Kunal Mali

KU Leuven | ku leuven · Department of Chemistry

Nanoporous supramolecular networks physisorbed on solid surfaces have been extensively used to immobilize a variety of guest molecules. Host-guest chemistry in such two-dimensional (2D) porous networks is a rapidly expanding field due to potential applications in separation technology, catalysis and nanoscale patterning. Diverse structural topologi...

A dominant theme within the research on two-dimensional chirality is the sergeant–soldiers principle, wherein a small fraction of chiral molecules (sergeants) is used to skew the handedness of achiral molecules (soldiers) to generate a homochiral surface. Here, we have combined the sergeant–soldiers principle with temperature-dependent molecular se...

Dynamically switchable supramolecular systems offer exciting possibilities in building smart surfaces, the structure and thus the function of which can be controlled by using external stimuli. Here we demonstrate an elegant approach where the guest binding ability of a supramolecular surface can be controlled by inducing structural transitions in i...

The ‘graphene rush’ that started almost a decade ago is far from over. The dazzling properties of graphene have long warranted a number of applications in various domains of science and technology. Harnessing the exceptional properties of graphene for practical applications however has proved to be a massive task. Apart from the challenges associat...

Two-dimensional (2D) crystallization on solid surfaces is governed by a subtle balance of supramolecular and interfacial interactions. However, these subtle interactions often make the prediction of supramolecular structure from the molecular structure impossible. As a consequence, surface-based 2D crystallization has often been studied on a case-b...

We report on the fast reaction kinetics of an imine based 2D polymer (2DP) formed from a single monomer carrying both aldehyde and amine groups. Our results point towards a direct monomer-to-crystalline polymer transition without an amorphous intermediate.

Chemical patterning surfaces is relevant in several different domains of science and technology with exciting possibilities in electronics, catalysis, sensing, and photonics. Here, we present a novel strategy for chemical patterning of graphite using a combination of covalent and non-covalent approaches. Building on our previous work, where self-as...

Tetrathiafulvalene is among the most well-known building block in molecular electronics due to its outstanding electron-donating and redox properties. Among its derivatives, dithiophene-tetrathiafulvalene (DT-TTF) received a lot of interest for organic electronics due to its high charge mobility. Herein we report the direct C-H arylation of DT-TTF...

Graphene, a single layer of carbon atoms in a two-dimensional (2D) hexagonal lattice, showcases key properties suitable for electrode materials such as high specific surface area, good electrical and thermal conductivities. ¹ Ionic liquids (ILs) are a class of molten salts that are entirely composed of ions. These liquids possess exceptional proper...

The chemistry of carbon surfaces has regained traction in recent years in view of its applicability towards covalent modification of a variety of (2D) materials. A general requisite is the formation of a dense and well-defined monolayer of aryl groups covalently bound to the surface. Given the use of reactive chemistries however, it is often not ea...

Covalent functionalization of graphene is highly sought after, not only in view of the potential applications of the chemically modified material, but also because it brings fundamental insight into the chemistry of graphene. Thus, strategies that yield chemically modified graphene with densely grafted films of aryl groups via simple experimental p...

Molecular flip‐flop: By pulsing the tip voltage in a scanning tunneling microscope, individual molecules in a monolayer of a polyaromatic salt can be switched reversibly from a bright (0) to a dark (1) state, at room temperature and outside of a vacuum. The information density of this single‐molecule binary memory can reach up to 41 terabits per cm...

We report a molecular dipole that self‐assembles into highly ordered patterns at the liquid–solid interface and that can be switched at room temperature between a bright and a dark state at the single molecule level. Using a scanning tunnelling microscope (STM) under suitable bias conditions, we can write binary information at a density of up to 41...

The self-assembly of an asymmetric perylene diimide (PDI) with a dove-tailed side chain is investigated after thermal annealing at various temperatures in solid-state. After annealing at low temperatures PDI dimers are formed through hydrogen bonding between the imide and carbonyl groups, together with π–stacking interactions leading to a helical p...

Synthetic two-dimensional polymers (2DPs) obtained from well-defined monomers via bottom-up fabrication strategies are promising materials that can extend the realm of inorganic 2D materials. The on-surface synthesis of such 2DPs is particularly popular, however the pathway complexity in the growth of such films formed on solid surfaces is poorly u...

