Modification of Supramolecular Binding Motifs Induced By Substrate Registry: Formation of Self‐Assembled Macrocycles and Chain‐Like Patterns

The self‐assembly properties of two Zn^II porphyrin isomers on Cu(111) are studied at different coverage by means of scanning tunneling microscopy (STM). Both isomers are substituted in their meso‐positions by two voluminous 3,5‐di(tert‐butyl)phenyl and two rod‐like 4′‐cyanobiphenyl groups, respectively. In the trans‐isomer, the two 4′‐cyanobiphenyl groups are opposite to each other, whereas they are located at right angle in the cis‐isomer. For coverage up to one monolayer, the cis‐substituted porphyrins self‐assemble to form oligomeric macrocycles held together by antiparallel CN???CN dipolar interactions and CN???H‐C(sp²) hydrogen bonding. Cyclic trimers and tetramers occur most frequently but everything from cyclic dimers to hexamers can be observed. Upon annealing of the samples at temperatures >150 °C, dimeric macrocyclic structures are observed, in which the two porphyrins are bridged by Cu atoms, originating from the surface, under formation of two CN???Cu???NC coordination bonds. The trans‐isomer builds up linear chains on Cu(111) at low coverage, whereas for higher coverage the molecules assemble in a periodic, densely packed structure. Both cis‐ and trans‐bis(4′‐cyanobiphenyl)‐substituted Zn^II porphyrins behave very differently on Cu(111) compared to similar porphyrins in literature on less reactive surfaces such as Au(111) and Ag(111). On the latter surfaces, there is no signal visible between molecular orientation and the crystal directions of the substrate, whereas on Cu(111), very strong adsorbate–substrate interactions have a dominating influence on all observed structures. This strong porphyrin–substrate interaction enables a much broader variety of structures, including also less favorable intermolecular bonding motifs and geometries.     

Controlling the Self‐Metalation Rate of Tetraphenylporphyrins on Cu(111) via Cyano Functionalization

The reaction rate of the self‐metalation of free‐base tetraphenylporphyrins (TPPs) on Cu(111) increases with the number of cyano groups (n=0, 1, 2, 4) attached at the para positions of the phenyl rings. The findings are based on isothermal scanning tunneling microscopy (STM) measurements. At room temperature, all investigated free‐base TPP derivatives adsorb as individual molecules and are aligned with respect to densely packed Cu substrate rows. Annealing at 400 K leads to the formation of linear dimers and/or multimers via CN‐Cu‐CN bonds, accompanied by self‐metalation of the free‐base porphyrins following a first‐order rate equation. When comparing the non‐cyano‐functionalized and the tetracyano‐functionalized molecules, we find a decrease of the reaction rate by a factor of more than 20, corresponding to an increase of the activation energy from 1.48 to 1.59 eV. Density functional theory (DFT) calculations give insights into the influence of the peripheral electron‐withdrawing cyano groups and explain the experimentally observed effects.     

Induction of periodic nanostructures in polythiophene films through block copolymer templating

A new class of periodically nanostructured polythiophene materials with high regularity and numerous morphologies is prepared through the cooperative self‐assembly of polythiophene derivatives with a templating block copolymer (BCP) and poly(1,4‐isoprene)‐block‐poly(methacrylic acid) (PMA). The selection of the hydrophilic and aprotic triethylene glycol (TEG) group as side chains on polythiophene and the use of hydrophilic and protic PMA are crucial to producing well‐ordered nanostructures in polythiophene films, as it enables selective coassembly within the hydrophilic domain through hydrogen bonding. The composite films are shown to have formed hexagonally packed cylinders with 28 nm periodicities based on small‐angle X‐ray scattering and transmission electron microscopy. The formation of hydrogen bonding is revealed by a shift in the carbonyl peak of PMA in the Fourier transform infrared spectra of the composite film relative to the neat film. This suggests that the TEG‐functionalized polythiophene selectively incorporates into PMA. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1105–1112     

On‐Surface Reactive Planarization of Pt(II) Complexes

A series of Pt(II) complexes with tetradentate luminophores has been designed, synthesized, and deposited on coinage metal surfaces with the aim to produce highly planar self‐assembled monolayers. Low‐temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations reveal a significant initial nonplanarity for all complexes. A subsequent metal‐catalyzed separation of the nonplanar moiety at the bridging unit via the scission of a C?N bond is observed, leaving behind a largely planar core complex. The activation barrier of this bond scission process is found to depend strongly on the chemical nature of both bridging group and coordination plane, and to increase from Cu(111) through Ag(111) to Au(111).     

