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The synthesis of a new triaminoguanidinium‐based ligand with three tris‐chelating [NNO]‐binding pockets and C 3 symmetry is described. The reaction of tris‐(2‐pyridinylene‐N‐oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single‐crystal X‐ray diffraction and is verified using computation., Cage bound: Synthesis of a new triaminoguanidinium‐based ligand with three tris‐chelating [NNO] binding pockets and C 3‐symmetry is described. Reaction with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds that in solution are able to bind fullerenes in their spherical cavities. The rapid encapsulation of C60 is observed by NMR spectroscopy and X‐ray diffraction and is validated by DFT.

A polycyclic aromatic hydrocarbon having a twisted cyclooctatetraene (COT) core was prepared by a formal [4+4] dimerization of an in situ generated indeno[2,1-a]fluorene derivative. The compound consists of two indenofluorene frameworks connected with two double bonds and adopts a twisted geometry to avoid intramolecular steric repulsion. It exhibits a long-wavelength absorption band with a maximum at 634 nm extending to about 850 nm, which is consistent with the moderate antiaromaticity of the twisted COT ring as indicated by the NICS value (+11.9). A mechanism for cycloaddition reaction is proposed in terms of stepwise bond formations due to the diradical character of the indenofluorene framework, on the basis of the completely different reaction product obtained from the extended benzo analogue.

Rotaxanes consisting of achiral axle and achiral ring components can possess supramolecular chirality due to their unique geometrical architectures. To synthesize such chiral rotaxanes, we adapted a prerotaxane method based on aminolysis of a metacyclophane type prerotaxane that had planar chirality, which is composed of an achiral stopper unit and a crown ether type ring component. The prerotaxanes were well resolved using chiral HPLC into a pair of enantiomerically pure prerotaxanes, which were transferred into corresponding chiral rotaxanes, respectively. Obtained chiral rotaxanes were revealed to have considerable enantioselectivity.

Internal substituents can serve the double purpose of generating stereogenic centers and (potentially) being identifiable with Scanning Tunneling Microscopy (STM) in 2D self-assembled molecular layers. We investigate computationally the origin of stark contrast variations in STM images of chirally substituted self-assembled organic films. STM images of alkyl derivatives with secondary –CH3 and –OH groups have been simulated. Density functional theory calculations reveal bias-dependent contrast reversals in the substituent regions: a lack of local density of states in the relevant energy regime results in ‘dark spots’ in the simulated STM images, which turn bright upon increasing the bias voltage.

To demonstrate key roles of multiple interactions between multiple components and multiple phases in the formation of an uncommon self-assembling pattern, we present here the construction of a porous hexagonal star (h-star) structure using a trigonal molecular building block at the liquid/ solid interface. For this purpose, self-assembly of hexaalkoxysubstituted dehydrobenzo[12]annulene derivatives DBA-OCns was investigated at the tetradecane/graphite interface by means of scanning tunneling microscopy (STM). Monolayer structures were significantly influenced by coadsorbed tetradecane molecules depending on the alkyl chains length (C13−C16) of DBA-OCn. However, none of DBA-OCn molecules formed the expected trigonal complexes, indicating that an additional driving force is necessary for the formation of the trigonal complex and its assembly into the h-star structure. As a first approach, we employed the “guest induced structural change” for the formation of the h-star structure. In the presence of two guest molecules, nonsubstituted DBA and hexakis(phenylethynyl)benzene which fit the respective pores, an h-star structure was formed by DBAOC15 at the tetradecane/graphite interface. Moreover, a tetradecane molecule was coadsorbed between a pair of alkyl chains of DBA-OC15, thereby blocking the interdigitation of the alkyl chain pairs. Therefore, the h-star structure results from the selfassembly of the four molecular components including the solvent molecule. The second approach is based on aggregation of perfluoroalkyl chains via fluorophilicity of DBA-F, in which the perfluoroalkyl groups are substituted at the end of three alkyl chains of DBA-OCn via p-phenylene linkers. A trigonal complex consisting of DBA-F and three tetradecane molecules formed an h-star structure, in which the perfluoroalkyl groups that orient into the alkane solution phase aggregated at the hexagonal pore via fluorophilicity. The present result provides useful insight into the design and control of complex molecular self-assembly at the liquid/solid interface. ispartof: Langmuir vol:31 issue:25 pages:7032-7040 ispartof: location:United States status: published