Halogen bonds, which provide an intermolecular interaction with moderate strength and high directionality, have emerged as a promising tool in the repertoire of non‐covalent interactions. In this review, we provide a survey of the literature where halogen bonding was used for the fabrication of supramolecular networks on solid surfaces. The definit...

Graphene-based two-dimensional (2D) materials are promising candidates for a number of different energy applications. A particularly interesting one is in next generation supercapacitors, where graphene is being explored as an electrode material in combination with room temperature ionic liquids (ILs) as electrolytes. Because the amount of energy t...

Halogen bonding has emerged as a promising tool in two-dimensional (2D) crystal engineering. Since halogen bonds are similar to hydrogen bonds in a number of aspects, the existing knowledge of hydrogen bonded systems can be applied to halogenated systems. Here we evaluate the applicability of a retrosynthetic approach based on topological similarit...

Two unprecedented porphyrin fused nanographene molecules 1 and 2 have been synthesized by Scholl reaction of tailor‐made precursors based on benzo[m]tetraphene‐substituted porphyrins. The chemical structures were validated by a combination of high‐resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HR MALDI‐TOF...

Two unprecedented porphyrin fused nanographene molecules 1 and 2 have been synthesized by Scholl reaction of tailor‐made precursors based on benzo[m]tetraphene‐substituted porphyrins. The chemical structures were validated by a combination of high‐resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HR MALDI‐TOF...

Strong electric fields are known to influence the properties of molecules as well as materials. Here we show that by changing the orientation of an externally applied electric field, one can locally control the mixing behavior of two molecules physisorbed on a solid surface. Whether the starting two-component network evolves into an ordered two-dim...

The performance of organic nanostructures is closely related to the organization of the functional molecules. Frequently, molecular chirality plays a central role in the way molecules assemble at the supramolecular level. Herein we report the hierarchical self-assembly of benzo-fused tetrathia[7]helicenes on solid surfaces, from a single surface-bo...

Ionic self-assembly of charged molecular building blocks relies on the interplay between long-range electrostatic forces and short-range, often cooperative, supramolecular interactions, yet has been seldom studied in two dimensions at the solid–liquid interface. Here, we demonstrate anion-driven switching of two-dimensional (2D) crystal structure a...

The application of supramolecular chemistry on solid surfaces represents an exciting field of research that continues to develop in new and unexpected directions. This review highlights recent advances in the field which range from the fundamental aspects of the thermodynamics of self-assembly through to the development of new materials with potent...

Recent advances in bottom-up synthesis of atomically defined graphene nanoribbons (GNRs) with various microstructures and properties have demonstrated their promise in electronic and optoelectronic devices. Here we synthesize N = 9 armchair graphene nanoribbons (9-AGNRs) with a low optical bandgap of ~1.0 eV and extended absorption into the infrare...

We report on the design and fabrication of a four-component supramolecular network using the 'core-shell' approach. Each 'core' component templates the formation of an outer 'shell' leading to formation of three concentric 'shells' around the central guest. The 'shells' are formed only in presence of guests thus demonstrating remarkable selectivity...

One current key challenge in graphene research is to tune its charge carrier concentration, i.e., p- and n-type doping of graphene. An attractive approach in this respect is offered by controlled doping via well-ordered self-assembled networks physisorbed on the graphene surface. We report on tunable n-type doping of graphene using self-assembled n...

The degree of order of poly(3-alkylthiophene)s on atomically flat surfaces is strongly influenced by interchain interactions. Regularly ordered, disordered and amorphous microstructures are observed for achiral, homochiral and meso poly(3-alkylthiophene)s, respectively, as revealed by scanning tunneling microscopy.

Two-dimensional supramolecular chirality is often achieved by confining molecules against a solid surface. The sergeants-soldiers principle is a popular strategy to fabricate chiral surfaces using predominantly achiral molecules. In this method, achiral molecules (the soldiers) are forced to assemble in a chiral fashion by mixing them with a small...

A multistep synthesis of hexa-peri-hexabenzocoronene (HBC) with four additional K-regions was developed through a precursor based on two benzotetraphene units bridged with p-phenylene, featuring pre-installed zigzag moieties. Characterization by laser desorption/ionization time-of-flight mass spectrometry, Raman and IR spectroscopy, and scanning tu...

Molecular self-assembly at the solid–liquid interface is highly developed, yet still faces several challenges, in particular related to reaching into the third dimension. Here, we demonstrate the spontaneous and reversible transition between two- and three-dimensional self-assembly of a charged polyaromatic molecule at the solid–liquid interface un...

