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In this work we investigate the behaviour of molecules at the nanoscale using scanning tunnelling microscopy in order to explore the origin of the cooperativity in the formation of self-assembled molecular networks (SAMNs) at the liquid/solid interface. By studying concentration dependence of alkoxylated dimethylbenzene, a molecular analogue to 5-alkoxylated isophthalic derivatives, but without hydrogen bonding moieties, we show that the cooperativity effect can be experimentally evaluated even for low-interacting systems and that the cooperativity in SAMN formation is its fundamental trait. We conclude that cooperativity must be a local effect and use the nearest-neighbor Ising model to reproduce the coverage vs. concentration curves. The Ising model offers a direct link between statistical thermodynamics and experimental parameters, making it a valuable tool for assessing the thermodynamics of SAMN formation.

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into otherwise-unstable CsPbI3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

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 similarity between hydrogen and halogen bonds to obtain predictable halogen bonded networks. The self-assembly of 1,3-dibromo-5-alkoxybenzene derivatives was studied in analogy with well-explored alkoxy isophthalic acids using a combination of experimental and theoretical tools. Scanning tunneling microscopy (STM) characterization of the networks formed at the liquid-graphite interface revealed that while the retrosynthetic approach works at the level of small clusters of molecules within the 2D network, the overall structure of the network deviates from the anticipated structure. The monolayers consist of fractured rows of halogen-bonded modules instead of the expected continuous lamellar structure. Each module consists of a discrete number of halogen-bonded molecules. The interactions responsible for the stabilization of halogen bonded dimers are delineated through detailed density functional theory (DFT) calculations coupled with natural bonding orbitals (NBO) and perturbation analysis. A modified force field that includes an extra charged site to imitate the σ hole on the halogen atom was developed and applied to extract total potential energies of the anticipated and observed networks. Plausible reasons for the deviation from the anticipated structure are discussed. Finally, a modified molecular design that allows successful application of the hydrogen bond-halogen bond analogy was tested experimentally.

Molecular islands of various shapes and sizes composed of a few tens of molecules only are formed at the liquid--solid interface, at room temperature, by an alkoxylated dehydrobenzo[12]annulene (DBA) derivative. Molecules are packed into hexagons. Scanning tunneling microscopy reveals the variety in molecular island structures and their stability. For molecular islands up to 7 hexagonal pores, all 244 possible structures are simulated and compared with experimental observations. Force field calculations give insights into the relative stability of the molecular islands and the factors contributing to it. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have attracted tremendous attention in photovoltaics due to their impressive optoelectronic properties. However, the poor stability of perovskite-based devices remains a bottleneck for further commercial development. Two-dimensional perovskites have great potential in optoelectronic devices, as they are much more stable than their three-dimensional counterparts and rapidly catching up in performance. Herein, we demonstrate high-quality two-dimensional novel perovskite thin films with alternating cations in the interlayer space. This innovative perovskite provides highly stable semiconductor thin films for efficient near-infrared light-emitting diodes (LEDs). Highly efficient LEDs with tunable emission wavelengths from 680 to 770 nm along with excellent operational stability are demonstrated by varying the thickness of the interlayer spacer cation. Furthermore, the best-performing device exhibits an external quantum efficiency of 3.4% at a high current density (J) of 249 mA/cm2 and remains above 2.5% for a J up to 720 mA cm−2, leading to a high radiance of 77.5 W/Sr m2 when driven at 6 V. The same device also shows impressive operational stability, retaining almost 80% of its initial performance after operating at 20 mA/cm2 for 350 min. This work provides fundamental evidence that this novel alternating interlayer cation 2D perovskite can be a promising and stable photonic emitter.

The reduction of carbon dioxide (CO2) using porphyrin‐containing 2D covalent organic frameworks (2D‐COFs) catalysts is widely explored nowadays. While these framework materials are normally fabricated as powders followed by their uncontrolled surface heterogenization or directly grown as thin films (thickness >200 nm), very little is known about the performance of substrate‐supported single‐layered (≈0.5 nm thickness) 2D‐COFs films (s2D‐COFs) due to its highly challenging synthesis and characterization protocols. In this work, a fast and straightforward fabrication method of porphyrin‐containing s2D‐COFs is demonstrated, which allows their extensive high‐resolution visualization via scanning tunneling microscopy (STM) in liquid conditions with the support of STM simulations. The as‐prepared single‐layered film is then employed as a cathode for the electrochemical reduction of CO2. Fe porphyrin‐containing s2D‐COF@graphite used as a single‐layered heterogeneous catalyst provided moderate‐to‐high carbon monoxide selectivity (82%) and partial CO current density (5.1 mA cm−2). This work establishes the value of using single‐layered films as heterogene ous catalysts and demonstrates the possibility of achieving high performance in CO2 reduction even with extremely low catalyst loadings. [ABSTRACT FROM AUTHOR]

