Hydrogen-bonded organic frameworks (HOFs) have become a unique class of crystalline materials, typically formed by connecting organic building units through intermolecular hydrogen bonds (HBs). Thanks to the strength and directionality of HBs, as well as their high flexibility, numerous HOFs can usually be engineered using specific organic blocks. In this study, a L-shaped push-pull dye molecule (compound 1), having multiple HB sites, is chosen to create a stable host HOF through molecular self-assembly, as revealed by scanning tunneling microscopy (STM) at the heptatonic acid (HA) and highly oriented pyrolytic graphite (HOPG) interface. Compound 1 self-assembles into a chiral Kagomé HOF, with saturated HB bonds. This porous structure is then used as a host-template to capture star-shaped 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT), a molecule containing three pyridyl-groups. STM shows that triangular TPT molecules are trapped within the cavities of the compound 1 host architecture at the HA/HOPG interface. The guest-TPT molecules, however, disrupt the initial compound 1 self-assembled arrangement. Structural transition was observed in HOFs: from Kagomé into honeycomb assembly triggered by adding guest-TPT. DFT calculations and molecular mechanics (MM) simulations demonstrate that the phase transition mechanism results from the formation of three acids–pyridine N···H HBs between compound 1 and TPT. In addition, the introduction of TPT decreases the energy of the adlayer–substrate system.

Molecular assemblies that form distinct out-of-equilibrium states in response to varying energy inputs represent a promising platform for designing advanced, autonomous adaptive materials capable of flexibly and diversely responding to environmental stimuli. Herein, we describe a supramolecular polymer system that integrates azobenzene photoisomerization with hydrogen-bond-directed supramolecular polymorphism, enabling the formation of distinct out-of-equilibrium states under varied light intensities. trans isomers of an azobenzene derivative featuring a barbituric acid merocyanine unit self-assemble into lamellar crystals via two-dimensional nanosheet stacking. Ultraviolet light irradiation of a nanosheet dispersion in nonpolar media at different intensities modulates the proportion of cis isomers, eliciting unique out-of-equilibrium states. Specifically, a strong light facilitates the coassembly of trans and cis isomers into one-dimensional nanofibers through hydrogen bond rearrangement, whereas weaker light drives Ostwald ripening, transforming two-dimensional nanosheets into three-dimensional multilayered structures. High-speed atomic force microscopy reveals the intricate dynamic processes driving these transitions.

The discovery of aggregation-induced emission (AIE) has revolutionized the research of luminescent materials, where the restriction of intramolecular motion model serves as a guiding principle for the design of AIE luminogens (AIEgens). Recent studies have uncovered an intriguing anti-heavy atom effect on their photophysical behavior; however, the role of halogen position remains underexplored. Herein, we synthesize a series of chloro1,1,2,2-tetrakis (4-(phenyl ethynyl) phenyl) ethane (ClTPPE) derivatives to systematically elucidate how chlorine substitution modulates their photophysical properties. The ClTPPE derivatives exhibit ultrahigh fluorescence quantum yields (Phi F), among which o-ClTPPE achieves an exceptional Phi F value of 86.5 % in the solid state, attributed to chlorine-based intermolecular contacts. Theoretical and crystallographic analyses reveal that the chlorine substitution plays a key role in enhancing molecular packing rigidity and significantly minimizing nonradiative decay, thereby synergistically enhancing the AIE property. This work establishes design principles for chlorine-mediated noncovalent engineering, providing a rational framework for the optimization of halogenated AIEgens.

The magnetic and structural properties of an organic film, composed of a beta-diketonato complex functionalized with iodine atoms (C30H18CuI4O4), deposited on a graphite surface are probed using synchrotron radiation spectroscopies and scanning tunneling microscopy. The Cu2+ complexes form a halogen-bonded network at the interface, and the molecules in the film preferentially remain parallel to the graphite surface. For a temperature of 2 K, the complex film is paramagnetic; no preferential easy axis of magnetization is detected. The engineering and characterization of organic films composed of molecular magnets is essential for developing novel applications in spintronics and nanomagnetism due to the appealing magnetic and electronic properties of these materials.

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 C54H34Br4CuO4, 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.

Magneto-dynamics and its interfacial modulation have attracted much attention in energy-efficient and nonvolatile spintronic devices. In particular, the antiferromagnetic coupling at the interface plays a crucial role in spin dynamic behaviors. In this work, we utilize rare-earth holmium (Ho) to interface with transition-metal alloy Ni80Fe20(Py) and achieve a naturally formed antiferromagnetic coupling between Py and interfacial Ho via the magnetic proximity effect, as confirmed by element-specific synchrotron radiation x-ray magnetic circular dichroism hysteresis loops. Importantly, the antiferromagnetic coupled interface is preserved even at a low temperature of 4.2 K, which is below the Curie temperature of Ho. Using ferromagnetic resonance analysis, we reveal that the Gilbert damping and the interfacial spin mixing conductance of the Py/Ho bilayers are much larger than those of the Py/Pt and Py/Pd, suggesting a superior spin transparent efficiency on such an interface with an antiferromagnetic coupling. More importantly, upon the insertion of 2-nm-thick Cu, the antiferromagnetic coupling disappears, associated with the evident suppression of Gilbert damping. This strengthens the critical role of the antiferromagnetic coupled interface in the magneto-dynamics of the transition-metal/rare-earth bilayers and provides a promising way of magneto-dynamics modulation in antiferromagnet-based devices.

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.

