Leo Gross

• PhD
• research staff member at IBM

Engineering sublattice imbalance is an intuitive way to induce high-spin ground states in bipartite polycyclic conjugated hydrocarbons (PCHs). Such molecules can be employed as building blocks of quantum spin chains, which are outstanding platforms to study fundamental models in quantum magnetism. This is exemplified by recent reports on the bottom...

The appearance of frontier molecular ion resonances measured with scanning tunneling microscopy (STM)—often referred to as orbital density images—of single molecules was investigated using a CO-functionalized tip in dependence on bias voltage and tip–sample distance. As model systems, we studied pentacene and naphthalocyanine on bilayer NaCl on Cu(...

Engineering sublattice imbalance is an intuitive way to induce high-spin ground states in bipartite polycyclic conjugated hydrocarbons (PCHs). Such high-spin molecules can be employed as building blocks of quantum spin chains, which are outstanding platforms to study many-body physics and fundamental models in quantum magnetism. Recent reports on t...

An increasing number of scanning-probe-based spectroscopic techniques provides access to diverse electronic properties of single molecules. Typically, these experiments can only study a subset of all electronic transitions, which obscures the unambiguous assignment of measured quantities to specific quantum transitions. Here we develop a single-mol...

We report the generation of a nonbenzenoid polycyclic conjugated hydrocarbon, which consists of a biphenyl moiety substituted by indenyl units at the 4,4′ positions, on ultrathin sodium chloride films by tip-induced chemistry. Single-molecule characterization by scanning tunneling and atomic force microscopy reveals an open-shell biradical ground s...

Molecular rings of N carbon atoms (cyclo[ N ]carbons, or C N ) are excellent benchmarking systems for testing quantum chemical theoretical methods and valuable precursors to other carbon-rich materials. Odd- N cyclocarbons, which have been elusive to date, are predicted to be even less stable than even- N cyclocarbons. We report the on-surface synt...

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in nonlinear optics and photovoltaics. Here we report the generation of unsubstituted indeno[1,2-a]fluorene on various surfaces by the cleavage of two C–H bonds in 7,12-dihydroindeno[1,2-...

Aromaticity is typically regarded as an intrinsic property of a molecule, correlated with electron delocalization, stability, and other properties. Small variations in the molecular geometry usually result in small changes in aromaticity, in line with Hammond’s postulate. For example, introducing bond-length alternation in benzene and square cyclob...

Synthetic carbon allotropes such as graphene ¹ , carbon nanotubes ² and fullerenes ³ have revolutionized materials science and led to new technologies. Many hypothetical carbon allotropes have been discussed ⁴ , but few have been studied experimentally. Recently, unconventional synthetic strategies such as dynamic covalent chemistry ⁵ and on-surfac...

Aromaticity is typically regarded as an in-trinsic property of a molecule. It is often correlated with electron delocalization, stability, and other properties. Small variations in the molecular geometry usually result in small changes in aromaticity, in line with Hammond’s postu-late: for example, introducing bond-length alternation in benzene and...

Aromaticity, most commonly defined as the ability to sustain a diatropic ring current, is typically regarded as an in-trinsic property of a molecule. It is often correlated with electron delocalization, stability, and other properties. Small variations in the molecular geometry usually result in small changes in aromaticity, in line with Hammond’s...

In molecular tunnel junctions, where the molecule is decoupled from the electrodes by few-monolayers-thin insulating layers, resonant charge transport takes place by sequential charge transfer to and from the molecule which implies transient charging of the molecule. The corresponding charge state transitions, which involve tunneling through the in...

Incipient soot early in the flame was studied by high-resolution atomic force microscopy and scanning tunneling microscopy to resolve the atomic structure and orbital densities of single soot molecules prepared on bilayer NaCl on Cu(111). We resolved extended catacondensed and pentagonal-ring linked (pentalinked) species indicating how small aromat...