Comparing Ullmann Coupling on Noble Metal Surfaces: On‐Surface Polymerization of 1,3,6,8‐Tetrabromopyrene on Cu(111) and Au(111)

The on‐surface polymerization of 1,3,6,8‐tetrabromopyrene (Br₄Py) on Cu(111) and Au(111) surfaces under ultrahigh vacuum conditions was investigated by a combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Deposition of Br₄Py on Cu(111) held at 300 K resulted in a spontaneous debromination reaction, generating the formation of a branched coordination polymer network stabilized by C?Cu?C bonds. After annealing at 473 K, the C?Cu?C bonds were converted to covalent C?C bonds, leading to the formation of a covalently linked molecular network of short oligomers. In contrast, highly ordered self‐assembled two‐dimensional (2D) patterns stabilized by both Br?Br halogen and Br?H hydrogen bonds were observed upon deposition of Br₄Py on Au(111) held at 300 K. Subsequent annealing of the sample at 473 K led to a dissociation of the C?Br bonds and the formation of disordered metal‐coordinated molecular networks. Further annealing at 573 K resulted in the formation of covalently linked disordered networks. Importantly, we found that the chosen substrate not only plays an important role as catalyst for the Ullmann reaction, but also influences the formation of different types of intermolecular bonds and thus, determines the final polymer network morphology. DFT calculations further support our experimental findings obtained by STM and XPS and add complementary information on the reaction pathway of Br₄Py on the different substrates.     

Orthogonally Self‐Assembled Multifunctional Block Copolymers

We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring‐opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen‐bonding moiety along the polymer side‐chains, together with a single hydrogen‐bonding‐based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side‐chain‐functionalized AB and ABA block copolymers through self‐assembly. The orthogonal natures of all side‐ and main‐chain self‐assembly events were demonstrated by ¹H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side‐ and main‐chain self‐assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self‐assembly structures found in nature.     

Tailoring Large Pores of Porphyrin Networks on Ag(111) by Metal–Organic Coordination

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu‐mediated metal–organic coordination networks based on two pyridyl‐ and cyano‐bearing free‐base porphyrins on Ag(111) are elucidated by use of low‐temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano‐terminated module directly forms 2D porous networks featuring fourfold‐coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm² only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two‐ and fourfold monoatomic coordination nodes with monotopic nitrogen‐terminated linkers on the very same metal substrate—a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low‐dimensional structures on surfaces.     

Hamilton Receptor‐Mediated Self‐Assembly of Orthogonally Functionalized Au and TiO2 Nanoparticles

A new prototype of reversible self‐assembly between functionalized gold and titanium dioxide nanoparticles (NPs) utilizing hydrogen bonding interactions was developed and established. The gold nanoparticles were functionalized with a Hamilton‐receptor functionality bearing a thiol moiety as anchoring group. The titanium dioxide nanoparticles were modified with cyanurate derivatives which contained phosphonic acids as anchoring groups. The host–guest type interaction between two functionalized nanoparticles yielded a highly integrated nanoparticle system in chloroform. Moreover, by presenting a competing ligand in an exchange reaction, the product of self‐assembly can be segregated into the individual soluble components of functionalized nanoparticles. The self‐assembly and the exchange reaction were followed and monitored in detail by UV/Vis spectroscopy. The structure of the self‐assembly product was investigated using scanning electron microscopy (SEM) and small‐angle X‐ray scattering (SAXS).     

Steering Surface Reaction Dynamics with a Self‐Assembly Strategy: Ullmann Coupling on Metal Surfaces

Ullmann coupling of 4‐bromobiphenyl thermally catalyzed on Ag(111), Cu(111), and Cu(100) surfaces was scrutinized by scanning tunneling microscopy as well as theoretical calculations. Detailed experimental evidence showed that initial formation of organometallic intermediates on the surface, as self‐assembled structures or sparsely dispersed species, is determined by the subsequent reaction pathway. Specifically, the assembled organometallic intermediates at full coverage underwent a single‐barrier process to directly convert into the final coupling products, while the sparsely dispersed intermediates at low coverage went through a double‐barrier process via newly identified clover‐shaped intermediates prior to formation of the final coupling products. These findings demonstrate that a self‐assembly strategy can efficiently steer surface reaction pathways and dynamics.     

