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Background/Context: Career and technical education (CTE) coursework in science, technology, engineering, mathematics, and medical/health (STEMM) fields has been supported by policy makers as a way to align the secondary-to-postsecondary-to-career pipeline. Yet, in the research, the focus has been on whether STEMM CTE coursetaking in high school predicts college-going or whether it predicts employment for non–college goers. Little attention has been paid to whether STEMM CTE coursetaking in high school aligns with college employment opportunities. Purpose/Objective/Research Question/Focus of Study: This study investigates the relationship between one promising educational practice—STEMM career and technical education (STEMM CTE) coursetaking—and outcomes along students’ college employment pathways. Specifically, we asked the following research questions: Does taking more STEMM CTE courses in high school link to “general” college employment outcomes? Does taking more STEMM CTE courses in high school link to “STEMM-specific” college employment outcomes? How do these relationships vary across important student subgroups, namely, those identified by the National Science Foundation as traditionally underrepresented in STEMM fields: low-income students, students with learning disabilities, women, and Black and Hispanic students? Research Design: We relied on data from the High School Longitudinal Study of 2009 (HSLS). Administered by the National Center for Education Statistics (NCES), HSLS is the most current, nationally representative data set that follows a cohort of more than 20,000 ninth-grade students across the United States throughout high school and after graduation. Our regression analyses relied on data collected during the baseline year school-level survey (2009), the high school transcript update (2013), and student-level surveys from all four data-collection waves (2009, 2012, 2013, 2016). Conclusions/Recommendations: Using these national data, we find that taking more STEMM CTE courses was associated with a higher chance of having a STEMM job during college and having higher expectations for future STEMM employment, though not with general employment outcomes such as wages. The findings were different for students from some underrepresented backgrounds in STEMM fields, and implications are discussed.

We have computationally studied the formation mechanism of the biphenylene network via the intermolecular HF zipping, as well as identified key intermediates experimentally, on the Au(111) surface. We elucidate that the zipping process consists of a series of defluorinations, dehydrogenations, and C–C coupling reactions. The Au substrate not only serves as the active site for defluorination and dehydrogenation, but also forms C–Au bonds that stabilize the defluorinated and dehydrogenated phenylene radicals, leading to "standing" benzyne groups. Despite that the C–C coupling between the "standing" benzyne groups is identified as the rate-limiting step, the limiting barrier can be reduced by the adjacent chemisorbed benzyne groups. The theoretically proposed mechanism is further supported by scanning tunneling microscopy experiments, in which the key intermediate state containing chemisorbed benzyne groups can be observed. This study provides a comprehensive understanding towards the on-surface intermolecular HF zipping, anticipated to be instructive for its future applications. Funding: Swedish Research council; Deutsche Forschungsgemeinschaft [223848855-SFB1083]; Knut and Alice Wallenberg (KAW) Foundation; Goran Gustafsson foundation; Collaborative Innovation Centre of Suzhou Nano Science Technology; Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD); 111 Project; Alexander von Humboldt-Foundation; National Natural Science Foundation of China (NSFC) [21790053, 51821002]; Ministry of Science and Technology [2017YFA0205002]; LOEWE Focus Group PriOSS

Defects play a critical role for the functionality and performance of materials, but the understanding of the related effects is often lacking, because the typically low concentrations of defects make them difficult to study. A prominent case is the topological defects in two-dimensional materials such as graphene. The performance of graphene-based (opto-)electronic devices depends critically on the properties of the graphene/metal interfaces at the contacting electrodes. The question of how these interface properties depend on the ubiquitous topological defects in graphene is of high practical relevance, but could not be answered so far. Here, we focus on the prototypical Stone–Wales (S–W) topological defect and combine theoretical analysis with experimental investigations of molecular model systems. We show that the embedded defects undergo enhanced bonding and electron transfer with a copper surface, compared to regular graphene. These findings are experimentally corroborated using molecular models, where azupyrene mimics the S–W defect, while its isomer pyrene represents the ideal graphene structure. Experimental interaction energies, electronic-structure analysis, and adsorption distance differences confirm the defect-controlled bonding quantitatively. Our study reveals the important role of defects for the electronic coupling at graphene/metal interfaces and suggests that topological defect engineering can be used for performance control.\ud \ud

We leverage nationally representative data and statewide data from Washington to investigate trends in occupational career and technical education (CTE) participation for students with and without disabilities. Consistent with prior work, we document declines in occupational CTE participation since the early 2000s, but we provide the first evidence that this decline can be explained by movement out of courses that are no longer considered CTE. Under the definitions operating at the time, though, we show that participation by students with disabilities in applied science, technology, engineering, mathematics, and medical/health (STEMM) CTE courses has increased over time, both nationally and in Washington. These trends are encouraging given prior evidence linking applied STEMM-CTE participation to better long-term outcomes for students with disabilities.