A tetramesityl derivative of hitherto unknown tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), which is a potential tetraradicaloid hydrocarbon, was synthesized. Theoretical calculations based on spin-flip time-dependent density functional theory predict that the closed-shell D2h form of TCPTP is more stable than the open-shell D4h form with its slightly tetraradical character. The tetramesityl derivative (Mes)4 -TCPTP exhibits remarkable antiaromaticity as a result of the peripheral 20-π-electron circuit, which causes an absorption maximum at a long wavelength and a small HOMO-LUMO gap. In solution, (Mes)4 -TCPTP most likely adopts rapidly equilibrating D2h structures that interconvert via the D4h transition state. X-ray crystallographic analysis showed (Mes)4 -TCPTP as an approximate D2h structure.

We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/solid interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration it formed a high-density hexagonal structure in which alkyl chains are not adsorbed on the surface (dense hexagonal structure). In the dense hexagonal structure, macrocyclic cores are linked by hydrogen bonds between the ester carbonyl oxygen and the aromatic hydrogen atoms of the neighboring macrocycles. The packing geometries of loose hexagonal structures of PEM-C6 and PBM-C8 are different due to the different distance between the attachment of the alkyl ester groups which are located in confined space. On the other hand, PEM-TEG and PBM-TEG formed dense hexagonal structures, similar to PBM-C8 at high concentration, with their TEG units not adsorbed on the surface.

Treatment of a twisted polycyclic aromatic hydrocarbon containing cyclooctatetraene fused by two 9,9′-bifluorenylidene units under the Scholl reaction conditions (FeCl3 or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and scandium trifluoromethanesulfonate) led to stepwise skeletal rearrangements to afford initially a hydrocarbon with a seven-membered ring and then tetrabenzo[a,d,j,m]coronene with all six-membered rings. The course of the rearrangement was interpreted in terms of the acid-catalyzed isomerization of 9,9′-bifluorenylidene into dibenzo[g,p]chrysene moieties on the basis of theoretical investigations.

The dimesityl derivative of fluoreno[2,3-b]fluorene (6b) was synthesized and its structure and physical properties were investigated to elucidate the effects of its enhanced open-shell character, which was predicted theoretically in comparison with the smaller congener indeno[2,1-b]fluorene (5b). All structural and physical properties are in accordance with the theoretical predictions and can be interpreted in terms of the resonance contributors. The most remarkable spectroscopic property is the larger excitation energy of 24π-electron hydrocarbon 6b than that of 20π-electron system 5b in their lowest energy absorption bands of electronic spectra, a trend that is contrary to the well-known feature for common, alternant aromatic hydrocarbons. The theoretical basis of this unusual behavior was elucidated on the basis of the balance between the diradical character, exchange integral, and HOMO-LUMO gap and was confirmed by a complete-active-space configuration-interaction method with two electrons in two orbitals for the corresponding parent hydrocarbons 5a and 6a.

Multicomponent network formation by using a shape-persistent macrocycle (MC6) at the interface between an organic liquid and Au(111) surface is demonstrated. MC6 serves as a versatile building block that can be coadsorbed with a variety of organic molecules based on different types of noncovalent interactions at the liquid–solid interface. Scanning tunneling microscopy (STM) reveals the formation of crystalline bicomponent networks upon codeposition of MC6 with aromatic molecules, such as fullerene (C60) and coronene. Tetracyanoquinodimethane, on the other hand, was found to induce disorder into the MC6 networks by adsorbing on the rim of the macrocycle. Immobilization of MC6 itself was studied in two different noncovalently assembled host networks. MC6 assumed a rather passive role as a guest and simply occupied the host cavities in one network, whereas it induced a structural transition in the other. Finally, the central cavity of MC6 was used to capture C60 in a complex three-component system. Precise immobilization of organic molecules at discrete locations within multicomponent networks, as demonstrated here, constitutes an important step towards bottom-up fabrication of functional surface-based nanostructures. ispartof: Chemistry - a European Journal vol:21 issue:4 pages:1652-1659 ispartof: location:Germany status: published