A series of novel toroidal cyclo-2,9-tris-1,10-phenanthroline macrocycles with an unusual hexaaza cavity are reported. Nickel-mediated Yamamoto aryl-aryl coupling was found to be a versatile tool for the cyclotrimerization of functionalized 1,10-phenathroline precursors. Due to the now improved processability, both liquid-crystalline behavior in th...

Formation of multiple polymorphs during two-dimensional (2D) crystallization of organic molecules is more of a routine occurrence than rarity. Although such diverse crystalline structures provide exciting possibilities for studying crystal engineering in 2D, predicting the occurrence of polymorphs for a given building block is often non-trivial. Mo...

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...

Structurally defined, long (>100 nm), and low-band-gap (∼1.2 eV) graphene nanoribbons (GNRs) were synthesized through a bottom-up approach, enabling GNRs with a broad absorption spanning into the near-infrared (NIR) region. The chemical identity of GNRs was validated by IR, Raman, solid-state NMR, and UV-vis-NIR absorption spectroscopy. Atomic forc...

We demonstrate the spontaneous and reversible transition between the two- and three-dimensional self-assembly of a supramolecular system at the solid–liquid interface under electrochemical conditions, using in situ scanning tunneling microscopy. By tuning the interfacial potential, we can selectively organize our target molecules in an open porous...

Wir zeigen mithilfe der Rastertunnelmikroskopie den spontanen und reversiblen Übergang zwischen zwei- und dreidimensionaler Selbstorganisation eines supramolekularen Systems an der Grenzflche zwischen Flüssigkeit und Metalloberflche unter elektrochemischer Kontrolle. Durch Abstimmen des Grenzflchenpotentials können wir unsere Zielmoleküle selektiv...

Using in situ electrochemical scanning tunnelling microscopy (EC-STM), we demonstrate fully reversible tuning of molecular tiling between self-assembled structures with supramolecular motifs containing 2, 3, 4, 6 or 7 tectons. The structures can be explained by electrocompression of the cationic adlayer at the solid-liquid interface.

Controlling crystal polymorphism constitutes a formidable challenge in contemporary chemistry. Two-dimensional (2D) crystals often provide model systems to decipher the complications in 3D crystals. In this contribution, we explore a unique way of governing 2D polymorphism at the organic liquid-solid interface. We demonstrate that a directional sol...

Nanostructured molecular thin films adsorbed on solid surfaces form the basis of numerous applications. Long-range order within adsorbed molecules is very often a desirable property for such systems. In this contribution, we report a simple and efficient method to fabricate well-aligned thin films of organic molecules over a few millimeter squares....

The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas 'top-down' methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a 'bottom-up' organic synthesis appro...

Functionalization and modification of graphene at the nanometer scale is desirable for many applications. Supramolecular assembly offers an attractive approach in this regard, as many organic molecules form well-defined patterns on surfaces such as graphite via physisorption. Here we show that ordered porous supramolecular networks with different p...

Ligand-protected gold nanoparticles exhibit large local curvatures, features rapidly varying over small scales, and chemical heterogeneity. Their imaging by Scanning Tunneling Microscopy (STM) can, in principle, provide direct information on the architecture of their ligand shell, yet STM images require laborious analysis and are challenging to be...

Self-assembled physisorbed monolayers consist of regular two-dimensional arrays of molecules. Two-dimensional self-assembly of organic and metal-organic building blocks is a widely used strategy for nanoscale functionalization of surfaces. These supramolecular nanostructures are typically sustained by weak non-covalent forces such as van der Waals,...

Ligand-protected gold nanoparticles exhibit large local curvatures, features rapidly varying over small scales, and chemical heterogeneity. Their imaging by Scanning Tunneling Microscopy (STM) can, in principle, provide direct information on the architecture of their ligand shell, yet STM images require laborious analysis and are challenging to be...

In this work, we provide evidence for multiple non-planar adsorption geometries of a novel pyrenocyanine derivative at the liquid-solid interface under ambient conditions. When adsorbed at the organic liquid-solid interface, lead pyrenocyanine forms well-ordered monolayers that exhibit peculiar non-periodic contrast variation. The different contras...

Gold nanoparticles protected by a binary mixture of thiolate molecules have a ligand shell that can spontaneously separate into nanoscale domains. Complex morphologies arise in such ligand shells, including striped, patchy, and Janus domains. Characterization of these morphologies remains a challenge. Scanning tunneling microscopy (STM) imaging has...