Supertetrahedral chalcogenido (semi)metalate cluster-based frameworks possess high selectivity for alkali metal cations, matching the specific charge density of their inner surfaces, which enables their use as ion-exchange materials. Aggregates of the supertetrahedral chalcogenido metalate cluster offer even new perspectives for metal ion capture and separation. Herein, we report on ionothermal preparation of two corresponding model compounds, (C$_2$C$_1$Im)$_7$[Cs@Ge$^{II}$$_4$(Ge$^{IV}$$_4$Se$_{10}$)$_4$] (1) and (C$_2$C$_1$Im)$_{10}$[Na$_5$(CN)$_6$@Cu$_6$(Ge$_4$Se$_{10}$)$_4$(Cu)] (2). Their formation is reliant on one specific cation type each, Cs$^+$ for 1 and Na$^+$ for 2, thus providing promising separation potential during crystallization. Compound 1 is based on the largest discrete binary selenido germanate cluster reported to date and the first mixed-valent chalcogenido germanate(II/IV) supertetrahedron. Moreover, it adds to the few examples of chalcogenides capable of capturing Cs$^+$ ions. Its high selectivity for Cs$^+$ compared to that of Li$^+$, Na$^+$, K$^+$, and Rb$^+$ was confirmed by single-crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, and electrospray ionization mass spectrometry. Quantum chemical studies indicate that smaller ions, K$^+$ and Rb$^+$, could also be embedded in an isolated cluster assembly, but as the cluster aggregate slightly distorts for crystallization, the selectivity for Cs$^+$ becomes exclusive in the salt. The anionic substructure of compound 2 is based on a two-dimensional network of supramolecular assemblies and exhibits an exclusive preference for Na$^+$. This work thus provides the first comprehensive insight into the selective incorporation of specific alkali metal ions into supramolecular aggregates of supertetrahedral chalcogenide clusters, as a promising basis for new ion trapping techniques─especially for heavy alkali metal ions that pose environmental challenges.

There has been a recent expansion of high school course offerings in science, technology, engineering, mathematics, and medical/health (STEMM) fields. The large span of courses now offered in STEMM are delineated across STEMM-general courses (i.e., chemistry) and STEMM-CTE courses (i.e., information technology). Little is known, however, about who are the teachers in these courses. This brief addresses this void by developing a taxonomy of the STEMM teaching workforce using statewide data from Maryland. Through this taxonomy, we examine the number of STEMM teachers by whether they teach general versus CTE STEMM courses, and whether they do so exclusively or across both types. We then examine what teaching courseloads look like across these groupings, as well as by qualifications and demographics. The aim of this brief is to understand not only the landscape of who teaches which STEMM courses, but also to identify disparities. This can help inform research on STEMM courses and teachers as well as policy, practice, and professional development.

