-guest complex formation was studied in detail by using (1)H?NMR, 2D NOESY, UV/Vis fluorescence, and time-resolved emission spectroscopy. The chloride salt of the TPA derivative was used for recognition studies with CB[7] and β-CD in an aqueous medium. The restricted internal rotation of the guest molecule on complex formation with either of these two host molecules was reflected in the enhancement of the emission quantum yield and the average excited-state lifetime for the triphenylamine-based excited states. Studies with DB24C8 as the host molecule were performed in dichloromethane, a medium that maximizes the noncovalent interaction between the host and guest fragments. The F?rster resonance energy transfer (FRET) process involving DB24C8 and 1(PF(6))(3), as the donor and acceptor fragments, respectively, was established by electrochemical, steady-state emission, and time-correlated single-photon counting studies.     

Propyne Gas Adsorption in a Cyclic Hexapeptoid: A Combined In Situ XRPD and DFTB Study**

Cyclic peptoids are macrocyclic N-substituted oligoglycines, with remarkable structural, chemical and physical properties. The gas adsorption properties of a permanently porous hexameric cyclopeptoid decorated with four propargyl and two methoxyethyl side chains were monitored by in situ X-ray powder diffraction (XRPD). High-resolution XRPD data together with Rietveld and density functional based tight binding (DFTB) method allowed us to locate propyne guest molecules inside the host channels, even though the powder sample contains more than one phase. We were able to characterize the host-guest interactions, providing useful information on the host recognition sites and discuss host adaptiveness and host–guest chemical affinity in comparison with analogous compounds.     

Inclusion of the regioisomeric nitrobenzene derivatives and ferrocene guests by β-cyclodextrin polymer and their transport through the polymer matrix

Host-guest equilibria have been investigated involving inclusion sites of the microparticulate amorphous β-cyclodextrin polymer, β-CDP-25, and a range of redox guests comprising regioisomeric nitrobenzene derivatives and ferrocene. The equilibria were studied by the batch method. Inclusion-governed, Langmuir-type sorption equilibria occurred in the β-CDP-25/guest systems studied in 1:1 (v/v) aqueous methanolic solutions. A 1:1 (host inclusion site)/guest stoichiometry was found and sorption equilibrium constants were determined. The values of the constants changed by a factor of 20 between the most weakly and strongly included guests. Regioselective discrimination of β-CDP-25 was most pronounced with respect to nitrophenols. Transport phenomena of guest molecules in the β-CDP-25 matrix have also been studied. The apparent diffusion coefficients of guest molecules were determined in the β-CDP-25 matrix by chronamperometry at the (β-CDP-25)-PTFE-carbon composite electrodes. These diffusion coefficients were almost four orders of magnitude lower than the corresponding coefficients of guest molecules in solution in the absence of β-CD. The diffusion mechanism was postulated for the guest molecules in the β-CDP-25 matrix, which invoked hopping of the molecules between inclusion sites.     

Selective self-organization of guest molecules in self-assembled molecular boxes

This article describes the synthesis and binding properties of highly selective noncovalent molecular receptors 1(3).(DEB)6 and 3(3).(DEB)6 for different hydroxyl functionalized anthraquinones 2. These receptors are formed by the self-assembly of three calix[4]arene dimelamine derivative molecules (1 or 3) and six diethylbarbiturate (DEB) molecules to give 1(3).(DEB)6 or 3(3).(DEB)6. Encapsulation of 2 occurs in a highly organized manner; that is, a noncovalent hydrogen-bonded trimer of 2 is formed within the hydrogen-bonded receptors 1(3).(DEB)6 and 3(3).(DEB)6. Both receptors 1(3).(DEB)6 and 3(3).(DEB)6 change conformation from staggered to eclipsed upon complexation to afford a better fit for the 2(3) trimer. The receptor selectivity toward different anthraquinone derivatives 2 has been studied using 1H NMR spectroscopy, X-ray crystallography, UV spectroscopy, and isothermal microcalorimetry (ITC). The pi-pi stacking between the electron-deficient center ring of the anthraquinone derivatives 2a-c and 2e-g and the relatively electron-poor melamine units of the receptor is the driving force for the encapsulation of the guest molecules. The selectivity of the hydrogen-bonded host for the anthraquinone derivatives is the result of steric interactions between the guest molecules and the calix[4]arene aromatic rings of the host.