Barbituric acid derivative (TDPT) is an achiral molecule, and its adsorption on a surface results in two opposite enantiomerically oriented motifs, namely TDPT-Sp and Rp. Two types of building blocks can be formed; block I is enantiomer-pure and is built up of the same motifs (format SpSp or RpRp) whereas block II is enantiomer-mixed and composes both motifs (format SpRp), 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 self-assembled structures of a hydrogen-bonding oligo(thiophene) molecule functionalized with a barbiturate unit is investigated at different hierarchical levels. Atomic force microscopy observations show that the nanostructures formed upon drop-casting the solution adopt either a nonhelical rodlike or a helical nanofiber. This suggests the existence of two distinct molecular self-assembly pathways. This is confirmed by scanning tunneling microscopy (STM) investigations at the solid liquid interface. STM reveals that the molecule can either adopt a lamellar or a hexameric macrocycle two-dimensional structure depending on the solute concentration. These arrangements are attributed to tape and rosette motifs stabilized by double hydrogen bonds between barbiturate groups. On the basis of the previous observation of two compounds that exclusively form rosette-based rodlike nanofibers and tape-based helical fibers, we propose the current molecule undergoes two specific hierarchical self-assembly pathways governed by tape and rosette hydrogen-bonding motifs leading the formation of rod and helical fibers, respectively.

Shape changes of Ag and Au nanoparticles supported on single crystal reconstructed SrTiO3(001) and (111) substrates were investigated using scanning tunneling microscopy. Both metals nucleate as multiply twinned particles (MTPs) and transform into face-centered-cubic single crystals (SCs) beyond a critical volume. On SrTiO3(001)-c(4 × 2) the critical volumes are measured as 141 ± 51 nm3 for Ag and 107 ± 23 nm3 for Au, whereas on SrTiO3(111)–(4 × 4)+(6 × 6) the critical volumes are 53 ± 26 nm3 for Ag and 26 ± 40 nm3 for Au. A much larger transition volume was observed on SrTiO3(001)–(2 × 1), where Ag remains as MTPs up to 3400 nm3, while Au nucleates as atomic monolayers instead of MTPs. This work demonstrates the significant impact of small variations of the surface structure of the substrate on the MTP–SC transition volume.

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.

Supramolecular polymerization of two regioisomeric naphthalene-azobenzene dyads bearing barbituric acid and tri(dodecyloxy)phenyl units were studied in nonpolar solvent. Supramolecular polymers of the two compounds differ considerably in their topologies. While the isomer of which azobenzene unit was introduced along to its longer molecular axis formed randomly coiled supramolecular polymers with intrinsic curvature, the other of which azobenzene unit was introduced along to its shorter molecular axis formed linearly extended supramolecular polymers. Furthermore, due to their different degrees of geometrical changes accompanied with photoisomerization of the azobenzene unit, only the former showed a large topological change upon photo-irradiation. The different structural and photoresponsive properties can be attributed to the distinct geometries of supermacrocyclic hydrogen-bonded intermediates (rosettes).

Century Gothic 11) Engineering two-dimensional (2D) covalent carbon-based nanoarchitectures has received tremendous attention during the resent years. We investigate on-surface bottom-up synthesis to create patterned graphene nanoarchitectures via Ullmann coupling. Starshaped 1,3,5-Tris(4-iodophenyl)benzene molecules self-assemble into halogen-bonded structures on graphite [1]. In contrast, our STM measurements reveal that on-surface synthesis of covalent nanoarchitectures is competing with the growth of self-assembled halogen-bonded structures when this molecule is deposited on Au(111) in vacuum [2]. We show that the molecules form covalent polygonal nanoachitectures at the gold surface step edges at low coverage. With coverage increasing two-dimensional halogen-bonded structures appear and grow on the surface terraces. At high coverage 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. We then investigated the on-surface synthesis of covalent nanoarchitectures of starshaped 1,3,5-tris(3,5-dibromophenyl)-benzene molecules on Au(111). This molecule has two bromine atoms at the extremity of each arm. At room temperature, the molecules selfassemble into a porous halogen-bonded network [3]. One-covalent-bond dimers appear on the surface after annealing at 145 °C. One-covalent-bond chains are created after annealing at 170 °C. One-covalent-bond hexagons as well as two-covalent-bond dimers are appearing on the surface after annealing at 175 °C. Annealing at 275 °C leads to the formation of a porous 2D hexagonal two-covalent-bond nanoarchitecture. STM images show that the number of intermolecular covalent bonds increases as the temperature rises, Fig.1.

Two new iodo derivatives of bis-salphen zinc complexes [salphen = N,N'-bis(salicylideneimine)-1,2diaminobenzene] have been synthesized and fully characterized. The 1 H NMR, 13 C NMR, IR, UV-Vis, TGA, elemental analysis and MALDI mass spectral data of these complexes are presented. In addition, X-Ray single crystal diffraction analysis of complex 1 has been recorded. These two compounds present a great potential interest for generating 2D covalent organic nanoarchitecture. (C) 2020 Elsevier B.V. All rights reserved.

We present a successful strategy to obtain a self-assembled material stabilized by halogen bonding with enhanced mechanochromic aggregation-induced emission (AIE). The meta-bromophenyl-substituted tetraphenylethene fluorophore (m-BrTBE) exhibits an emission which is more red-shifted compared to the phenyl-ring-substituted tetraphenylethene fluorophore (TBE) in film. Remarkably, m-BrTBE molecules self-assemble into uniform ball-like aggregates with high photoluminescence quantum yield up to 85.3 %, which indicates that the molecular conformation and intermolecular interactions are different from those in the crystalline state. Based on single-crystal analysis, scanning tunneling microscopic observations, and theoretical calculations, the unusual self-assembly enhanced AIE behavior is attributed to the important effect of meta-bromide substituents which not only form intermolecular Br...pi halogen bonding and H...Br hydrogen bonding interactions to block nonradiative relaxation pathways effectively but also promote radiative processes.

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.

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.