Der Risikobegriff bezieht sich auf die Wahrscheinlichkeit eines Schadens aufgrund einer Gefährdungsexposition, in der Finanzwelt meist finanzielle Verluste. Viele Risiken der globalen Finanzwirtschaft sind unbekannt. „Wir wissen es, wenn wir es sehen“, um Potter Stewart (1964) zu paraphrasieren. Der Financial Risk Meter (FRM) soll Aufschluss über die Entstehung systemischer Risiken geben. Durch Verwendung von Quantilregressionstechniken ist der FRM nicht nur ein Maß für finanzielle Risiken. Er bietet durch seine Netzwerktopologie einen tiefen Einblick in die Spill-over-Effekte, die sich als systemische Risikoereignisse manifestieren können. Das FRM-Framework wird in verschiedenen Märkten und Regionen entwickelt. Die FRM-Daten werden für Risiko-Prognose sowie für Portfoliooptimierung genutzt. In Kapitel 1 wird der FRM vorgestellt und auf die Aktienmärkte in den USA und Europa, sowie auch auf die Zinsmärkte und Credit-Default-Swaps angewendet. Der FRM wird dann verwendet, um wirtschaftliche Rezessionen zu prognostizieren. In Kapitel 2 wird der FRM auf den Markt der Kryptowährungen angewendet, um das erste Risikomaß für diese neue Anlageklasse zu generieren. Die errechneten FRM-Daten zu Abhängigkeiten, Spillover-Effekten und Netzwerkaufbau werden dann verwendet, um Tail-Risk-optimierte Portfolios zu erstellen. Der Portfoliooptimierungsansatz wird in Kapitel 3 weitergeführt, in dem der FRM auf die sogenannten Emerging Markets (EM)-Finanzinstitute angewendet wird, mit zwei Zielen. Einerseits gibt der FRM für EM spezifische Spillover-Abhängigkeiten bei Tail-Risk-Ereignissen innerhalb von Sektoren von Finanzinstituten an, zeigt aber auch Abhängigkeiten zwischen den Ländern. Die FRM-Daten werden dann wieder mit Portfoliomanagementansätzen kombiniert. In Kapitel 4 entwickelt den FRM for China ist, eines der ersten systemischen Risikomaße in der Region, zeigt aber auch Methoden zur Erkennung von Spill-Over-Kanälen in Nachbarländer und zwischen Sektoren., The concept of risk deals with the exposure to danger, in the world of finance the danger of financial losses. In a globalised financial economy, many risks are unknown. "We know it when we see it", to paraphrase Justice Potter Stewart (1964). The Financial Risk Meter (FRM) sheds light on the emergence of systemic risk. Using of quantile regression techniques, it is a meter for financial risk, and its network topology offers insight into the spill-over effects risking systemic risk events. In this thesis, the FRM framework in various markets and regions is developed and the FRM data is used for risk now- and forecasting, and for portfolio optimization approaches. In Chapter 1 the FRM is presented and applied to equity markets in the US and Europe, but also interest rate and credit-default swap markets. The FRM is then used to now-cast and predict economic recessions. In Chapter 2 the FRM is applied to cryptocurrencies, to generate the first risk meter in this nascent asset class. The generated FRM data concerning dependencies, spill-over effects and network set-up are then used to create tail-risk optimised portfolios. In Chapter 3 the FRM is applied to the global market Emerging Market (EM) financial institutions. The FRM for EM gives specific spill-over dependencies in tail-risk events within sectors of financial institutions, but also shows inter-country dependencies between the EM regions. The FRM data is then combined with portfolio management approaches to create tail-risk sensitive portfolios of EM Financial institutions with aim to minimize risk clusters in a portfolio context. In Chapter 4 the Financial Risk Meter for China is developed as the first systemic risk meter in the region, but also derives methods to detect spill-over channels to neighbouring countries within and between financial industry sectors.

Acepleiadylene (APD), a nonbenzenoid nonalternant isomer of pyrene, exhibits different electronic properties from pyrene, but has been rarely studied since its first synthesis in 1956, probably due to the difficulties in synthesis and further derivatization. In this work, we revisited this long-known compound and developed a new two-step synthetic route to efficiently access APD on the gram scale. Theoretical and experimental characterizations elucidated the unique properties of APD as compared with its benzenoid isomer pyrene, particularly revealing its dipolar structure with a narrow optical gap. The functionalization of APD was demonstrated for the first time, providing doubly brominated APD as a key precursor for further π-extension. As a proof of concept, a π-extended APD and a cyclotrimer nanographene (C48H24) were constructed, opening up new avenues to nonbenzenoid nanographenes with low HOMO-LUMO gaps.

Herein we report the facile reductive O-triflylation and O-silylation of naphthalene diimide as a scalable one-step approach. The resulting highly reactive 1,3,6,8-tetratriflato-2,7-diazapyrene was prepared at the 3 gram scale and serves as a versatile platform for further functionalizations via Sonogashira cross coupling or nucleophilic aromatic substitution by piperidine or iodide leading to tetrasubstituted diazapyrenes with tunable optoelectronic properties. Fine tuning is demonstrated by means of absorption and emission maxima varying within a range of more than 100 nm. The different diazapyrenes are characterized by means of XRD diffraction, UV-Vis and photoluminescence spectroscopy as well as cyclic voltammetry and TD-DFT calculations. The applicability of so far unaccessible tetra-1-alkynyl diazapyrenes for organic molecular beam epitaxy (OMBE) is demonstrated by characterization of a sub-monolayer on Cu(111) using scanning tunneling microscopy (STM).

