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The self-assembly of star-shaped 1,3,5-tris(4-carboxyphenyl)benzene molecules on Au(111) is investigated by using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM shows that for one monolayer deposition, the molecules self-assemble into two compact nanoarchitectures: one with a rectangular unit cell and a second one with a parallelogram unit cell. DFT calculations reveal that these two compact structures are stabilized by hydrogen bonds and that the rectangular nanoarchitecture has the lowest energy. The rectangular unit cell is stabilized by two hydrogen bonds per molecule with an energy of 0.3 eV, whereas the parallelogram unit cell is stabilized by 1.2 hydrogen bonds per molecule with an energy of 0.25 eV each.

The structural and magnetic properties of a drop-cast film of flat C 54 H 34 Br 4 CuO 4 , a β-diketonato complex functionalized with bromine atoms, on a graphite surface are investigated using scanning tunneling microscopy, synchrotron X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Experimental measurements reveal that the Cu-complexes preferentially lay flat on the graphite surface. The magnetic hysteresis loops show that the organic thin film remains paramagnetic at 2 K with an easy axis of magnetization perpendicular to the graphite surface and is therefore perpendicular to the plane of the Cu-complex skeleton.

Barbituric acid derivative (TDPT) is an achiral molecule, and its adsorption on a surface results in two opposite enantiomerically oriented motifs, namely TDPT-S p and R p . Two types of building blocks can be formed; block I is enantiomer-pure and is built up of the same motifs (format S p S p or R p R p ) whereas block II is enantiomer-mixed and composes both motifs (format S p R p ), respectively. The organization of the building blocks determines the formation of different nanoarchitectures which are investigated using scanning tunneling microscopy at a liquid/HOPG interface. Sophisticated, highly symmetric "nanowaves" are first formed from both building blocks I and II and are heterochiral. The "nanowaves" are metastable and evolve stepwisely into more close-packed "nanowires" which are formed from enantiomer-pure building block I and are homochiral. A dynamic hetero- to homochiral transformation and simultaneous multi-scale phase transitions are demonstrated at the single-molecule level. Our work provides novel insights into the control and the origin of chiral assemblies and chiral transitions, revealing the various roles of enantiomeric selection and chiral competition, driving forces, stability and molecular coverage.

The ability to engineer sophisticated two-dimensional tessellation organic nanoarchitectures based on triangular molecules and on-surface-synthesized covalent multimers is investigated using scanning tunneling microscopy. 1,3,5-Tris(3,5-dibromophenyl)benzene molecules are deposited on high-temperature Au(111) surfaces to trigger Ullmann coupling. The self-assembly into a semi-regular rhombitrihexagonal tiling superstructure not only depends on the synthesis of the required covalent building blocks but also depends on their ratio. The organic tessellation nanoarchitecture is achieved when the molecules are deposited on a Au(111) surface at 145 °C. This halogen-bonded structure is composed of triangular domains of intact molecules separated by rectangular rows of covalent dimers. The nearly hexagonal vertices are composed of covalent multimers. The experimental observations reveal that the perfect semi-regular rhombitrihexagonal tiling cannot be engineered because it requires, in addition to the dimers and intact molecules, the synthesis of covalent hexagons. This building block is only observed above 165 °C and does not coexist with the other required organic buildings blocks.

The trapping of coronene and zinc phthalocyanine (ZnPc) molecules at low concentration by a two-dimensional self-assembled nanoarchitecture of a push-pull dye is investigated using scanning tunneling microscopy (STM) at the liquid-solid interface. The push-pull molecules adopt an L-shaped conformation and self-assemble on a graphite surface into a hydrogen-bonded Kagomé network with porous hexagonal cavities. This porous host-structure is used to trap coronene and ZnPc guest molecules. STM images reveal that only 11% of the Kagomé network cavities are filled with coronene molecules. In addition, these guest molecules are not locked in the host-network and are desorbing from the surface. In contrast, STM results reveal that the occupancy of the Kagomé cavities by ZnPc evolves linearly with time until 95% are occupied and that the host structure cavities are all occupied after few hours.