We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12]annulene)s (tetrakis-DBAs). Intramolecular three-fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner's Mo catalyst furnished tetrakis-DBAs 8 a and 8 b substituted with tert-butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c-g have also been prepared. The one-photon absorption spectrum of tetrakis-DBA 8 a bearing tert-butyl groups revealed a remarkable bathochromic shift of the absorption cut-off (λcutoff ) compared with those of previously reported graphyne fragments due to extended π-conjugation. Moreover, in the two-photon absorption spectrum, 8 a showed a large cross-section for a pure hydrocarbon because of the planar para-phenylene-ethynylene conjugation pathways. Hexakis(arylethynyl)-DBAs 9 c-e and 9 g and tetrakis-DBA 8 b bearing electron-withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π-π interactions between the extended π-cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time-resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge-carrier mobility of 0.12 cm(2) V(-1) s(-1) . These results indicate that large graphyne fragments can serve as good organic semiconductors.

Smaller can be better: The first example of meta-quinodimethane embedded in an indenofluorene framework has been synthesized. 10,12-Dimesitylindeno[2,1-b]fluorene exhibits extremely low-energy light absorption, despite the small conjugation space of the molecule, which consists of only 20 π electrons.

On-surface chemical reactions hold the potential for manufacturing nanoscale structures directly onto surfaces by linking carbon atoms in a single-step reaction. To fabricate more complex and functionalized structures, the control of the on-surface chemical reactions must be developed significantly. Here, we present a thermally controlled sequential three-step chemical transformation of a hydrocarbon molecule on a Cu(111) surface. With a combination of high-resolution atomic force microscopy and first-principles computations, we investigate the transformation process in step-by-step detail from the initial structure to the final product via two intermediate states. The results demonstrate that surfaces can be used as catalysing templates to obtain compounds, which cannot easily be synthesized by solution chemistry., On-surface chemical reactions provide an attractive route for making tailored nanostructures. Here the authors present a thermally-controlled sequential on-surface transformation of a hydrocarbon molecule, characterized via high-resolution atomic force microscopy and density functional theory calculations.

We present here the periodic functionalization of a two-dimensional (2D) porous molecular network using a tailored molecular building block. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, 1-isoDBA, having an isophthalic acid unit connected by an azobenzene linker to a C12 alkyl chain and five C14 chains, was designed and synthesized. After the optimization of monolayer preparation conditions at the 1,2,4-trichlorobezene (TCB)/graphite interface, scanning tunneling microscopy (STM) observation of the self-assembled monolayer of 1-isoDBA revealed the formation of extended domains of a porous honeycomb-type molecular network, which consists of periodically located nanowells each functionalized by a cyclic hexamer of hydrogen-bonded isophthalic acid units and those without functional groups. This result demonstrates that the present strategy based on precise molecular design is a viable route to site-specific functionalization of surface-confined nanowells. The nanowells of different size can be used for guest coadsorption of different guests, coronene COR and hexakis[4-(phenylethynyl)phenylethynyl]benzene HPEPEB, whose size and shape match the respective nanowells. STM observation of a ternary mixture (1-isoDBA/COR/HPEPEB) at the TCB/graphite interface revealed the site-selective immobilization of the two different guest molecules at the respective nanowells, producing a highly ordered three-component 2D structure. ispartof: ACS Nano vol:10 issue:2 pages:2113-2120 ispartof: location:United States status: published

Supramolecular self-assembly in two-dimensional (2D) spaces on solid surfaces is the subject of intense current interest because of perspectives for various applications in nanoscience and nanotechnology. At the liquid/graphite interface, we found by means of scanning tunneling microscopy molecules with a rigid triangular core, a twelve-membered phenylene-ethynylene macrocycle called dehydrobenzo[12]-annulene (DBA), substituted by six flexible alkoxy chains selfassembled to form hexagonal porous 2D molecular networks via van der Waals interactions between interdigitated alkyl chains as the directional intermolecular linkages. Factors that affect the formation of the porous 2D molecular networks including alkyl chain length, solvent, solute concentration, and temperature were elucidated through a systematic study. Because DBA molecules are versatile for chemical modification, they turned out to be highly adaptive for on-surface supramolecular chemistry with respect to (i) pore size control by changing the chain length, (ii) study of parity effect due to even or odd number chains, (iii) generation of supramolecular chirality on surfaces by introducing stereocenters, (iv) chemical modification of the pore interior for selective co-adsorption of guest molecules by introducing functional groups. Additionally, formation of superlattice structures on surfaces was incidentally observed by mixing DBAs of different alkoxy chain parity or by addition of guest molecules via an induced-fit mechanism. These results made significant contribution to advancement of supramolecular chemistry in 2D space. ispartof: Bulletin of the Chemical Society of Japan vol:89 issue:11 pages:1277-1306 status: published

