Donors and Acceptors Based on Triangular Dehydrobenzo[12]annulenes: Formation of a Triple-Layered Rosette Structure by a Charge-Transfer Complex

Columnar Organization of Nonalternant Fluorinated Dehydrobenzannulenes

Two new partially fluorinated dehydrobenzannulenes have been prepared by inter- and intramolecular oxidative homocoupling of diyne precursors. These systems contain fluorinated and nonfluorinated arene rings in a desymmetrized non-alternant arrangement. Both macrocycles are roughly planar and organize into extended columns in the solid state. The assembly of these columns is mediated by the combination of dispersion interactions, slipped [π⋅⋅⋅π] stacking interactions of the perfluorinated rings with each other, and their association with the nonfluorinated rings in the molecules of the neighboring macrocycles. These results suggest that partial fluorination of dehydrobenzannulenes can serve as a versatile motif for their assembly into columnar superstructures.

Self-Assembly of Wheel-Shaped Nanographdiynes and Self-Template Growth of Graphdiyne

Graphdiyne (GDY) multilayers show stacking-style-dependent physical properties; thus, controlling the stacking style of nanostructures is crucial for utilizing their electrical, optical, and transport properties in electro-optical devices. Herein, we report the assemblies of nanographdiynes decorated with substituents with different steric hindrances to adjust the stacking style. We show that the π-stacked aggregates were influenced by peripheral substituents and the substrate. Steric hexaterphenyl-substituted nanoGDY scaffolds led to dimer structures stacked in the AB-3 configuration with a twist angle of 26.01° or the AB-1 configuration with an in-plane shift along one diyne link. With the interval replacement of steric substituents with long C12 alkyl chains, nanoGDYs were stacked in the AB-2 configuration to decrease the steric congestion, eventually leading to one-dimensional (1D) nanofibrous aggregates. Self-assembly in the presence of substrates can result in ABC-stacked nanoGDYs, which endowed us with the possibility of using nanoGDY as the template for GDY growth in a homogeneous reaction. High-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and near-infrared-ultraviolet-visible (NIR-UV-vis) absorption spectroscopy indicate that the crystalline GDY prepared in this way is a 1.18 eV bandgap semiconductor.

Prospects of 2D graphdiynes and their applications in desalination and wastewater remediation

Water is an indispensable part of human life that affects health and food intake. Water pollution caused by rapid industrialization, agriculture, and other human activities affects humanity. Therefore, researchers are prudent and cautious regarding the use of novel materials and technologies for wastewater remediation. Graphdiyne (GDY), an emerging 2D nanomaterial, shows promise in this direction. Graphdiyne has a highly symmetrical π-conjugated structure consisting of uniformly distributed pores; hence, it is favorable for applications such as oil-water separation and organic-pollutant removal. The acetylenic linkage in GDY can strongly interact with metal ions, rendering GDY applicable to heavy-metal adsorption. In addition, GDY membranes that exhibit 100% salt rejection at certain pressures are potential candidates for wastewater treatment and water reuse via desalination. This review provides deep insights into the structure, properties, and synthesis methods of GDY, owing to which it is a unique, promising material. In the latter half of the article, various applications of GDY in desalination and wastewater treatment have been detailed. Finally, the prospects of these materials have been discussed succinctly.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Revisiting Dehydrothiopheno[12]annulenes: Synthesis, Electronic Properties, and Aromaticity