Transformation of metastable supramolecular stacks of hydrogen-bonded rosettes composed of an ester-containing barbiturated naphthalene into crystalline nanosheets occurs through the rearrangement of hydrogen-bonding patterns. The involvement of the ester group in the crystalline hydrogen-bonded pattern is demonstrated, guiding us to a new molecular design that can afford supramolecular polymorphs with soft and hard molecular packing.

The self-assembly of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) with the star-shaped 1,3,5-tris(4-aminophenyl)benzene (TAPB) on Au(111) is investigated using scanning tunneling microscopy. PTCDI forms a compact canted arrangement on the gold surface. When TAPB is sublimated at a high temperature, the molecule dissociates into a 4-aminophenyl group and a boomerang-shaped compound. The boomerang molecule self-assembles with PTCDI to create a two-dimensional (2D) nanoarchitecture stabilized by N-H···O-C hydrogen bonds between the dissociated TAPB and PTCDI. The molecular ratio of this multicomponent structure is 1:1., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Star-shaped 2,4,6-tris(4',4'',4'''-trimethylphenyl)-1,3,5-triazine molecules self-assemble at the solid-liquid interface into a compact hexagonal nanoarchitecture on graphite. High resolution scanning tunneling microscopy (STM) images of the molecules reveal intramolecular features. Comparison of the experimental data with calculated molecular charge density contours shows that the molecular features in the STM images correspond to molecular LUMO+2., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Kinetically formed metastable molecular assemblies have attracted increasing interest especially in the field of supramolecular polymers. In most cases, metastable assemblies are ensemblies of aggregates based on the same supramolecular motif but with different lengths or sizes, and therefore their kinetic stabilities are experimentally indistinguishable. Herein, we demonstrate a topological effect on kinetic stabilities in a complex mixture of metastable supramolecular polymers. Our azobenzene-incorporated monomer upon heating in nonpolar solvent at ambient temperature kinetically forms complex mixtures of supramolecular polymers with cyclized and open-ended randomly coiled topologies. Upon further heating, we obtained thermodynamically stable twisted fibrils organizing into crystalline fibers. Through the direct visualization of the complex supramolecular polymer mixtures by atomic force microscopy, we demonstrate that the cyclized supramolecular polymer has superior kinetic stability compared to the open-ended species toward the thermal transformation into twisted fibrils. Since the superior kinetic stability of the cyclized species can be attributed to the absence of aggregate termini, we could convert them fully into the thermodynamic species through photoinduced opening of the cyclized structures.

Helical self-assembly of functional π-conjugated molecules offers unique photochemical and electronic properties in the spectroscopic level, but there are only a few examples that demonstrate their positive impact on the optoelectronic device level. Here, we demonstrate that hydrogen-bonded tapelike supramolecular polymers of a barbiturated oligo(alkylthiophene) show notable improvement in their photovoltaic properties upon organizing into helical nanofibers. A tapelike hydrogen-bonded supramolecular array of barbiturated oligo(butylthiophene) molecules was directly visualized by STM at a liquid-solid interface. TEM, AFM and XRD revealed that the tapelike supramolecular polymers further organize into helical nanofibers in solution and bulk states. Bulk heterojunction solar cells of the helical nanofibers and soluble fullerene showed a power conversion efficiency of 4.5%, which is markedly high compared to that of the regioisomer of butyl chains organizing into 3D lamellar agglomerates.

The self-assembly of star-shaped 1,3,5-tris(3,5-dibromophenyl)benzene molecules on Au(111)-() in a vacuum is investigated using scanning tunneling microscopy and core-level spectroscopy. Scanning tunneling microscopy shows that the molecules self-assemble into a hexagonal porous halogen-bonded nanoarchitecture. This structure is stabilized by X 3-A synthons composed of three type-II halogen-interactions (halogen-bonds). The molecules are oriented along the same direction in this arrangement. Domain boundaries are observed in the hcp region of the herringbone gold surface reconstruction. Molecules of the neighboring domains are rotated by 180°. The domain boundaries are stabilized by the formation of X 3-B synthons composed of two type-II and one type-I halogen-interactions between molecules of the neighboring domains. Core-level spectroscopy confirms the existence of two types of halogen-interactions in the organic layer. These observations show that the gold surface reconstructions can be exploited to modify the long-range supramolecular halogen-bonded self-assemblies.