Using alkoxylated derivatives of triangular dehydrobenzo[12]annulene (DBA) as building blocks, we demonstrate control of a formation of 2D molecular networks on Au(111). The tunability of intermolecular interactions by substituting alkoxy groups can improve the homogeneity of the 2D molecular network by restricting the number of polymorphs, and it can induce domain-specific chirality. The π-conjugated triangular core of each alkoxylated DBA derivative is locked on a specific site on the Au(111) surface by the interaction between the oxygen atoms of the molecule and the gold (Au) surface atoms, and the relative importance of intermolecular hydrogen bonding versus van der Waals interactions depends on the length of the alkoxy groups. Such tunable intermolecular interactions balanced with surface–molecule interaction may eventually enable control of the formation of 2D molecular networks. These results could lead to potential applications in tailoring 2D molecular networks or allow the use of these networks ...

We present a systematic scanning tunneling microscopic study on the mixing behavior of molecules (DBAs) with different alkyl substituents at the solid-liquid interface to reveal the phase behavior of complex systems. The phase behavior of binary mixtures of alkylated DBAs at the solid-liquid interface can be predicted by the 2D isomorphism coefficient. In addition, we also investigated the influence of coadsorption of template molecules on the phase behavior of DBA mixtures. Coadsorption of these molecules significantly promotes mixing of DBAs, possibly by affecting the recognition between alkyl chains. Monte Carlo simulations prove that the 2D isomorphism coefficient can predict the phase behavior at the interface. These results are helpful for the understanding of phase behavior of complex assembling systems and also for the design of programmable porous networks and hierarchical architectures at the solid-liquid interface.

Tris-(2-hydroxybenzylidene)triaminoguanidinium salts having six alkyl chains with proper spacing served as new molecular building blocks for the formation of porous honeycomb networks by van der Waals interaction between interdigitated alkyl chains at the liquid/graphite interfaces.

Self-assembled monolayers of a series of tetraalkoxy-substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1c-g possessing butadiyne linkages were studied at the 1,2,4-trichlorobenzene (TCB) or 1-phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two-dimensional (2D) monolayers, but also to assess a possibility for peri-benzopolyacene formation by two-dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule-substrate interactions per unit area and network density. The selective appearance of the linear structure of 1d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (approximately 0.6 nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic-pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on-surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare.

beta-formyl-beta-nitroenamines possess both an electrophilic formyl group and a nucleophilic amino group and, therefore, serve as C3N1 building blocks having a nitro group to afford nitropyridones and aminonitropyridines with a functional group at the 3-position. Upon treatment with malonic acid derivatives or beta-keto esters, nitropyridones were obtained, whereas reactions with functionalized acetonitriles afford aminonitropyridines, via a formal transfer of an alkyl group from the ring nitrogen to the imino group. These procedures provide practical and useful methods for preparation of heterocycles with a nitro group.

Design, synthesis, and demonstration of a prototype of a shuttling molecular machine with a reversible brake function are reported. It is a photochemically and thermally reactive rotaxane composed of a dianthrylethane-based macrocycle as the ring component and a dumbbell shaped molecular unit with two, secondary ammonium stations separated by a phenylene spacer as the axle component. The rate of shuttling motion was shown to be reduced to less than 1 % (from 340 to

A concept and demonstration of a switching in frequencies of molecular motions are described using a pseudorotaxane system. The setup consists of dibenzylammonium hexafluorophosphate and a photochromic dianthrylethane-based [24]crown-8-type macrocycle, which we designed as a key ring component for the pseudorotaxane system having photocontrollable threading functionality by changing the size of ring component due to the action of light.