Tailoring the Self-assembly of Melamine on Au (111) via Doping with Cu Atoms

The doping effect of Cu on the self-assembly film of melamine on an Au(111) surface has been investigated with scanning tunneling microscopy (STM). The evaporated Cu adatoms occupy the positions underneath the amino groups and change the hydrogen bonding pattern between the melamine molecules. Accordingly, the self-assembly structure has changed stepwise from a well-defined honeycomb into a track-like and then a triangular structure depending on the amount of Cu adatoms. The interaction between Cu adatom and melamine is moderate thus the Cu adatoms can be released upon mild heating to around 100℃. These findings are different from previous observations of either the coordination assembly or the physically trapped metal adatoms.     

On‐Surface Assembly of Hydrogen‐ and Halogen‐Bonded Supramolecular Graphyne‐Like Networks

Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen‐ and halogen‐bonded graphyne‐like two‐dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N???H?C(sp) bonds and N???Br?C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density‐functional theory calculations. It is revealed that the N???Br?C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen‐bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X₃‐synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X₆‐synthon for our bromotriethynyl derivatives.     

Dense or Porous Packing? Two‐Dimensional Self‐Assembly of Star‐Shaped Mono‐, Bi‐, and Terpyridine Derivatives

The self‐assembly behavior of five star‐shaped pyridyl‐functionalized 1,3,5‐triethynylbenzenes was studied at the interface between an organic solvent and the basal plane of graphite by scanning tunneling microscopy. The mono‐ and bipyridine derivatives self‐assemble in closely packed 2D crystals, whereas the derivative with the more bulky terpyridines crystallizes with porous packing. DFT calculations of a monopyridine derivative on graphene, support the proposed molecular model. The calculations also reveal the formation of hydrogen bonds between the nitrogen atoms and a hydrogen atom of the neighboring central unit, as a small nonzero tunneling current was calculated within this region. The title compounds provide a versatile model system to investigate the role of multivalent steric interactions and hydrogen bonding in molecular monolayers.     

Identifying Multinuclear Organometallic Intermediates in On‐Surface [2+2] Cycloaddition Reactions

We investigate the on‐surface [2+2] cycloaddition reaction of 2,3,6,7,10,11‐hexabromotriphenylene (HBTP) on Ag(111), Cu(111), Au(111), and Cu‐dosed Au(111) surfaces using STM and DFT simulation focusing on the organometallic intermediates. The fully debrominated HBTP molecules form an organo‐silver framework on Ag(111) and an organo‐copper framework on Cu(111), both incorporating multinuclear metal adatom clusters. The organo‐silver framework is converted into porous covalent networks via [2+2] cycloaddition above 240 °C. In contrast, the organo‐copper framework is very stable and does not undergo [2+2] cycloaddition even at 300 °C. On Au(111), no organo‐gold intermediate of [2+2] cycloaddition is observed. After loading Cu onto Au(111), the partially debrominated HBTP molecules bind to Cu adatom dimers to form multinuclear organo‐copper complexes at 100 °C which undergo [2+2] cycloaddition at 140 °C. This study shows that the choice of surface can direct the reaction pathway.     

Self‐Assembly of Decoupled Borazines on Metal Surfaces: The Role of the Peripheral Groups

Two borazine derivatives have been synthesised to investigate their self‐assembly behaviour on Au(111) and Cu(111) surfaces by scanning tunnelling microscopy (STM) and theoretical simulations. Both borazines form extended 2D networks upon adsorption on both substrates at room temperature. Whereas the more compact triphenyl borazine 1 arranges into close‐packed ordered molecular islands with an extremely low density of defects on both substrates, the tris(phenyl‐4‐phenylethynyl) derivative 2 assembles into porous molecular networks due to its longer lateral substituents. For both species, the steric hindrance between the phenyl and mesityl substituents results in an effective decoupling of the central borazine core from the surface. For borazine 1 , this is enough to weaken the molecule–substrate interaction, so that the assemblies are only driven by attractive van der Waals intermolecular forces. For the longer and more flexible borazine 2 , a stronger molecule–substrate interaction becomes possible through its peripheral substituents on the more reactive copper surface.     

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self‐Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System

A facile approach for the fabrication of novel black plasmonic colloidosomes assembled from Au nanospheres is developed by an emulsion‐templating strategy. This self‐assembly process is based on a new reverse water‐in‐1‐butanol emulsion system, in which the water emulsion droplets can dissolve into 1‐butanol (oil) phase at an appropriate rate. These Au colloidosomes possess hexagonal close‐packed multilayer shells and show a low reflectivity and intense broadband absorption owing to the strong interparticle plasmonic coupling, which is further investigated by a finite‐difference time‐domain method. This method is universal and is suitable for self‐assembly of different noble‐metal nanoparticles into different colloidosomes. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.     