Barbituric acid derivatives are prochiral molecules, i.e. they are chiral upon adsorption on surfaces. Scanning tunneling microscopy reveals that barbituric acid derivatives self-assemble into a chiral guest-host supramolecular architecture at the solid-liquid interface on graphite. The host nanoarchitecture has a sophisticated wavy shape pattern and paired guest molecules are nested insides the cavities of the host structure. Each unit cell of the host structure is composed of both enantiomers with a ratio of 1:1. Furthermore, the wavy patterns of the nanoarchitecture are formed from alternative appearance of left- and right-handed chiral building blocks, which makes the network heterochiral. The functional guest-host nanoarchitecture is the result of two-dimensional chiral amplification from single enantiomers to organizational heterochiral supramolecular self-assembly.

Benzodithiophene-functionalized oligothiophene with barbituric acid hydrogen-bonding unit self-assembles into nanoscopic structures via the formation of rosettes. The nanostructures show a power conversion efficiency of 3% upon mixing with PC61BM in bulk-heterojunction solar cells without thermal annealing.

The competition between the on-surface synthesis of covalent nanoarchitectures and the self-assembly of star-shaped 1,3,5-Tris(4-iodophenyl)benzene molecules on Au(111) in vacuum is investigated using scanning tunneling microscopy above room temperature. The molecules form covalent polygonal nanoachitectures at the gold surface step edges and at the elbows of the gold reconstruction at low coverage. With coverage increasing two-dimensional halogen-bonded structures appear and grow on the surface terraces. Two different halogen-bonded nanoarchitectures are coexisting on the surface and hybrid covalent-halogen bonded structures are locally observed. At high coverage covalent nanoarchitectures are squeezed at the domain boundary of the halogen-bonded structures. The competitive growth between the covalent and halogen-bonded nanoarchitectures leads to formation of a two-layer film above one monolayer deposition. For this coverage, the covalent nanoarchitectures are propelled on top of the halogen-bonded first layer. These observations open up new opportunities for decoupling covalent nanoarchitectures from catalytically active and metal surfaces in vacuum.

The conformation and the two-dimensional self-assembly of 4'-(3',4″-dihexyloxy-5,2':5',2″:5″,2‴-quaterthien-2,5‴-diyl)-bis(2,2':6',2″-terpyridine) molecules are theoretically and experimentally investigated. This molecular building block forms a hydrogen-bonded chiral supramolecular nanoarchitecture on graphite at the solid/liquid interface. Scanning tunneling microscopy (STM) shows that the molecule adopts an S-shaped conformation in this structure. DFTB+ calculations reveal that this conformation is not the lowest-energy conformation. The molecular nanoarchitecture appears to be stabilized by hydrogen bonding as well as van der Waals interactions. I-, L-, and D-shaped molecular conformations are, however, locally observed at the domain boundary, but these conformations do not self-assemble into organized 2D structures.

We selectively engineer three two-dimensional self-assembled hybrid PTCDI-NaCl nanoarchitectures, i.e. a flower-structure, a mesh-structure and a chain-structure on Au(111). Scanning tunneling microscopy reveals that NaCl-dimers selectively interact with molecular N-H groups. The PTCDI···NaCl-dimer binding appears to be highly directional. Hybrid molecular-ionic self-assembly is a promising alternative to metal-coordinated and multicomponent organic nanostructures to engineer novel nanoarchitectures on surfaces.