The aromaticity and electronic properties of acetylene-bridged hexadehydrotristhiopheno[12]annulenes (HDTAs) were revisited using a combined experimental and theoretical approach. Moreover, we attempted the synthesis of the butadiyne-bridged octadehydrobisthiopheno[12]annulenes (ODTAs). While the formation of ODTAs was indicated by NMR spectroscopy, mass spectrometry, and UV-vis absorption measurements, our attempts to isolate ODTAs were unsuccessful on account of its instability. Instead, their structure and energetic properties were predicted using DFT calculations. HDTA isomers in which the position where the thiophene rings are fused to the 12-membered ring differs (b- vs c-position) show distinct differences in their HOMO-LUMO energy gaps (E_Gap). ODTAs also show large E_Gap differences depending on the fusion position of the thiophene rings. The diene character of the thiophene ring significantly changes the electronic properties; i.e., E_Gap differences of >1 eV were observed between the isomers of both HDTAs and ODTAs. A theoretical evaluation of HDTAs and ODTAs revealed significant variation in the local aromaticity/antiaromaticity between the b- and c-isomers. The antiaromatic character of the 12-membered ring is attenuated for the b-isomers, whereas it is decreased substantially for the c-isomers. The results of this study are useful for a detailed understanding of the fundamental aspects of dehydrothiopheno[12]annulenes.

Chalice-Type Tridentate Silicon Lewis Acids of C3 Symmetry in a Single Step Starting from Hexadehydrotribenzo[12]annulene

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl3 or SiCl2 Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF3 . Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures.

What Is Special about Aromatic-Aromatic Interactions? Significant Attraction at Large Horizontal Displacement

High-level ab initio calculations show that the most stable stacking for benzene-cyclohexane is 17% stronger than that for benzene-benzene. However, as these systems are displaced horizontally the benzene-benzene attraction retains its strength. At a displacement of 5.0 Å, the benzene-benzene attraction is still ∼70% of its maximum strength, while benzene-cyclohexane attraction has fallen to ∼40% of its maximum strength. Alternatively, the radius of attraction (>2.0 kcal/mol) for benzene-benzene is 250% larger than that for benzene-cyclohexane. Thus, at relatively large distances aromatic rings can recognize each other, a phenomenon that helps explain their importance in protein folding and supramolecular structures.

Synthesis of radiaannulene oligomers to model the elusive carbon allotrope 6,6,12-graphyne

Graphyne allotropes of carbon are fascinating materials, and their electronic properties are predicted to rival those of the “wonder material” graphene. One allotrope of graphyne, having rectangular symmetry rather than hexagonal, stands out as particularly attractive, namely 6,6,12-graphyne. It is currently an insurmountable challenge, however, to design and execute a synthesis of this material. Herein, we present synthesis and electronic properties of molecules that serve as model compounds. These oligomers, so-called radiaannulenes, are prepared by iterative acetylenic coupling reactions. Systematic optical and redox studies indicate the effective conjugation length of the radiaannulene oligomers is nearly met by the length of the trimer. The HOMO-LUMO gap suggested by the series of oligomers is still, however, higher than that expected for 6,6,12-graphyne from theory, which predicts two nonequivalent distorted Dirac cones (no band gap). Thus, the radiaannulene oligomers present a suitable length in one dimension of a sheet, but should be expanded in the second dimension to provide a unique representation of 6,6,12-graphyne.

6,6,12-graphyne is an intriguing synthetic allotrope of carbon that is predicted to have unique electronic properties but has not been successfully synthesized. Here, the authors prepare a series of radiaannulene oligomers that can be regarded as large segments of this elusive graphyne allotrope.

Solvation-Enhanced Intermolecular Charge Transfer Interaction in Organic Cocrystals: Enlarged C-C Surface Close Contact in Mixed Packing between PTZ and TCNB

The mixed π-π packing of the donor (D) and acceptor (A) molecules is the highlighting feature of the intermolecular interactions following charge transfer (CT) issues in organic cocrystal systems. There is an inverse relationship between the D-A interplanar distance and the intermolecular CT interaction. However, the D-A C-C surface close contact (relative areas) on the intermolecular CT interactions in organic cocrystal systems is rarely investigated. Herein, we designed and constructed a novel cocrystal and its solvate cocrystal. The structural and electrostatic potential analyses suggest that the solvation destroys the N-H···N hydrogen bond interaction between phenothiazine (PTZ) and 1,2,4,5-tetracyanobenzene (TCNB), which causes the TCNB molecules to have a 90° rotation along the normal axis of the PTZ plane. Thus, the D-A C-C surface close contact is enlarged, strengthening the intermolecular π-π stacking interactions and intermolecular CT interaction between PTZ and TCNB, which are further evidenced by the absorption and Raman spectroscopic analyses. This study provides rare evidence of the enlarged C-C surface close contact in the mixed packing between D and A that greatly contributes to the intermolecular CT interaction in a D-A cocrystal system. It also provides a deeper understanding of the role of solvation in the structure-property relationship of organic cocrystal materials.