The synthetic carbon allotropes graphene, carbon nanotubes and fullerenes have revolutionised materials science and led to new technologies. Recently, unconventional synthetic strategies such as dynamic covalent chemistry and on-surface synthesis have been used to create new forms of carbon, including γ-graphyne, covalent fullerene polymers, and bi...

Cyclocarbons are rings of carbon atoms, often formed as gas-phase carbon clusters. The only cyclocarbons yet to be well characterized are C10 and C18, which are doubly aromatic with 4n+2 carbon atoms (where n is an integer), resulting in enhanced thermodynamic stability. Cyclocarbons with 4n atoms have been predicted to be less stable and doubly an...

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in non-linear optics and photovoltaics. Here, we report the generation of unsubstituted indeno[1,2-a]fluorene, the final and yet unreported parent indenofluorene regioisomer, on various s...

In scanning tunneling microscopy (STM) experiments of molecules on insulating films, tunneling through molecular resonances implies transiently charging the molecule. The transition back to the charge ground state by tunneling through the insulating film is crucial, for example, for understanding STM-induced electroluminescence. Here, using STM, we...

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied vo...

Controlling selectivity of reactions is a quest in chemistry. Here, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from...

Asphaltenes are complex chemical mixtures which represent a solubility fraction of crude oil and of carbonaceous materials, typically defined as toluene soluble and n-heptane insoluble. Almost every chemical attribute of asphaltenes has been the subject of significant literature debate, especially asphaltene molecular weight. This debate was resolv...

Ring-forming reactions are at the heart of organic synthesis. Now, phenylene rings are synthesized from two isopropyl moieties on a gold surface. Resolving the intermediates of this (3+3) cycloaromatization reaction with atomic force microscopy offers mechanistic insight into the dimerization process.

We report the on-surface synthesis of a nonbenzenoid triradical through dehydrogenation of truxene (C27H18) on coinage metal and insulator surfaces. Voltage pulses applied via the tip of a combined scanning tunneling microscope/atomic force microscope were used to cleave individual C-H bonds in truxene. The resultant final product truxene-5,10,15-t...

Using high‐resolution atomic force microscopy (AFM) with CO‐functionalized tips, we atomically resolved individual molecules from Murchison meteorite samples. We analyzed powdered Murchison meteorite material directly, as well as processed extracts that we prepared to facilitate characterization by AFM. From the untreated Murchison sample, we resol...

We report the on-surface synthesis of a non-benzenoid triradical through dehydrogenation of truxene (C27H18) on coinage metal and insulator surfaces. Voltage pulses applied via the tip of a combined scanning tunneling microscope/atomic force microscope were used to cleave individual C-H bonds in truxene. The resultant final product truxene-5,10,15-...

The Diels–Alder reaction is one of the most popular reactions in organic chemistry. However, its use in the field of on‐surface synthesis is hampered by the spatial restrictions of this cycloaddition reaction. Herein we selected a cyclic strained triyne to demonstrate an on‐surface hexadehydro‐Diels–Alder reaction in a single molecule. The reaction...

The Diels‐Alder reaction is one of the most popular reactions in organic chemistry. However, its use in the field of on‐surface synthesis is hampered by the spatial restrictions of this cycloaddition reaction. Herein we selected a cyclic strained triyne to demonstrate an on‐surface hexadehydro‐Diels‐Alder reaction in a single molecule. The reaction...

Soot emitted from incomplete combustion of hydrocarbon fuels contributes to global warming and causes human disease. The mechanism by which soot nanoparticles form within hydrocarbon flames is still an unsolved problem in combustion science. Mechanisms proposed to date involving purely chemical growth are limited by slow reaction rates, whereas mec...

The nonequilibrium triplet state of molecules plays an important role in photocatalysis, organic photovoltaics, and photodynamic therapy. We report the direct measurement of the triplet lifetime of an individual pentacene molecule on an insulating surface with atomic resolution by introducing an electronic pump-probe method in atomic force microsco...