A 2-nitrated 3-oxoester reacted with amines or alcohols to afford unsymmetrical malonic acid derivatives as a result of nucleophilic substitution accompanying C–C bond cleavage. The 2-nitrated 3-ox...

Compound (I), a derivative of the hitherto unknown title compound which is a potential tetraradicaloid hydrocarbon, is synthesized in five steps starting from a known polycyclic tetracarboxylic acid (synthetic pathway not shown).

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.

In order to develop a chiral stationary phase (CSP), which has even higher separation ability than the corresponding commercially available crown ether based CSP (OA-8000 having a pseudo-18-crown-6 ether with an OMe group as a selector), chemically bonded type CSP having a phenolic OH group on a crown ring was developed. Normal mobile phases with or without acid additive can be used with this OH type CSP in contrast to the conventional OMe type CSP which has a neutral chiral selector. Enantiomers of 25 out of 27 amino compounds, including 20 amino acids, 5 amino alcohols, and 2 lipophilic amines, were efficiently separated on a column with this CSP. Nine amino compounds out of 27 were separated with better separation factors than the corresponding OMe type CSP. It is noteworthy that the chromatography on this CSP exhibited excellent enantiomer-separations for amines and amino alcohols when triethyl amine was used as an additive in the mobile phase. Comparison of enantiomer separation ability on this OH type of CSP and on the OMe type of CSP and correlation between the enantioselectivity in chiral chromatography and that of the corresponding model compounds in solution imply that the chiral separation arose from chiral recognition in host guest interactions.

Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in 1H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown-substrate mixtures in methanol-d4 causes shifts in the spectra of substrates and often enhances the chiral discrimination in the 1H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.

Chiral recognition in the host–guest complexation systems of chiral crown ether hosts and amino ester guests was thoroughly examined using the electrospray ionization (ESI) mass spectrometry/enantiomer labeled (EL)-guest method. In this method, the mass spectra of a mixture of three components in a solution, a chiral host (H), an equal amount of an ( S)-enantiomer guest labeled with deuterium atoms (GS-dn+) and an unlabeled ( R)-enantiomer guest (G R+), were measured and the relative peak intensity value [ I(H+G R)+ / I(H + GS-dn)+= IRIS] of the host–guest complex ions, observed with an excess guest concentration, was taken to provide the chiral recognition ability of the host. In our earlier report (1996), we demonstrated that the apparent chiral recognition abilities using a mass spectrometer with a homemade ESI interface were depressed by about one tenth compared with the corresponding abilities obtained by fast-atom bombardment (FAB) MS. In the present study, the enantioselective complexation behaviors of various combinations of chiral crown hosts with chiral guests were further investigated in detail mainly using a modern commercial ESI/ion trap (IT) mass spectrometer. Consequently, it was found that the apparent IRIS values from the ESI-MS/EL-guest method changed significantly, depending upon the instrument used, and in particular, upon the ESI interfaces. Moreover, under the specific measuring conditions in ESI-IT-MS, the degrees of depression of the apparent chiral recognition abilities are roughly grouped into three classes, depending upon the number (or probably the type) of the hydrophobic substituents of the hosts. Representing the degrees by the slopes when plotting the apparent IRIS values in ESI-MS versus those in FAB-MS, the slopes for the three classes are (1) 1.0, (2) 0.7 and (3) 0.3; the higher the hydrophobicity of the hosts (and then, the host–guest complex ions), the lower the slope (the apparent enantioselectivity). Strengthening the degree of depression may be caused by an increase in the local concentration of the host close to the surface of the droplets produced during the electrospary ionization process. The chiral recognition ability ( KR/KS) in an equilibrated solution agrees quite well with the IRIS value in FAB-MS rather than that in ESI-MS.