Dynamic polyimine macrobicyclic cryptands - self-sorting with component selection

Self-assembling macrobicyclic cryptand-type organic cages display remarkable self-sorting behavior with efficient component selection.

Self-assembling macrobicyclic cryptand-type organic cages display remarkable self-sorting behavior with efficient component selection. Making use of the dynamic covalent chemistry approach, eight different cages were synthesized by condensation of tris(2-aminopropyl)amine with structurally different dialdehydes. A series of self-sorting experiments were first carried out on simple dynamic covalent libraries. They reveal the influence of different structural features of the aldehyde components on the condensation with two triamine capping units. Subsequently, self-sorting experiments were performed on more complex systems involving several dialdehyde building blocks. Altogether, the results obtained describe the effect of the presence of a heteroatom, of electrostatic interactions, of delocalization and of the flexibility/stiffness of the propensity of a component to undergo formation of a macrobicyclic cage. In the presence of a catalytic amount of acid, the macrobicyclic structure undergoes dynamic component exchange.

The structures of liquid pyridine and naphthalene: the effects of heteroatoms and core size on aromatic interactions

Spatial and orientational structures of liquid naphthalene and pyridine revealed using neutron scattering combined with empirical potential structure refinement.

Third- and high-order nonlinear optical properties of an intramolecular charge-transfer compound

An oligo(phenylenevinylene) bridged intramolecular charge-transfer (ICT) compound, (TCNQ)2OPV3, has been synthesized and its third- and fifth-order nonlinear optical properties have been determined by measurement with the 4f system with a phase-object.

Fast water transmission of zigzag graphyne-3 nanotubes

We report the MD simulation of water molecules permeating fast through the wall of zigzag graphyne-3 nanotubes. The water fluxes are about 5 orders of magnitude higher than that of the commercial forward osmosis membranes.

Position of Substitution: A Facile Way to Tune the Spectroscopic Properties of Dimethylamino-Substituted Arylene-Ethynylenes

A series of dimethylamino-substituted arylene-ethynylenes were synthesised by Sonogashira coupling reactions and characterised by the methods of 1H, 13C NMR, UV-Vis, fluorescence, HRMS and theoretical calculations. Effects on spectroscopic properties caused by the different positions of the dimethylamino group in arylene-ethynylenes were studied and discussed. The shortest absorption maximum, the largest Stokes shift and the highest fluorescence efficiency were observed for arylene-ethynylenes with a dimethylamino group present in the ortho-position.

A C3-symmetric macrocycle-based, hydrogen-bonded, multiporous hexagonal network as a motif of porous molecular crystals

A C3-symmetric π-conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58%. The frameworks were obtained through non-interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO2 up to 96 cm(3) g(-1) at 195 K under 1 atm.

Arylene ethynylene macrocycles: from molecular hosts to components of high-performance supramolecular architectures

This perspective highlights the recent utilization of arylene ethynylene macrocycles as supramolecular synthons—and speculates on what future may hold.

macrocycle embrace: encapsulation of fluoroarenes by m-phenylene ethynylene host

We report structural characterization of a new member of m-phenylene ethynylene ring family. This shape-persistent macrocycle also co-crystallizes with hexafluoro-, 1,2,4,5-tetrafluoro-, 1,3,5-trifluoro, and 1,4-difluorobenzene. The four complexes are almost isostructural, and all show the fluoroarene included into the central cavity of the macrocycle. Characterized by multiple short C - H⋅⋅⋅F - C contacts, these inclusion complexes further dimerize in the solid state into a 2+2 assembly, in which the two macrocycles embrace each other by their large hydrophobic groups that are rotated by 60° relative to one another.