By employing single charge injections with an atomic force microscope, we investigated redox reactions of a molecule on a multilayer insulating film. First, we charged the molecule positively by attaching a single hole. Then we neutralized it by attaching an electron and observed three channels for the neutralization. We rationalize that the three...

Titan, Saturn's largest moon, has its atmosphere filled with a thick organic photochemical haze. These suspended solid nanoparticles are one of the most complex organic materials in the Solar System. In situ measurements from the successful Cassini space mission gave first clues on the aerosol's chemical composition: Pyrolysis coupled to mass spect...

The initial thermal reactions of aromatic hydrocarbons are relevant to many industrial applications. However, tracking the growing number of heavy polycyclic aromatic hydrocarbon (PAH) products is extremely challenging because many reactions are unfolding in parallel from a mixture of molecules. Herein, we studied the reactions of 2,7-dimethylpyren...

The initial thermal reactions of aromatic hydrocarbons are relevant to many industrial applications. However, tracking the growing number of heavy polycyclic aromatic hydrocarbon (PAH) products is extremely challenging because many reactions are unfolding in parallel from a mixture of molecules. Herein, we studied the reactions of 2,7-dimethylpyren...

The initial thermal reactions of aromatic hydrocarbons are relevant to many industrial applications. However, tracking the growing number of heavy polycyclic aromatic hydrocarbon (PAH) products is extremely challenging because many reactions are unfolding in parallel from a mixture of molecules. Herein, we studied the reactions of 2,7-dimethylpyren...

By employing single charge injections with an atomic force microscope, we investigated redox reactions of a molecule on a multilayer insulating film. First, we charged the molecule positively by attaching a single hole. Then we neutralized it by attaching an electron and observed three channels for the neutralization. We rationalize that the three...

Glaser‐like coupling of terminal alkynes by thermal activation is extensively used in on‐surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser‐like coupling between terminal alkyne carbons within a custom‐synthesized precursor molecul...

Glaser-like coupling of terminal alkynes by thermal activation is extensively used in on-surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser-like coupling between terminal alkyne carbons within a custom synthesized precursor molecul...

We demonstrated a Glaser‐like coupling reaction by atom manipulation. The intramolecular reaction was performed within a single molecule, facilitated by the design of the precursor molecule. By using high‐resolution atomic force microscopy, we revealed precursors, intermediates and products. Resolving and manipulating the positions of individual hy...

Cyclo[18]carbon (C18, a molecular carbon allotrope) can be synthesized by dehalogenation of a bromocyclocarbon precursor, C18Br6, in 64% yield, by atomic manipulation on a sodium chloride bilayer on Cu(111) at 5 K, and imaged by high-resolution atomic force microscopy. This method of generating C18 gives a higher yield than that reported previously...

Previously, asphaltene science had been saddled with many significant uncertainties regarding molecular weight, molecular structure, and nanocolloidal characteristics in laboratory solvents and in crude oils. These debates were of sufficient magnitude to forestall development and utility of asphaltene modeling for various applications. In the last...

Continuously improving precision in length measurements increases understanding of our world and its phenomena, both at small and large scales, as Leo Gross reveals.

Four decades after the first (and only) reported synthesis of kekulene, this emblematic cycloarene has been obtained again through an improved route involving the construction of a key synthetic intermediate, 5,6,8,9-tetrahydrobenzo[m]tetraphene, by means of a double Diels-Alder reaction between styrene and a versatile benzodiyne synthon. Ultrahigh...

Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[n]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized, due to their high reactivity. We generated cyclo[18]carbon (C18) using atom manipulation on bilayer NaCl on Cu(111) at 5 Kelvin by eliminating carbon m...

Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[ n ]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized, due to their high reactivity. We generated cyclo[18]carbon (C 18 ) using atom manipulation on bilayer NaCl on Cu(111) at 5 Kelvin by eliminating carb...