A new method for the formation of conjugated polyynes has been developed based on both the rearrangement of vinylidenes to alkynes and the [2+1] cheletropic fragmentation of dialkynylmethylenebicyclo[4.3.1]deca-1,3,5-triene derivatives. A model study of the photolysis of simple dialkynylmethylenebicyclo[4.3.1]deca-1,3,5-trienes resulted in cheletropic fragmentation followed by 1,2-migration to give the corresponding linear polyynes, although undesired isomerization to methylenebicyclo[5.3.0]triene derivatives took place concurrently. Expanded [3]-, [4]-, [5]-, and [6]radialene derivatives with exocyclic bicyclo[4.3.1]decatriene units were prepared by oxidative coupling of the monomeric units as precursors to the corresponding cyclo[n]carbons, monocyclic forms of carbon clusters. The spectroscopic properties of the expanded radialenes were investigated in connection with cross conjugation of the core pi system and with its perturbation by the extraannular bicyclic pi system. In negative-mode laser-desorption time-of-flight (LD-TOF) mass spectra, the expanded radialenes exhibited peaks due to the corresponding cyclo[n]carbon anions (n = 18, 24, 30, and 36) formed by the stepwise loss of the aromatic indane fragments.

Chiral crown ether (S,S)-3 having a pseudo-24-crown-8 ring and chiral podand (R,R)-4 were prepared and both exhibited good chiral recognition ability toward secondary amines, N-α-dimethylbenzylamine (15) and propranolol (16).

Dendritic diarylcarbenium ions exhibited sufficient electrophilicity to react with unfunctionalized polystyrenes. The polymers obtained by the reaction of the first and the second generation dendritic diarylcarbenium ions with polystyrenes were well characterized by MALDI-TOF MS and SEC-MALLS analyses and observed by AFM.

An anthracene cyclic dimer with two different linkers and a dodecyl group was synthesized by means of coupling reactions. The calculated structure had a planar macrocyclic π core and a linear alkyl chain. Scanning tunneling microscopy observations at the 1-phenyloctane/graphite interface revealed that the molecules formed a self-assembled monolayer that consisted of linear striped bright and dark bands. In each domain, the molecular network consisted of either Re or Si molecules that differed in the two-dimensional chirality about the macrocyclic faces, which led to a unique conglomerate-type self-assembly. The molecular packing mode and the conformation of the alkyl chains are discussed in terms of the intermolecular interactions and the interactions between the molecules and the graphite surface with the aid of MM3 simulations of a model system.

We present here the construction of self-assembled two-dimensional (2D) molecular networks that contain pores equipped with functional groups that promote guest-specific binding at the liquid/solid interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-F, having perfluoroalkyl groups at the end of the three alternating alkoxy chains connected by para-phenylene linkers was synthesized. For comparison DBA-H, having the same carbon backbone without fluorine substituents, was also prepared. STM observations revealed that these molecules formed porous 2D networks whose pores were decorated with either fluoroalkane or simple alkane perimeters. Hexakis(phenylethynyl)benzene, HPEB, and its octadecafluoro derivative, HPEB-F surrounded by 18 fluorine atoms, were employed as planar guest molecules of suitable size. The fluoroalkane-lined pores present in the network of DBA-F exhibited good binding ability toward both guest molecules via fluorophilicity and electrostatic interaction, respectively. In contrast the binding ability of the alkane-lined pore of the network of DBA-H for the fluorinated guest HPEB-F was poor as a result of weaker electrostatic interaction. Interestingly, with HPEB as a guest, this network underwent a periodical structural deformation through an induced-fit mechanism to form a superlattice structure consisting of free and occupied pores. These observations are discussed based on modeling experiments using molecular mechanics and quantum chemical methods to elucidate the roles of lateral noncovalent interactions and size matching between the pore and the guest molecules used for 2D guest binding.

Through the precisemolecular design for alkoxy dehydro[12]annulene derivatives harnessed by a diacetylene unit in each alkyl chain, porous two-dimensional networks with giant pores were formed at the liquid/graphite interface. ispartof: Chemical Communications vol:50 issue:22 pages:2831-2833 ispartof: location:England status: published

Chiral recognition ability of crown ether hosts toward organic amine salt guests has been evaluated using the FAB mass spectrometry coupled with our enantiomer-labeled guest method for the total 97 sets of chiral host-guest complexations. The hosts include various chiral crown ethers containing a dimethoxyphenyl group (1-16) and the related derivatives (17-22) and the guests include 1-(1-naphthyl)ethylamine salt (23) and α-amino acid methyl ester salts (24-28). In the case of the α-amino ester salt guests, the chiral crown ether (1 or 2) having sterically effective phenyl substituents as chiral barriers with a less flexible backbone-structure showed relatively higher degree of chiral recognition ability among the 22 chiral host series studied. On the other hand, toward the 1-(1-naphthyl)ethylamine salt guest, the most hosts gave relatively lower chiral recognition ability except for the specific hosts (6 and 7) having certain spatial constraint toward a complexing naphthyl group.