Synthesis, π-face-selective aggregation, and π-face chiral recognition of configurationally stable C(3)-symmetric propeller-chiral molecules with a π-core

The C3 -symmetric propeller-chiral compounds (P,P,P)-1 and (M,M,M)-1 with planar π-cores perpendicular to the C3 -axis were synthesized in optically pure states. (P,P,P)-1 possesses two distinguishable propeller-chiral π-faces with rims of different heights named the (P/L)-face and (P/H)-face. Each face is configurationally stable because of the rigid structure of the helicenes contained in the π-core. (P,P,P)-1 formed dimeric aggregates in organic solutions as indicated by the results of (1) H NMR, CD, and UV/Vis spectroscopy and vapor pressure osmometry analyses. The (P/L)/(P/L) interactions were observed in the solid state by single-crystal X-ray analysis, and they were also predominant over the (P/H)/(P/H) and (P/L)/(P/H) interactions in solution, as indicated by the results of (1) H and 2D NMR spectroscopy analyses. The dimerization constant was obtained for a racemic mixture, which showed that the heterochiral (P,P,P)-1/(M,M,M)-1 interactions were much weaker than the homochiral (P,P,P)-1/(P,P,P)-1 interactions. The results indicated that the propeller-chiral (P/L)-face interacts with the (P/L)-face more strongly than with the (P/H)-face, (M/L)-face, and (M/H)-face. The study showed the π-face-selective aggregation and π-face chiral recognition of the configurationally stable propeller-chiral molecules.

Graphdiyne and graphyne: from theoretical predictions to practical construction

Flat carbon (sp(2) and sp) networks endow the graphdiyne and graphyne families with high degrees of π-conjunction, uniformly distributed pores, and tunable electronic properties; therefore, these materials are attracting much attention from structural, theoretical, and synthetic scientists wishing to take advantage of their promising electronic, optical, and mechanical properties. In this Review, we summarize a state-of-the-art research into graphdiynes and graphynes, with a focus on the latest theoretical and experimental results. In addition to the many theoretical predictions of the potential properties of graphdiynes and graphynes, we also discuss experimental attempts to synthesize and apply graphdiynes in the areas of electronics, photovoltaics, and catalysis.

Hydrogen-bond-driven controlled molecular marriage in covalent cages

A supramolecular approach that uses hydrogen-bonding interaction as a driving force to accomplish exceptional self-sorting in the formation of imine-based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes (A, B, and D) and the flexible triamine tris(2-aminoethyl)amine (X), three new [3+2] self-assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H-bonding) reacted to form the corresponding cage B3X2 selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B3X2 from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non-hydroxy) cage into a preferred (hydroxy) cage B3X2 by treating the former with aldehyde B. The role of the H-bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage-to-cage transformation is reported.

Syntheses and properties of graphyne fragments: trigonally expanded dehydrobenzo[12]annulenes

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.

Molecular marriage through partner preferences in covalent cage formation and cage-to-cage transformation

Unprecedented self-sorting of three-dimensional purely organic cages driven by dynamic covalent bonds is described. Four different cages were first synthesized by condensation of two triamines and two dialdehydes separately. When a mixture of all the components was allowed to react, only two cages were formed, which suggests a high-fidelity self-recognition. The issue of the preference of one triamine for a particular dialdehyde was further probed by transforming a non-preferred combination to either of the two preferred combinations by reacting it with the appropriate triamine or dialdehyde.