Intramolecular structural relaxations occurring upon electron transfer are crucial in determining the rate of redox reactions. Here, we demonstrate that subangstrom structural changes occurring upon single-electron charging can be quantified by means of atomically resolved atomic force microscopy (AFM) for the case of single copper(II)phthalocyanin...

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity and aromaticity, with implications for on-surface synthesis, catalysis, photo conversion and applications in molecular electronics. On insulating, multilayer NaCl films we control the charge state of organic molecules and resolve their structures...

Visualizing molecular charging High-resolution atomic force microscopy (AFM) has been used to control and image the charge state of organic molecules adsorbed on multilayer sodium chloride films. Fatayer et al. biased an AFM probe tip with a voltage to charge and discharge molecules such as azobenzene and porphine from cations to anions. Subsequent...

Determination of the molecular structures of petroporphyrins has been crucial to understand the diagenetic pathways and maturation of petroleum. However, these studies have been hampered by their structural complexity and the challenges associated with their isolation. Compared to the skeletal macrocyclic structures, much less is known about the su...

Atomic force microscopy (AFM) as well as scanning tunneling microscopy induced light emission (STM-LE) are, each on their own, powerful tools to investigate a large variety of properties of single molecules adsorbed on a surface. Yet, accessing both structural information by AFM as well as optical information by STM-LE on the same molecule so far r...

A route to generate cyclacenes by on‐surface synthesis is explored. We started by synthesizing two tetraepoxycyclacenes by sequences of Diels–Alder cycloadditions. Subsequently, these molecules were deposited onto Cu(111) and scanning‐tunneling‐microscopy(STM)‐based atom manipulation was employed to dissociate the oxygen atoms. Atomic force microsc...

A route to generate the thus far elusive cyclacenes by on‐surface synthesis is explored. We started by synthesizing two tetraepoxycyclacenes by sequences of Diels‐Alder cycloadditions. Subsequently, these molecules were deposited onto Cu(111) and scanning tunnelling microscopy (STM)‐based atom manipulation was employed to dissociate the oxygen atom...

The early stages of soot formation, namely inception and growth, are highly debated and central to many ongoing studies in combustion research. Here, we provide new insights into these processes from studying different soot samples by atomic force microscopy (AFM). Soot has been extracted from a slightly sooting, premixed ethylene/air flame both at...

By atom manipulation we performed on-surface chemical reactions of a single molecule on a multilayer insulating film using noncontact atomic force microscopy. The single-electron sensitivity of atomic force microscopy allows us to follow the addition of single electrons to the molecule and the investigation of the reaction products. By performing a...

This study addresses the effect of sample preparation conditions on the structural integrity and composition of heavy hydrocarbon mixtures imaged by non-contact atomic force microscopy (nc-AFM). We designed and prepared a set of organic molecules mimicking well-accepted key characteristics of heavy oil asphaltenes including molecular architecture,...

This study addresses the effect of sample preparation conditions on the structural integrity and composition of heavy hydrocarbon mixtures imaged by non-contact atomic force microscopy (nc-AFM). We designed and prepared a set of organic molecules mimicking well-accepted key characteristics of heavy oil asphaltenes including molecular architecture,...

The synthesis of a threefold symmetric nanographene with 19 cata‐fused benzene rings distributed within six branches is reported. This flat dendritic starphene, which is the largest unsubstituted cata‐condensed PAH that has been obtained to date, was prepared in solution by means of a palladium‐catalyzed aryne cyclotrimerization reaction and it was...

Rearrangements that change the connectivity of a carbon skeleton are often useful in synthesis, but it can be difficult to follow their mechanisms. Scanning probe microscopy can be used to manipulate a skeletal rearrangement at the single-molecule level, while monitoring the geometry of reactants, intermediates and final products with atomic resolu...

Combustion-generated soot particles can have significant impact on climate, environment and human health. Thus, understanding the processes governing the formation of soot particles in combustion is a topic of ongoing research. In this study, high-resolution atomic force microscopy (AFM) was used for direct imaging of the building-blocks forming th...