The synthesis and structural characterization of hitherto unknown tetradehydrodinaphtho[10]annulene, a hydrocarbon whose synthesis had been attempted four decades ago, was achieved for the first time. Moreover, the dinaphtho[10]annulene was transformed smoothly into stable zethrene derivatives substituted at its 7,14-positions, showing that it serves as a good reservoir of zethrene derivatives. Optical and electrochemical properties of a disubstituted zethrene derivative are also presented.

All-carbon materials with novel topologies are of interest in regard to their materials properties. These novel structures include graphite-like two-dimensional networks as well as fullerene-like three-dimensional cages. This article reviews recent developments in the synthesis of scaffolds for novel forms of carbon made of a core π-system carrying alkyne appendages, such as hexaethynylbenzene and its derivatives, pentaethynylcyclopentadienyl metal complexes, and tetraethynylcyclobutadiene metal complexes. Also included are the syntheses and properties of macrocyclic π-systems derived of these units which represent important substructures for the infinite lattices of novel carbon allotropes.

Homochiral crown ether ( S , S )- 1 containing 1-naphthyl groups as chiral barriers together with the phenol moiety was prepared by using ( S )- 3 as a chiral subunit which was resolved in enantiomerically pure form by lipase-catalyzed enantioselective acylation of (±)- 3 . Homochiral phenolic crown ether ( S , S )- 2 , containing phenyl groups as chiral barriers, was also prepared from ( S )- 5 which was derived from ( S )-mandelic acid. The association constants for their complexes with chiral amines in CHCl 3 were determined at various temperatures by the UV–visible spectroscopic method demonstrating that the crown ethers ( S , S )- 1 and ( S , S )- 2 displayed the large Δ R − S Δ G values of 6.2 and 6.4 kJ mol −1 , respectively, towards the amine 21 at 15°C. Thermodynamic parameters for complex formation were also determined and a linear correlation between T Δ R − S Δ S and Δ R − S Δ H values was observed.

Crown ether (S,R,R,S)- 1 containing chiral subunits derived from (1R,2S)-cis-1,2,3,4-tetrahydronaphthalene-1,2-diol and the phenol moiety bearing the intra-annular OH group and the 2,4-dinitrophenylazo group at its para-position have been prepared in enantiomerically pure form. The association constants for the complexes with chiral amines have been determined at various temperatures by the UV-visible spectroscopic method and thermodynamic parameters of complex formation have been calculated.

Azophenolic crown ethers (S,S)-1, (R,R)-2 and (S,S)-3 have been prepared in enantiomerically pure forms by using (S)-1-(1′-adamantyl)ethane-1,2-diol, (R)-3,3-dimethylbutane-1,2-diol and (S)-propane-1,2-diol, respectively, as chiral subunits, and the association constants for their complexes with chiral amines have been determined by 1H NMR or UV–VIS spectroscopic methods at various temperatures. The enantiomer selectivities of crown ethers (S,S)-1 and (R,R)-2 in complexation with 2-aminopropan-1-ol are reversed at ca. 6 °C and increase with increasing temperature above the isoenantioselective temperature.

Supramolecular self-assembly of suitably functionalized building blocks on surfaces can serve as an excellent test-bed to gain understanding and control over multicomponent self-assembly in more complex matter. Here we employ a powerful combination of scanning tunnelling microscopy (STM) and molecular modeling to uncover two-dimensional (2D) crystallization and mixing behavior of a series of alkylated building blocks based on dehydrobenzo[12]annulene, forming arrays of nanowells. Thorough STM investigation employing high-resolution spatial imaging, use of specially designed marker molecules, statistical analysis and thermal stability measurements revealed rich and complex supramolecular chemistry, highlighting the impact of odd–even effects on the phase behavior. The methodology and analysis presented in this work can be easily adapted to the self-assembly of other alkylated building blocks.