Theoretical investigations of sp-sp2 hybridized zero-dimensional fullerenynes

Widely recognized as the quintessential material, sp(2) hybridized carbon material with low dimensions, such as zero-dimensional fullerene, one-dimensional carbon nanotube and two-dimensional graphene, has already compiled an impressive list of superlatives. Quite recently, one-dimensional sp-sp(2) hybridized carbon tubular arrays with a wall thickness of about 40 nm and two-dimensional carbon films with the average thickness of 970 nm have been synthesized successfully. Thus, we expect that the existence of a sp-sp(2) hybridized zero-dimensional carbon allotrope is possible. A novel and stable zero-dimensional carbon allotrope (fullerenyne) with sp-sp(2) hybridization is introduced by means of density functional theory calculation and molecular dynamics confirmation. Unique porous characteristic C(96) fullernenyne with an O(h) symmetry group exhibits exceptionally high stability. We hope that the present study will lead to a further development of a broad new class of carbon materials.

Porphyrin hexamer with a triphenylene core unit: Spectroscopy, electrochemistry and controllable supramolecular formation

A series of free-base and zinc porphyrin hexamers, where six porphyrin units are linked to a triphenylene core through amide or ester linkage, was designed and synthesized in an effort to study their spectroscopic and electrochemical properties, and aggregate formation. The distances between triphenylene core and porphyrin moieties are tuned by changing the lengths of spacer alkyl chains. The absorption spectral studies indicates that the porphyrin units in a hexamer behave like monomeric porphyrins, while a strong fluorescence quenching of triphenylene core was observed suggesting the deactivation of the excited state of triphenylene. The redox potentials of porphyrin units in a hexamer were estimated by differential pulse voltammetry (DPV). These values are very similar to those of the corresponding monomer. Consequently, absorption and electrochemical data demonstrate that six porphyrin units of (H2PAC5)6TPh behave like monomers independently in the ground state. The hexamers undergo supramolecular aggregation spontaneously in different fashions based on the solvent systems as well as spacer lengths. Highly ordered and aligned monolayer-based patterns are formed when hexamers are allowed to aggregate from toluene solution onto carbon-coated copper films. In contrast, hexamers undergo aggregation to nanoparticles in toluene/acetonitrile mixed solvent system and the particle sizes increase with increasing the spacer alkyl chain lengths.

Cucurbit[8]uril mediated donor-acceptor ternary complexes: a model system for studying charge-transfer interactions

A supramolecular self-assembly approach is described which allows for the convenient preparation of a wide range of charge-transfer (CT) donor-acceptor complexes in aqueous solutions. When one equiv of the macrocyclic host cucurbit[8]uril (CB[8]) is added to an aqueous donor and acceptor solution, a heteroternary complex forms inside the host's cavity with a well-defined face-to-face π-π-stacking geometry of the donor and acceptor. This heteroternary, CB[8]-mediated complex offers the opportunity to study the CT phenomena at low concentrations and free from complications arising from any donor-donor and acceptor-acceptor interactions as a result of the large binding affinities and the very high selectivity over the formation of these homoternary complexes. Thus, this supramolocular self-assembly strategy is a practical donor-acceptor mix-and-match approach with synthetic advantages over much more cumbersome tethering schemes. While the characteristic UV/vis features of a few CB[8] ternary systems had been described as a CT band, we present for the first time systematic evidence for the existence of CT interactions between several donor-acceptor pairs that are mediated by the host CB[8]. Correlation of the experimentally obtained CT λ(max) to computed HOMO-LUMO energies demonstrated that the CT process in the host's cavity can be described by the Mulliken model. Furthermore, the literature claim of a "CT driving force" for the formation of CB[8] ternary complexes was scrutinized and evaluated by calorimetric (ITC) and ESI-MS measurements. The findings indicated that neither in the aqueous medium nor in the "gas-phase" is CT of energetic relevance to the Gibbs free binding energy. In contrast, electrostatic considerations combined with solvation effects are much better suited to rationalize the observed trends in binding affinities. Additionally, the CT λ(max) was found to be much more red-shifted (≥75 nm) inside the CB[8] cavity than in any polar organic solvents or water, indicating a significant stabilization of the CT excited state within the host cavity, further demonstrating the unique electrostatic, polar properties of the host cavity.