Here we present a new method that integrates atomic force microscopy (AFM) with analytical tools such as high-performance liquid chromatography (HPLC) with diode-array ultraviolet-visible (UV) absorbance and mass spectrometry (MS) along with synthetic chemistry. This allows the detection, identification, and quantification of novel polycyclic aroma...

Dissolved organic carbon (DOC) is the largest pool of exchangeable organic carbon in the ocean. However, less than 10% of DOC has been molecularly characterized in the deep ocean to understand DOC’s recalcitrance. Here we analyze the radiocarbon (14C) depleted, and presumably refractory, low molecular weight (LMW) DOC from the North Central Pacific...

Intermolecular single-electron transfer on electrically insulating films is a key process in molecular electronics1-4 and an important example of a redox reaction5,6. Electron-transfer rates in molecular systems depend on a few fundamental parameters, such as interadsorbate distance, temperature and, in particular, the Marcus reorganization energy...

Antiaromatic and open-shell molecules are attractive because of their distinct electronic and magnetic behaviour. However, their increased reactivity creates a challenge for probing their properties. Here, we describe the on-surface and in-solution generation and characterisation of a highly reactive antiaromatic molecule: indeno[1,2-b]fluorene (IF...

In this chapter, we illustrate the great potential of combining organic synthesis with atomic resolution AFM and STM to address relevant and classic issues in chemistry, by summarizing selected examples in which we were involved in recent years. As case studies, the long-standing chemical challenges covered here include the experimental discriminat...

Using scanning probe microscopy techniques, at low temperatures and in ultrahigh vacuum, individual molecules adsorbed on surfaces can be probed with ultrahigh resolution to determine their structure and details of their conformation, configuration, charge states, aromaticity, and the contributions of resonance structures. Functionalizing the tip o...

Mit der Rastersondenmikroskopie kann man auf einer Oberfläche adsorbierte Moleküle individuell und mit hoher Auflösung untersuchen. Die Technik, die bei tiefen Temperaturen und im Ultrahochvakuum durchgeführt wird, liefert Informationen über Struktur, Konfiguration, Ladungszustand, Aromatizität und die Beteiligung von Resonanzstrukturen. Durch Funk...

Sequential tunneling of electrons through a single chlorine vacancy on a multilayer NaCl film on Cu(100) in the junction of a non-contact atomic force microscope with a conductive tip can lead to a negative damping of the cantilever. The characteristic features in the damping signal as a function of NaCl-layer thickness, tip position and tip-sample...

We describe the generation of a meta-aryne at low temperature (T = 5 K) using atomic manipulation on Cu(111) and on bilayer NaCl on Cu(111). We observe different voltage thresholds for dehalogenation of the precursor and different reaction products depending on the substrate surface. The chemical structure is resolved by atomic force microscopy wit...

Using combined low temperature scanning tunneling microscopy and atomic force microscopy (AFM), we demonstrate hydrogen passivation of individual, selected dangling bonds (DBs) on a hydrogen-passivated Si(100)-2 × 1 surface (H–Si) by atom manipulation. This method allows erasing of DBs and thus provides a promising scheme for error-correction in hy...

Heavy oil molecular mixtures were investigated on the basis of single molecules resolved by atomic force microscopy. The eight different samples analyzed include asphaltenes and other heavy oil fractions of different geographic/geologic origin and processing steps applied. The collected AFM data of individual molecules provide information about the...

Using combined low temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM), we demonstrate hydrogen passivation of individual, selected dangling bonds (DBs) on a hydrogen-passivated Si(100)-2$\times$1 surface (H-Si) by atom manipulation. This method allows erasing of DBs and thus provides an error-correction scheme for hyd...

Si dangling bonds without H termination at the interface of quasi-free standing monolayer graphene (QFMLG) are known scattering centers that can severely affect carrier mobility. In this report, we study the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atom...