The synthesis of a series of Ni(II) -salen-based complexes with the general formula of [Ni(H2 L)] (H4 L=R(2) -N,N'-bis[R(1) -5-(4'-benzoic acid)salicylidene]; H4 L1: R(2) =2,3-diamino-2,3-dimethylbutane and R(1) =H; H4 L2: R(2) =1,2-diaminoethane and R(1) =tert-butyl and H4 L3: R(2) =1,2-diaminobenzene and R(1) =tert-butyl) is presented. Their electronic structure and self-assembly was studied. The organic ligands of the salen complexes are functionalized with peripheral carboxylic groups for driving molecular self-assembly through hydrogen bonding. In addition, other substituents, that is, tert-butyl and diamine bridges (2,3-diamino-2,3-dimethylbutane, 1,2-diaminobenzene or 1,2-diaminoethane), were used to tune the two-dimensional (2D) packing of these building blocks. Density functional theory (DFT) calculations reveal that the spatial distribution of the LUMOs is affected by these substituents, in contrast with the HOMOs, which remain unchanged. Scanning tunneling microscopy (STM) shows that the three complexes self-assemble into three different 2D nanoarchitectures at the solid-liquid interface on graphite. Two structures are porous and one is close-packed. These structures are stabilized by hydrogen bonds in one dimension, while the 2D interaction is governed by van der Waals forces and is tuned by the nature of the substituents, as confirmed by theoretical calculations. As expected, the total dipolar moment is minimized., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Truncated pyramid-shaped Ni nanocrystals were epitaxially grown on SrTiO(3)(001) surfaces and characterised by scanning tunneling microscopy (STM). These nanocrystals were shown to be catalytically active for the synthesis of carbon nanotubes (CNTs). The narrow size distribution of the Ni nanocrystals results in a similar narrow distribution of CNT diameters.

Two-dimensional self-assembly of 1-octanol molecules on a graphite surface is investigated using scanning tunneling microscopy (STM) at the solid/liquid interface. STM images reveal that this molecule self-assembles into a compact hydrogen-bonded herringbone nanoarchitecture. Molecules are preferentially arranged in a head-to-head and tail-to-tail fashion. A Moiré pattern appears in the STM images when the 1-octanol layer is covering the graphite surface. The large Moiré stripes are perpendicular to the 1-octanol lamellae. Interpretation of the STM images suggests that the Moiré periodicity is governed by the electronic properties of the graphite surface and the 1-octanol layer periodicity.

A novel mechanism of hybrid assembly of molecules on surfaces is proposed stemming from interactions between molecules and on-surface metal atoms which eventually got trapped inside the network pores. Based on state-of-the-art theoretical calculations, we find that the new mechanism relies on formation of molecule-metal atom pairs which, together with molecules themselves, participate in the assembly growth. Most remarkably, the dissociation of pairs is facilitated by a cooperative interaction involving many molecules. This new mechanism is illustrated on a low coverage Melamine hexagonal network on the Au(111) surface where multiple events of gold atoms trapping via a set of so-called "gate" transitions are found by kinetic Monte Carlo simulations based on transition rates obtained using ab initio density functional theory calculations and the nudged elastic band method. Simulated STM images of gold atoms trapped in the pores of the Melamine network predict that the atoms should appear as bright spots inside Melamine hexagons. No trapping was found at large Melamine coverages, however. These predictions have been supported by preliminary STM experiments which show bright spots inside Melamine hexagons at low Melamine coverages, while empty pores are mostly observed at large coverages. Therefore, we suggest that bright spots sometimes observed in the pores of molecular assemblies on metal surfaces may be attributed to trapped substrate metal atoms. We believe that this type of mechanism could be used for delivering adatom species of desired functionality (e.g., magnetic) into the pores of hydrogen-bonded networks serving as templates for their capture.

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.

Engineering and tuning multi-component supramolecular self-assemblies on surfaces is one of the challenges of nanotechnology. We use scanning tunneling microscopy to investigate the influence of molecular ratio on the self-assembly of PTCDA-melamine structures on Au(111)-(22 x complex square root of 3). Our observations reveal that three different chiral supramolecular networks having a PTCDA:melamine ratio of 3:2, 1:2, 1:4 can be selectively created by tuning the ratio of molecules deposited on the surface. The 1:2 ratio network having melamine in excess has been observed previously but the 1:4 network has not yet been reported. In comparison, the multi-component 3:2 network having PTCDA in excess is a completely new structure.