Metal complexes at surfaces and interfaces play an important role in many areas of modern technology, including catalysis, sensors, and organic electronics. An important aspect of these interfaces is the possible exchange of the metal center, because this reaction can drastically alter the properties of the metal complex and thus of the interface. Here, we demonstrate that such metal exchange reactions are indeed possible and can proceed already at moderate temperatures even in the absence of solvents. Specifically, we studied the redox transmetalation of a monolayer of lead(ii)-tetraphenylporphyrin (PbTPP) with copper from a Cu(111) surface under ultrahigh-vacuum (UHV) conditions using multiple surface-sensitive techniques. Temperature-dependent X-ray photoelectron spectroscopy (XPS) reveals that the Pb/Cu exchange starts already below 380 K and is complete at 600 K. The identity of the reaction product, CuTPP, is confirmed by mass spectrometric detection in a temperature-programmed reaction (TPR) experiment. Scanning tunneling microscopy (STM) sheds light on the adsorbate structure of PbTPP at 300 K and uncovers the structural changes accompanying the transmetalation and side-reactions of the phenyl substituents. Moreover, individual free Pb atoms are observed as a product of the metal exchange.

Hybrid systems of two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) and organic semiconductors (OSCs) have become subject of great interest for future device architectures. Although OSC–TMDC hybrid systems have been used in first device demonstrations, the precise preparation of ultra-thin OSC films on TMDCs has not been addressed. Due to the weak van der Waals interaction between TMDCs and OSCs, this requires precise knowledge of the thermodynamics at hand. Here, we use temperature-programmed desorption (TPD) and Monte Carlo (MC) simulations of TPD traces to characterize the desorption kinetics of pentacene (PEN) and perfluoropentacene (PFP) on MoS2 as a model system for OSCs on TMDCs. We show that the monolayers of PEN and PFP are thermally stabilized compared to their multilayers, which allows preparation of nominal monolayers by selective desorption of multilayers. This stabilization is, however, caused by entropy due to a high molecular mobility rather than an enhanced molecule–substrate bond. Consequently, the nominal monolayers are not densely packed films. Molecular mobility can be suppressed in mixed monolayers of PEN and PFP that, due to intermolecular attraction, form highly ordered films as shown by scanning tunneling microscopy. Although this reduces the entropic stabilization, the intermolecular attraction further stabilizes mixed films.

Polymorphism of organic molecular materials plays a prominent role in organic (opto)electronic devices, where the structural properties of metal/organic interfaces determine performance-critical pa...

Ring/chain competition in oligomerization reactions represents a long‐standing topic of synthetic chemistry and was treated extensively for solution reactions but is not well‐understood for the two‐dimensional confinement of surface reactions. Here, the kinetic and thermodynamic principles of ring/chain competition in on‐surface synthesis are addressed by scanning tunneling microscopy, X‐ray photoelectron spectroscopy, and Monte Carlo simulations applied to azulene‐based organometallic oligomers on Cu(111). Analysis of experiments and simulations reveals how the ring/chain ratio can be controlled through variation of coverage and temperature. At room temperature, non‐equilibrium conditions prevail and kinetic control leads to preferential formation of the entropically favored chains. In contrast, high‐temperature equilibrium conditions are associated with thermodynamic control, resulting in increased yields of the energetically favored rings. The optimum conditions for ring formation include the lowest possible temperature within the regime of thermodynamic control and a low coverage. The general implications are discussed and compared to the solution case., The competition between macrocycle and chain formation in organometallic on‐surface polymerization can be steered by variation of coverage and temperature. The entropically favored chains are preferentially formed under non‐equilibrium conditions and high coverage, whereas the more stable macrocycles prevail when the on‐surface synthesis is performed in equilibrium at low coverages.

Corroles on metal surfaces show substantial reactivity and aromaticity-driven interfacial electron transfer of their transient σ/π-radicals. These effects are much more pronounced than for the clos...

Science advances 8(29), eabn0819 (2022). doi:10.1126/sciadv.abn0819, Published by American Association for the Advancement of Science, Washington, DC [u.a.]