Longest planar rylene dyes hexarylene diimide (HDI) and octarylene diimide (ODI), with extended conjugated cores (2.8 and 3.7 nm in length) have been prepared by a facile syntheses. Both HDI and ODI exhibit broad and intense NIR absorption. Scanning tunneling microscopy (STM) study reveals that HDI forms ordered herringbone bilayer or multilayers w...

Long and planar: Facile syntheses of soluble hexarylene diimides (HDI) and octarylene diimides (ODI) are described. They are stable in both solution and the solid state, and exhibit broad and intense NIR absorption. Scanning tunneling microscopy (STM) reveals that HDI, after deposition from solution, forms a unique herringbone bilayer or stable mul...

We report the synthesis, characterization, and self-assembly of a new gemini-type amphiphilic hexathienocoronene (HTCGemini), which owes its amphiphilicity to two hydrophobic dodecyl chains on one side of the HTC core and two hydrophilic triethylene glycol (TEG) chains on the other. Bearing a “softer” aromatic HTC core than the conventional hexa-pe...

Understanding and controlling the structural polymorphism in self-assembled networks of functional molecules merit special attention. In this contribution, we describe the concentration controlled structural evolution in self-assembled monolayers of a large triangular discotic macrocycle at the liquid-solid interface. Scanning tunneling microscopy...

Controlling the molecular conformation of oligomers on surfaces through noncovalent interactions symbolizes an important approach in the bottom-up patterning of surfaces with nanoscale precision. Here we report on the design, synthesis, and scanning tunneling microscopy (STM) investigation of linear oligoamides adsorbed at the liquid-solid interfac...

A good sort: A racemate is observed to segregate in situ upon diastereoselective adsorption on an achiral surface by surface-mediated complex formation in a liquid (see picture; yellow: enantiopure resolving agents, ovals: the enantiomers of the racemate to be resolved).

Induction of chirality in achiral monolayers has garnered considerable attention in the recent past not only due to its importance in chiral resolutions and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. In this contribution, we demonstrate emergence of macroscopic chirality in por...

Oxidative cyclodehydrogenation of laterally extended polyphenylene precursor allowed bottom-up synthesis of structurally defined graphene nanoribbons (GNRs) with unprecedented width. The efficiency of the cyclodehydrogenation was validated by means of MALDI-TOF MS, FT-IR, Raman, and UV-vis absorption spectroscopies as well as investigation of a rep...

The objective of this chapter is to provide a brief account of the progress in the understanding of physisorbed monolayers through illustration of some key examples from contemporary literature. The discussion is limited to the self-assembly of weakly adsorbed molecules at the liquid–solid interface as studied by scanning probe microscopy methods,...

The use of self-assembly to fabricate surface-confined adsorbed layers (adlayers) from molecular components provides a simple means of producing complex functional surfaces. The molecular self-assembly process relies on supramolecular interactions sustained by noncovalent forces such as van der Waals, electrostatic, dipole–dipole, and hydrogen bond...

Pyrene-fused tetraazaporphyrins were synthesized from pyrene-4,5-dicarbonitrile precursors using a recently reported procedure as the key step for the asymmetric substitution of pyrene. Metal-free, zinc- and lead-centered pyrenocyanines were obtained and their optical properties as well as their molecular assembly in the solution and bulk phases an...

The liquid/solid interface provides an interesting medium for molecular self-assembly and scanning tunneling microscopy is the preferred technique to analyse the structural features of the surface-supported self-assembled monolayers in this medium. An interesting aspect is the phenomenon of molecular dynamics at the liquid/solid interface. In this...

Physisorbed monolayers based on relatively weak noncovalent interactions can serve as excellent model systems for understanding crystallization of materials in reduced dimensionality. Here we employ a powerful combination of scanning tunneling microscopy (STM), differential scanning calorimetry (DSC), and computational modeling to reveal two-dimens...

We report on the observation and manipulation of a two-dimensional crystal formed by a positively charged discotic polycyclic aromatic hydrocarbon at the liquid-solid interface. Using scanning tunneling microscopy (STM) as a tool, the supramolecular scaffolds of charged molecules could be switched between dissimilar polymorphs of different molecula...

The structures of the self-assembled monolayers of various 4-alkoxybenzoic acids physisorbed at the liquid-solid interface were established by employing scanning tunnelling mi