Si dangling bonds without H termination at the interface of quasi-free standing monolayer graphene (QFMLG) are known scattering centers that can severely affect carrier mobility. In this report, we study the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atom...

C60-functionalized tips are used to probe C60 molecules on Cu(111) with scanning tunneling and atomic force microscopy. Distinct and complex intramolecular contrasts are found. Maximal attractive forces are observed when for both molecules a [6,6] bond faces a hexagon of the other molecule. Density functional theory calculations including parameter...

Triangulene, the smallest triplet-ground-state polybenzenoid (also known as Clar’s hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized. Despite containing an even number of carbons (22, in six fused benzene rings), it is not possible to draw Kekulé-style resonant structures for the whole molecule: any attemp...

Using atomic manipulation, one can dissociate, form and rearrange bonds, as well as alter the conformation or charge state of molecules. The molecular structures of reactants, intermediates and products are revealed at unprecedented resolution by using atomic force microscopy (AFM) and a suitably functionalized tip. Our present capabilities of mani...

We designed and studied hydrocarbon model compounds by high-resolution noncontact atomic force microscopy. In addition to planar polycyclic aromatic moieties, these novel model compounds feature linear alkyl and cycloaliphatic motifs that exist in most hydrocarbon resources – particularly in petroleum asphaltenes and other petroleum fractions – or...

It is known that individual metal atoms on insulating ionic films can occur in several different (meta)stable charge states, which can be reversibly switched in a controlled fashion. Here we show that the diffusion of gold adatoms on NaCl thin films depends critically on their charge state. Surprisingly, the anionic species has a lower diffusion ba...

Aiming to study new motifs, potentially active as functional materials, we performed the synthesis of a naphthodiazaborinine (the BN isostere of the phenalenyl anion) that is bonded to a hindered di-ortho-substituted aryl system (9-anthracene). We used atomic force microscopy (AFM) and succeeded in both the verification of the original nonplanar st...

We present the on-surface reduction of diepoxytetracenes to form genuine tetracene on Cu(111). The conversion is achieved by scanning tunneling microscopy (STM) tip-induced manipulation as well as thermal activation and is conclusively demonstrated by means of atomic force microscopy (AFM) with atomic resolution. We observe that the metallic surfac...

Reliability is one of the major concerns and challenges in designing organic/inorganic interfaces for (opto)electronic applications. Even small structural differences for molecules on substrates can result in a significant variation in the interface functionality, due to the strong correlation between geometry, stability and electronic structure. H...

Metal tips decorated with CO molecules have paved the way for an impressively high resolution in Atomic Force Microscopy (AFM). Although Pauli repulsion and the associated CO tilting play a dominant role at short distances, experiments on polar and metallic systems show that electrostatic interactions are necessary to understand the complex contras...

The Bergman cyclization is one of the most fascinating rearrangements in chemistry, with important implications in organic synthesis and pharmacology. Here we demonstrate a reversible Bergman cyclization for the first time. We induced the on-surface transformation of an individual aromatic diradical into a highly strained ten-membered diyne using a...

In the past, current-distance spectroscopy has been widely applied to determine variations of the work function at surfaces. While for homogeneous sample areas this technique is commonly accepted to yield at least qualitative results, its applicability to atomic-scale variations has not been proven neither right nor wrong. Here we benchmark measure...

[Formula: see text]-functionalized tips are used to probe [Formula: see text] molecules on Cu(111) with scanning tunneling and atomic force microscopy. Distinct and complex intramolecular contrasts are found. Maximal attractive forces are observed when for both molecules a [6,6] bond faces a hexagon of the other molecule. Density functional theory...

The field of molecular electronics aims at using single molecules as functional building blocks for electronics components, such as switches, rectifiers or transistors. A key challenge is to perform measurements with atomistic control over the alignment of the molecule and its contacting electrodes. Here we use atomic force microscopy to examine ch...