Closed‐chain oligopyrroles such as porphyrins or corroles have been well‐established in literature and experience a steadily strong interest by several fields of science. However, their open‐chain derivatives are comparatively underrepresented, despite their intriguing properties and promising applications. Here, we aim to review typical synthetic routes, as well as point towards several emergent properties, marking them as interesting candidates for various fields of study. The review focuses on two traditional methods (each starting from highly symmetric metalloporphyrins) and then expands its scope towards more recent variations before moving on to more exotic and recent highlights that have yet to be included into the canon. Key chemical reactivities (ring closure, substitution and fragmentation) are then followed by notable physicochemical properties, placing special emphasis on potential uses in molecular electronics and sensors. [ABSTRACT FROM AUTHOR]

Here, we report on the synthesis of discrete oligomers of alkyl‐bridged naphthalenediimides (NDIs) and study their molecular nanostructures both in bulk, in solution, and at the liquid‐solid interface. Via an iterative synthesis method, multiple NDI cores were bridged with short and saturated alkyl‐diamines (C3 and C12) or long and unsaturated alkyl‐diamines (u2C33 to u8C100) at their imide termini. The strong intermolecular interaction between the NDI cores was observed by probing their photophysical properties in solution. In bulk, the discrete NDI oligomers preferentially ordered in lamellar morphologies, irrespective of whether a saturated or unsaturated spacer was employed. Moreover, both the molecular architecture as well as the crystallization conditions play a significant role in the nanoscale ordering. The long unsaturated alkyl chains lead preferably to folded‐chain conformations while their saturated analogues form stretched arrangements. At the solution‐solid interface, well‐defined lamellar regions were observed. These results show that precision in chemical structure alone is not sufficient to reach well‐defined structures of discrete oligomers, but that it must be combined with precision in processing conditions. [ABSTRACT FROM AUTHOR]

In recent years, there has been significant focus on investigating and controlling chiral self‐assembly, specifically in the context of enantiomeric separation. This study explores the self‐assembly behavior of 4‐dodecyl‐3,6‐di(2‐pyridyl)pyridazine (DPP−C12) at the interface between heptanoic acid (HA) and highly oriented pyrolytic graphite (HOPG) using a combination of scanning tunneling microscopy (STM) and multiscale molecular modeling. The self‐assembled monolayer structure formed by DPP−C12 is periodic in one direction, but aperiodic in the direction orthogonal to it. These structures resemble 1D disordered racemic compounds. Upon introducing palladium [Pd(II)] ions, complexing with DPP−C12, these 1D disordered racemic compounds spontaneously transform into 2D racemic conglomerates, which is rationalized with the assistance of force‐field simulations. Our findings provide insights into the regulation of two‐dimensional chirality. [ABSTRACT FROM AUTHOR]

MXenes are electrically conductive 2D transition metal carbides/nitrides obtained by the etching of nanolaminated MAX phase compounds, followed by exfoliation to single‐ or few‐layered nanosheets. The mainstream chemical etching processes have evolved from pure hydrofluoric acid (HF) etching into the innovative "minimally intensive layer delamination" (MILD) route. Despite their current popularity and remarkable application potential, the scalability of MILD‐produced MXenes remains unproven, excluding MXenes from industrial applications. This work proposes a "next‐generation MILD" (NGMILD) synthesis protocol for phase‐pure, colloidally stable MXenes that withstand long periods of dry storage. NGMILD incorporates the synergistic effects of a secondary salt, a richer lithium (Li) environment, and iterative alcohol‐based washing to achieve high‐purity MXenes, while improving etching efficiency, intercalation, and shelf life. Moreover, NGMILD comprises a sulfuric acid (H2SO4) post‐treatment for the selective removal of the Li3AlF6 impurity that commonly persists in MILD‐produced MXenes. This work demonstrates the upscaled NGMILD synthesis of (50 g) phase‐pure Ti3C2Tz MXene clays with high extraction yields (>22%) of supernatant dispersions. Finally, NGMILD‐produced MXene clays dry‐stored for six months under ambient conditions experience minimal degradation, while retaining excellent redispersibility. Overall, the NGMILD protocol is a leap forward toward the industrial production of MXenes and their subsequent market deployment. [ABSTRACT FROM AUTHOR]

Boosted by the emerging need for highly integrated gas sensors in the internet of things (IoT) ecosystems, electronic noses (e‐noses) are gaining interest for the detection of specific molecules over a background of interfering gases. The sensing of nitrogen dioxide is particularly relevant for applications in environmental monitoring and precision medicine. Here we present an easy and efficient functionalization procedure to covalently modify graphene layers, taking advantage of diazonium chemistry. Separate graphene layers were functionalized with one of three different aryl rings: 4‐nitrophenyl, 4‐carboxyphenyl and 4‐bromophenyl. The distinct modified graphene layers were assembled with a pristine layer into an e‐nose for NO2 discrimination. A remarkable sensitivity to NO2 was demonstrated through exposure to gaseous solutions with NO2 concentrations in the 1–10 ppm range at room temperature. Then, the discrimination capability of the sensor array was tested by carrying out exposure to several interfering gases and analyzing the data through multivariate statistical analysis. This analysis showed that the e‐nose can discriminate NO2 among all the interfering gases in a two‐dimensional principal component analysis space. Finally, the e‐nose was trained to accurately recognize NO2 contributions with a linear discriminant analysis approach, thus providing a metric for discrimination assessment with a prediction accuracy above 95 %. [ABSTRACT FROM AUTHOR]