Although the exact knowledge of the binding energy of organic adsorbates on solid surfaces is of vital importance for the realization of molecular nanostructures and the theoretical modelling of molecule–substrate interactions, an experimental determination is by no means trivial. Temperature-programmed desorption (TPD) is a widely used technique that can provide such information, but a quantitative analysis requires detailed knowledge of the pre-exponential factor of desorption and is therefore rarely performed on a quantitative level for larger molecules that often exhibit notable mutual intermolecular interactions. Here, we provide a thorough anlysis of TPD data of monolayers of pentacene and perfluoropentacene adsorbed on Au(111) that serve as a model system for polycyclic aromatic hydrocarbons adsorbed on noble metal surfaces. We show that the pre-exponential factor varies by several orders of magnitude with the surface coverage and evolves in a step-like fashion due to the sudden activation of a rotational degree of freedom during thermally controlled monolayer desorption. Using complementary coverage-dependent work function measurements, the interface dipole moments were determined. This allows to identify the origin and quantify the relative contributions of the lateral intermolecular interactions, which we modelled by force field calculations. This analysis clearly shows that the main cause for intermolecular repulsion are electrostatic interactions between the intramolecular charge distributions, while interface dipoles play only a minor role.

Graphene nanoribbons (GNRs) are of enormous research interest as a promising active component in electronic devices, for example, field-effect transistors (FET). The recently developed “bottom-up” ...

The synthesis of cycloarenes in solution is challenging because of their low solubility and the often hindered cyclodehydrogenation reaction of their nonplanar precursors. Using an alternative on-surface synthesis protocol, we achieved an unprecedented double-stranded hexagonal cycloarene containing 108 sp2 carbon atoms. Its synthesis is based on hierarchical Ullmann coupling and cyclodehydrogenation of a specially designed precursor on a Au(111) surface. The structure and other properties of the cycloarene are investigated by scanning tunneling microscopy/spectroscopy, atomic force microscopy, and density functional theory calculations.

The binary lead fluoride Pb3F8 was synthesized by the reaction of anhydrous HF with Pb3O4 or by the reaction of BrF3 with PbF2. The compound was characterized by single-crystal and powder X-ray diffraction, IR, Raman, and solid-state MAS 19F NMR spectroscopy, as well as thermogravimetric analysis, XP and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Solid-state quantum-chemical calculations are provided for the vibrational analyses and band assignments. The electronic band structure offers an inside view of the mixed valence compound.

QUESTIONS: Long‐term programs monitoring the impact of climate change on alpine vegetation necessarily involve changing observers. We aim at quantifying observer errors and ask if the signal of alpine vegetation transformation due to climate change exceeds pseudo‐changes caused by observer errors. LOCATION: Two mountain regions in the Alps, Schrankogel and Hochschwab (both Austria), and one in the High Tatra Mountains (Slovakia). METHODS: Vascular plant species presence and cover were recorded on 10–12 1‐m² plots by 13–14 observers per site. Observer errors were calculated as species turnover, and deviations of species cover and the plot thermic vegetation indicator (which is correlated with temperature) from the mean over all observers. Observer errors in estimating species cover were split into a random and systematic part. The influence of plot and species characteristics on observer errors was investigated using (generalized) linear mixed‐effect models. Changes over time from three surveys in species turnover, cover and the thermic vegetation indicator were related to the amount of observer error using a bootstrap approach. RESULTS: Species cover was the most influential factor affecting observer errors in recording species lists and in species cover estimation. Plot attributes and observer identity had a weak but significant influence on errors in the thermic vegetation indicator. Systematic errors in estimating species cover were ≤5%. Changes over time in estimating species cover, as well as in species turnover and the thermic vegetation indicator exceeded observer errors in all cases where the observation period was ≥10 years. CONCLUSIONS: The thermic vegetation indicator, which combines species composition and cover with species’ elevational distributions, provides a reliable estimate of warming‐related vegetation changes. Our results underline the importance of long‐term monitoring and long observation periods, which enable us to account for short‐term fluctuations and observer errors alike.

In polymerization reactions, controlling the formation of open-chain versus cyclic product topologies is necessary because of the different properties of polymer chains and macrocycles. Here, we report a topology-selective Ullmann coupling on metal surfaces with control of the ring/chain competition. The precursor employed is 4,4''-dibromo-ortho-terphenyl (DBOTP), which features a 60° bent feature and polymerizes into zigzag polyphenylene chains on both Au(111) and Ag(111) surface via Ullmann coupling. However, the cyclotrimerization of the precursor occurs only on Ag(111) but not Au(111). It is proposed that the cyclotrimerization reaction on Au(111) is blocked, because the necessary C-C coupling of two carbon radicals with different vertical heights is unfavored. Such height difference stems from the intrinsic steric repulsion between the two ortho-substituted phenyl groups. On Ag(111), the stronger adsorbate-substrate interaction reduces the extent of the tilting of the phenyl group, resulting in a smaller height difference of the carbon radicals and consequently in the increased probability for the formation of the cyclic trimer.