The two-dimensional (2D) crystal engineering of molecular architectures on surfaces requires controlling various parameters related respectively to the substrate, the chemical structure of the molecules, and the environmental conditions. We investigate here the influence of temperature on the self-assembly of hexakis(n-dodecyl)-peri-hexabenzocoronene (HBC-C(12)) adsorbed on gold using scanning tunneling microscopy (STM) at the liquid/solid interface. We show that the packing density of 2D self-assembled HBC-C(12) can be precisely tuned by adjusting the substrate temperature. Increasing the temperature progressively over the 20-50 degrees C range induces three irreversible phase transitions and a 3-fold increase of the packing density from 0.111 to 0.356 molecule/nm(2). High-resolution STM images reveal that this 2D packing density increase arises from the stepwise desorption of the n-dodecyl chains from the gold surface. Such temperature-controlled irreversible phase transitions are thus a versatile tool that can then be used to adjust the packing density of highly ordered functional materials in view of applications in organic electronic devices.

We show by means of STM that C(60) molecules can be trapped into specific sites of a 2D double-cavity open network, thus forming long-range alignments of single molecules. Since only one of the two cavities has the right size to host C(60), the smallest cavity remains empty and is thus available to trap additional species of smaller size. This novel 2D supramolecular network opens new perspectives in the design of multicomponent guest-host architectures with electronic functionalities.

The temperature-dependent structure transition of supported Cu nanocrystals on SrTiO3(001)-(2 x 1) is investigated by scanning tunneling microscopy (STM). We experimentally determine the phase map of supported Cu icosahedral, decahedral, and truncated octahedral nanocrystal shapes as a function of substrate temperature during Cu deposition. We show that a supported nanocrystal of 8500 atoms at a nucleation temperature of 480 degrees C has the same probability of adopting an icosahedral or octahedral shape.

The growth of multi-layer NaCl islands on Au(111)-([Formula: see text]) surfaces was investigated using scanning tunneling microscopy (STM). We observed that the aspect of the NaCl islands drastically differs depending on the tunneling conditions. It is therefore possible to observe the layers forming an NaCl island or to image the gold reconstruction below the first NaCl layer. Atomically resolved STM images obtained on the first NaCl layer demonstrate that NaCl grows as an epitaxial crystalline film on Au(111)-([Formula: see text]). STM images also suggest that some NaCl layers can be non-crystalline.

A supramolecular grating of single Lu@C(82) molecules was obtained by depositing Lu@C(82) molecules onto a room temperature PTCDI-melamine network.

The mixing of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine) at room temperature in a ratio of 3 : 4 on Au(111) leads to the formation of a new chiral "pinwheel" structure.

The ability to select the way in which atoms and molecules self-organize on a surface is important for synthesizing nanometre scale devices. Here we show how endohedral fullerenes (Er(3)N@C(80)) can be assembled into four distinctive arrangements on a strontium titanate surface template. Each template pattern correlates to a particular reconstruction on n-doped SrTiO(3)(001), made in whole or in part by self-assembled arrays of non-stoichiometric oxide nanostructures. Close-packed assemblies of Er(3)N@C(80) molecules are formed, as well as one-dimensional chains and two-dimensional grids. This method of template-assisted molecular ordering provides a new platform for the development of experimental schemes of classical and quantum information processing at the molecular level.

Developing useful molecular systems, such as planar networks for novel molecular electronics, requires the ability to control the way molecules assemble at surfaces. Here we report how an oxide crystal surface can be used as a template to controllably order endohedral fullerenes, Er3N@C80, into two-dimensional (2D) open-grid arrays. The crystal surface is made of highly ordered oxide nanostructures which self-assemble on the surface of SrTiO3(001). This method of molecular ordering can be applied to other fullerenes and has the potential to provide a basis for developing a wide range of molecular architectures.