Variations in Complementary Hydrogen Bonds Direct Assembly Patterns of Isosteric Polyheteroaromatics at Surfaces

Intermolecular interactions guide self-assembly on the surface. Precise control over these interactions by rational design of the molecule should allow fine control over the self-assembly patterns. Functional groups installed for electronic modulation often induce significant changes in the molecular dimensions, thereby disrupting the original assembly pattern. To overcome this challenge, we have employed a family of isosteric phenazine derivatives, DHP , DAP , and DBQD , to investigate the impacts of hydrogen bonding on two-dimensional molecular self-assembly. While these molecules are similar in size and chemical composition, the strength and directionality of hydrogen bonding differ significantly depending on the chemical structure of donor-acceptor pairs and prototropic tautomerization from positional isomerism. Scanning tunneling microscopy (STM) characterization of the assembled structures on Ag(111), Au(111), and Cu(100) surfaces revealed that minimal changes in molecular structure have a profound impact on the self-assembly patterns. While DHP exhibits highly ordered and robust assemblies, DAP and DBQD show either spatially confined or ill-defined assemblies. In conjunction with hydrogen bonding, prototropic tautomerism is a potent strategy to modulate molecular 2D lattices on surfaces.     

Investigation of the Adsorption and Self Assembly of Isocyanide Derivatives on Au（111） Surface

The adsorption and self-assembly of isocyanide derivatives on Au（111） surface were investigated by density functional theory （DFF） and molecular dynamics simulation. The calculation for phenyl isocyanide by DFT was based on cluster and slab models. The self-assembled monolayers of 2-isocyanoazulene and 1,3-diethoxycarbony 1- 2-isocyanoazulene on Au（111） were simulated using Au-C force field parameters developed by us. It was found that the top site was the most preferred position, and the isocyanoazulene and its derivatives could form the ordered face to edge self-assembled monolayer on gold surface indeed, and the molecules stood on the gold surface vertically.     

Orthogonal Insertion of Lanthanide and Transition‐Metal Atoms in Metal–Organic Networks on Surfaces

The orthogonal coordinative properties of tetrapyrrole macrocycles and nitrile ligands have been used in a multistep procedure towards interfacial d‐f hetero‐bimetallic nanoarchitectures based on a free‐base porphyrin derivative functionalized with meso‐cyanobiphenylene substituents. Molecular‐level scanning tunneling microscopy studies reveal that the porphyrin module alone self‐assembles on Ag(111) in a close‐packed layer with a square unit cell. Upon co‐deposition of Gd atoms, a square‐planar motif is formed that reflects the fourfold coordination of CN ligands to the rare‐earth centers. The resulting nanoporous network morphology is retained following exposure to a beam of Co atoms, which induces selective porphyrin metalation and ultimately yields a gridlike 2D metallosupramolecular architecture.     

Understanding the Supramolecular Self‐Assembly of the Fullerene Derivative PCBM on Gold Surfaces

We report a DFT study on the self‐assembly of the fullerene derivative PCBM on the Au(111) surface. Recent STM experiments (Angew. Chem. 2007 , 119, 8020–8023^[1]) show a coverage‐dependent transition of the adsorption and self‐assembly of PCBM on this surface. To understand the origin of this observation, we compute the geometries and relative energies of ten PCBM dimers and four tetramers. The calculations show that the self‐assembly of PCBM at high coverage is mainly controlled by hydrogen bonding between the PCBM tails. Due to the large size of the fullerene cage, the hydrogen bonds are formed far away from the surface; hence they are very similar to those found in the gas phase. This picture successfully explains the observed site‐insensitive adsorption at high coverage and the 2D arrangement of PCBM on the surface.     

A Supramolecular Sorting Hat: Stereocontrol in Metal–Ligand Self‐Assembly by Complementary Hydrogen Bonding

A combination of self‐complementary hydrogen bonding and metal–ligand interactions allows stereocontrol in the self‐assembly of prochiral ligand scaffolds. A unique, non‐tetrahedral M₄L₆ structure is observed upon multicomponent self‐assembly of 2,7‐diaminofluorenol with 2‐formylpyridine and Fe(ClO₄)₂. The stereochemical outcome of the assembly is controlled by self‐complementary hydrogen bonding between both individual ligands and a suitably sized counterion as template. This hydrogen‐bonding‐mediated stereoselective metal–ligand assembly allows the controlled formation of nonsymmetric discrete cage structures from previously unexploited ligand scaffolds.