Scientific advances in the fields of chemistry and engineering have established the critical impact of solvents on the rate of a wide array of chemical reactions. This has triggered the interest of academia and industry for the search of solvents that optimize reaction kinetics. Yet, there are only a few systematic approaches to guide such solvent selection currently. In this work, a methodology was developed to identify suitable solvents that will enhance the reaction rate of an industrial process at minimum experimental effort. For the rapid data generation and quantification, a modular continuous reactor coupled with real-time in situ analytics was set up. The data generation is guided by a computational method that consists of two steps: the formulation of a model identification problem based on the solvatochromic equation and the computer-aided screening of a solvent database that provides a list of the most promising solvents. The methodology is applied to the amination of ethyl trichloroacetate wit...

Pyrene derivatives play a prominent role in organic electronic devices, including field effect transistors, light emitting diodes, and solar cells. The flexibility in the desired properties has previously been achieved by variation of substituents at the periphery of the pyrene backbone. In contrast, the influence of the topology of the central π‐electron system on the relevant properties such as the band gap or the fluorescence behavior has not yet been addressed. In this work, pyrene is compared with its structural isomer azupyrene, which has a π‐electron system with non‐alternant topology. Using photoelectron spectroscopy, near edge X‐ray absorption fine structure spectroscopy, and other methods, it is shown that the electronic band gap of azupyrene is by 0.72 eV smaller than that of pyrene. The difference of the optical band gaps is even larger with 1.09 eV, as determined by ultraviolet–visible absorption spectroscopy. The non‐alternant nature of azupyrene is also associated with a more localized charge distribution. Further insight is provided by density functional theory (DFT) calculations of the molecular properties and ab initio coupled cluster calculations of the optical transitions. The concept of aromaticity is used to interpret the major topology‐related differences., Topological Tuning: Molecular organic materials for application in organic electronics can be tailored by topological design of their π‐electron systems, instead of conventional tailoring by peripheral substituents. This is shown by a multi‐technique comparison of pyrene with its topological isomer azupyrene. The non‐alternant topology of azupyrene causes a more localized charge distribution, smaller electronic and optical gaps, and different fluorescence behavior.

openaire: EC/H2020/839242/EU//EMOF | openaire: EC/H2020/845060/EU//QMKPFM | openaire: EC/H2020/788185/EU//E-DESIGN The quest for planar sp2-hybridized carbon allotropes other than graphene, such as graphenylene and biphenylene networks, has stimulated substantial research efforts because of the materials’ predicted mechanical, electronic, and transport properties. However, their syntheses remain challenging given the lack of reliable protocols for generating nonhexagonal rings during the in-plane tiling of carbon atoms. We report the bottom-up growth of an ultraflat biphenylene network with periodically arranged four-, six-, and eight-membered rings of sp2-hybridized carbon atoms through an on-surface interpolymer dehydrofluorination (HF-zipping) reaction. The characterization of this biphenylene network by scanning probe methods reveals that it is metallic rather than a dielectric. We expect the interpolymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.

Herein, we present the synthesis of two pyrene‐functionalized clusters, [(RpyrSn)4S6]⋅2 CH2Cl2 (4) and [(RpyrSn)4Sn2S10]⋅n CH2Cl2 (n=4, 5 a; n=2, 5 b; Rpyr=CMe2CH2C(Me)N‐NC(H)C16H9), both of which form in reactions of the organotin sulfide cluster [(RNSn)4S6] (C; RN=CMe2CH2C(Me)N‐NH2) with the well‐known fluorescent dye 1‐pyrenecarboxaldehyde (B). In contrast, reactions using an organotin sulfide cluster with another core structure, [(RNSn)3S4Cl] (A), leads to formation of small molecular fragments, [(RpyrCl2Sn)2S] (1), (pyren‐1‐ylmethylene)hydrazine (2), and 1,2‐bis(pyren‐1‐ylmethylene)hydrazine (3). Besides synthesis and structures of the new compounds, we report the influence of the inorganic core on the optical properties of the dye, which was analyzed exemplarily for compound 5 a via absorption and fluorescence spectroscopy. This cluster was also used for exploring the potential of such non‐volatile clusters for deposition on a metal surface under vacuum conditions., A first series of pyrene‐terminated organotin sulfide compounds and unprecedented side products, [(RpyrCl2Sn)2S] (1), (pyren‐1‐ylmethylene)hydrazine (2), 1,2‐bis(pyren‐1‐ylmethylene)hydrazine (3), [(RpyrSn)4S6]⋅2 CH2Cl2 (4), and [(RpyrSn)4Sn2S10] (5), were synthesized. The combination of inorganic Sn/S moieties with the pyrene units affects optical absorption and fluorescence properties as well as the deposition on a metal surface.