Novel chiral stationary phases consisting of silica gel covalently bound with chiral pseudo-18-crown-6 type hosts, which possess either an OH or OMe group as a binding functionality, were prepared for enantiomer-separation of lipophilic amines.

The self-assembly of multicomponent networks at the liquid-solid interface between Au(111) or highly oriented pyrolytic graphite (HOPG) and organic solvents was investigated using scanning tunneling microscopy. Alkoxylated dehydrobenzo[12]annulene (DBA) derivatives form hexagonal nanoporous networks, which trap either single molecules of coronene (COR) or small clusters of COR and isophthalic acid to form multicomponent networks. The pattern of interdigitation between alkyl chains from DBA molecules produces hexagonal pores that are either chiral or achiral. On Au(111) substrates multicomponent networks display an ordered superlattice arrangement of chiral and achiral pores. In comparison, similar networks on HOPG display only chiral pores. The unique superlattice structure observed on Au(111) is related to a lower energetic preference for chiral pores than on HOPG and increased diffusion barriers for guest molecules. The increased diffusion barriers for guests allow them to act as nucleation sites for the formation of achiral pores. Following the initial nucleation of an achiral pore, restrictions imposed by the accommodation of guests within the porous network mean that subsequent growth naturally leads to the formation of the superlattice structure.

Homochiral 1-(1-adamantyl)ethane-1,2-diol ( 5 ) was prepared and its absolute configuration was determined to be ( S )-(+)- 5 by enzymatic and 1 H n.m.r. spectroscopic methods. Using ( S )-(+)- 5 as a chiral subunit, the homochiral crown ether (+)- 18 was synthesized and its enantioselectivity in complexation of methionine methyl ester perchlorate was also examined by the 1 H n.m.r. spectroscopic method.

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 Kagome 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.

Highly Li + -selective ionophores based on 14-crown-4 derivatives were designed and synthesized, and the relationship of their molecular structures and ion selectivities was investigated in order to obtain a highly Li + -selective electrode. The ion selectivities were examined with 11 kinds of 14-crown-4 derivatives, which were prepared a ccording to the proposed two types of Li + ionophore models. Excellent Li + -selective ionophores were obtained by introducing a bulky «block» subunit into the ethano-bridge section of the base crown ring, which effectively prevents the formation of a 2:1 or 3:1 sandwich-type complex consisting of the crown ether and cations larger than Li +

Pig liver esterase, lipase from porcine pancreas, lipase from Pseudomonas sp. (lipase YS), and lipase from Candida cylindracea catalyzed hydrolyses of the cis-diacetate 1 and the trans-diacetate (±)-4 to give the cis-monoacetate 3 and the trans-monoacetate 6 in optically active forms, respectively. Lipase YS-catalyzed acylations of the cis-diol 2 and the trans-diol (±)-5 with an acylating agent in cyclohexane yielded (−)-3 and (−)-6, respectively. The group adjacent to the R stereogenic center preferentially reacted in lipase YS-catalyzed hydrolyses of 1 and (±)-4 and acylations of 2 and (±)-5, and the enantioselectivities are rationalized by our rule recently proposed for lipase YS.

The synthesis and structural characterization of a hitherto unknown tetradehydro - dinaphtho(10)annulene, which had eluded isolation since attempts initiated during the late 1960s, was achieved. Moreover, the dehydroannulene was transformed into stable derivatives of zethrene, which was first reported in 1955, but forgotten for a long time. These molecules are substituted at the 7,14-positions and open the door to the zethrene family for potential ap- plication as optoelectronic materials.

An acid-catalyzed rearrangement of tricyclo[5.4.0.01,5]undecan-ll-one gave tricyclo[5.3.1.01,5]undecan-11-one in a nonnucleophilic media and tricyclo[5.4.0.03,8]undecane-7, 8-diol in the presence of a nucleophile, respectively. Tricyclo[5.4.0.01,5]undecan-11-ols also rearranged to tricyclo[5.4.0.03,8]undecan-7-ol. A reductive rearrangement with a hydride transfer of the alcohol gave only tricyclo[5.4.0.03,8]undecane.