The quest for planar sp2-hybridized carbon allotropes other than graphene, such as graphenylene and biphenylene sheet, has stimulated substantial research efforts because of the materials' predicted unique mechanical, electronic and transport properties. However, their synthesis remains challenging due to the lack of reliable protocols for generating non-hexagonal rings during the in-plane tiling of carbon atoms. Here, we report the bottom-up growth of ultra-flat biphenylene sheet with periodically arranged four-, six-, and eight-membered rings of sp2 carbon atoms, via an unprecedented on-surface inter-polymer hydrogen fluoride (HF)-zipping reaction. The characterization of this biphenylene sheet by scanning probe methods solves the long-standing controversy over its dielectric or metallic nature. We expect the inter-polymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.

Metal complexes at surfaces and interfaces play a prominant role in many areas of modern technology, including catalysis, sensors, and organic electronics. An important aspect of these interfaces is the possible exchange of the metal center, because this reaction can drastically alter the properties of the metal complex and thus of the interface. Here, we demonstrate that such metal exchange reactions are indeed possible and can proceed already at moderate temperatures even in the absence of solvents. Specifically, we studied the redox transmetalation of a monolayer of lead(II)-tetraphenylporphyrin (PbTPP) with copper from a Cu(111) surface under ultrahigh-vacuum (UHV) conditions using multiple surface-sensitive techniques. Temperature dependent X-ray photoelectron spectroscopy (XPS) reveals that the Pb/Cu exchange starts already below 380 K and is complete at 600 K. The identity of the reaction product, CuTPP, is confirmed by mass spectrometric detection in a temperature-programmed reaction (TPR) experiment. Scanning tunneling microscopy (STM) sheds light on the adsorbate structure of PbTPP at 300 K and uncovers the structural changes accompanying the transmetalation and side-reactions of the phenyl substituents. Moreover, individual free Pb atoms are observed as a product of the metal exchange. Our study suggests that surfaces functionalized with metal complexes may consist of other species than intended under operation conditions, which often involve elevated temperatures.

Here, we use temperature-programmed desorption (TPD) and Monte Carlo (MC) simulationsof TPD traces to characterize the desorption kinetics of pentacene (PEN) and perfluoropentacene (PFP) on MoS2 as a model system for OSCs on TMDCs. We show that the monolayers of PEN and PFP are thermally stabilized compared to their multilayers, which allows to prepare nominal monolayers by selective desorption of multilayers. This stabilization is, however, caused by entropy due to a high molecular mobility rather than an enhanced molecule-substrate bond. Consequently, the nominal monolayers are not densely packed films.

ACS nano 14(11), 15766-15775 (2020). doi:10.1021/acsnano.0c06798, Published by American Chemical Society, Washington, DC

To explore the possibility of tuning the oxidation state of a coordinated metal ion in an adsorbed tetrapyrrole complex by a minor modification of the ligand structure, multilayers and monolayers of 3H-hexaethyl-dimethyl-corrole (3H-HEDMC) on Ag(111) were in situ metalated under ultrahigh vacuum (UHV) conditions and subsequently analyzed with spectroscopic and microscopic methods. The metalation reaction leads to the formation of Fe(III)-hexaethyl-dimethyl-corrole (Fe-HEDMC). The results were compared with those for Fe-octaethyl-porphyrin (Fe-OEP), in which the Fe metal center has a formal Fe(+II) character. The analysis of the nearly unperturbed iron-corrole in the multilayer regime with X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy shows that the electronic structure of the corrole-coordinated iron is consistent with an Fe(+III) state in Fe-HEDMC. In the monolayers, the Fe centers in Fe-HEDMC and Fe-OEP interact similarly with the Ag(111) surf...